Semiconductor element emitting light in ultraviolet range

IPC classes for russian patent Semiconductor element emitting light in ultraviolet range (RU 2262156):

H01L33 - Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof (H01L0051500000 takes precedence;devices consisting of a plurality of semiconductor components formed in or on a common substrate and including semiconductor components with at least one potential-jump barrier or surface barrier, specially adapted for light emission H01L0027150000; semiconductor lasers H01S0005000000)

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Semiconductor element emitting light in ultraviolet range / 2262156
Proposed semiconductor element that can be used in light-emitting diodes built around broadband nitride elements of A^IIIB^V type and is characterized in ultraviolet emission range extended to 240 -300 nm has structure incorporating substrate, buffer layer made of nitride material, n contact layer made of Si doped nitride material Al_XIIn_X2Ga_I-XI-X2N, active layer made of nitride material Al_VIIn_Y2Ga_I-YI-Y2N, and p contact layer made of Mg doped nitride material Al_ZIIn_Z2Ga_I-ZI-Z2N; active layer is divided into two areas; area abutting against contact layer is doped with Si and has n polarity of conductivity; other area of active layer is doped with Mg and has p polarity of conductivity; molar fraction of Al (YI) in p area of active layer is continuously and monotonously reducing between its boundary with n contact layer and boundary with p area of contact layer and is within the range of 0.1 ≤ VI ≤ 1; difference in VI values at boundaries of active-layer n area is minimum 0.04 and width of forbidden gap in active-layer p area at its boundary with active-layer n area exceeds by minimum 0.1 eV the maximal width of n area forbidden gap.

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Light-emitting diode incorporating optical component / 2265917
Proposed light-emitting diode has light-emitting chip covered by optical component made of translucent material whose outer surface is aspherical in shape due to rotation of curve f(x) built considering optical properties of light-emitting chip and optical component material about symmetry axis of light-emitting diode. This surface emits light and f(x) curve in coordinate system whose origin coincides with geometric center of active area of light-emitting diode has initial point A₀ disposed on ordinate axis at distance corresponding to characteristic size of light-emitting diode which is, essentially, optical component height or its desired diameter, and is formed by plurality of points A, (i = 1, 2... n); coordinates of intersection point of straight line drawn from coordinate origin point at angle α_ini to ordinate axis drawn from preceding point A_{i - 1} at angle G_i to abscissa axis drawn to point A_{i - 1} are taken as coordinates of each of them;; α_ini is angle of propagation of i_in light beam pertaining to plurality of beams emitted by light-emitting chip chosen between 0 and 90 deg. Angle G_i is found from given dependence. Angle α_outi is found by pre-construction of directivity pattern DP_in of beam emitted by light-emitting chip. Coordinates of A points are checked by means of light-emitting diode simulator that has optical component whose outline is formed by plurality of A_i points as well as light-emitting chip whose beam directivity pattern is DP_in; this chip is used as distributed light source having three-dimensional emitting area whose size and appearance correspond to those of emitting area used in light-emitting diode of light-emitting chip. Light emitting points in light-emitting chip of simulator under discussion are offset relative to origin of coordinates within its emitting area; coordinates of A_i points are checked by comparing directivity pattern DP_out and directivity pattern DP_sim of beam emitted by light-emitting diode simulator, both displayed in same coordinate system. When these directivity patterns coincide, coordinates of points A_i function as coordinates of points forming curve f(x); if otherwise, coordinates of points A_i are found again, and DP_outj is given as directivity pattern DP_out whose points are disposed above or below the latter, respectively, depending on disposition of directivity pattern DP_sim below or above directivity pattern DP_out in the course of check.

FIELD: semiconductor emitting devices.

SUBSTANCE: proposed semiconductor element that can be used in light-emitting diodes built around broadband nitride elements of A^IIIB^V type and is characterized in ultraviolet emission range extended to 240 -300 nm has structure incorporating substrate, buffer layer made of nitride material, n contact layer made of Si doped nitride material Al_XIIn_X2Ga_I-XI-X2N, active layer made of nitride material Al_VIIn_Y2Ga_I-YI-Y2N, and p contact layer made of Mg doped nitride material Al_ZIIn_Z2Ga_I-ZI-Z2N; active layer is divided into two areas; area abutting against contact layer is doped with Si and has n polarity of conductivity; other area of active layer is doped with Mg and has p polarity of conductivity; molar fraction of Al (YI) in p area of active layer is continuously and monotonously reducing between its boundary with n contact layer and boundary with p area of contact layer and is within the range of 0.1 ≤ VI ≤ 1; difference in VI values at boundaries of active-layer n area is minimum 0.04 and width of forbidden gap in active-layer p area at its boundary with active-layer n area exceeds by minimum 0.1 eV the maximal width of n area forbidden gap.

EFFECT: enlarged ultraviolet emission range, enhanced inherent emissive efficiency, simplified design of light-emitting component.

1 cl, 1 dwg, 1 tbl

The invention relates to the field of semiconductor emitting devices, more particularly to led-based wide bandgap nitride compounds of the type A^IIIB^V.

Known semiconductor light-emitting element containing a substrate, a buffer layer, an n-contact layer made of GaN and doped Si, p-contact layer made of GaN and doped Mg, F.Calle et al., MRS J.Nitride Semicond. Res. 3 (1998) 24.

This solution provides maximum simplicity of construction of the device, however, does not allow to obtain high internal efficiency of radiation and the radiation wavelength less than 365 nm.

Also known semiconductor element emitting light in the ultraviolet range, the structure of which sequentially includes a substrate, a buffer layer made of a nitride material, an n-contact layer made of a nitride material Al_x1In_y1Ga_1-x1-y1N-doped Si, an active layer made of nitride material Al_x2In_y2Ga_1-x2-y2N doped simultaneously donors and acceptors, and the p-contact layer made of a nitride material Al_x3In_y3Ga_1-x3-y3N doped with Mg, where the above-mentioned layers form either unilateral or bilateral heterostructure, US 6005258.

In this design to improve the internal quantum efficiency is aktivnosti light-emitting element is either colagiovanni donors and acceptors in the active layer heterostructures, or replacement unilateral bilateral patterns.

This solution is chosen as the prototype of the present invention.

However, this semiconductor light-emitting element is suitable primarily for the generation of radiation with a wavelength of 350 nm or more. In the shorter-wavelength range of the internal efficiency of the radiation device prototype degrades sharply.

This is because for the work item in the ultraviolet spectral range (wavelength 300 nm or less) require the use of nitride compounds with a high content of AlN. In this case, the most significant factors that determine the effectiveness of radiation, are the limitation of carriers in the active layer and the suppression of the potential barriers associated with the polarization charges that occur at the interfaces to the stepwise change of the composition. The device prototype limitation of carriers within the active layer is not enough. In the injected holes can freely penetrate into the n-contact layer, and electrons in the p-contact layer, where they recombine predominantly bestlocation, leading to a sharp decrease in internal efficiency.

This invention laid the task of expanding the range of ultraviolet radiation to 240-300 nm, is ysenia internal emission efficiency while simplifying the design of the light-emitting element.

According to the invention this problem is solved due to the fact that in a semiconductor element, sluchayem light in the ultraviolet range, the structure of which sequentially includes a substrate, a buffer layer made of a nitride material, an n-contact layer made of a nitride material Al_X1In_X2Ga_1-X1-X2N-doped Si, an active layer made of nitride material Al_Y1In_Y2Ga_1-Y1-Y2N, and the p-contact layer made of a nitride material Al_Z1In_Z2Ga_1-Z1-Z2N doped with Mg, the active layer is divided into two areas, while adjacent to the contact layer region doped Si and has a conductivity of n-type and the other region of the active layer doped with Mg and has a conductivity of p-type, the mole fraction of Al (Y1) in the area of the active layer with n-type conductance continuously and monotonically decreases from the boundary with the n-contact layer to the border with the region of the active layer, having conductivity of p-type, and is within 0.1≤Y1≤1, and the difference values Y1 on the borders of the area of the active layer with n-type conductance is at least 0.04, and the width of the forbidden zone in the region of the active layer with a conductivity of p-type on its border region with n-type conductance at least 0.1 eV greater than the maximum width of the forbidden zone field with n-type conductance.

The applicant has not identified the sources containing information about technical solutions, identical to the present invention, which allows to make a conclusion about its compliance with the criterion of "novelty".

Implementation characteristics of the invention provides improved emission efficiency due to the expansion of the active layer as compared with the traditional bilateral structures based on quantum wells, where the critical factor is the quality of the interfaces and the doping profile near them. In addition, a wide active area reduces the heat load on the active layer, which further favors the efficiency of the device.

The use of the contents of InN layers of the heterostructure with the specified molar shares In, on the one hand, reduces the concentration of intrinsic point defects in the material, which is favourable for increasing the internal efficiency of the radiation, and on the other hand, does not decay phase solid solutions of Al_xIn_yGa_1-x-yN, accompanied by the generation of extended defects, drastically reducing the quantum yield of radiation.

To suppress the penetration holes in the n-contact layer in the proposed design applies a smooth change in the width of the forbidden zone in the n-region of the active layer due to the variation of its composition. This creates for the of Iroc built-in electric field, dilatory them from the n-contact layer toward the boundary of the p-n junction. The magnitude of the pull field is controlled by the difference of the values at the boundaries of the areas of the active layer with n-type conductance in the range of 0.04.

To prevent the penetration of electrons into the p-contact layer is formed leap composition (and, hence, the width of the forbidden zone) on the border regions of the active layer with a conductivity of n - and p-type (n - and p-regions). To a potential barrier for electrons created by this leap was effective and at high levels of injection, it is necessary that the width of the forbidden zone in the p-region of the active layer on the boundary of the n-region was 0.1 eV greater than the maximum width of the forbidden zone in the n-region of the active layer.

The applicant has not found any sources of information containing data about the impact of an alleged distinguishing characteristics to be achieved as a result of their implementation of the technical result. This, according to the applicant demonstrates compliance with this technical solution, the criterion of "inventive step".

The semiconductor element in a specific implementation, all of the examples has a structure which includes in series:

the substrate 1 made of sapphire, of a thickness of 500 microns;

- a buffer layer 2 of AlN with a thickness of 20 nm;

- the n-contact layer 3 made of AL₁ IN_X2GA_1-X1-X2N, in this example, X₁=0,52; X₁can vary from 0.1 to 1.0; X₂can vary from 0 to 0.05. Layer 3 doped with silicon to a concentration of 5·10¹⁸cm^-3thickness 1.5 mm;

an active layer made of Al_Y1In_Y2Ga_1-Y1-Y2N, where Y₁=0,52, may lie in the range from 0.1 to 1, Y₂=0, and can be in the range from 0 to 0.05; the active layer includes a region 4, Si alloy with a concentration of 5·10¹⁸cm^-3with n-type conductance, and region 5, Mg alloy with a concentration of 5·10¹⁹cm^-3having conductivity of p-type;

- the p-contact layer 6 made of Al_Z1In_Z2Ga_1-Z1-Z2N, where the value of Z₁=0,52; Z₁may vary in the range from 0.1 to 1.0; Z₂may be in the range from 0 to 0.05. Layer G is alloyed with magnesium concentration 5·10¹⁹cm^-3thickness of 100 nm.

The semiconductor element represents one side of the led heterostructure with a variable composition of the active layer, which allows to obtain the internal efficiency at the level of 15-35% at current densities varying in the range of 1 A/cm²to 100 A/cm²and of threading dislocations ˜10⁹cm^-2. It should be noted that the decrease of the dislocation density in the led leads to a sharp appreciation is of its internal efficiency. When the density of dislocations ˜10⁷cm^-2it is possible to obtain the internal quantum efficiency exceeding 90%.

To test the heterostructure was grown on a sapphire substrate by the method of ISO-hydride epitaxy at subatmospheric pressure and temperatures between 1000°1100°C, n-contact layers and the n-region of the active layer legionares Si to a concentration of 5·10¹⁸cm^-3that was installed by using Sims (secondary ion mass spectrometry). the p-region of the active layer and the p-contact layers were legionares Mg to a concentration of 5·10¹⁹cm^-3.

After the growth process, the structure was subjected to dry (ion) etching to form a Mesa to a depth corresponding to the level n-contact layer. Further etched and the remaining parts of the structure were applied respectively n - and p-contacts, which is a multilayered metal compositions, respectively, Ti/Al/Pt/Au and Ni/Au. Contacts were vigilis in nitrogen atmosphere at a temperature of 850°C for 30 seconds.

Forth from patterns cut out the individual LEDs, which are mounted on the heat sink p-contact down, and they were soldered gold electrodes for supplying electric current.

To study fluorescence characteristics of the LEDs used spectrometer HLCAS-12 with specially selected, diffractio the Noah bars, allows measurements in the ultraviolet spectral range. As detector we used a photomultiplier tube PMT-100. The signal from the photomultiplier via a digital voltmeter Is transferred to the computer for final processing of the measurement data.

Accurate measurements of the radiation intensity was not less than 0.02%.

To measure the external efficiency of the led used calibrated photodetector based on amorphous Si:H (silicon doped with hydrogen). The measurements were performed at a fixed geometry of the experiment, which allows to quantitatively compare the radiation of different samples.

The electroluminescence of the LEDs were measured at the output of the radiation through the sapphire substrate.

The resulting test characteristics of the semiconductor light-emitting elements are shown in table 1.

Table 1
Number example	The parameters of semiconductor element	The internal quantum efficiency at current density of from 1 to 10²A/cm²	The wavelength range (nm)
1	Share Al Y₁=0,42 in the n-region (50 nm), and Y₁=0.62 in the p-region (50 nm); the proportion of Al in the p-contact layer Z₁=0.62	0,14-0,11	250-290
2	Share Al Y₁=0,42 in the n-region (50 nm), and Y₁=0,70 (10 nm) near the boundary with the n-region and Y₁=0,52; the proportion of Al in the p-contact layer Z₁=0.52	0,13-0,14	250-290
3	The proportion of Al decreases from Y₁=value of 0.52 to 0.42 in the thickness of 10 nm in the n-region, and then increases from Y₁=0,42 to Y₁=0,62 on the thickness of 10 nm in the p-region; the proportion of Al in the p-contact layer Z₁=0.62	0,15-0,23	250-290
4	The proportion of Al decreases from Y₁=value of 0.52 to 0.42 in the thickness of 20 nm in the n-region, and then increases from Y₁=0.52 to Y₁=0,70 on the thickness of 10 nm in the p-region; the proportion of Al in the p-contact layer Z₁=0.52	0,17-0,32	250-290
5	The proportion of Al decreases from Y₁=value of 0.52 to 0.42 in the thickness of 50 nm in the n-region, and then is Y₁=0,62 on the thickness of 20 nm in the p-region; the proportion of Al in the p-contact layer Z₁=0.62	0,15-0,34	250-290
6	The proportion of Al decreases from Y₁=value of 0.52 to 0.42 in the thickness of 20 nm in the n-region, and then is Y₁=0,62 on the thickness of 20 nm in the p-region; the proportion of Al in the p-contact layer Z₁=0.62	0,17-0,22	250-290
7	The proportion of Al decreases from Y₁=0,52 0,62 to the thickness of 20 nm in the n-region, and then increases from Y₁=0,42 l is Y ₁=0,54 on the thickness of 50 nm in the p-region; the proportion of Al in the p-contact layer Z₁=0.54	0,02-0,12	250-290

In examples 3, 4, 5, 6 internal quantum efficiency of the semiconductor device exceeds 15% and reaches into separate structures more than 30% at a current density of 100 a/cm². A further increase in current density leads to increase of efficiency of up to ˜50% at the current density ˜1 kA/cm²that it is important to create powerful LEDs and lasers in the ultraviolet range.

Examples confirm the high efficiency of radiation in the shortwave part of the ultraviolet spectrum.

For the realization of light-emitting elements used in the standard industrial equipment, which makes the invention according to the criterion of "industrial applicability".

The semiconductor element emitting light in the ultraviolet range, the structure of which sequentially includes a substrate, a buffer layer made of a nitride material, an n-contact layer made of a nitride material Al_X1In_X2Ga_1-X1-X2N-doped Si, an active layer made of nitride material Al_Y1In_Y2Ga_1-Y1-Y2N, and the p-contact layer made of a nitride material Al_Z1In_Z2Ga_1-Z1-Z2N doped with Mg, the best of the decomposing those the active layer is divided into two areas, while adjacent to the contact layer region doped Si and has a conductivity of n-type and the other region of the active layer doped with Mg and has a conductivity of p-type, the mole fraction of Al (Y₁in areas of the active layer with n-type conductance continuously and monotonically decreases from the boundary with the n-contact layer to the border with the region of the active layer, having conductivity of p-type and is within 0.1≤Y₁≤1, and the difference of the values of Y₁on the borders of the area of the active layer with n-type conductance is at least 0.04, and the width of the forbidden zone in the region of the active layer with a conductivity of p-type on its border region with n-type conductance at least 0.1 eV greater than the maximum width of the forbidden zone field with n-type conductance.