Semiconductor infrared photodiode. RU patent 2521156.

FIELD: physics, optics.

SUBSTANCE: invention relates to semiconductor optoelectronics, specifically to infrared detectors, and can find application in spectrometers, detection and monitoring systems, security, fire-protection and communication systems. The infrared photodiode (1) has p and n regions (2, 3, 7) with current-conducting opaque contacts (4, 5) and an active region which is electrically connected to the p-n junction (6), wherein one or more contacts on the surface of the region which receives photons from the investigated object have a common perimeter, the value of which is selected from a range of values associated with the current spreading length. Contacts on the surface of the region receiving photons from the investigated object have elements with a repeating geometric shape, e.g. in form of a spiral or cellular structure. The active region of the photodiode is made of INAsSb, InAs, InGaAsSb, and the layer on the illuminated side is made of INAs_1-x-y Sb_xP_y (o<x<0.2, y=(2-2.2)·x) and has contacts from a series of metal layers Cr-Au_1-w-Zn_w-Ni-Au, wherein the Cr layer adjoins the surface of the p region, and w=0.01-0.2.

EFFECT: photodiode according to the invention provides high photosensitivity to radiation in the middle infrared region of the spectrum.

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The invention relates to the field of semiconductor optoelectronics, specifically - to the receivers infrared (IR) radiation, and can be used in spectrometers, in systems of detection, tracking, security and fire systems and communications.

In the spectral region (3-5 microns) dominant position by the volume of use to take photodetectors of CdHgTe and PdSe(PbS). This stems in part from a well-developed technology podrostkovoy processing of these materials and an extremely large range for the width of the forbidden zone in CdHgTe, allowing to manufacture photodiodes both in the first and in the second window transparency of the atmosphere [1, 2]. Methods of obtaining PbSe(PbS) is easy, and research photodetectors based on them were started in the middle of the last century. At the same time, both of these materials are characterized by the presence of noise (1/f, besides obtaining high values of detecting abilities required, as a rule, thermoelectric cooling.

The alternative materials are semiconductors A 3 B 5 , which, unlike the above have the metallurgical stability and resistance to moisture. Basic research aimed at the creation of photodiodes of the most suitable for the range (3-5 microns) semiconductor - indium arsenide - were made in the 70 years of the last century, and for several decades on the market are produced by industrial firms Hamamatsu, AG&G photodiodes with a red border at 3.6 microns, based on Homo-p-n-structures. However, photodiodes on the basis of Homo p-n junctions have low resistance values at zero offset. For example, in [3] lists the values of R 0 =30-55 Ohm (R 0 A~0.1 Ohm·cm-2 ) for structures obtained on a substrate of p-InAs MOCVD method that is not enough for many applications. Therefore, actual photodiodes that use heterostructures, allowing to achieve high values of R 0 A. For example, when using a wide gap window on the surface of InAs, widening of the spectral curve in the area of short wavelengths, managed to reduce surface recombination [4] and to avoid the problems associated with the formation of inversion layer on the surface of gallium indium p - type [5] with a simultaneous increase in the values of R 0 A.

The creation of photodetectors with border photosensitivity at a wavelength of 4-5 mm was mainly connected with the use of Nanoheterostructures as a material of the active region. Covered with epitaxially hand layers Nanoheterostructures received on substrates n-InAs (more precisely, for the buffer layers of n-Nanoheterostructures, previously grown on InAs) [6], on GaAs substrates [7] or GaSb [8]. In the latter case were applied solid solution composition Nanoheterostructures 0.1 having the same with GaSb the lattice period at the temperature epitaxy.

Known photodiode for the middle infrared range of the spectrum, including p - and n-region with the current-carrying contacts, divided p-n-junction, active area, electrically connected with p-n-junction, with at least one of the contacts on the surface of the region, receiving photons from the examined object, made transparent in the work area wavelengths [9]. In a decision on the surface patterns GaSb/In(Al)GaAsSb by the method of sputtering in vacuum suffered continuous current-carrying contacts from CdO, or ZnO, or RuSiO4. These materials contact had the transparency of >80%, which provided the ability minimize shading contact hotspots and increased photosensitivity. However, the materials used have a low refractive index (see table 1), so the contacts of these materials on svetoprinimayuschego surface creates difficulties for production of effective immersion photodiodes. The dependence of the detecting ability of immersion FD from the refractive index layer located between FD and lenses are described in [10].

Optical properties of materials contacts

Contact material

The refractive index λ=2.2 microns

Known photodiode for the middle infrared range of the spectrum [11], which coincides with the proposed technical solution for the highest number of essential features and taken as a prototype, with photodiode prototype reflects the most common version of the design used in practice [12], [13]. Photodiode prototype includes p - and n-region with the current-carrying opaque contacts, divided p-n-junction, active area, electrically connected with p-n junction, and one contact on the surface of the region, receiving photons from the examined object. Epitaxial structures for photodiode was obtained on the substrate GaSb serial growing by the method of molecular-beam epitaxy layer of solid solution of n-GaInAsSb, LEGIROVANNOGO tellurium (Te) of thickness 2 mkm, and the layer p-GaInAsSb doped with germanium (Ge) thickness of 1 mm. This active region was made of solid solution InGaAsSb with the lattice period, close to the lattice period GaSb, diameter Mesa-diode, i.e. the diameter of the active area of 300 microns, contacts, consisting of alloy AuGe, occupied only a small part of the structure. Diameter of contact according to [12] was 50 microns.

The disadvantage of the photodiode for the middle infrared range of the spectrum is the low sensitivity at room temperature and unacceptably low at elevated temperatures.

The objective of the invention is development of such photodiode for the middle infrared range of the spectrum, which would have increased photosensitivity both at room and elevated temperatures.

The problem is solved by the fact that the photodiode for the middle infrared range of the spectrum includes p - and n-region with the current-carrying opaque contacts divided p-n-junction, active area, electrically connected with p-n-junction, with one or more contacts on the surface of the region, receiving photons from the target, have a common perimeter, the value of which is chosen from the interval:

where P p n ,S p-n - perimeter and area of the active part of the p-n junction, respectively, P cont - total perimeter of all areas of the contact(s)involved in the collection of the photocurrent L spr - length current spreading,

- perimeter contact with the lowest production processes in the area.

Each of the contacts on the surface of the region, receiving photons from the studied object that can contain elements with duplicate geometry.

At least part of the contact(s) may be made in the form of a spiral.

At least part of the contact(s) may have a cellular structure.

In some cases, the minimum distance between the edges of adjacent elements of the contact(s) does not exceed half the length of the current spreading L spr .

A hotspot can be made of Nanoheterostructures.

The hotspot can also optionally contain a gallium atoms, while the lattice active area close to the lattice InAs.

The hotspot can also optionally contain phosphorus atoms.

Region, receiving radiation, can be made of solid solution InAs 1-x-y Sb x P y (o<x<0.2, y=2-2 .2)·x).

Region, receiving radiation can optionally contain a gallium atoms.

Contact(s) to p-region can be performed(s) from the sequence of metal layers Cr-Au 1-w-Zn w-Ni-Au, and the layer of Cr is adjacent to the surface of p-region, a w=0.01-0.2.

Unlike photodiode prototype in the present PD pin on the illuminated surface (contact involved in the collection of the photocurrent) has increased the perimeter, in the prototype perimeter contact was value

, i.e. had the size, due to the requirement of obtaining a minimum of shading active area while maintaining the possibility of electrical connection with wire, typical for production processes. Enlarged perimeter of contact allows the collection of the photocurrent more effectively than in the photodiodes with a small perimeter of the contact. In photodiodes for middle infrared range of the spectrum of the photocurrent are unevenly distributed over the surface: in the immediate vicinity of the contact he's maximum and minimum in areas remote from the contact. The specified property irregularity increases with the decrease of the band gap and/or by increasing the temperature of the photodiode. Therefore, photodiodes with small size of the contact (i.e. at small perimeter) efficiency, especially at the wavelengths longer than 3 microns, or at temperatures above 40 C, low. On the contrary, photodiodes with enlarged perimeter even if shading significant part of the active region (for example, when using solid contact all forms) have increased efficiency.

Values of optimal total perimeter of all areas of the contact(s)involved in the collection of the photocurrent R cont , is inside the interval:

where R the p-n ,S p-n - perimeter and area of the active part of the p-n junction accordingly, R cont - total perimeter of all areas of the contact(s)involved in the collection of the photocurrent L spr - length current spreading,

- perimeter contact with the lowest production processes in the area.

The length of the current spreading L spr , i.e. the distance over which the current decreases in the (e) time from values close contact is defined by the ratio between dynamic resistance of the p-n junction in the zero offset (R (o ) and the resistance of the p - and n-areas and the relation between the geometrical characteristics of the sample (thickness, lateral size, location and shape). To calculate values L spr use the formalism presented in the monograph by Franz Schubert [14], articles [15] or determined experimentally using the methods of atomic force microscopy together with methods Kelvin (Kelvin probe), allowing to determine the potential distribution on the surface of [16], or use the infrared image (i.e. 2D distribution of intensity) surface FD, which is filed with the offset [17, 18].

contact with the appropriate geometry is not possible to collect a large part of the photocurrent and efficiency photodiode low, despite a small degree of shading active area.

a large part of those born in the active region of pairs of electron-hole contributes to the high overall number of born couples is low due to shading greater part of the active area of the contact. Because of this efficiency also a small photodiode.

The implementation of each of the contacts on the surface of the region, receiving photons from the examined object, with elements with duplicate geometry increases the perimeter of interaction with pairs of photoexcited electron-hole, as described above, and thus it leads to increase of efficiency of the photodiode.

Perform at least part of the contact(s) in the form of a spiral increases the efficiency of the photodiode, because this form of communication provide minimum shading active area with maximum perimeter of contact in case, when the width of spiral contact parts maximally reduced in relation to the used technological processes.

Part of the contact(s) in a honeycomb structure, it is important to increase stability (strength) contact connection with the semiconductor, i.e. to increase the efficiency of photodiode at a continuous operating time or under adverse conditions, such as thermal Cycling.

The implementation of contacts with minimum distance between the edges of adjacent elements of the contact(s)in excess of half the length of the current spreading L spr, allows to receive a photodiode with maximum efficiency, because it ensures the efficient collection of the photocurrent with minimum shading active area. In photodiodes, in which the distance between the edges of adjacent elements of the contact(s) more than half L spr , collection of the photocurrent is carried out effectively, and therefore they are ineffective.

With an active area of Nanoheterostructures provides creation affecting photodiodes, durable at elevated temperatures because unlike other materials for the middle-IR range (for example, CdHgTe) solid solution InAsSd has metallurgical stability.

With an active area of Nanoheterostructures with additional content gallium atoms and lattice, close to the lattice InAs, provides an additional increase of durability at high temperatures due to the "hardening" of solid solution InGaAsSb. The proximity of the lattice periods layer InGaAsSb and InAs provides, on the one hand, the necessary wavelength range in the middle IR range, and on the other, allows a perfect crystal (and, therefore, effective) photodiodes.

Introduction the fifth component - phosphorus - provides the ability to accommodate not only the lattice, and coefficients of thermal expansion and substrate material layer, which increases the efficiency with long-term experience in the conditions of changing temperature..

Performing region, receiving radiation from solid solution InAs 1-x-y SbxPy(o<x<0.2, y=(2-2 .2)·x) provides increased efficiency due to the increase in the total height of the barrier on hetero p-n junction, provided that the material is not created defects (dislocations inconsistencies), i.e. y=(2-2 .2)·H. When x>0.2 obtained compounds InAs 1-x-y SbxPy are within the field of nesmeshivaemost, i.e. in areas with unstable properties where obtain qualitative layers difficult.

Introduction in the area of solid solution InAs 1-x-y Sb x P y fifth component - gallium - provides the ability to accommodate not only the lattice, and coefficients of thermal expansion and substrate material layer, which increases the efficiency with long-term experience in the conditions of changing temperature.

The execution of the contact(s) to p-region of the sequence of metal layers Cr-Au 1-w-Zn w-Ni-Au in which a layer of Cr is adjacent to the surface of p-region, a w=0.01-0.2, increases the efficiency with long-term experience in the conditions of high temperatures, as is the most reliable and long-lived of all known author.

The proposed device is illustrated by drawings, where

figure 1 illustrates schematically the first variant of realization of the claimed photodiode for the middle infrared range of the spectrum,

figure 2 schematically shows the second variant of the photodiode for the middle infrared range spectrum,

figure 3 shows schematically the third variant of realization of the claimed photodiode for the middle infrared range of the spectrum,

Declare photodiode for the middle infrared range of the spectrum 1 (see figure 1)includes the p - 2 and n-region 3 with the current-carrying opaque pins 4, 5, divided p-n-junction 6, the active area 7, electrically connected with p-n-junction 6, with one or more contacts on the surface of the region, receiving photons from the target 8 have a total perimeter, the value of which is chosen from the range of values derived by calculation.

The second variant of the incarnation of the photodiode for the middle infrared range of the spectrum 1 (see figure 2) is different from the first version that the contact has elements with duplicate geometry, creating a cellular form. In addition, the second contact is formed not on the back of the photodiode, as in the first option, and on the side facing the studied object.

The third variant of the incarnation of the photodiode for the middle infrared range of the spectrum 1 (see figure 3) is different from the first version fact that at least part of the contact 4 is made in the form of a spiral. From the second variant it also differs in that second contact 5 performed a limited area, i.e. the "point".

Declare photodiode for the middle infrared range of the spectrum is as follows. The external energy source, such as registered object, with increased compared with the background temperature produces a stream of photons, which are active in the region 7 through the surface, taking photons from the target 3, where absorbed, producing a pair electron-hole, shared a potential barrier on the p-n junction 6. Separated couples create an electric field, preventing further movement of excess carriers to the p-n-transition 6. The change in voltage across the p-n junction with pins 4, 5 registered in external circuit in the form of the useful signal. With the closure of pins 4, 5 V circuit current flows, which is a useful signal to the photocurrent.

Example 1. An example of executing the photodiode was implemented in LLC "Offered using standardized processes of graded structures InAsSbP on the substrate InAs method LPE. The samples were similar to those described earlier [19] and had a smooth change of the composition of the thickness of the gradient layers InAsSbP. After conducting photolithography and removal of the substrate by chemical etching photodiode included the p-region of Nanoheterostructures (2), n is the area of Nanoheterostructures (7), InAsSbP (5), limited mesaj etching by the diameter 300 mm with the current-carrying opaque contacts (4, 5), divided p-n-junction p-InAsSbP/n-InAs (6), the active area of Nanoheterostructures (7), electrically connected with p-n-junction, with a contact surface area p-Nanoheterostructures taking photons from the studied object (4, anode), formed by the deposition of metal compositions Cr-Au 1-w-Zn w-Ni-Au (w=0.05) in vacuum, had a diameter of 50 microns and was located in the center Mesa; rear opaque metal contact to n-InAsSbP (5, cathode), formed by the deposition of metal compositions Cr-AuGe-Ni-Au in vacuum, was solid, occupying the entire surface of n-InAs. Before the measurements of photosensitivity FD mount in standard enclosure-18, and the contact with the lowest production processes in the area had a diameter of 50 microns, and the length of the current spreading (L spr ) was 280 mcm. The upper contact to metal disk with a diameter of 50 microns was carried out by welding or soldering indium gold wire with a diameter of 30 mm. In the second case there is a possibility to change the contact area, conducting repeated soldering of contact with different mass solder. As a radiation source served Globe with a temperature of 300 C.

Figure 4 presents the data of measurements of photosensitivity (photocurrent at a fixed density of the incident flow) in a series of identical FD described above and differ only in diameter D cont , (perimeter P cont ) non-transparent anode on the receiving photons surface. As can be seen from the data in figure 4, the sensitivity of photodiodes in which the perimeter of the anode to satisfy the condition

meet the range of values dotted lines, was at least two times higher than in known FD with point contact cont D =50 mm. Outside of the interval from the side of large diameter contact photosensitivity decreased due to shading actions of contact and advantages over known photodiode was not.

Example 2. In the second example, the execution of the photodiode, and the last was made of heterostructures, are similar to those described in the first example, but Mesa (active area p-n junction) had the form of a square with a side of 450 mm. Besides, the contact on the receiving photons surface consisted of United together recurring rectangular elements forming a "comb" of 3 strips of a width of 20 micron, located in parallel each other and electrically connected together by a rectangular element 300 x 100 mm. Extreme elements of the "comb" contact shaped like the letter "W" Russian alphabet, were located from the edge of the Mesa at a distance of 75 microns, and the contact had perimeter R cont =1800 mm, the value of which was inside optimal from our point of view interval 275......2275 microns, calculated using the proposed ratios. For comparison was made with FD point contact (cont D =50 mm), located in the centre of the square Mesa. Both PD had been installed as described above, with photosensitivity FD with point contact was 5 times lower than that claimed FD with a "W"-shaped contact.

Example 3. The samples were similar to the previous described in examples 1 and 2, and had a solid bottom pin (n-InAs). The top terminal (p-Nanoheterostructures(P)) had four modifications: 1) a circle with a diameter of 80 microns, located in downtown Mesa, 2) contact according to claim 1, which added to strips of width 10 microns, the components of a pattern in a clamshell window frames without vents"; the Central strip of contact was connected with the circle, 3) contact according to claim 2, which added two more stripes that form unshaded areas in the form of elongated rectangle, 4) the contact in section 3 with the addition of another four bars, two "new" strips connected (crossed) the Central circle. The geometry of the contacts shown in the sidebar to the right of figure 5. Photosensitivity was measured by using the model of a black body heated up To 573; it was expected that in the FD dominates Consonance (thermal) noise and when calculating D*shadowing contact was not taken into account, the calculations include full power flux incident on the whole Mesa; in measurements of the photoresponse spectra were used Globe.

Figure 5 shows the current-voltage characteristics (I-V) for the four types of samples described above. Range of photosensitivity received diodes had a maximum at ~ 5.3 flash off (300 K) (l) cut-off. =5.8 flash off) and was caught in a wavelength region due to diffusion of photogenerated carriers to the p-n-transition.

As can be seen from Figure 5, three out of four samples (№2-4), with a developed structure of contact, have approximately the same values dark current saturation (I sat approximately 40 mA); the average values of stresses more current is followed by the increase in the area of the anode. Diode with point contact (no. 1) was characterized by almost 2 times less in comparison with the above FD-current and the absence of a pronounced saturation in the return leg of the I-V characteristics. In our case, the increase in the perimeter of the contact (it was possible to increase photosignal at least three times; figure 6 shows the dependence of the sensitivity (S I ), detecting ability (D λ ), dynamic resistance at zero offset (R'o ) from perimeter of the anode, confirming what was said.

Remember that if you increase the perimeter of the contact is not only the increase photosensitivity, but also a decrease in the dynamic resistance FD due to increasing the area participating in ecoprogetti, i.e. gathering area of the photocurrent. Therefore, when working with such FD need to match the increase in the photocurrent with the possibility of increased noise photoreception device consisting of FD & amp signal. The approach for this analysis is given in [20].

The author thanks Zakheim A.L., Elias N, Karandasheva S.A., Galskogo I.V., Polovinkina WATTS. Belt M.A., Rybalchenko, A., Stusa N.M. and Chernyakova AU for use in experiments.

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1. Photodiode for the middle infrared range of the spectrum, including p - and n-region with the current-carrying opaque contacts divided p-n-junction, active area, electrically connected with p-n-junction, with one or more contacts on the surface of the region, receiving photons from the target, have a common perimeter, the value of which is chosen from the interval:

where R the p-n , S p-n - perimeter and area of the active part of the p-n junction, respectively, P cont - total perimeter of all areas of the contact(s)involved in the collection of the photocurrent L spr - length current spreading, the perimeter of contact with the lowest production processes in the area.

2. Photodiode according to claim 1, wherein each of the contacts on the surface of the region, receiving photons from the studied object that contains elements with such geometry.

3. Photodiode according to claim 1, wherein at least a portion of the contact(s) made in the form of a spiral.

4. Photodiode according to claim 1, wherein at least a portion of the contact(s) has a cellular structure.

5. Photodiode according to claim 1, characterized in that the minimum distance between the edges of adjacent elements of the contact(s) does not exceed half the length of the current spreading L spr .

6. Photodiode on any one of claims 1 to 5, wherein the active area is made of Nanoheterostructures, or InGaAsSb, or INGaAsPSb.

7. Photodiode on any one of claims 1 to 5, wherein the region, receiving radiation, is made of solid solution InAs 1-x-y Sb x y P (a<x<0.2, y=(2-2 .2)·x).

8. Photodiode according to claim 7, wherein the contact(s) to p-region performed(s) from the sequence of metal layers Cr-Au 1-w Zn w-Ni-Au, and the layer of Cr is adjacent to the surface of p-region, a w=0.01-0.2.