Semiconductor laser

FIELD: physics.

SUBSTANCE: semiconductor laser has a heterostructure in form of a thin plane-parallel plate, two mirrors which form an optical resonator having an optical axis and lying on both sides of the heterostructure, and pumping apparatus. Using the pumping apparatus, a volume is excited in the heterostructure, having a dimension along the axis of the resonator which is considerably smaller than across the axis of the resonator. The optical resonator has at least one extra absorbing layer in which nonequilibrium-carrier recombination takes place. The extra absorbing layer lies perpendicular the optical axis in the resonator mode unit, whose wavelength lies on the maximum of the spectrum of optical amplification of the heterostructure. Said absorbing layer absorbs spontaneous radiation propagating at an angle to the optical axis outside the fundamental mode of the resonator.

EFFECT: increase in power of the laser owing increase in cross dimensions of the excitation region.

32 cl, 1 dwg

 

The invention relates to the field of quantum electronics and electronic engineering and can be used in devices with a powerful light beam, in particular in teleprotection, laser locators.

Known laser type radiant mirror, which is a semiconductor laser with longitudinal e-beam pumped and containing a pulsed source of high-energy electrons, laser target, representing a monocrystalline semiconductor plate was highly reflective mirror coating from bombarded by electrons, glued to headproposes transparent substrate, and the external reflecting mirror (Overorganized, Saarthak, Begaliev. Semiconductor lasers. M., Nauka, 1976. S).

To increase the radiation power by increasing transverse to the axis of the cavity size of the excited region of the semiconductor wafer is cut into cells, the size of which is chosen smaller than the reciprocal of the gain at the lasing threshold of α1to exclude the influence of the reset amplified spontaneous noise characteristics of the laser.

The disadvantage of this device is that it operates at too high energies of electrons above 150 Kev. With decreasing electron energy of 50 Kev and below, under which a wide practical application of these instruments, Oreg generation at room temperature grows, the thickness of the plate and transverse dimensions of the field excitation must be reduced, which leads to rapid degradation of the device. In addition, the orientation of such lasers is not high enough.

Known laser cathode-ray tube containing a source of an electron beam and means for its control, laser target, made in the form heterostructures and includes forming an optical cavity with two mirrors, one of which was highly reflective and the other is partially permeable, active semiconductor medium with strained quantum wells placed between the mirrors, and a support substrate for an optical resonator (V.I. Kozlovsky, Lavrushin BM Laser cathode-ray tube. RF patent №2056665).

This device is a semiconductor laser with longitudinal pumping astrosociology scanning electron beam. The use of strained heterostructures with quantum wells can significantly reduce the threshold at room temperature and to extend the range of materials that can be used, which, ultimately, allows for the generation in the visible and ultraviolet regions of the spectrum.

The disadvantage of this device is that the transverse dimensions of the field excitation, limited by the size of the diameter of electricity is the main beam, can't be more than 100 μm due to the discharge inversion amplified spontaneous noise propagating generated outside of the cavity modes. In addition, the resonator in this device has a length of several microns and cannot provide high directivity of radiation.

Closest to the claimed technical solution is a semiconductor laser with optical pumping, containing resonant-periodic nanostructure with quantum wells of InGaAs/GaAsP and a Bragg mirror of the epitaxial layers of AlGaAs/GaAs attached to hadproved, external spherical semitransparent mirror and the means for optical pumping, consisting of laser diodes and a matching optical system (Andrea Caprara, Chilla Juan L., Spinelli Luis A., High-power external-cavity optically-pumped semiconductor laser, US Patent 6,285,702 September 4, 2001; J. Chilla, St. Butter-worth, A. Zeitschel, J. Charles, A. Carpara, M. Reed, L, Spinelli High power optically pumped semiconductor lasers, Proc/ of SPIE, Vol.5332, P.143-150 (2004).)

In this nanostructure quantum wells placed at the antinodes of the resonator mode, which provides approximately two times greater coefficient of optical gain in the direction of the optical axis of the resonator than in the transverse direction. The transverse size of the region of excitation was varied from 500 to 900 μm, and the length of the active region along the cavity axis was equal to about 1.5 μm. In this case it was possible to obtain a laser power up to 30 watts in continuous mode the e excitation at a wavelength of 970 nm when the pump power, the laser diode 70 watts. The angular divergence of the radiation was 3 diffraction limit at the generation wavelength of 980 nm.

The disadvantage of this device is that a further increase of the laser power by increasing the cross-sectional dimension not only in the continuous pumping mode, but in the pulse of reset inversion amplified spontaneous noise, extending across the axis of the resonator. Although this effect device reset inversion weakened in comparison with the above-described counterparts due to differences in coefficient of optical gain along and across the axis of the resonator, but it still remains a determining factor in limiting the size of the excited region of the nanostructure by one millimeter.

The problem solved by the invention is the increased power of a semiconductor laser by increasing the transverse dimensions of the region of excitation.

The problem is solved in a semiconductor laser containing heterostructure in the form of a thin plane-parallel plate, two mirrors that form an optical cavity with an optical axis located on both sides of the heterostructure, and the pumping means, by means of which the heterostructure is excited volume, having a much smaller size along the cavity axis than across, and the optical resonator comprises at least one additional on amausi layer, located perpendicular to the optical axis in the node of the resonator mode, the wavelength of which is in the spectrum maximum optical gain heterostructures.

The invention consists in that the laser to create a high gain optical amplification only for the main transverse resonator mode and avoid amplifying spontaneous emission propagating in other directions. If the inside of the resonator additional absorbing layer is placed in a node of a standing electromagnetic wave in the resonator mode, the electromagnetic field is poorly absorbed in this layer. However, for any electromagnetic wave traveling this absorption significantly (10-1000 times) increases. When using a sufficient number of additional absorbing layer with a sufficiently high absorption coefficient at the wavelength of the spontaneous emission heterostructure can completely suppress spurious amplification of the spontaneous emission noise, which resets the inversion and worsen the performance of the laser. In the complete suppression of the amplification of the transverse size of the excited region can be arbitrarily large, at least when pulsed pumping, which allows to significantly increase the radiation power of the laser. In case of incomplete suppression is achieved partial improvement of the characteristics of the laser described above.

At least one additional absorbing layer can be placed between the heterostructure and one of the resonator mirrors. In this case, this layer will limit the amplification of spontaneous emission outside the main resonator mode that comes out of the heterostructure and returns to it after reflection from the external mirror. However, most of the spontaneous emission will be distributed within the heterostructure.

To suppress the amplification of spontaneous emission propagating along the heterostructure having a relatively small thickness (0.1-1 μm), more absorbing layers is applied at least on one surface of the heterostructure. In this case, the electromagnetic wave propagating along the structure, will be pushed in an additional absorbent layer and at a sufficiently high absorption coefficient will not be enhanced by the optical gain of the active layer.

In the most simple embodiment, the heterostructure contains the active layers separated by barrier layers and oriented perpendicular to the cavity axis.

In the case of thicker heterostructures (1-20 μm) of the active and barrier layers of the heterostructure to form the waveguide. Waveguide electromagnetic wave spontaneous emission is poorly absorbed more popadayuschiesya, deposited on the surface of the heterostructure. In this case, to suppress the amplification of spontaneous additional noise absorbing layers are injected directly into the heterostructure during growth.

The active layers of the heterostructure can be a homogeneous layers with a bandgap less than the width of the bandgap barrier layers. In this case, the band diagram of the heterostructure is such that either the conduction band or the valence band, or in both zones are formed, the energy of the hole for the non-equilibrium electrons and holes, respectively. To reduce the oscillation threshold of the laser active layers do quite thin (0.1-10 nm), in this case, the energy of electrons and holes in the energy pits quantized, and the active layers are quantum wells.

To effectively limit the electrons and holes in quantum wells (CB) at room temperature (kT=25 MeV) is appropriate to the CB depth was greater than 25 MeV. With less energy even in the case of a CB nonequilibrium carriers will be subjected to the heat release from the CB. The best results in the limitation of carriers in the CB are achieved when the difference in width of forbidden zone CB and the barrier layer is greater than 300 MeV.

The active layer may have even wider bandgap than the barrier layer in the heterostructure with rupture zones of Deuteronomy is the second type. In this case, the active layer CB is only one of nonequilibrium charge carriers: electrons or holes. Other media will be attracted to interface with CB being in the barrier layer. In this case, the optical amplification is possible, although the gain is less.

The active layers of the heterostructure can also be a layer set of quantum lines, when restricting the movement of carriers occurs in two directions. To achieve an effective limitation of carriers in the quantum lines at room temperature, the depth of the energy pits must be greater than 25 MeV.

In another embodiment, the active layer heterostructure is a layer matrix quantum dots, when restricting the movement of carriers occurs by three coordinates. The depth of the energy pits must be greater than 25 MeV for quantum dots is large in size. With decreasing size of the quantum dots the depth of the energy pits should be increased. Alternatively, when the active layer is a layer set of quantum disks, when the quantization of energy carriers is due to restrictions of movement for one coordinate along the optical axis, as in quantum wells, but unlike CB total area of the disks is significantly less than the area of the layer on which they are placed. E is om case there is additional electronic limitation, which reduces the lasing threshold of the laser, but the line width of the radiation quantum disks is equal to the line width of the radiation CB, that is not observed inhomogeneous broadening of the line due to the sheer size of quantum dots, which is the case for most materials used for their formation.

The active layers are placed at the antinodes of the resonator mode, the wavelength of which is in the spectrum maximum gain. Fine-tuning the resonator mode in the spectrum maximum amplification is carried out by changing the length of the resonator and/or the magnitude of the phase shift of the electromagnetic wave upon reflection from one of the mirrors of the resonator. In General, the position of the active layer is characterized by a distance s from one of the mirrors, which is one of the solutions of the equation

where N(z) is the refractive index of the medium filling the cavity, depending on the z coordinate measured along the cavity axis from the position selected mirrors, φ is the phase shift of the electromagnetic wave upon reflection from this mirror, λ is the wavelength of the laser. Then the position of the additional absorbing layers will be characterized by the distance s1from this mirror, which is one of the solutions of the equation

Preferably, the active layers of the ima and the thickness of 0.3-10 nm. The minimum limit is determined by the typical distance between the crystal planes of the materials used or the thickness of one molecular layer. If the thickness of the active layer is greater than 10 nm, the difference between quantization levels will be small, which will lead to an increase in the oscillation threshold of the laser.

Preferably, additional absorbing layers had a thickness of 0.3-10 nm. The minimum limit is determined by the thickness of one molecular layer, as in the case of active layers. If the thickness of the additional absorbing layer is greater than 10 nm, it will lead to a noticeable increase in the total losses in the laser and increase the generation threshold.

To simplify the fabrication of heterostructures her make periodic with a period that is a multiple of λ/2N, where λ is the wavelength of the generated radiation, and N is the average refractive index period of the structure. The period change is performed by changing the thickness of the barrier layers. Since generated by pumping nonequilibrium charge carriers accumulate mainly in the active layers, the longer the period of the structure, the greater the concentration of nonequilibrium carriers in these layers with efficient carrier transport. This leads to the reduction of the oscillation threshold. However, the effective transport is achieved when the thickness of the barrier layers of the heterostructure is less than twice the length of the diff is Ziya nonequilibrium carriers in these layers. If the period of the structure is more than twice the diffusion length of carriers, they will recombine before they can reach the active layers, which would reduce the efficiency of the laser.

Required high transport and high radiation efficiency of heterostructures can be achieved only at the low concentration of defects. To reduce the concentration of defects it is necessary that the active barrier and additional absorbing layers of the heterostructure have the same period of the crystal lattice in the plane of the layers. If this condition is not met, then the heterostructure any structural defects in the mismatch of the lattices layers, which significantly deteriorates the characteristics of the laser.

The same period of the crystal lattice of all layers in the heterostructure can be achieved if the materials used to obtain heterostructures, have the same lattice period in the free state. However, this condition restricts the range of materials that can be used, and therefore narrows the spectral range of laser radiation based on them. To increase the spectral range is necessary to use a greater variety of materials with different periods of the crystal lattices. If you do layers of these materials are quite thin which, they will inherit the crystal lattice of the previous layers without the formation of defects. In this case, the layers are elastically strained. If the layer thickness exceeds the critical thickness for the formation of dislocation inconsistencies, the elastic stress in the layer will relax with formation of defects. To ensure that voltage is not accumulated as growing heterostructures, it is advisable to choose the materials and thicknesses of the layers in such a way as to compensate for the elastic stress. Periodic heterostructures, it is desirable to do so within the same period.

Most high performance laser will be achieved provided that the number N and the absorption coefficients αiadditional absorbing layers are selected from the condition

where hithe thickness of the i-th layer, Los - loss of the resonator in one traversal. If

the amplification of the spontaneous noise is not suppressed completely. Indeed, the threshold gain of all active layers in one traversal of the resonator is equal to the losses. Therefore, compared with a loss equivalent to the comparison of the total gain of the active layer. If

,

the loss to the additional absorption in the absorbing layers for fashion resonator will be comparable to losses without these layers that will increase the threshold.

Periodic heterostructure number of additional absorbing layer is approximately equal to the number of active layers. These layers are separated by a thick barrier layer having a wider bandgap. Therefore, approximately half of nonequilibrium charge carriers will accumulate additional absorbing layers. This leads to an increase of the oscillation threshold. To reduce the oscillation threshold introduce additional barrier layers, having a width of the forbidden zone longer than wide bandgap barrier layers, at least 25 MeV and located between the barrier layers and additional absorbent layers. The introduction of these layers prevents the transport of nonequilibrium carriers from a wide barrier layers in additional absorbing layers due to the formation of energy barriers, at least for one of the charge carriers. To effectively limit this transport at room temperature the height of the barrier should be above 25 MeV.

Additional barrier layers have a thickness of 1-10 nm. If their thickness is less than 1 nm, the media will effectively tunnel through them. If the thickness of these layers is greater than 10 nm, it becomes comparable with the thickness of the barrier layers. In this case, has an appreciable fraction of the carriers generated in the additional barrier layers, and half of the C dumped them in more absorbing layers, which again will lead to an increase in the oscillation threshold.

To heterostructure had a low concentration of defects, which impair the characteristics of lasers, all the layers of the heterostructure, including additional barrier layers must have the same period of the crystal structure in the plane of the layers.

To fulfill this condition it is possible to use materials with different periods of crystal lattices, if you do layers of these materials are quite thin. In this case, the layers are elastically strained. To ensure that the voltage is not accumulated as growing heterostructures, it is advisable to choose the materials and thicknesses of the layers in such a way as to compensate for the elastic stress. Periodic heterostructures, it is desirable to do so within the same period.

The region of excitation of the heterostructure has a size along the axis of the resonator in the range of 0.05-10 μm. Size of 0.05 μm corresponds to about a quarter wavelength generation within the heterostructure. When the thickness that is less than 0.05 μm, the heterostructure can not be accommodated simultaneously active layer in the antinodes of the standing wave resonator and an additional absorbent layer. If these layers are placed at a distance smaller than 0.05 μm, the characteristics of the laser worse. When growing a periodic heterostructure thickness of 10 MK is active layers, placed at the antinodes of the resonator mode, the period heterostructures should be designed with a precision of 0.05 μm, that is 0.5%. This is the limit of the possibilities of modern technology of epitaxial growth. Therefore, if the thickness of the heterostructure to do more than 10 μm, it is not all active layers and additional absorbing layers will be placed accordingly in the antinodes and nodes of the resonator mode, which is generated, which degrades the characteristics of the laser.

The size of the excitation area of the heterostructure, at least in one direction exceeds the length along the axis of the resonator more than 100 times. When the size of the region of excitation along the axis of the resonator 10 μm transverse size is 1 mm, This is only slightly more than in the known technical solution. Therefore, if the dimensions along and across the axis of the resonator correlate less than 100 times, then the proposed solution has no advantages over the known solutions.

At least one of the mirrors of the device is made in the form of mirror coating on one surface of the heterostructure. In this laser with small total length of the gain along the axis of the resonator must be used was highly reflective mirrors with a reflectivity of greater than 90%. The fewer active layers, the higher coeff is consistent with a person's reflection should be. Such mirrors can be made of dielectric or semiconductor layers, absorbing or weakly absorbing the generated radiation. It is advisable to use interference coatings of alternating quarter-wave layers with low and high refractive index. Can be used, for example, such pairs of oxides, as SiO2-TiO2, SiO2-ZrO2, SiO2-HfO2, SiO2Ta2O5, Al2O3Ta2O5and others. To increase the reflection of a mirror with a relatively small thickness can be used combined metal-dielectric mirror. In this case, first applied dielectric coating, and above it a thin (50-1000 nm) layer of metal, such as Al, Ag, Au and other elements. When designing the mirror, you should consider its phase response.

The heterostructure can be fabricated so that the first active layer is located at a distance of λ/2N from the surface to be coated mirror coating, designed for the wavelength λ. Then the first layer mirror coating has a lower refractive index. In this case, the phase shift is equal to zero, and the first active layer is in the antinodes of the generated fashion.

Active and barrier layers of the heterostructure made of at least two of the semiconductor, the ellite materials group A2B6 or group A3B5. The choice of semiconductor materials is determined, first of all, what is required wavelength generation. For the ultraviolet region of the spectrum can be used compounds ZnS (group A2B6): ZnSSe, ZnMgS, ZnMgSSe, ZnCdS, ZnCdSSe with the crystal lattice, almost consistent with the crystal lattice of the substrate GaP, as well as connections based on GaN (group A3B5): GaInN, AlGaN, AlGaInN on substrates of Al2O3, GaN, AlN, Si, and others. For the visible area of the preferred compounds based on ZnSe (group A2 B6): ZnMgSSe, ZnSSe, ZnCdSe, ZnCdSSe, ZnCdMgSe on GaAs substrates, InP, ZnSe, CdS, as well as connections GaInP, AlGaInP (group A3B5) on GaAs substrates. For the infrared spectral region are used in the main semiconductor compounds A3B5: AlGaAs, AlInGaAs, GaInSbAs and others.

Additional barrier layers made of semiconductor materials of the group A2B6 or group A3B5. From the point of view of growing technology barrier, an additional barrier and active layers should consist of similar materials, distinguished mainly by the composition of the used solution. For example, for the blue region of the spectrum all of these layers may be made from compounds of Zn1-xMgxSySe1-ymoreover , in the active layers x=y=0, and the additional barrier layers, the concentration of x and y is greater than the barrier layers. In this case, all layers will be weak, massoglia the Ana on the lattice with the GaAs substrate.

Additional absorbing layers in a heterostructure is also easier to perform from the materials group A2B6 or group A3B5. However, unlike active barrier and additional barrier layers, they must be of low lifetime of nonequilibrium carriers. Otherwise, they may form a high concentration of nonequilibrium carriers that will lead to saturation of the absorption. To achieve the small lifetime of nonequilibrium carriers in additional absorbing layers in one embodiment, these layers are alloyed impurities, which form effective channels of nonradiative recombination. These impurities can be, for example, atoms of Cr, Fe, Ni, and others. Nonradiative channels recombination can also be formed due to the intrinsic point defects of non stoichiometry.

You, on the contrary, additional absorbing layers to make defect-free high yield radiative recombination. Furthermore, any additional absorbing layers must have the same composition and thickness. In this case, the decrease in the lifetime of nonequilibrium carriers will be achieved through the creation of inversion in these layers and optical gain at a wavelength of λ1smaller the wavelength of the laser λ. This will lead to effective emptying of additional absorbing layers due to induzirovannich transitions and amplified spontaneous noise at wavelength λ 1.

When additional absorbing layer is applied on the surface of the heterostructure or additional element inside the resonator, this layer may be made of Si, Ge or metal, for example Al, Ag, Au, Cu and other elements.

To simplify the fabrication of heterostructures and resonator, as well as to improve heat transfer from the excited region and increase the service life of the laser, it is advisable, at least one of the mirrors of the resonator to do in the form of the Bragg reflector of the epitaxial layers made of semiconductor materials of the group A2B6 or group A3B5. For infrared and red spectral regions using the Bragg mirror made of alternating quarter-wave layers of AlAs and AlGaAs.

As a means of pumping in one embodiment, the device uses an electron beam. In this case, the laser is made in the form of a sealed vacuum flask, one end of which there is an electron gun that generates an electron beam propagating along the optical axis of the bulb, the other end of the two mirrors and the heterostructure between them, one surface of which intersects the optical axis of the bulb. Both mirrors can be made in the form of a coating on the surface of the heterostructure, thereby forming microresonator. In this embodiment, the energy of the electron beam on who should be large enough (more than 35 Kev), to the energy loss of electrons in the mirror, through which is pumped were immaterial. The generated radiation is output as bombarded through the mirror and through the opposite mirror coating.

In another embodiment, the mirror may be external, and electron beam pumps heterostructure directly through its surface, bypassing the external mirror. In this embodiment, the electron energy can be reduced up to 10 Kev or lower. The generated radiation can deduce as through the external mirror, and through the mirror coating on the opposite surface of the heterostructure.

In one embodiment, as a means of pumping uses a different laser with a quantum energy of the radiation, slightly exceeding the width of the bandgap barrier layers of the heterostructure. The device is equipped with an optical system that directs the laser beam on one surface of the heterostructure to form the region of excitation. As the pump laser can be used, in particular, the laser diode array on the basis of A3B5 compounds that emit in the infrared region, and also on the basis of nitrides of group III, emitting radiation in the near ultraviolet region of the spectrum.

Figure 1 shows the semiconductor laser, which is the closest technical solution to savla is the PTO unit.

On figa presents an active element with a microcavity semiconductor laser pumped by an electron beam according to well-known decision, and PIGB - according to the claimed technical solution.

Figure 3 presents the dependence of the energy position of the edges of the permitted areas of the nanostructure in the direction of the optical axis.

The known semiconductor laser device, represented schematically in figure 1, contains a heterostructure 1, with the first 2 and second 3 surface, two mirrors: was highly reflective flat 4 and the translucent spherical 5, forming an optical cavity with an optical axis 6, and a means of pumping radiation 7, which in the heterostructure is excited volume 8. Was highly reflective flat mirror 4 is located on the side of the first surface 2 of the heterostructure 1, and the translucent spherical mirror 5 is located on the second side surface 3 heterostructures 1. Heterostructure 1 with mirror 4 is fixed on headproposes opaque substrate 9. The means of the pump 7 may be a line of laser diodes with a wavelength smaller than the wavelength of lasing semiconductor laser or electron gun.

Semiconductor laser operates in the following manner. Radiation 10 means pumping radiation is directed to the second surface 3 GE is aerostructure 1 and excites volume 8. In volume 8 occurs spontaneous emission propagating in all directions, and the optical amplification of this spontaneous emission with a maximum in the direction of the optical axis 6. Mirrors 4 and 5 are partially return of spontaneous radiation propagating along the axis of the resonator, back to the excited volume 8, creating a positive feedback. In the generated radiation 11 on one or more of the basic transverse modes of the optical resonator. The radiation 11 is partially out through the semi-transparent mirror 5. If the transverse dimensions of the excitation area of 8 will increase the spontaneous noise, extending across the axis of the resonator, will grow and at some transverse volume 8 will be so great that will reset the inversion population in the heterostructure. This will lead to a decrease in optical amplification and to the breakdown of generation in an optical resonator.

On figa presents in more detail the active element of the semiconductor laser in the variant with microcavity according to known technical solution. In contrast to the variant presented in figure 1, an optical cavity formed by the mirror coatings: 12 was highly reflective and translucent 13, applied directly to both surfaces heterostructures 1. Since the thickness of the heterostructure status is made by one micron, the resonator on figa called microcavity, and the resonator 1 resonator with an external mirror feedback. Hetero 1 on figa contains layers of quantum wells 14 and barrier layers 15. Translucent cover 13 consists of alternating quarter-wave layers 16 and 17 with a smaller and a large refractive indices, respectively. Was highly reflective mirror coating 12 also consists of alternating quarter-wave layers 18 and 19 with a smaller and a large refractive indices, respectively, and a thin metal layer 20. Layers of quantum wells 14 are placed at the antinodes fashion 21 of the optical resonator. Heterostructure 1 with mirror coatings 12 and 13 are placed on the transparent substrate 22 with fastening layer 23.

On figb presents the active element of a semiconductor laser according to one of the variants of the proposed technical solution. Unlike devices on figa heterostructure 24 contains additional absorbing layers 25, located in the nodes of the resonator mode.

The device in figure 2 are as follows. Electron beam 26 impinges on the structure from the side was highly reflective mirror coating 12, penetrates through it in the heterostructure 1 or 24 and generates a nonequilibrium electron-hole pairs in layers of quantum wells 14, the barrier layers 15 and an additional absorbing layer 25. Jus what I mass of nonequilibrium charge carriers generated in the barrier layers 15, because of their thickness considerably greater than the thickness of other layers. Nonequilibrium carriers during the life time to achieve layers of quantum wells 14 and an additional absorbing layer 25 and to gather them in. In one embodiment, additional absorbing layers 25 made of material in which the lifetime of the trapped carriers are few, and they quickly bestlocation recombine. Therefore, in such additional absorbing layers of non-equilibrium carriers are not accumulated, and adsorption properties of these layers does not depend on the excitation level. Nonequilibrium carriers in quantum wells recombine radiantly and, in addition, create optical gain.

In a variant on figa without additional absorbing layers spontaneous emission of quantum wells, extending across the optical axis increases, and with relatively large transverse dimensions volume excitation becomes large enough to force forced to recombine non-equilibrium carriers in quantum wells under the influence of amplified spontaneous noise. As a result, the lasing threshold of the main resonator mode will not be achieved.

In the present embodiment, presented on figb, additional absorbing layers 25 absorb the spontaneous emission propagating at an angle to the optical axis 27 outside the main fashion 21 of the resonator. On the other the part, absorbing layers 25 not introduce additional losses in the main resonator mode, because they are in the nodes, where the electromagnetic field is minimal. As a result of spontaneous noise does not increase with the increase in the transverse dimensions of the volume excitation and does not impair the characteristics of the laser.

In another embodiment, additional shock-absorbing layers accumulated in them nonequilibrium carriers generates optical radiation at the wavelength, the smaller the wavelength quantum wells. As a result of their own amplified spontaneous emission, they are forced to recombine, not accumulating additional absorbing layer, thereby not lost the ability of these layers to absorb the spontaneous noise quantum wells at high pumping levels.

However, part of the nonequilibrium carriers generated by the electron beam is lost due to their transport to additional absorbent layers upon excitation of the heterostructure. To reduce these losses, in another embodiment, the claimed technical solution is introduced an additional barrier layers around an additional absorbing layer. Figure 3 shows the band diagram of the heterostructure with an additional barrier layer 28. These layers prevent the transport of nonequilibrium carriers of the barrier layers 15 in additional absorbing layers 25. In the result of the t is part of the generated nonequilibrium carriers falls within the layers of the quantum well 14.

The proposed technical solution can be proillyustrirovat the following examples.

Example 1. Semiconductor laser in a sealed flask contains a known type electron source with an accelerating voltage of 50 Kev and a means of modulation of the optical resonator with an external semi-transparent mirror feedback was highly reflective and the second Bragg mirror deposited on a conductive substrate is GaAs, and a new heterostructure placed between them. The GaAs substrate is placed on headproposes substrate of an alloy of Cu and W with the coefficient of thermal expansion (CTE)that is equal to a CTE of GaAs. Translucent mirror deposited on the semiconductor flat substrate of ZnSe having an electrical contact with the GaAs substrate and consists of five pairs of alternating quarter-wave layers of SiO2and Ta2O5with the first layer of SiO2on the surface of the ZnSe substrate. The reflectivity of this mirror is equal to 95% at a wavelength of 640 nm. The second surface of the substrate ar-coated ZnSe in a known manner and has a transmittance at a wavelength of 640 nm more than 99%. Bragg mirror consists of 40.5 pairs of alternating quarter-wave layers of AlAs and Al0.5Ga0.5As it is designed for a wavelength of 640 nm, begins and ends with a layer of AlAs. The reflectivity of this mirror more than 99.9% at a wavelength of 640 nm.

The new model has 17 active SL is a MP in the form of quantum wells Ga 0.5ln0.5P with a thickness of 8 nm and 16 additional absorbing layers In0.5Ga0.5As with the thickness of 6 nm, placed in the middle between the active layers. For each additional devouring layer on both sides adjoin additional barrier layers made of (Al09Ga0.1)0.5In0.5P a thickness of 3 nm. Active and additional barrier layers separated by barrier layers of (Al0.6CA0.4)0.5In0.5P with a thickness of 136 nm. The first layer heterostructures side Bragg mirror and the last layer on the external side of the semitransparent mirror is made of (Al0.7CA0.3)0.5In0.5P with a thickness of 191 nm. Total thickness is about 5 μm.

The active laser element that includes a growth substrate GaAs Bragg mirror and the heterostructure, grown in a single process known method of vapor-phase epitaxy from ORGANOMETALLIC compounds.

Upon excitation of the heterostructure electron beam with a diameter of 5 cm with an electron energy of 50 Kev, a current of 1.5 kA and duration of 20 off-peak laser power is 8 MW at a wavelength of 640 nm when the angle of divergence less than 10-4happy. The energy of the light pulse is 0.1 joules. The energy conversion efficiency of the electron beam in the red radiation exceeds 6.5%. Frequent is the pulse repetition pump 300 Hz average power is 30 watts.

Example 2. Laser cathode-ray tube contains at one end sealed flask continuous source of electrons known type, comprising the combination of accelerating and focusing electrodes forming the electron beam with electron energy of 10 Kev and a current of 200 mA, and the other end of the flat laser target located at an angle to the optical axis of the bulb. The device is equipped with a deflecting electromagnetic coil located outside the bulb. Electromagnetic coil scans the electron beam over the surface of the laser target. The target is hedoproduced substrate, water cooled, on which is fixed a heterostructure of a new type. Heterostructure fixed by means of a metal solder surface on which the pre-applied was highly reflective coating of alternating quarter-wave layers of oxides of the type SiO2with a smaller refractive index and oxides of type Ta2O5with a large refractive index. The reflectance of the coating exceeds 99.9%.

The heterostructure contains 4 CB thickness of 6 nm of the compounds ZnSe, separated by barrier layers of Zn0.82Mg0.18S0.24Se0.76the thickness of 86 nm. The top and bottom layers are made of a thickness of 89 nm from the same compounds as barrier layers. On the surface of GE is aerostructure, the opposite surface mounting to headproposes substrate, napalan additional absorbing Si layer thickness of 6 nm. The heterostructure has an active area in the form of a rectangle with sides 4 and 3, see At a distance of 3 cm from the surface of the heterostructure bulb contains a plane-parallel optical window with the illuminated surfaces. Outside of the bulb at a distance of 4 cm from the surface of the heterostructure is placed external flat translucent mirror elements alignment. The reflectivity of the external mirror is equal to 99%.

Electron beam diameter of 1 mm scans on the surface of the laser target with a speed of 1 cm/μs. In the laser target generates radiation at a wavelength of 460 nm with a power of 16 W and angular divergence of less than 10-3happy.

Example 3. The semiconductor laser includes a laser target, as in example 2, the outer flat mirror, a set of arrays of laser diodes on the basis of AlGaInN, emitting at a wavelength of 410 nm. Rulers have fiber bundles forming the round diverging beams of radiation. The emission lines using the focusing lens is directed onto the surface of the heterostructure, where a spot of pumping. When using 10 lines with an output of 35 watts each spot is formed of a pump with a diameter of 3 mm, the result is the generation at the wavelength of 465 nm with a power of 90 W and Lu is ω divergence of less than 3·10 -4happy.

1. Semiconductor laser containing heterostructure in the form of a thin plane-parallel plate, two mirrors that form an optical cavity with an optical axis located on both sides of the heterostructure, and the pumping means, by means of which the heterostructure is excited volume, having a much smaller size along the cavity axis than across, characterized in that the optical resonator includes at least one additional absorbing layer, in which recombination of nonequilibrium carriers, located perpendicular to the optical axis in the node of the resonator mode, the wavelength of which is in the spectrum maximum optical gain of the heterostructure, and the specified absorbing layer absorbs spontaneous radiation propagating at an angle to the optical axis outside the main resonator mode.

2. The laser according to claim 1, characterized in that the additional absorbing layer is placed at least on one surface of the heterostructure.

3. The laser according to claim 1, characterized in that at least one additional absorbing layer is within the heterostructure.

4. The laser according to claim 1, wherein the heterostructure contains the active layers separated by barrier layers, and all layers are oriented perpendicular to the cavity axis.

5. The laser according to claim 4, from which causesa fact, the active layers represent the quantum well, which is the energy well depth of not less than 25 MeV, for at least one of the charge carriers: electrons and holes.

6. The laser according to claim 4, characterized in that the active layers are a set of quantum lines, which is the energy well depth of not less than 25 MeV, for at least one of the charge carriers: electrons and holes.

7. The laser according to claim 4, characterized in that the active layers are a collection of quantum dots, which is the energy well depth of not less than 25 MeV, for at least one of the charge carriers: electrons and holes.

8. The laser according to claim 4, characterized in that the active layers are placed at the antinodes of the resonator mode, the wavelength of which is in the spectrum maximum gain.

9. The laser of claim 8, wherein each active layer is placed at a distance s from one of the mirrors, which is one of the solutions of the equation
,
where N(z) is the refractive index of the medium, depending on the distance from the mirror;
φ is the phase shift on the mirror;
λ - wavelength laser generation.

10. The laser according to claim 1, characterized in that each additional absorbing layer placed at a distance of s1from one of the mirrors, which is one of the solutions of the equation

where N(z) is the refractive index of the medium, depending on the distance from the mirror;
φ is the phase shift on the mirror;
λ - wavelength laser generation.

11. The laser according to claim 4, characterized in that the active layers have a thickness of 0.3 to 10 nm.

12. The laser according to claim 1, characterized in that the additional absorbing layers have a thickness of 0.3 to 10 nm.

13. The laser according to claim 4, wherein the heterostructure is periodic with a period that is a multiple of λ/2N, where λ is the wavelength of the generated radiation, and N is the average refractive index period of the structure.

14. The laser 13, characterized in that period heterostructures less than twice the diffusion length of non-equilibrium carriers in the barrier layers.

15. The laser according to claim 4, characterized in that the active barrier and additional absorbing layers of the heterostructure have the same period of the crystal lattice in the plane of the layers.

16. The laser 15, characterized in that the active barrier and additional absorbing layers of the heterostructure elastically strained due to differences in the periods of the crystal lattice of the material of these layers, in the free state, and these elastic stresses mutually compensated within the same period heterostructures.

17. The laser according to claim 1, characterized in that the number N and the absorption coefficients αiadditional absorbing layer you yaytsa of conditions:
,
where hithe thickness of the i-th layer;
Los - loss of the resonator in one traversal.

18. The laser according to claim 1, characterized in that the additional absorbing layers placed inside the heterostructure containing active layers enclosed between the barrier layers, having a width of the forbidden zone is larger than the width of the forbidden zone of active layers, at least 25 MeV, and an additional barrier layers, having a width of the forbidden zone longer than wide bandgap barrier layers, at least 25 MeV and located between the barrier layers and additional absorbent layers, and all layers of the heterostructure are oriented perpendicular to the cavity axis.

19. Laser p, characterized in that the additional barrier layers have a thickness of 1-10 nm.

20. Laser p, characterized in that all layers of the heterostructure have the same period of the crystal structure in the plane of the layers.

21. The laser according to claim 20, characterized in that the active barrier, additional absorbing and additional barrier layers of the heterostructure elastically strained due to differences in the periods of the crystal lattice of the material of these layers, in the free state, and these elastic stresses mutually compensated.

22. The laser according to claim 1, characterized in that the active region of excitation among the s has a size along the axis of the resonator in the range of 0.05-10 microns.

23. The laser according to claim 1, characterized in that the region of excitation of the active medium has a size at least in one direction perpendicular to the cavity axis, greater than the dimension along the axis of the resonator more than 100 times.

24. The laser according to claim 1, characterized in that at least one of the mirrors is made in the form of mirror coating on one surface of the heterostructure.

25. The laser according to claim 4, characterized in that the active and barrier layers made of at least two semiconductor materials of group A2B6 or group A3B5.

26. Laser p, characterized in that the additional barrier layers made of semiconductor materials of the group A2B6 or group A3B5.

27. Laser p, characterized in that the additional absorbing layers, placed inside the heterostructure made of materials of the group A2B6 or group A3B5, signalisierung atoms of transition metals or other elements, in the presence of which in the absorbing layers dominated by nonradiative recombination of nonequilibrium charge carriers.

28. Laser p, characterized in that the additional absorbing layers inside heterostructures, have the same dimensions and made of the same material, capable in optical pumping to create optical gain at a wavelength of λ1.

29. Laser p is 1, characterized in that the additional absorbing layers located outside of heterostructures made of Si, Ge or metal.

30. The laser point 24, characterized in that the mirror coating is epitaxial Bragg reflector made of semiconductor materials of the group A2B6 or group A3B5.

31. The laser according to claim 1, characterized in that the laser is made in the form of a sealed vacuum flask, one end of which posted by means of pumping in the form of an electron gun that generates an electron beam propagating along the optical axis of the bulb, the other end of the two mirrors and the heterostructure between them, one surface of which intersects the optical axis of the flask.

32. The laser according to claim 1, characterized in that the pumping means is a laser with energy of a quantum of radiation exceeding the width of the forbidden zone barrier layers of the heterostructure, which is provided with an optical system that guides the laser beam on one surface of the heterostructure to form the region of excitation.



 

Same patents:

Semiconductor laser // 2408119

FIELD: physics.

SUBSTANCE: semiconductor laser has a heterostructure in form of a thin plane-parallel plate, two mirrors which form an optical resonator having an optical axis and lying on both sides of the heterostructure, and pumping apparatus. Using the pumping apparatus, a volume is excited in the heterostructure, having a dimension along the axis of the resonator which is considerably smaller than across the axis of the resonator. The optical resonator has at least one extra absorbing layer in which nonequilibrium-carrier recombination takes place. The extra absorbing layer lies perpendicular the optical axis in the resonator mode unit, whose wavelength lies on the maximum of the spectrum of optical amplification of the heterostructure. Said absorbing layer absorbs spontaneous radiation propagating at an angle to the optical axis outside the fundamental mode of the resonator.

EFFECT: increase in power of the laser owing increase in cross dimensions of the excitation region.

32 cl, 1 dwg

Injection laser // 2443044

FIELD: optics.

SUBSTANCE: heterostructure based laser contains waveguide layer placed between wide-gap emitters of p and n-conductivity type that are simultaneously the limiting layers, active zone consisting of quantum-dimensional active layer, optical Fabry-Perot cavity and stripe ohmic contact under which the injection zone is located. In the waveguide layer outside the injection area there is the introduction of the area of semiconductor material with the width of energy gap that is less than the width of energy gap of active area. The factor of optical confinement of closed mode of abovementioned semiconductor material fits the ratio: where: - values of the compounds of optical confinement factor G for closed mode in the introduced area of semiconductor material with the width of energy gap that is less than the width of energy gap of active area, relative units; αNB - optical losses related to interband absorption of closed mode radiation in the introduced area of semiconductor material with the width of energy gap that is less than the width of energy gap of active area, cm-1.

EFFECT: increase of output optic power in both continuous and pulse current injection mode, as well as increased time stability of output active power.

13 cl, 4 dwg

Injection laser // 2444101

FIELD: physics.

SUBSTANCE: heterostructure-based laser has a waveguide layer enclosed between wide-gap emitters with p and n conductivity type, which are simultaneously bounding layers, an active region consisting of quantum size active layer, an optical Fabry-Perot resonator and a strip ohmic contact with an injection region underneath. In the waveguide layer outside the injection region there is a doped region, where the optical limiting factor of the closed mode in the doped region and concentration of free charge carriers in the doped region satisfy the relationship: where: is the value of the component of the optical limiting factor GY in the amplification region for the closed mode, arbitrary units; is the mode loss at the output of the Fabry-Perot resonator, cm-1; αi is loss due to absorption on free charge carriers in the amplification region, cm-1; Δα denotes losses associated with closed mode radiation scattering on irregularities (αSC), inter-band absorption (αBGL) and absorption on free charge carriers in lateral parts of the injection laser, cm-1; is the closed mode optical limiting factor in the doped region, arbitrary units; n, p denote concentration of free electrons and holes in the doped region, respectively, cm-3; σn, σp denote the absorption cross-section on free electrons and holes in the doped region, respectively, cm2.

EFFECT: high optical power output in both continuous and pulsed modes of current pumping, high stability of the output optical power.

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FIELD: physics.

SUBSTANCE: semiconductor infrared source includes a semiconductor substrate (1) with two optically connected and geometrically spaced-apart disc resonators (2) or annular resonators (10) in form of a heterostructure. On the surface of the semiconductor substrate (1) lying opposite the surface with the disc resonators (2) or annular resonators (10) there a first ohmic contact (3). A second ohmic contact (8) is deposited on the face of the corresponding disc resonator (2) or annular resonator (10). The distance from the outer edge of the second contact to the inner edge of the resonator is not more than 100 mcm. The disc resonators (2) or annular resonators (10) lie from each other at a distance L or overlap in the region of waveguides at a depth D, said distance and depth satisfying certain relationships.

EFFECT: simple design and reducing optical loss during single-mode oscillation in the middle infrared spectrum.

2 cl, 14 dwg

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