RU2469438C1 - Semiconductor photodiode for infrared radiation - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention provides a high-efficiency semiconductor photodiode for detecting infrared radiation, which has two mesas formed on the substrate, the surface of one of which is a sensitive area and the other is a contact area, and back and front ohmic contacts. The back contact is solid and is deposited on the side of the substrate and the front contact is in form of a bridge, wherein the longitudinal axis of the bridge is directed at an angle of 40-50° to the crystal direction {110} of an A³B⁵ substrate. The bridge is electrically insulated from the mesa with the contact area by an anodic oxide and at least one dielectric layer deposited on it.

EFFECT: high efficiency of the photodiode owing to simultaneous increase in operating speed and detecting capacity of the device.

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Description

The invention relates to optoelectronic technology, namely to semiconductor photosensitive devices for detecting infrared (IR) radiation at room temperature. These semiconductor IR photodiodes can be used in various fields of science and technology, in industry: in diode-laser spectroscopy, in medicine, in ranging and location systems, in optical superfast computing and switching systems, in optical communication and information transmission systems, including , through the open air channel.

Currently, there is an urgent need for photodiodes for detecting short laser pulses in the infrared spectrum. Various types of lasers have been developed for this spectral range: semiconductor lasers based on GaSb and its solid solutions - quantum cascade, with a Fabry-Perot resonator and with a disk resonator operating at room temperature, as well as powerful compact solid-state lasers based on YAG and Nd crystals -KGW doped with ions of Ho, Tm and Er. However, the problem of creating highly efficient high-speed receivers for detecting radiation from such lasers has not been solved.

For example, there are high-speed Ge-based photodiodes for the spectral range of 1.0-1.7 μm. However, receivers with a speed above 100 ps in the wavelength range 1.7–5.0 μm are absent. This prevents the creation of medical equipment such as a new type of optical tomograph, delays the development of optical communication lines in open space (Free-Space Optics Communication), which do not require the laying of expensive fiber-optic communication channels (FOCL). Modern photodiodes of the spectral range 1.7–5.0 μm have a number of significant drawbacks. As a result of intensive research, both in Russia and abroad, photodiodes based on A ³ B ⁵ semiconductors have been created to date, based on both binary compounds (InAs, InSb, GaSb) and multicomponent solid solutions (GalnAsSb / GaAlAsSb, InAs (Sb) / InAsSbP). One of the main drawbacks of InAs, InSb, and InAs / InAs (Sb) / InAsSbP photodiodes is the inability to provide high efficiency without deep cooling, and such photodiodes demonstrate acceptable performance only at cryogenic temperatures (-196 ° C).

The task of creating high-performance high-speed infrared receivers operating at room temperature makes us look for new alternative approaches to the principles of operation and design of devices. An increase in the efficiency of photodiodes is possible by increasing the detection ability and increasing speed. The detectability of a D * photodiode is determined by the following formula [Jones R.C. Performance of Detectors for Visible and Infrared Radiation in book Advances in Electronics, Academic, New York, 5, 1 (1953)]:

where R _i is the current monochromatic sensitivity, A / W, S is the area of the sensitive area, cm ² ; i _n - noise current value, A.

From formula (1) it follows that to increase the detecting ability of the photodiode, it is necessary to reduce the value of the noise current, which is associated as follows with the value of the inverse dark current:

where i _d is the value of the inverse dark current, A; q is the electron charge, C

On the other hand, to increase the D * of the photodiode, it is necessary to increase the area of the sensitive area S, which leads to an increase in the intrinsic capacitance and, consequently, a decrease in the speed of the photodiode.

Thus, the task of increasing the efficiency of the photodiode for infrared radiation based on A ³ B ⁵ semiconductors due to a simultaneous increase in its detecting ability and speed has not been solved.

One of the drawbacks of existing photodiodes for infrared radiation based on A ³ B ⁵ semiconductors is a decrease in their efficiency due to shadowing of the sensitive area by a metal front contact located on its surface. The area of the sensitive area S decreases by the size of the contact area on its surface, while the D ^{* of the} photodiode decreases. In formula (1), S is the effective area of the sensitive area, namely, the area of the surface sensitive to infrared radiation, not occupied by contacts.

For semiconductor device types such as transistors [LI Xian-Jie, CAI Dao-Min, ZENG Qing-Ming, LIU Shi-Yong, LIANG Chun-Guanng, Self-Aligned InP / InGaAs single heterojunction bipolar transistor with novel micro-airbrige structure and quasi-coplanar contacts, Chin. Phys. Lett. 20 (2), 311 (2003)], Schottky diodes [A.Notargiacomo, R. Bagni, E. Giovine, V. Foglietti, S. Carta, M. Pea, L. Di Gaspare, G. Capellini, F. Evangelisti , Fabrication of air-bridge Schottky diodes on germanium for high speed IR detectors, Microelectron. Eng. (2011), doi: 10.1016 / j.mee.2010.11.046] bridge contacts are known.

Known pin photodiode for infrared radiation based on InAsSb for the spectral range of 2.5-4.9 μm [V.V. Sherstnev, D. Starostenko, I.A. Andreev, G. G. Konovalov, N. D. Ilyinskaya, O. Yu. Serebrennikova, Yu.P. Yakovlev, Letters in ZhTF 37 (1), 11-17 (2011)], taken as an analogue. The photodiode includes a mesa with a sensitive area formed on the surface of a semiconductor heterostructure, ohmic contacts. The heterostructure on the n-InAs substrate consists of a wide-band InAsSbP layer, an active region of InAs _0.88 Sb _0.12, and a wide-gap InAsSbP window. The diameter of the sensitive area of the photodiode is 300 microns. The frontal contact to the p-InAsSbP layer is point with a diameter of 30 μm and the contact area is located on the surface of the sensitive area of the photodiode. The back contact to the n-InAs substrate is continuous. The long-wavelength boundary of the spectral sensitivity of the photodiode reaches 4.9 μm at T = 300 K. The short-wavelength boundary of the spectral sensitivity of the photodiode is 2.5 μm. The current monochromatic sensitivity of the photodiodes at the maximum of the spectrum (λ _max = 4.0–4.6 μm) has a value of R _i = 0.6–0.8 A / W, which corresponds to a quantum efficiency of 15–20%. The density value of the reverse dark currents of the photodiode is (1.3-7.5) × 10 ^-2 A / cm ² at a reverse bias voltage of U = -0.2 V. The speed of the photodiode is typical for devices based on A ³ B ⁵ and is 1-5 ns. The detecting ability of photodiodes at the maximum spectral sensitivity, taking into account the current monochromatic sensitivity and the magnitude of the noise determined by shot noise of resistance of 200-500 Ohms, reaches D ^* = (5-8) × 10 ⁸ W ^-1 × cm × Hz ^1/2 .

The advantages of this photodiode include the ability to work at room temperature in the long wavelength range of 2.5-4.9 microns.

The main disadvantage of the analog device is the low efficiency due to the low detection ability and speed of the photodiode. The detecting ability of the D ^* photodiode is reduced due to the shadowing of the sensitive area by a metal frontal contact located on its surface. In addition, in this design, a decrease in the area of the sensitive area, which allows to reduce its own capacitance and, accordingly, increase the speed of the photodiode, will lead to a further decrease in the detection ability.

Known pin photodiode for infrared radiation based on GaInAsSb for the spectral range of 0.9-2.4 μm [I.A. Andreev, O. Yu.Serebrennikova, G.S.Sokolovsky, E.V. Kunitsyna, V.V. Dudelev, I. M. Gadzhiev, A.G. Deryagin, E.A. Grebenshchikova, G.G. Konovalov, M.P. Mikhailov, N.D. Ilyinskaya, V.I. Kuchinsky, Yu.P. Yakovlev, Letters in ZhTF 36 (9 ), (2010)], taken as an analog. The photodiode includes a mesa with a sensitive area formed on the surface of a semiconductor heterostructure, ohmic contacts. The heterostructure on the n-GaSb substrate consists of the active region of n-Ga _0.78 In _0.22 As _0.18 Sb _0.82 and the wide-gap p-Ga _0.66 Al _0.34 Sb _0.025 As _{0.975 window} . The diameter of the sensitive area of the photodiode is 100 μm. The frontal contact to the p-GaAlAsSb layer is point with a diameter of 30 μm and the contact area is located on the surface of the sensitive area of the photodiode. The back contact to the n-GaSb substrate is continuous. The long-wavelength boundary of the spectral sensitivity of the photodiode reaches 2.4 μm at T = 300 K. The short-wavelength boundary of the spectral sensitivity of the photodiode is 0.9 μm. At zero bias, the photodiodes had their own capacitance of 2.0-3.0 pF. At a reverse bias of 3.0 V, the capacitance of the photodiode is 0.9–1.2 pF. The monochromatic current sensitivity at a wavelength of λ = 2.1 μm reaches R _i = 0.9-1.1 A / W, which corresponds to a quantum efficiency of 0.6-0.7 without antireflection coating. The inverse dark current for the best photodiode samples is (500-1000) nA at a reverse voltage U = - (0.5-3.0) V. The detecting ability of photodiodes, determined by the formula [1], at the maximum of the spectrum has the value D * = 9.0 × 10 ¹⁰ W ^-1 × cm × Hz ^1/2 . The speed of the photodiode, determined by the rise time of the photoresponse pulse at the level of 0.1-0.9, is (130-150) ps. The passband of photodiodes reaches a value of 2 HGz.

The advantages of this photodiode include a fairly high speed for infrared detectors in the spectral range of 0.9-2.4 μm with a high detection ability, i.e. quite high efficiency at room temperature.

The main disadvantages of the analog device are a decrease in efficiency due to shading of the sensitive area by a metal frontal contact located on its surface, which leads to a decrease in the effective area of the sensitive area and, thus, to a decrease in the D ^{* of the} photodiode, as well as the impossibility of further reducing the intrinsic capacity of the photodiode, therefore, increasing its speed while maintaining / increasing the detection ability by reducing the area of the sensitive area.

Known fast-acting pin photodiode based on InGaAs for a selective tunable receiving device - a filter operating at a wavelength of 1.55 μm with a tuning range of 44 nm [C. Dhanavantri, H. Halbritter, OPDaga, JP Pachauh, F. Riemenschneider, P. Meissner, and BRSingh, Fabrication of PIN diodes for WDM tunable and wavelength selective receivers, in Proc. 7th Conference on Optoelectronics, Fiber Optics & Photonics (Photonics), Cochin, Indien, Dezember 2004, p. 340], taken as a prototype. The photodiode includes a mesa with a sensitive area formed on the surface of a semiconductor heterostructure based on A ³ B ⁵ , ohmic contacts. The heterostructure on the n-lnP substrate consists of buffer layers of In _0.52 Al _0.48 As and In _0.53 Ga _0.47 As, with a total thickness of 65 nm, doped n ⁺ layers of In _0.52 Al _0.48 As, In _0.53 Ga _0.47 As and In _0.52 Al _0.48 As, 200 nm thick, 50 nm and 500 nm, respectively; undoped active region In _0.53 Ga _0.47 As; the upper p ⁺ layers In _0.52 Al _0.48 As and In _0.53 Ga _0.47 As, 200 nm and 50 nm thick. A Bragg dielectric mirror of 7 SiO _s / Ta ₂ O ₅ pairs is applied to the structure from the InP substrate side, which is necessary for using the photodiode as a selective tunable filter. Wet etching was used to create the mesa. At the first stage, all layers to the contact n ⁺ -In _0.53 Ga _0.47 As layer were removed from the front surface of the heterostructure around the sensitive Mesa site. In the second stage of step etching, on one side of the mesa, all layers were removed to the InP substrate. The diameter of the sensitive area of the photodiode is 100 μm. The ohmic contacts p ⁺ and n ^{+ are} made frontal, since a Bragg mirror is deposited on the back side of the substrate. Two contact pads are formed on opposite sides of the Mesa on the frontal surface: n ⁺ -Ti / Pt / Au - on the contact n ⁺ -In _0.53 Ga-As layer, p ⁺ -Pd / AuGe / Au - on the surface of the InP substrate. The ohmic contact p ⁺ -Pd / AuGe / Au, reinforced with electrolytic gold 2.5 microns thick, is made in a bridge configuration. One end of the bridge in the form of a ring with a diameter close to the diameter of the mesa lies on a sensitive area. The other end of the bridge is connected to the contact p ⁺ platform on the surface of the InP substrate.

The peak spectral sensitivity of InGaAs-based photodiodes grown on an InP substrate lies at a wavelength of 1.55 μm. The spectral sensitivity range of the photodiodes is narrow — the half-width of the peak at half maximum is 0.2 nm and the peak tuning range is 44 nm. Photodiodes with a Mesa diameter of 100 μm have their own capacitance at a zero bias of ~ 2.5 pF. At a reverse bias of 3.0 V, the capacitance of the photodiode drops to ~ 1.0 pF. The capacitance density varies from 7.7 μF × cm ^-2 to 9.7 μF × cm ^-2 with a change in mesa diameter from 500 μm to 60 μm. The reverse dark current density of 100 μm photodiodes is ~ 10 nA at a reverse voltage of U = -3.0 V. The bandwidth of the InGaAs / InAlAs / InP photodiodes reaches 2.5 GHz.

This bridge photodiode design minimizes stray capacitance. Namely, when the photodiode is included in the circuit as a selective filter, the contact wires supplied to the n ⁺ and p ⁺ contact pads are not located above the working mesa of the device, and the stray capacitance arising between the contact wire and the conducting layers of the working mesa is absent. However, due to the location of the p ⁺ contact pad directly on the InP substrate, an additional capacitance appears, which reduces the speed of the photodiode. Since one end of the contact bridge lies on the sensitive area and the other is connected to the contact area on the surface of the InP substrate, the bridge is located in different planes and undergoes double bending. Such a bend leads to mechanical stresses and a decrease in the reliability of the structure, which, in turn, requires the creation of a sufficiently thick bridge and a large area ring at its end connected to the sensitive area. This ring obscures the sensitive area, the effective area of the photodiode decreases, and the detection ability of the device decreases.

The creators of the prototype device managed to minimize parasitic capacitance, but the intrinsic capacitance of the InGaAs / InAlAs / lnP photodiode was not reduced to the limiting values for this material. Thus, the passband of this photodiode is 20 times smaller than the known Ge-based photodiodes operating in the same spectral range of 1.55-1.7 μm [Klinger, M. Berroth, M. Kaschel, M. Oehme, E. Kasper, Photonics Technology Letters, IEEE 21 (13), 920 (2009)].

The advantages of this photodiode include an increase in its efficiency, namely, an increase in speed due to a decrease in stray capacitance due to the bridge front contact.

The main disadvantages of the prototype photodiode are low reliability and lack of efficiency. The reliability of the design of the photodiode decreases with mechanical stresses arising due to the bending of the bridge frontal contact. Losses in detecting ability occur due to significant shading of the sensitive area by the annular part of the bridge contact, and in speed due to the high intrinsic capacitance for the photodiode based on these materials and the occurrence of additional capacitance when the contact area is located on the substrate.

The problem solved by the invention is to increase the efficiency of a semiconductor photodiode for infrared radiation based on A ³ B ⁵ heterostructures.

The problem is solved semiconductor photodiode for infrared radiation, comprising a heterostructure based on semiconductor compounds A ³ B ⁵ on the substrate A ³ B ⁵ with two formed mezami, the rear and front ohmic contacts to geterostrukgure, the back contact is formed to be continuous and applied to the substrate, and the front is made in as a bridge connecting the mesa of the bridge, the longitudinal axis of which is oriented at an angle from 40 ° to 50 ° to the crystalline direction {110} of the substrate A ³ B ⁵ , which is electrically isolated from one of the mesas by the anode layer oxide with at least one dielectric layer deposited on this layer.

The technical result when using the present invention is to increase the efficiency of the photodiode by simultaneously increasing the speed and detecting ability of the device.

In such a photodiode, as the authors revealed, the formation of two meshes allows one to remove most of the frontal contact outside the sensitive area on the surface of one mesa and place it on the surface (contact area) of another mesa. Unlike a prototype having one mesa and, as a result, a metal contact bridge bending in two places, the contact bridge in the proposed photodiode is located in the same plane and does not require a large area of the contact ring to increase the mechanical strength of the contact ring at its end connected to the sensitive area . The frontal contact in the form of a bridge does not obscure the sensitive area, thereby increasing the detection ability D ^{* of the} device. The authors found that, unlike the prototype, in a photodiode with two mesas, it is possible to reduce the area of the sensitive area regardless of the frontal contact area. And if in the prototype the performance increases slightly, only by reducing the parasitic capacitance when creating a bridge contact, then in the proposed photodiode the speed increases both by reducing the parasitic capacitance and, more significantly, by reducing the device’s own capacitance. Orientation of the bridge contact in the desired crystalline direction allows one to obtain a smooth (without steps) etching profile of the heterostructure under the contact, which leads to a decrease in the reverse dark currents of the photodiode, therefore, the noise level and, as a result, to an increase in the detection ability.

The performance of a semiconductor photodiode with a pn junction is determined by three factors - the diffusion time of carriers created by infrared radiation to the space charge region, the time of flight of the space charge region of the carriers, and the RC time constant. The proposed photodiode (like the prototype) has a wide-gap window that is transparent to the received radiation in the infrared spectral range. Such a design makes it possible to suppress surface recombination and ensure carrier generation in the space charge region, thus eliminating the contribution of the diffusion component determined by the carrier diffusion time to the space charge region. Since the time of flight by carriers of the space charge region of the pn junction, whose thickness for semiconductors in heterostructures based on A ³ B ⁵ is 2-3 μm, the authors estimate that it is less than 10 ps (τ = 10 ^-11 -10 ^-12 s), which determines speed factor is the inherent capacitance of the photodiode. Thus, an increase in the speed of the photodiode can be achieved by reducing the intrinsic capacity of the device. In turn, the intrinsic capacitance of a semiconductor photodiode is determined by the concentration of carriers in the active region and the area of the sensitive area. The concentration of carriers in the epitaxial layers of A ³ B ⁵ can be reduced to such a low level as 10 ¹⁴ -10 ¹⁵ cm ^-3 with high structural perfection of the layer and low density of misfit dislocation (<10 ⁴ cm ^-2 ) at the heteroboundaries, which should be attributed to the advantages of photodiodes based on A ³ B ⁵ heterostructures. Further reduction of the area of the sensitive area in the prototype photodiode is practically impossible, because a bridge frontal contact located in different planes and undergoing double bending is connected to a sensitive area with a large-area metal ring to increase the reliability of the structure. A decrease in the area of the sensitive area with this design will lead to a decrease in the detection ability of the photodiode due to the significant shadowing of the sensitive area by the annular part of the frontal contact. In contrast to the prototype, the proposed photodiode has two mesas formed, which makes it possible to independently reduce the sensitive area of one of them and increase the area of the contact area of the other. The sensitive and contact pads are connected by a frontal ohmic contact made in the form of a metal bridge isolated from the contact pads with anode oxide and deposited on it with at least one more dielectric layer. With this design of the photodiode, the layers of the heterostructure under the bridge contact are etched simultaneously with the etching of the mes. The etching depth should be sufficient to etch the layers under the metal bridge and, thus, the formation of two mesas. In addition, the etching should provide a smooth (without steps) etching profile. Otherwise, each of the steps and inhomogeneities will lead to an increase in the leakage currents of the photodiode, making, as found by the authors, the suppressing contribution to the magnitude of the inverse dark current of photodiodes with small diameters of the sensitive area (<300 μm). As a result, the noise level will increase and the detection ability of the photodiode will drop. To solve this problem, the authors propose to orient in a certain way a metal bridge relative to the crystallographic directions in the material, taking into account the difference in etching rates in different directions. The proposed photodiode is based on semiconductors A ³ B ⁵ . For all A ³ B ⁵ compounds, dissolution rates depend on the orientation as follows: V {111} B> V {110}> V {100} >> V {111} A. The authors found that if the longitudinal axis of the contact bridge is oriented at an angle of (40-50) ° to the crystallographic direction {110}, then, for example, wet etching makes it possible to obtain a smooth (without steps) profile under the contact. This leads to a decrease in the value of the reverse dark currents of the photodiode and, consequently, the noise level and, ultimately, to an increase in the detection ability. This statement is valid for all crystalline semiconductors A ³ B ⁵ .

To electrically isolate the metal bridge contact from the contact pad, and thereby the contact pad from the sensitive one, a dielectric is used. The authors found that the use of a multilayer dielectric consisting of anode oxide and other dielectric layers simultaneously allows:

- get a sufficiently thick dielectric layer with a thickness of at least 0.3 μm, providing reliable electrical isolation of the bridge contact from the material of the heterostructure A ³ B ⁵ ;

- reduce the height of the step of the dielectric due to the characteristics of the anodic oxidation process.

It is known that the presence of sharp steps of the dielectric is undesirable in the manufacture of devices due to the occurrence of cracks during thermal deposition of the metal, as well as due to possible defects during photolithographic processes associated with the heterogeneity of the deposition and exposure of the photoresist on the topological steps. A feature of the chemical properties of the materials A ³ B ⁵ under consideration determines the need to create a topological pattern only by explosive photolithography, as a result of which a sharp edge of the dielectric step is obtained a priori. Anodic oxide on the surface of the A ³ B ⁶ heterostructure is formed deep into the material. This makes it possible to obtain a total dielectric thickness of not less than 0.3 μm with a decrease in the height of the dielectric step by 2/3 of the magnitude compared to the height of the dielectric step formed in the absence of anode oxide.

The invention is illustrated in figure 1 and figure 2.

Figure 1 schematically shows the proposed semiconductor photodiode for the infrared spectrum, where

1 - substrate;

2 - a mesa with a sensitive area;

3 - a mesa with a contact pad;

4 - spoilers of dielectrics;

5 - rear ohmic contact;

6 - front ohmic contact in the form of a bridge.

Figure 2 schematically shows a top view of a semiconductor photodiode for the infrared spectrum, where

2 - a mesa with a sensitive area;

3 - a mesa with a contact pad;

6 - front ohmic contact in the form of a bridge.

Photodiode operates as follows. When a photon of infrared radiation hits a mesa surface with a sensitive area 2, it passes through a wide-gap window and is absorbed in the space charge region of the pn junction between the wide-gap window and the active region. When a photon is absorbed, an electron-hole pair is formed, which is separated by the electric field of the space charge. Electrons reach the rear ohmic contact 5 and the holes to the front ohmic contact 6 and form a photocurrent in the external circuit. The photocurrent, passing in the external circuit, forms a voltage on the load resistance, which is proportional to the photocurrent. This voltage is measured in the external circuit by an oscilloscope or voltmeter.

Example 1

The created semiconductor photodiode included a heterostructure based on A ³ B ⁵ semiconductor compounds on a GaSb substrate 1, two mesa 2 and 3 formed on the heterostructure surface, rear 5 and front 6 ohmic contacts. The heterostructure on substrate 1 made of n-GaSb consisted of an active region (n-Gao _0.78 In _0.22 As _0.18 Sb _0.82 ) of a thickness of 1-3 μm and a wide-gap window (p-Ga _0.66 Al _0.34 Sb _0.025 As _0.975 ) with a thickness of 0.5-2.5 μm. Based on the heterostructure, a semiconductor photodiode for IR radiation with two mesas was fabricated. The surface of one Mesa 2 was a sensitive area, and the surface of another Mesa 3 was a contact area. The sensitive area was made in the form of a circle with a diameter of 50 μm, the contact area was in the form of a rectangle with dimensions of 50 × 70 μm. The rear AuTe / Au ohmic contact 5 was deposited on an n-GaSb substrate and made continuous. Frontal ohmic contact 6 was formed to the p-GaAlAsSb layer and was a bridge 20 μm wide and 85 μm long. The bridge was formed by deposition of Cr-Au with a thickness of 2200 Å, and deposition of galvanic Au with a thickness of 3-6 μm. To ensure contact, on one side, the bridge went to the sensitive area 2 by 10 μm, and on the other side - on the contact area 3, covered by dielectric 4. From the side of the contact area, the bridge ended with a rectangular part 60 × 40 μm in size. The longitudinal axis of the bridge was oriented at an angle of 45 ° to the crystalline direction {110} of the substrate. Mesa formed by wet etching after contact. The bridge contact 6 is isolated from the contact pad 3 and, therefore, the semiconductor material of the heterostructure with a two-layer dielectric 4 with a thickness of 0.3 μm, consisting of an anode oxide layer with a thickness of 0.2 μm and a Si ₃ N ₄ layer with a thickness of 0.1 μm.

The long-wavelength limit of the spectral sensitivity of the photodiode reached 2.4 μm at T = 300 K. The short-wavelength limit of the spectral sensitivity of the photodiode was 0.9 μm. To reduce the concentration of the main carriers in the active region, tellurium was used as a dopant. The study of the capacitance-voltage characteristics showed that the impurity distribution in the heterostructure was sharp, and the carrier concentration in the active region was (0.7–2) 10 ¹⁵ cm ^–3 . At zero bias, the photodiodes had their own capacitance of 1.0-2.0 pF. At a reverse bias of 3.0 V, the photodiode capacitance was 0.5–1.9 pF. The monochromatic current sensitivity at a wavelength of λ = 2.1 μm was R _i = 0.9-1.1 A / W, which corresponds to a quantum efficiency of 0.6-0.7 without antireflection coating. The inverse dark current for the best photodiode samples was 200-500 nA at a reverse voltage U = - (0.5-3.0) V. The detecting ability of photodiodes, estimated by formula (1), at the maximum of the spectrum has the value D ^* = 1.2 × 10 ¹¹ W ^-1 × cm × Hz ^1/2 . The speed of the photodiode, determined by the rise time of the photoresponse pulse at the level of 0.1-0.9, amounted to 50-100 ps. The passband of photodiodes reaches 5 HGz.

This infrared photodiode has high efficiency due to its record-breaking detectability and speed in this spectral range up to 2.4 microns. Unlike the prototype, in this photodiode, the frontal bridge contact slightly approaches the sensitive area and obscures less than 1/10 of its area, which makes it possible to obtain a high value of detection ability. In the prototype device, the speed was increased by reducing the parasitic capacitance, while in the proposed photodiode, the speed was increased by reducing both the parasitic and the device’s own capacitance. In contrast to the prototype, the presence of two meshes allows, regardless of the area of the contact pad, to reduce the area of the sensitive pad, reducing its own capacity. In addition, in the prototype, the location of the contact area on the substrate leads to the appearance of additional capacity. In the proposed device, the contact pad is the surface of one of the mesas, which avoids additional capacity.

Comparison with the prototype is possible only by design. Comparison of the parameters of the developed photodiode and prototype is difficult, since the parameter values, including the spectral range of the device, depend on the selected material. However, the new design solutions described in the claims allow for a photodiode based on any A ³ B ⁵ semiconductor compounds to obtain an increase in efficiency due to a simultaneous increase in its detecting ability and speed. Also, in comparison with the prototype, the reliability of the design of the developed photodiode is higher, since the bridge frontal contact is located in the same plane and does not undergo bends.

Example 2

The same as in Example 1, but the longitudinal axis of the bridge was oriented at an angle of 40 ° to the crystalline direction {110} of the substrate. As a result, the inverse dark current for the best photodiode samples increased slightly compared to the photodiode in Example 1 and amounted to 300-600 nA, which led to a slight decrease in the detection ability of photodiodes to D ^* = 1.0 × 10 ¹¹ W ^-1 × cm × Hz ^{1 / 2} and did not affect the values of the remaining parameters of the photodiode. It is shown that, in comparison with the prototype, the photodiode has the same advantages as the photodiode in Example 1.

Example 3

The same as in Example 1, but the longitudinal axis of the bridge was oriented at an angle of 50 ° to the crystalline direction {110} of the substrate. As a result, the inverse dark current for the best photodiode samples increased slightly compared to the photodiode in Example 1 and amounted to 300-600 nA, which led to a slight decrease in the detection ability of photodiodes to D ^* = 1.0 × 10 ¹¹ W ^-1 × cm × Hz ^{1 / 2} and did not affect the values of the remaining parameters of the photodiode. It is shown that, in comparison with the prototype, the photodiode has the same advantages as the photodiode in Example 1.

Example 4

The same as in Example 1, but the longitudinal axis of the bridge was oriented at an angle of 35 ° to the crystalline direction {110} of the substrate. During the formation of mesas with a given pattern, etching under a metal frontal contact in the form of a bridge did not occur, and two formed mesas were not isolated from each other. Further etching led to a distortion of the shape of the side walls of the mes.

Example 5

The same as in Example 1, but the longitudinal axis of the bridge was oriented at an angle of 55 ° to the crystalline direction {110} of the substrate. During the formation of mesas with a given size pattern, etching under the metal frontal contact in the form of a bridge was incomplete and the shape of the side walls of the mesas in the region of the bridge was strongly distorted.

Claims (1)

A semiconductor photodiode for infrared radiation, comprising a heterostructure based on semiconductor compounds A ³ B ⁵ on the substrate A ³ B ⁵ with two formed mezami, the rear and front ohmic contacts to the heterostructure, the back contact is formed to be continuous and applied to the substrate, and the wheel is designed as a connecting Mesa bridge, the longitudinal axis of which is oriented at an angle of 40 ° to 50 ° to the crystal direction of the {110} substrate of A ³ B ⁵ are electrically insulated from one of the mesas anodic oxide layer and Nana ennym this layer at least one dielectric layer.

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