Photodetector for the infrared region of the spectrum

 

(57) Abstract:

Usage: FPU relates to electronic devices, in particular to the photodetector having sensitivity in the infrared range of the spectrum, multiple or singleton with impurity photoconductivity. The inventive FPU contains a substrate of semiconductor, compensated deep high-z impurity, creating a double negatively charged levels. On both sides of the FPU created conductive bus, consisting of the contact layer in the substrate and deposited material that generates electrical contact with the substrate. The contact layer in contrast to the prototype consists of two fields at 300 K with different impurity concentrations, enriching this layer. The first region of maximum concentration, providing a width of greater than or equal to the length of diffusion of majority carriers. A second area with a concentration of impurities enriched (1 - 2) % above the concentration of small impurities in the substrate. The width of this field must be greater than the length of the shielding media with accurate compensation of impurities. When cooled FPU in the near contact region manifests the transition region n+- n (p+- p) with an injecting properties, the investing of media injected from a contact. The second area allows electrical contact to a compensated semiconductor is divided into two contacts with different functions: the contact film of Nickel and enriched region of the substrate, which is resistive; the second contact region and the substrate, which is an injecting contact. 1 C. p. F.-ly, 2 ill., 3 table.

Photodetector FPU relates to electronic devices, in particular to the photodetector having sensitivity in the infrared range of the spectrum, multiple or singleton with impurity photoconductivity.

FPU for the infrared region of the spectrum is generally used in pulse mode survey. Photovoltaic parameters of the FPU are determined by the properties of the electrical contact to a compensated semiconductor. When the enable pulse voltage to the FPU from contact injections main current carriers, and part of them is captured on traps. During the pause between pulses is the release of trapped carriers of heat or fotogaleria. The magnitude of the photocurrent is proportional to the current recharge levels of traps.

Known photodetector (C. G. Ivanov. FTP, 1979, vol. 9, T. 13, S. 1838 1841), which contains poluprovodnikovogo half of the band gap of the substrate material. The admixture is multiply charged with twice negatively charged level for the major carriers. FPU has an outer layer of the tire is made from a material forming an ohmic contact with the substrate and is transparent to the projected radiation. Photodetector has a number of disadvantages: the instability of the electrical properties of the resulting contact of the outer layer to the substrate, the influence of the surface properties of the substrate and properties of the outer layer on the photovoltaic parameters FPU, poor reproducibility of the technological process in the manufacture of the ohmic contact.

Known infrared detector matrix (patent GB N 2125217) containing a substrate made of silicon doped with boron and offset controlled divacancies, on both sides of which are formed conductive perpendicular tires of the Au, which in turn consist of the contact layer, an area of enrichment and metal film deposited on the contact layer. Such contact at low temperatures forms a transition of type n+-n(p+-p), which is formed close to the surface, which leads to a dependence of the properties of the transition from the surface of the contact, the possibility of increasing the photosensitivity.

The primary object of the present invention is, firstly, an increase in the photosensitivity FPU in the pulse mode of the survey, and secondly, the increase in the uniformity of the distribution of photosensitivity on the field FPU and obtaining a stable reproducible photovoltaic parameters of the FPU.

The positive effect from the use of the invention to create a stable an injecting contact to a compensated semiconductor, which does not depend on the surface properties and metal deposited on the surface and increase the photosensitivity FPU in a pulsed mode in comparison with the stationary regime.

This effect is achieved by the fact that in the proposed FPU for the IR region of the spectrum containing a substrate of semiconductor doped shallow donor impurity and accurately compensated deep multi-charged acceptor impurity, creating a double negatively charged levels, on both sides of which a conductive bus consisting of created in the substrate contact layer enriched with specially designed small impurity of the same conductivity type as the substrate, and the applied film of metal, the scrap with a maximum impurity concentration equal to

< / BR>
under the condition of L1L the WPPT. where D is the diffusion coefficient of the major carriers: Lthe WPPT.the length of the diffusion of majority carriers; the coefficient of recombination of charge carriers; L1the thickness of the first region and the second region with an impurity concentration of 1 2 higher concentration of shallow donor impurities of the substrate, and their thickness are correlated as follows:

< / BR>
where L2the thickness of the second region; to improve the ohmic properties of the metal used film of Nickel.

Thus, in the proposed FPU contact layer at room temperature consists of at least 2 areas: the first area enrichment of N++(p++); the second area of enrichment with a lower concentration of n+(p+). When cooled in this contact appears the third transition region of the uniform n+n (p+p), the height of the potential barrier which is equal to the difference between the Fermi levels in region 2 and in the volume of the substrate. In the transition n+n (p+p) there is a plane in which impurities are accurately compensated. Injected carriers captured on traps are non-equilibrium and create additional volume charge, which screens an injecting contact. where Ntnodark concentration of carriers in the conduction band at the exact compensation of impurities; the height of the potential barrier (n+-n) transition.

The width of the area 2 must be greater than or equal to the maximum length of the escape transition of n+n(p+p), which is defined by the formula (2) and the condition record

< / BR>
The concentration of the injected trapped charge carriers at a voltage limit of filling of traps is equal to the concentration of empty seats on the acceptor level in the substrate. The thickness of the first field must be greater than or equal to the diffusion length of the main current carrier, which is determined by the formula

< / BR>
where D is the diffusion coefficient of small impurities in 1 region; -the coefficient of recombination of majority carriers, Nmaxthe maximum impurity concentration in 1 area.

In order to fulfill the condition L1Lthe WPPTyou must enter in area 1 impurity concentration

NmaxD/L2dInterfax.< / BR>
The contact metal and the region 1 is formed a space charge region with the height of the potential barrieroand the maximum electric field Emaxat a depth equal to otter-substrate. Each area of such contact performs its functions: the first function ohmic (injects) contact metal enriched layer of N++the second region at low temperatures an injecting contact N+region and the substrate FPU, i.e. forms directly injects transition n+-n (p+p). The distribution of the concentration of charge carriers in such a contact is shown in Fig. 1. Next we will show how increasing the sensitivity in the proposed FPU. The concentration of charge carriers injected from the contact is determined by the properties of an injecting contact, the voltage and the dimensions of the elements FPU. In the pulse mode of survey FPU considerable increase of photosensitivity in comparison with the stationary regime. In the first moment when the supply voltage impulse flows injection belovoskey current, the peak value of which

< / BR>
dielectric constant; m is the mobility of carriers; V - supply voltage; L is the distance between the electrodes; and S the area of the element. The amount of current in a stationary mode through the same element is expressed

< / BR>
where nArt.the concentration of photocarriers in the conduction band in a stationary mode. HC is the pulse duration and pause between them, from the background oblojennosti. The pulse amplitude of the photocurrent is given by the expression

(6)

wheretothe capture of carriers in the impurity level;

timp.the pulse duration;pausethe duration of a pause; With parameter-dependent properties of an injecting contact.

Increasing the photosensitivity is represented as the ratio of the currents

< / BR>
In FPU prototype surface of the substrate is covered with a gold film. Gold in Germany creates acceptor levels.

However, technologically reproducible contact cannot be obtained, because the gold by sputtering and subsequent annealing was diffundiruet in germanium at a depth greater than the width of the enriched region 1, therefore, was created much precompositional a thin layer of Ge(Au,Sb), which at low temperatures becomes more resistive than the transition n+n and all voltage drops on this layer, resulting in the loss of an injecting contact properties and photosensitivity.

In the proposed FPU when applying Nickel is also its diffusion, however, the region 2 is much greater than the length, which manages to prodifferentiating Nickel, and therefore retained the transition n n, from which the following properties of n+n (p+p) transition and the benefits of such contact.

In Fig. 1 shows the distribution of the carrier concentration of the current in the FPU of Fig. 2 FPU based on the structure matrix type: 1 substrate; 2 enrichment of N++=1019cm-3; 3 range of enrichment of N+=1015cm-3; 4 film metal; 5 transition n+- n (p+p).

An example of a specific implementation. FPU can be a single-element or multi-element matrix or linear types. The proposed FPU is shown in Fig. 2, FPU consists of a substrate Germany, doped with antimony and compensated silver (1), the enrichment of (2), in which the maximum concentration impurity enrichment 1019cm-3the area of enrichment (3) with a concentration of 1015cm-3, region (5), shown at low temperatures and forming the transition n+n (p+p), and a metal film (4), deposited on a substrate. Concentration in region (5) is changed from 1015cm-3to the concentration of charge carriers in the substrate no.

FPU matrix type on one bus which serves the voltage pulses to the other buses connected to the amplifier. In the steady state substrate at room temperature is ora clearly apparent. When cooled to t To the substrate is high impedance and area 2 is transformed into two regions, where one of them low with concentrations greater than (1 2) than the concentration of the shallow donor impurity in the substrate, the second transition region nn (p+p). The height of the potential barrier of the transition is determined by the formula

< / BR>
N N++In the prototype

N=N+in our case

The width of the transition n+n is determined by the formula

< / BR>
When switching on the voltage pulse media injections of contact, prediffusion area 1 and 2, the carriers recombine. The injected carriers are partially captured in the transition region and into the substrate, creating a non-equilibrium associated charge. This charge screens the contact, the screening length of charge carriers is determined by the formula in the exact degree of compensation

< / BR>
Changing the photosensitivity FPU is determined by non-stationary processes in the transition, so the creation of an area 2 allows to form a passage whose width is determined by the length of the shielding carriers on the depth L. In the prototype transition is formed close to the surface of the substrate and properties depend on the surface condition.

v+of 0.14 EV, Ec-0,28 EV, Ec-0,09 eV. If two levels are completely filled, partially filled and the upper, nois determined by the formula

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The concentration of photocarriers is determined by the formula

< / BR>
where NSbthe concentration of antimony in the substrate; Ncm3- the effective density of States, given to the top level of silver; 3=NAg/NSbthe degree of compensation of impurities in the substrate, gfthe photoionization cross section of the upper level of silver; (g recombination coefficient; I is the radiation intensity, mothe concentration of electrons at the top level of silver.

In table.1 shows the parameter regions FPU.

Theoretically estimated increase sensitivity in a pulsed mode in comparison with the stationary regime, for different degrees of compensation of the substrate, which can be obtained, are given in table. 2. Practically the prototype has 10 yield, the proposed solution 30 the Calculation is performed according to the formula

< / BR>
where 10-12cm-3with-1; gf=10-17cm2; I 51012Kwan/cm2s; V 1B; e 16th cent to 8.85 10-14FSM-1; L 310-2see

As can be seen from table 2, the increase of the photocurrent can be obtained on the substrate with precompetitive with the stationary regime. The variation of the degree of compensation on the substrate is mainly defined by the distribution of antimony in Germany when the radial distribution 2 (3 1,02 1,0), which leads to a change of photosensitivity in a stationary mode at 40Kn1/n34,1 1012/8 1075 104again, in the pulse mode, this ratio will 4,11012/8107125= 4102times, i.e., the photocurrent increases 5104/4102< / BR>
102time.

When allocating 0.5 % of n1/n2= 4,11012/3 108103using the pulse mode 4,11012/310831=30, i.e., the photocurrent increases 30 times.

Since the increase of the photocurrent in precommissioning the portions of the substrate is greater than in areas with exact compensation, when the pulse mode of the survey reduced the heterogeneity of the distribution of photosensitivity on the working field of the FPU. When the degree of compensation 3 = 1,0; 3 = 1,02 variation of the photocurrent is 5 104once in stationary mode, pulse mode 4 102times.

Thus, when creating the transition region 2 with a thickness there is a separation of the functions of an injecting contact to offset the substrate into two: the first function of the ohmic contact performs the contact metal and poverhnosti volume of the substrate. The width of the area 2 should be L, n+-n junction at the exact compensation of impurities. This allows to obtain technologically reproducible contact, reducing the heterogeneity of the distribution of photosensitivity, increase the photosensitivity in the pulse mode survey at low temperatures, eliminates the effect of surface on an injecting contact.

2. Compared with gold, deposited on a substrate was obtained more stable ohmic contact compensated Germany.

In table. 3 presents FPU with different metal films.

1. Photodetector for the infrared region of the spectrum containing a substrate of semiconductor doped shallow donor impurity and accurately compensated deep multi-charged acceptor impurity, creating a double negatively charged levels, on both sides of which a conductive bus consisting of created in the substrate contact layer enriched with specially designed small impurity of the same conductivity type as the substrate, and the applied metal film, creating an electrical contact, wherein the contact layer comprises a first region in contact with meth what/SUB>,

where D is the diffusion coefficient of majority carriers;

Lthe WPPTthe diffusion length;

the coefficient of recombination of carriers;

L1the thickness of the first region and the second region with an impurity concentration of 1 to 2% above the concentration of the shallow donor impurity of the substrate, and their thickness are correlated as follows:

< / BR>
where L2the thickness of the second region;

dielectric constant;

Dv the height of the potential barrier of the n+n - or p+p - transition;

e the electron charge;

Ntthe concentration of traps in the levels of the acceptor impurity in the exact compensation of impurities equal to the dark concentration of carriers;

Emaxthe maximum field of the space charge region of the contact metal substrate;

vothe height of the potential barrier of the contact metal substrate.

2. The device under item 1, characterized in that the metal film is Nickel.

 

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