RU2769232C1 - Structure photosensitive to infrared radiation and method for its manufacture - Google Patents

Abstract

FIELD: optical detector technology.SUBSTANCE: invention relates to photodetector devices of the infrared wavelength range and the technology for their manufacture. The structure photosensitive to infrared radiation includes a substrate, a first layer of CdxHg1-xTe with a variable composition located on the substrate, in which x varies from 1 at the boundary with the substrate to xPSat the boundary with the absorbing layer, a homogeneous absorbing layer of CdxHg1-xTe with a composition of xPS=0.22-0.4 2-4 microns thick located on the absorbing layer, a second layer of CdxHg1-xTe with a variable composition located on the first layer with a variable composition , in which x varies from xPSat the boundary with the absorbing layer to xBat the boundary with the barrier layer, located on the second layer with a variable composition, a homogeneous barrier layer of CdxHg1-xTe with a composition of xB= 0.6-0.7 0.2-0.5 microns thick, located on the barrier layer, a third layer of CdxHg1-xTe with a variable composition, in which x varies from xBat the boundary with the barrier layer to xCat the boundary with the contact layer, located on the third layer with a variable composition, a homogeneous contact layer of CdxHg1-xTe with a composition of xCS=0.22-0.4 1-2 microns thick, the fourth layer of CdxHg1-xTe with variable composition located on the contact layer, in which x varies from xCSat the boundary with the contact layer to xD= 0.6-1.0, while a passivating layer is located on the fourth layer of CdxHg1-xTe with a variable composition, and a metal field electrode of In is applied to the surface of the passivating layer, and the geometric dimensions of the field electrode are chosen so that the minimum distance from the edge of the field electrode to the edge of the area bounding the region of the photosensitive structure would be equal to 1.0-1.2 microns. A method for manufacturing this photosensitive structure is also proposed.EFFECT: invention provides for the elimination of the observed contribution of surface leakage currents to the formation of a dark signal of a photosensitive nBn structure based on HgCdTe.22 cl, 4 dwg

Description

SUBSTANCE: invention relates to infrared technology and technology for manufacturing devices of infrared technology, specifically, to photodetectors in the infrared wavelength range and technology for their manufacture.

The need to develop third-generation photodetectors imposes increased requirements on detectors for the mid-infrared (IR) region of the spectrum (MWIR) and far-IR region of the spectrum (LWIR) regions of the spectrum, including an increase in operating temperature, as well as a decrease in the cost, weight and dimensions of devices [ 12]. From the point of view of fundamental properties, the semiconductor solid solution HgCdTe (CdHgTe, MCT) is an ideal material for creating IR detectors.

HgCdTe is widely used in the development of highly sensitive IR detectors for various spectral regions [3]. The operating temperatures of the detectors, at which it is possible to implement the mode of limiting the threshold characteristics by background radiation noise, are determined by the generation-recombination mechanisms in HgCdTe, which determine the magnitude of dark currents (noise). To suppress dark currents, it is necessary to cool the sensitive elements of photodetectors to sufficiently low temperatures (for example, up to 77 K in LWIR detection). The key condition for creating a high-temperature detector is to minimize thermal generation in the active region without reducing the quantum efficiency.

One of the approaches to minimizing thermal generation in the active region of an IR photodetector without deep cooling is the suppression of Auger generation mechanisms with nonequilibrium semiconductor depletion, as well as the use of new natural and modified semiconductor materials and semiconductor structures with reduced thermal generation. One of the promising concepts in this direction is the so-called barrier photosensitive structures [4, 5].

To date, many different architectures of barrier detectors based on HgCdTe have been proposed, among which, when using the MBE method, unipolar configurations (in particular, nBn) seem to be the most promising, which make it possible to simplify the technology of obtaining detectors and reduce dark currents [6].

Further progress in infrared detectors based on HgCdTe is associated with the development of technologies for obtaining epitaxial material, such as MBE and HFEMOS. These technologies make it possible to grow films with a precisely controlled distribution of the component composition and dopant concentration over the thickness. This provides opportunities for the development of new architectures of device structures, providing, for example, an increase in the operating temperature of detectors and simplification of the technological cycle of their manufacture [7].

At present, the technology of creating n-on-p type photodiodes based on HgCdTe MBE by implanting boron ions into an epitaxial film (without annealing), as well as p-on-n type photodiodes by implanting arsenic ions and subsequent activation annealing, has become widespread. The use of the nBn architecture in the case of MCT can provide a significant advantage over traditional photodiodes due to an increase in the quality of the material in the absence of post-implantation defects [8, 9]. Eliminating the need for ion implation will simplify the technology for creating detectors.

However, when implementing the nBn architecture in HgCdTe, a problem arises related to the fact that the barrier layer heterointerfaces in HgCdTe are characterized by type I arrangement of energy bands, which implies a nonzero break of the valence band. Such band gap means the presence of a barrier that prevents the current of minority photocarriers.

To solve this problem, it was proposed to increase the bias voltage across the structure [10–12]. But at high voltages, the shape of the barrier in the conduction band tends to triangular, so the barrier to electrons decreases, which leads to an increase in noise and a decrease in detectivity values.

Another approach to minimizing the valence band gap is to create a p-type barrier [5]. Such an approach is not very promising when using MBE and, apparently, is possible only when growing heterostructures by metal organic vapor phase epitaxy (MOCVD) [13].

There are also a number of works in which, in addition to the above-described mechanisms for increasing the efficiency of a photosensitive nBn structure, additional optimization of its structural elements (compositions, thicknesses, levels, and doping profiles of the contact, barrier, and absorbing layers) is carried out. For example, in [5], the authors consider various options for implementing the contact layer and demonstrate a significant effect of the contact configuration on the current-voltage characteristics and sensitivity of the device.

The MBE method is also applicable to the direction associated with the use of multilayer barriers, including barriers in the form of superlattices [14], which, with a strict selection of the superlattice parameters, completely eliminate the barrier for minority photocarriers. However, experimentally, these methods for lowering the barrier in the valence band have not been sufficiently developed.

Another problem of nBn detectors based on HgCdTe is the insufficient height (less than 1 eV) of the potential barrier for electrons, which increases the probability of electron tunneling through the barrier or overcoming it above the barrier. To solve this problem, careful selection of the barrier thickness and dopant concentration in the contact layer is required [15]. An important task in the fabrication of nBn structures is the elimination of surface leakage currents [5].

Despite a significant number of publications (about 100) devoted to the theoretical substantiation of the potential advantages of nBn structures, there are only a few attempts at practical implementation of nBn detectors made of HgCdTe.

Known semiconductor structure [16], designed for highly stable detection of infrared radiation in the mid-infrared region (3-8 μm) or in the far infrared region (8-14 μm), or ultra-far infrared region (>15 μm), with enhanced functionality . This structure can be used in various photodetectors, in particular, in matrices of MIS structures (structures of the metal-insulator-semiconductor type), in photoresistor and photodiode matrices.

The described structure contains a substrate, the upper layer of which is formed by CdTe, the lower graded-gap layer, made of Hg _1-x Cd _x Te, in which the value of x smoothly decreases from a value within (x _D +0.1)-1 to the value x _D , working detector layer made of Hg _1-x Cd _x Te, where x=x _D =0.2-0.3, upper graded-gap layer made of Hg _1-x Cd _x Te, in which the value of x is smoothly increases from the value of x _D to a value within 1-(x _D +0.1), an insulating layer of CdTe, dielectric layers and an upper, transparent to infrared radiation, conductive layer. A distinctive feature of the invention is that a layer of quantum wells and two barrier layers are additionally introduced into the detector layer, located on both sides of the layer of quantum wells, made of Hg _1-x Cd _x Te, at the boundaries between the layer of quantum wells and the barrier layer of the value x stepwise vary within x _B ⁼ 0.5-1.0 and x R = _0-0.15 with a thickness of each of the barrier layers of 20-100 nm and a thickness of the quantum well layer of 5-20 nm.

The presence of graded-gap layers ensures the matching of lattice constants at the boundary of MCT semiconductor layers of different composition, which leads to an increase in the stability of the characteristics of the photosensitive structure. The use of passivating dielectric coatings leads to the same result.

The problem solved by the present invention is the creation of a highly stable structure photosensitive to IR radiation with a sensitivity region extended to the long-wavelength part of the spectrum, which can be used in various photodetector devices, in particular, in matrices of MIS structures (in CCD structures), in photoresistor and photodiode arrays.

The expansion of the spectral characteristics of this structure was carried out mainly by introducing a layer of quantum wells made of Hg _1-x Cd _x Te and two barrier layers located on both sides of the layer of quantum wells into the working detector layer. This was the distinguishing feature of this invention.

The disadvantages of the proposed structure include the following. Despite the fact that the patent description speaks of a low level of surface leakage current, the authors also mention that this level is achieved by forming a high-quality interface between the insulating layer and the upper graded-gap layer. It is known [17] that in certain cases the presence of a passivating coating does not completely eliminate the influence of the surface on the electrical and optical properties of the device and, in particular, on the formation of a dark current. The presence of a built-in charge in a passivating dielectric layer affects the surface potential of a semiconductor, and fast and slow surface states act as generation-recombination centers. Thus, the issue of minimizing or completely eliminating the surface leakage current, being essentially a technological one, is beyond the scope of the description of the invention and can be considered open.

Another disadvantage of this invention can be considered that in the case of implementation on the basis of the presented structure of the photodiode receiver of infrared radiation, the use of technological operations of inversion of the conductivity type of a part of the detector layer is required to form a p-n junction.

Also known is a semiconductor structure [18], designed to create a long-wavelength intrinsic photoconductive detector with high resistance. The high detector resistance is designed to minimize the problem of large reverse biased dark currents.

The submitted patent describes the construction of an infrared detector in which a barrier region is introduced between the emitter and the collector. This region consists of a material that provides a minimum rupture of the valence band at the boundary with the emitter layer and has a much larger band gap than the emitter material. The barrier layer prevents the current of the main carriers from flowing and, as a result, gives a high electrical resistance of the structure.

Described infrared detector contains: an emitter region formed from a material that is photosensitive to infrared radiation; collector area; a pair of contacts (emitter contact, collector contact) and a barrier region adjacent to both the emitter region and the collector region, which creates an obstacle for the flow of majority carriers from the emitter region and at the same time is conductive for minority charge carriers.

The essential and distinctive features of the invention are as follows. Preferably, the emitter and barrier materials should be made from ternary solid solutions of the same chemical compound. Examples of ratios of materials and types of conductivity of the layers: cadmium and mercury telluride n-type/n-type, n-type/p-type or p-type/n-type; or indium gallium arsenide; or aluminum gallium arsenide. However, the barrier layer can be made from other materials, provided that the emitter and barrier layers have a minimum gap in the valence band. The barrier material may be a binary alloy or compound having a common anion with the ternary material. Examples: cadmium-mercury telluride and cadmium telluride; aluminum and gallium arsenide and gallium arsenide; or indium gallium arsenide and indium arsenide. In this case, it is preferable that the emitter and barrier materials are n-type and p-type, respectively.

The collector region may be of the same conductivity type as the emitter material. This material should have a common or at least close to the level of the barrier material edge of the valence band. Alternatively, it may be of a high work function metal or of a heavily doped semiconductor material with the main carrier type opposite to that of the emitter. In the case of metal, the collector region is formed by the collector contact itself.

The disadvantages of the proposed structure include, first of all, the fact that in most of the implementations, the authors propose to use a p-type barrier layer, which is practically unrealizable in the case of MCT material grown by the MBE method. Direct application of the n-type barrier significantly reduces the quantum efficiency of such a structure due to the potential barrier for holes and requires additional measures to eliminate it. The authors also provide a wide list of materials suitable for the implementation of the described design, which, also due to the fundamental differences between the materials of groups A2B6 and A3B5, requires different approaches to improve the efficiency of the photodetector, which the authors do not talk about.

Separately, among the shortcomings of the described structure, it should be noted the absence of measures to protect the side surfaces of the structure (passivation), which in such a configuration should inevitably lead to the limitation of the operation of the photosensitive structure by dark surface leakage currents.

There is also a patent [19] describing the designs of semiconductor photosensitive structures that allow the use of infrared detectors at higher temperatures and/or their implementation on less expensive semiconductor substrates to reduce production costs.

The patent describes infrared detectors and detector arrays based on minor charge carriers in cadmium-mercury telluride and methods for their manufacture. Exemplary embodiment: substrate, lower contact layer located on the substrate, first mercury-cadmium telluride layer having a first bandgap energy value located on the lower contact layer, second mercury-cadmium telluride layer having a second bandgap energy value greater than than the band gap energy of the first layer, located on the first layer of cadmium-mercury telluride, and the collector layer, located on the second layer of cadmium-mercury telluride, and the first and second layers of cadmium-mercury telluride are doped with an n-type impurity.

The essential and distinctive features of the invention are as follows. The invention implements a barrier nBn structure based on n-type MCT in the classical representation. Only donor doping is used. There are no acceptor-type conduction layers in the construction. The claimed advantages are achieved by optimizing the parameters of the individual layers of the structure (compositions, doping levels, layer thicknesses), as well as the bias voltage. The authors also take measures to passivate the side surface of the area of contacts of the barrier layer with the layers surrounding it. Passivation using CdTe or ZnS

Despite the fact that, by means of optimization, the authors managed to improve the characteristics of the device structure, they did not succeed in completely eliminating the barrier for minority carriers (holes). Also in the patent description there is no information about the contribution of surface leakage currents to the dark current.

The closest photosensitive to infrared radiation structure (prototype) and method of its manufacture in relation to the claimed structure and method of its manufacture are described in [20]. The aim of the invention was to provide a barrier-type semiconductor structure made of semiconductor materials of the same group, which does not require special doping of the barrier layer, different from the doping of the absorbing layer and the collector layer, and also does not have a potential barrier for minor charge carriers, while the potential barrier for major carriers maintains efficiency even at high reverse bias voltages.

The patent describes a semiconductor structure, which includes: the first (absorbing) and the second (collector) semiconductor layers of the same material (MCD) with electronic type of conductivity; a barrier layer of MCT, located between the first and second layers, to create an energy barrier for the majority charge carriers of the first and second layers, and the barrier layer has a minimized energy gap; as well as two interface layers of MCT of variable composition, intended for conjugation of the first and second layers with the barrier layer.

The compositions of the first and second layers X1 and X2 respectively have the same values. The material of the second layer has the type of conductivity and the concentration of the main carriers, identical to their values in the material of the first layer. The electronic type of conductivity is achieved by doping the structure with indium. The concentration of the main carriers is from 5⋅10 ¹⁴ to 5⋅10 ¹⁵ cm ^-3 .

The material of the first layer is selected based on which range of electromagnetic radiation detection the structure is supposed to be adopted for, and is: X1=0.4 for detecting IR radiation with λ<3 μm, X1=0.3 for detecting IR radiation with λ <5 µm and X1=0.22 for detecting IR radiation with λ<10 µm.

The thickness of the first layer is at least 2 µm.

The thickness of the barrier layer is 100-300 nm.

The composition of the MCT material constituting the barrier layer, as well as the composition of the material of the first layer, is selected depending on the wavelength range of the detected IR radiation: Xm=0.85 for detecting IR radiation with λ<3 μm, Xm=0.65 for detecting IR radiation with λ<5 µm and Xm=0.6 for detecting IR radiation with λ<10 µm.

The interface layers of variable composition have a linear (or close to linear) composition distribution profile. The composition in the interface layers varies from the composition of the barrier layer to the composition of the first and second layers.

Electrical contacts are made of titanium or gold.

The passivation of the surface of the structure is performed from cadmium telluride CdTe or zinc sulfide ZnS.

The bias voltage applied to the structure should be in the order of several hundred millivolts.

The essential and distinctive features of the invention are as follows. As in the previous patent, the optimization of the parameters of individual layers of the structure is implemented here. Only donor doping is used in the structure; there are no acceptor-type conduction layers in the structure. As the main distinguishing feature, one can distinguish the introduction of additional elements into the structure - interface graded-gap layers at the boundaries of the barrier layer, which reduce the inconsistency at sharp heterointerfaces and, therefore, eliminate defectiveness and the space charge region.

In the presence of graded-gap layers, the application of a negative bias to the structure and the correct selection of its value reduces the jumps of the edge of the valence band, makes its bending smoother, which reduces the obstacle to the current of photocarriers (holes).

The method for manufacturing the described photosensitive structure includes the following steps:

- choice of a plate of cadmium and zinc telluride (CdZnTe) as a substrate;

- deposition on the substrate of the MCT material with the composition X1, which forms the first layer (absorbing);

- applying to the first (absorbing) layer of the first interface layer MCT variable composition with a composition varying from the value of the composition in the first layer X1 to the composition of the barrier layer Xm;

- application to the first interface layer of MCT variable composition of the barrier layer with the composition Xm;

- application to the barrier layer of the second MCT interface layer of a variable composition with a composition varying from the value of the composition in the barrier layer Xm to the composition in the second layer X2;

- application to the second interface layer of a variable composition of the second MCT layer with the composition X2;

- formation of the first and second electrical contacts on the first (absorbing) and second (collector) layers, respectively;

- application of a passivating layer on all surfaces of the structure, excluding metal contacts.

Semiconductor layers can be deposited by molecular beam epitaxy and metal-organic vapor phase epitaxy.

Based on the grown semiconductor heterostructure, a mesastructure is fabricated, in which one of the contact electrodes is deposited directly on the second (collector) layer, and the other on the first (absorbing) layer. To passivate the side surface of the area of contacts of the barrier layer with the surrounding layers, the authors, as in the previous patent, use CdTe or ZnS.

The disadvantages of the prototype structure include the following. As can be seen from the calculated band diagrams given in the patent, despite the minimization of the barrier for holes in the structure, large values of the reverse bias lead to deformation of the barrier for the majority charge carriers, which contributes to an increase in the probability of electron tunneling through the barrier or overcoming them above the barrier. This requires further optimization of the structure parameters, in particular, as one of the possible solutions, an increase in the composition of the barrier layer.

On the other hand, it is known that to ensure the maximum values of the detectivity of nBn detectors, the composition in the barrier layer must take smaller values (x=0.6-0.7). However, in practice, in structures with such values of the barrier layer composition, despite passivation, the dark current is limited by the surface leakage current. As mentioned earlier, it is known [17] that passivation does not always completely eliminate the influence of the surface on the electrophysical and optical properties of the device and, in particular, on the formation of a dark current. The presence of a built-in charge in a passivating dielectric layer affects the surface potential of a semiconductor, and fast and slow surface states act as generation-recombination centers.

The task to be achieved by the proposed solution is the creation of a structure photosensitive to infrared radiation (sensitive in the MWIR or LWIR range) with increased operating temperature and detectivity, as well as a method for its manufacture.

The technical result to which the proposed solution is directed is the elimination of the observed contribution of surface leakage currents to the formation of a dark signal of a photosensitive nBn structure based on MCT.

The solution of this problem is achieved by the fact that in a barrier structure that is photosensitive to infrared radiation, including a substrate (layer 1), the first layer of Cd _x Hg _1-x Te with a variable composition located on the substrate (layer 2), in which x changes from 1 to at the boundary with the substrate up to x _PS at the border with the absorbing layer, located on the first layer with a variable composition, a homogeneous absorbing layer of Cd _x Hg _1-x Te (layer 3) with a composition of x _PS = 0.22-0.4 with a thickness of 2 -4 μm, located on the absorbing layer, the second layer of Cd _x Hg _1-x Te with a variable composition (layer 4), in which x varies from x _PS at the interface with the absorbing layer to x _B at the interface with the barrier layer, located on the second layer with a variable composition, a homogeneous barrier layer of Cd _x Hg _1-x Te (layer 5) with a composition x _B = 0.6-0.7 with a thickness of 0.2-0.5 μm, located on the third barrier layer layer of Cd _x Hg _1-x Te with variable composition (layer 6), in which x varies from x _B at the boundary with a barrier layer up to x _CS at the boundary with the contact layer, located on the third layer with a variable composition, a contact layer of uniform composition from Cd _x Hg _1-x Te (layer 7) with a composition x _CS \u003d 0.22-0.4 with a thickness of 1 -2 μm, located on the contact layer, the fourth layer of Cd _x Hg _1-x Te with a variable composition (layer 8), in which x varies from x _COP at the border with the contact layer to x _D \u003d 0.6-1, 0, a passivating layer (layer 9) is located on the fourth layer of Cd _x Hg _1-x Te with a variable composition, and a metal field electrode of In (layer 10) is deposited on the surface of the passivating layer, and the geometric dimensions of the field electrode are chosen in such a way that the minimum distance from the edge of the field electrode to the edge of the site, limiting the area of the photosensitive structure, would be equal to 1.0-1.2 microns.

In a particular case, the structure can be doped with In with a dopant concentration of 10 ¹⁴ -10 ¹⁶ cm ^-3 uniformly over the entire thickness.

In a particular case, the In doping profile can be non-uniform over the thickness of the structure with a dopant concentration of 10 ¹⁴ -10 ¹⁶ cm ^-3 .

In a particular case, the substrate (layer 1) is made of GaAs, and a ZnTe layer and a CdTe layer, which are part of the substrate, are deposited on it.

In a particular case, the substrate (layer 1) is made of Si, and a ZnTe layer and a CdTe layer, which are part of the substrate, are deposited on it.

In a particular case, the substrate (layer 1) is made of CdZnTe, and a ZnTe layer and a CdTe layer, which are part of the substrate, are deposited on it.

In a particular case, the substrate (layer 1) is made of CdZnTe, and a CdTe layer, which is part of the substrate, is deposited on it.

In a particular case, the substrate (layer 1) is made of CdTe.

In a particular case, the passivating layer (layer 5) is made of Al ₂ O ₃ .

In a particular case, the passivating layer (layer 5) is made of SiO ₂ coated with Si ₃ N ₄ on top.

In a particular case, the passivating layer (layer 5) is made of SiO ₂ with ZnTe deposited on top.

The solution of this problem is also achieved by the fact that in the method of manufacturing a barrier structure photosensitive to infrared radiation, including preparation of the substrate (layer 1) for deposition of subsequent layers on it and deposition in a growth chamber by the method of molecular beam epitaxy in succession of the first layer of Cd _x Hg _{1- x} Te with variable composition (layer 2), in which x changes from 1 at the interface with the substrate to x _PS at the interface with the absorbing layer, of a homogeneous absorbing layer of Cd _x Hg _1-x Te (layer 3) with the composition x _PS \u003d 0.22-0.4 with a thickness of 2-4 microns, the second layer of Cd _x Hg _1-x Te with a variable composition (layer 4), in which x varies from x _PS at the border with the absorbing layer to x _B by border with the barrier layer, homogeneous in composition of the barrier layer of Cd _x Hg _1-x Te (layer 5) with the composition x _B = 0.6-0.7 with a thickness of 0.2-0.5 μm, the third layer of Cd _x Hg _1-x Te with variable composition (layer 6), in which x varies from x _B at the boundary with the barrier layer to x _CS by boundary with the contact layer, homogeneous in composition of the contact layer of Cd _x Hg _1-x Te (layer 7) with the composition x _KS \u003d 0.22-0.4 with a thickness of 1-2 μm, the fourth layer of Cd _x Hg _1-x Te with a variable composition (layer 8), in which x varies from x _CS at the boundary with the contact layer to x _D = 0.6-1.0, removal of the heterostructure grown by molecular beam epitaxy from the growth chamber, on the fourth layer from Cd _x Hg _1-x Te with a variable composition, one of the low-temperature methods is to apply a passivating layer (layer 9), on top of which a field electrode of In (layer 10) is applied by low-temperature thermal spraying in such a way that the minimum distance from the edge of the field electrode to the edge of the site, limiting the area of the photosensitive structure, would be equal to 1.0-1.2 microns.

In a particular case, the semiconductor structure can be doped with In with a dopant concentration of 10 ¹⁴ -10 ¹⁶ cm ^-3 uniformly over the entire thickness directly in the growth chamber.

In a particular case, the semiconductor structure can be doped with In with a dopant concentration of 10 ¹⁴ -10 ¹⁶ cm ^-3 with a profile that is inhomogeneous over the thickness of the structure directly in the growth chamber.

In a particular case, the substrate (layer 1) can be made of GaAs, and a ZnTe layer and a CdTe layer are deposited on it in the growth chamber before growing the absorbing layer.

In a particular case, the substrate (layer 1) can be made of Si, and a ZnTe layer and a CdTe layer are deposited on it in the growth chamber before growing the absorbing layer.

In a particular case, the substrate (layer 1) can be made of CdZnTe, and a ZnTe layer and a CdTe layer are deposited on it in the growth chamber before growing the absorbing layer.

In a particular case, the substrate (layer 1) can be made of CdZnTe, and a CdTe layer is deposited on it in the growth chamber before growing the absorbing layer.

In a particular case, the substrate (layer 1) can be made of CdTe.

In a particular case, after removing the heterostructure from the growth chamber, one of the low-temperature methods can be used to fabricate a passivation layer (layer 5) from Al ₂ O ₃ .

In a particular case, after removing the heterostructure from the growth chamber, one of the low-temperature methods can be used to fabricate a passivation layer (layer 5) of SiO ₂ with Si ₃ N ₄ deposited on top of it.

In a particular case, after removing the heterostructure from the growth chamber, one of the low-temperature methods can be used to fabricate a passivation layer (layer 5) from SiO2 with ZnTe deposited _on top of it.

The implementation of such a design of the photosensitive structure by the proposed method ensures the localization of the space charge region, "induced" by the electric field from the field electrode, inside the volume of the semiconductor structure. Thus, the space charge region is located at a considerable distance from the side face of the semiconductor structure, which obviously excludes surface leakage processes from among those affecting the signal formation of the photosensitive structure in the dark mode.

The drawing (Fig. 1) shows one of the options for implementing the proposed photosensitive structure to infrared radiation (a single cell of the matrix of mesa structures). The scale of the thicknesses of different layers of the structure is chosen arbitrarily.

The drawing shows:

1 - GaAs substrate with layers of ZnTe and CdTe deposited on it;

2 - the first layer of Cd _x Hg _1-x Te with a variable composition x=[1; 0.29];

3 absorbing layer of Cd _x Hg _1-x Te with composition x=0.29;

4 second layer of Cd _x Hg _1-x Te with variable composition x=[0.29; 0.60];

5 barrier layer of Cd _x Hg _1-x Te with composition x=0.6;

6 third layer of Cd _x Hg _1-x Te with variable composition x=[0.6; 0.29];

7 - contact layer of Cd _x Hg _1-x Te with composition x=0.29;

8 - the fourth layer of Cd _x Hg _1-x Te with a variable composition x=[0.29; one];

9 - passivating layer of Al ₂ O ₃ with passivation of the side face of the mesa structure;

10 - field electrode from In with a diameter D1, having a value that provides the condition D2=1.0-1.2 μm, where D2 is the distance from the edge of the field electrode to the edge of the area that limits the area of the photosensitive structure.

11 - Reverse electrical contact from In.

On the basis of the proposed structure, an infrared radiation matrix photodetector can be manufactured. The drawing (Fig. 2) shows a diagram of one of the options for its implementation. To manufacture a matrix of photodetector elements, etching (for example, in a 0.5% solution of Br in HBr) of the HgCdTe heterostructure grown by molecular beam epitaxy to an absorbing layer (layer 2) is performed for subsequent deposition of a return electrode (layer 7), as well as for physical separation of individual nBn elements by forming mesa structures.

The drawing (Fig. 3) shows the dependence of the reciprocal of the product of the resistance of the barrier layer (R _B ) nBn-structures on the area of the field electrode (A), on the ratio of the perimeter of the field electrode (P) to its area. This dependence was obtained from a study of the admittance of MIS structures based on nBn structures using an automated setup for measuring the immittance of nanoheterostructures, the main elements of which were an Agilent E4980A immitance meter, a Janis non-optical cryostat, and a Lake Shore temperature controller. The structures of the nBn structure with the composition in the absorbing and contact layer x=0.29 and the composition of the barrier layer x=0.6 were studied. The field electrode diameter varied from 130 to 480 μm.

From FIG. It can be seen from Fig. 3 that the slope of the graph reflecting this dependence is very small, since the resistance of the barrier layer in the structure designed in this way is determined by the bulk component of the dark current. Surface leakage does not affect this dependence, since the width of the space charge region protruding beyond the edge of the field electrode is much smaller than the distance from the edges of the field electrode to the side walls of the mesa structure.

Fig. 4 shows the dependence of the barrier layer resistance in nBn structures on the field contact area. It can be seen that the resistance of the barrier, i.e., the efficiency of dark current suppression by the barrier, is the higher, the smaller the diameter of the field electrode and, consequently, the greater the distance from the electrode edge to the edge of the mesa structure.

Information sources

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Claims (22)

1. Photosensitive to infrared radiation structure, including a substrate, located on the substrate, the first layer of Cd _x Hg _1-x Te with a variable composition, in which x changes from 1 at the interface with the substrate to x _PS at the interface with the absorbing layer, located on the first layer with a variable composition, a homogeneous absorbing layer of Cd _x Hg _1-x Te with a composition x _PS = 0.22-0.4 with a thickness of 2-4 μm, located on the absorbing layer, the second layer of Cd _x Hg _1-x Te with with a variable composition, in which x varies from x _PS at the boundary with the absorbing layer to x _B at the boundary with the barrier layer, located on the second layer with a variable composition, a homogeneous barrier layer of Cd _x Hg _1-x Te with the composition x _B \u003d 0.6-0.7 with a thickness of 0.2-0.5 μm, located on the barrier layer, the third layer of Cd _x Hg _1-x Te with a variable composition, in which x varies from x _B at the border with the barrier layer up to x _CS at the boundary with the contact layer, located on the third layer with a variable composition of one uniform in composition contact layer of Cd _x Hg _1-x Te with composition x _KS = 0.22-0.4 1-2 μm thick, located on the contact layer fourth layer of Cd _x Hg _1-x Te with variable composition, in in which x varies from x _COP at the boundary with the contact layer to x _D = 0.6-1.0, characterized in that on the fourth layer of Cd _x Hg _1-x Te with a variable composition there is a passivating layer, and a metal field In electrode is deposited on the surface of the passivating layer, and the geometric dimensions of the field electrode are chosen so that the minimum distance from the edge of the field electrode to the edge of the area that limits the area of the photosensitive structure would be equal to 1.0-1.2 μm. 2. The structure according to claim 1, characterized in that the semiconductor layers are doped with In with a dopant concentration of 10 ¹⁴ -10 ¹⁶ cm ^-3 uniformly throughout the entire thickness. 3. The structure according to claim 2, characterized in that the In doping profile may be non-uniform over the thickness of the structure with a dopant concentration of 10 ¹⁴ -10 ¹⁶ cm ^-3 . 4. The structure according to claim 1, characterized in that the substrate is made of GaAs and a ZnTe layer and a CdTe layer, which are part of the substrate, are deposited on it. 5. The structure according to claim 1, characterized in that the substrate is made of Si and a ZnTe layer and a CdTe layer, which are part of the substrate, are deposited on it. 6. The structure according to claim 1, characterized in that the substrate is made of CdZnTe and a ZnTe layer and a CdTe layer, which are part of the substrate, are deposited on it. 7. The structure according to claim 1, characterized in that the substrate is made of CdZnTe and a CdTe layer, which is part of the substrate, is deposited on it. 8. Structure according to claim 1, characterized in that the substrate is made of CdTe. 9. Structure according to claim 1, characterized in that the passivation layer is made of Al ₂ O ₃ . 10. The structure according to claim 1, characterized in that the passivating layer is made of SiO ₂ with Si ₃ N ₄ deposited on top of it. 11. The structure according to claim 1, characterized in that the passivating layer is made of SiO ₂ with ZnTe deposited on top of it. 12. A method for manufacturing a barrier photosensitive to infrared radiation structure according to claim 1, including preparing a substrate for applying subsequent layers on it and applying the first layer of Cd _x Hg _1-x Te with a variable composition in a growth chamber by molecular beam epitaxy, in in which x changes from 1 at the interface with the substrate to x _PS at the interface with the absorbing layer, an absorbing layer of homogeneous composition from Cd _x Hg _1-x Te with the composition x _PS = 0.22-0.4 2-4 μm thick, the second layer of Cd _x Hg _1-x Te with a variable composition, in which x varies from x _PS at the boundary with the absorbing layer to x _B at the boundary with the barrier layer, a barrier layer of uniform composition Cd _x Hg _1-x Te with composition x _B \u003d 0.6-0.7 with a thickness of 0.2-0.5 μm, the third layer of Cd _x Hg _1-x Te with a variable composition, in which x varies from x _B at the border with the barrier layer to x _CS at the boundary with the contact layer, homogeneous in composition of the contact layer of Cd _x Hg _1-x Te with the composition x _COP = 0.22-0.4 with a thickness of 1-2 microns, the fourth layer of Cd _x Hg _1-x Te with a variable composition, in which x varies from x _COP at the border with the contact layer to X _D = 0.6 -1.0, removal of the heterostructure grown by molecular beam epitaxy from the growth chamber, characterized in that one of the low-temperature methods is the deposition of a passivating layer, on top of which a field electrode is applied by low-temperature thermal spraying in such a way that the minimum distance from the edge of the field electrode to the edge of the site, limiting the area of the photosensitive structure, would be equal to 1.0-1.2 microns. 13. The method according to p. 12, characterized in that the semiconductor structure is doped with In with a dopant concentration of 10 ¹⁴ -10 ¹⁶ cm ^-3 uniformly throughout the entire thickness directly in the growth chamber. 14. The method according to p. 13, characterized in that the semiconductor structure is doped with In with a dopant concentration of 10 ¹⁴ -10 ¹⁶ cm ^-3 with a profile that is inhomogeneous in thickness of the structure directly in the growth chamber. 15. The method according to claim 12, characterized in that the substrate is made of GaAs, and a ZnTe layer and a CdTe layer are deposited on it in the growth chamber before growing the absorbing layer. 16. The method according to claim 12, characterized in that the substrate is made of Si, and a ZnTe layer and a CdTe layer are deposited on it in the growth chamber before growing the absorbing layer. 17. The method according to claim 12, characterized in that the substrate is made of CdZnTe, and a ZnTe layer and a CdTe layer are deposited on it in the growth chamber before growing the absorbing layer. 18. The method according to claim 12, characterized in that the substrate is made of CdZnTe, and a CdTe layer is deposited on it in the growth chamber before growing the absorbing layer. 19. Method according to claim 12, characterized in that the substrate is made of CdTe. 20. The method according to p. 12, characterized in that after removing the heterostructure from the growth chamber, a passivation layer of Al ₂ O ₃ is made by one of the low-temperature methods. 21. The method according to p. 12, characterized in that after removing the heterostructure from the growth chamber, one of the low-temperature methods is used to make a passivation layer of SiO ₂ with Si ₃ N ₄ deposited on top of it. 22. The method according to p. 12, characterized in that after removing the heterostructure from the growth chamber, one of the low-temperature methods is used to make a passivation layer of SiO ₂ with ZnTe deposited on top of it.

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