RU2357321C1 - Method of making chemically deposited lead selenide films sensitive to infrared radiation - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: present invention relates to obtaining semiconductor materials, particularly to photosensitive lead selenide films, used for making infrared photodetectors in the 1-5 mcm range. The method of making chemically deposited lead selenide films sensitive to infrared radiation involves heating the films in atmospheric air in a sealed container. Thermal treatment is done at ratio of volume of the container to the surface area of the treated film equal to 20-40. Heating is done in the presence of selenium powder.

EFFECT: design of a method of making chemically deposited PbSe films sensitive to infrared radiation, providing for maximum values of voltage sensitivity and detectivity for use without cooling or light cooling.

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Description

The invention relates to the field of obtaining semiconductor materials, namely photosensitive films of lead selenide, used for the manufacture of infrared photodetectors in the wavelength range of 1-5 microns.

At present, the problem of achieving high photoelectric characteristics and ensuring their reproducibility for single and multi-element photodetectors and matrix structures used in the mid-IR range of the spectrum (3-5 μm) is very important. Its solution will increase the tactical and technical data of detection and surveillance equipment, photodetectors used in automation, robotics, pyrometry, thermal imaging equipment, fire fighting equipment, as well as reduce the cost of their production (especially matrix structures) by increasing yield. As an effective material used for the mid-IR range, lead selenide is used.

However, chemically deposited PbSe films require a mandatory operation of sensitization to infrared radiation, which ensures their use in photodetectors.

In most cases, heat treatment at temperatures of 320–450 ° C is used as a method for sensing chalcogenide films [1–4]. For PbSe films, this operation is still prescription in nature, when the processing time, temperature, and gas medium are experimentally determined. There are no reliable justifications for choosing these parameters. However, the generally accepted point of view is the decisive role of oxygen in achieving the required photoelectric characteristics of PbSe layers. It is known that heating of films in the presence of atmospheric oxygen leads to the formation of oxidation products in them, which are the phases PbO, PbSeO ₃ , 2PbO · PbSeO ₃ , 4PbO · PbSeO ₃ [5]. It is believed that it is these compounds that are responsible for the sensitization of films. However, a noticeable increase in their content contributes to a sharp increase in the dark resistance of the layers and the deterioration of their semiconductor properties. A significant change in the sensitivity towards its growth also causes an additional introduction of selenium atoms into the PbSe film. It is known that non-stoichiometry for this component exists in chemically deposited layers due to the entry of various impurity anions — decomposition products of selenium urea and other reactants — into the crystal lattice. The ordering of the PbSe structure leads to stable “hole” conductivity of the films with optimization of the “hole” concentration up to (3-4) · 10 ¹⁸ cm ^-3 [6]. It is believed that, in order to ensure optimal photoelectric characteristics, the PbSe film should contain a well-defined amount of oxygen both in the composition of the above oxidized forms of lead and in the form of surface sorption complexes, as well as the absence of a significant number of vacancies in selenium. In [7], based on the results of 12-hour annealing of PbSe at 370 ° С, a model was proposed that explains the role of oxygen in the photosensitivity process, suggesting the appearance of deep localized centers in the semiconductor layer. These centers are traps for non-major carriers and increase the photosensitivity of lead selenide films.

However, control over the oxygen content in the film is difficult and entry is practically unregulated, especially during annealing in an open volume. In this case, there is a high probability of reoxidation of PbSe films, leading to a deterioration of their threshold characteristics.

It was indicated in [2] that the activation of PbSe films must be carried out in a strictly controlled flow of oxygen and iodine. However, the technical support of such conditions is extremely complex.

. Указанная величина обнаружительной спососбности не может быть достаточной для разработки высокочувствительных ИК-детекторов. К недостатку используемого способа сенсибилизации следует также отнести его двухстадийный характер - термообработка и последующая активация в парах галогенов.In the patent [3], PbSe films deposited from a reaction mixture containing lead acetic acid, selenourea, potassium triiodide and gelatin and having a thickness of 1 μm were heat treated for 10 minutes in an air atmosphere with a temperature increase from 350 to 450 ° C. The heat-treated films were aged for 7 seconds in pairs of iodine or bromine. The PbSe layers treated in this way had maximum detection values of no more than

. The indicated value of the detection ability cannot be sufficient for the development of highly sensitive infrared detectors. The disadvantage of the used method of sensitization should also include its two-stage nature - heat treatment and subsequent activation in halogen vapors.

In [4], which we took as a prototype, the sensitization of PbSe was proposed to be carried out in a closed volume (sealed ampoule) or in a limited volume (bucks). The initial layers were synthesized from a reaction mixture containing lead salt, selenourea, ammonium acetate, ethylenediamine, potassium iodide, and also the addition of tin chloride to increase the adhesion of the film to the substrate. It is noted that a noticeable photosensitivity of the obtained films is manifested when the activation temperature reaches 320 ° C. After heating to a temperature of 360 ° C, the photosensitivity of the layers decreases. As conclusions, the authors of the work note that in the manufacture of layers intended for work with cooling to 77 K, the activation of the films should be carried out in the open volume of the furnace at temperatures up to 330 ° C. In the manufacture of uncooled and cooled to 195 K devices, the activation of PbSe films is carried out in a closed sealed volume at a temperature of 360 ° C. The obtained level of the main parameters of PbSe layers according to the technology proposed in [4] at 293 and 195 K is shown in Table 1.

The indicated values of the detection ability of PbSe films are significantly lower than the theoretical limit for this region of the spectrum (1.2 · 10 ¹¹ cm · W ^-1 · W ^1/2 ), and have great potential for improvement.

The present invention is to develop a method of sensitization of PbSe films to infrared radiation, ensuring the achievement of high volt sensitivity and detectability for use without cooling or with shallow cooling.

Table 1 The main parameters of PbSe films made according to [4] Parameter Working temperature 195 K 293 K

Detection ability

4.1 · 10 ⁹ -2.55 · 10 ¹⁰ 3.1 · 10 ⁸ -2.7 · 10 ⁹ Dark resistance, megohms 1,0-20,0 0.3-1.0 Time constant, μs <30 <5 The position of the maximum spectral sensitivity, microns 4.0-4.4 3,5-3,8

This problem is solved by the fact that the inventive method of sensitizing PbSe films to infrared radiation by heat treatment is carried out in an untightly closed container while maintaining a certain ratio between the volume of the container and the surface area of the activated films, and heating is carried out in the presence of metal selenium powder.

The claimed method of sensitization is implemented for chemically precipitated PbSe films deposited from reaction mixtures of various compositions under the following conditions:

- the films are placed in an unsealed closed container (bottle, crystallizer with an unpressurized lid), in which a certain ratio is created between the volume, the heated capacity and the surface area of the activated films, equal to 20-40;

- heating is carried out in the presence of a metal selenium powder.

This creates the conditions for a more controlled entry of oxygen into the composition of the lead selenide layer, achievement of its optimal content, reduces the probability of reoxidation of films, and also reduces the number of selenium vacancies in the PbSe crystal lattice. As a result, prerequisites arise for obtaining higher photoelectric characteristics of the films and increasing their reproducibility.

содержание кислорода недостаточно для обеспечения требуемой степени окисления PbSe и получения высокой чувствительности слоев. При соотношении

пленки снижают свой уровень фоточувствительности по сравнению с оптимальными условиями из-за их переокисления. Пленки, обработанные при

обладают темновым сопротивлением 0,2-1,0 МОм, вольтовой чувствительностью при частоте модуляции 1200 Гц и напряжении смещения 10 В/мм от 800 до 1800 мкВ. Это позволяет иметь обнаружительную способность образцов при 293 K

(573 К, 1200 Гц)=(0,5-1,1)·10¹⁰ см·Вт^-1·Вт^1/2. Введение навески порошка селена дополнительно повышает уровень фоточувствительности на 20-30% при одновременном снижении оптимальной температуры термообработки на 20-30°С.Обнаружительная способность слоев PbSe при 293 К возрастает до (1,2-1,3)·10¹⁰ см·Вт^-1·Гц^1/2. Постоянная времени при этом составляет 3-5 мкс, максимум спектральной чувствительности - 3,5-3,8 мкм. Охлаждение слоев до 195 К позволяет увеличить обнаружительную способность для лучших образцов до (5-6)·10¹⁰ см·Вт^-1·Гц^1/2.The limited air volume of the container during thermosensitization, on the one hand, protects the films from uncontrolled entry of impurities from the atmosphere, and on the other hand, unlike sealed conditions, creates a great opportunity to reduce the mass content of oxygen and, therefore, its partial pressure. This is due to the fact that part of the oxygen is removed with air from the leaky closed volume through leaks, starting from the first minutes of heating, and is not involved in oxidative processes. When heated to 330-390 ° C, the mass of air and, therefore, oxygen in the tank volume decreases 2.0-2.2 times due to a decrease in the density of gases. The remaining oxygen is involved in the oxidation of the films. This simplifies the organization of the heat treatment process due to the exclusion of the sealing operation of the heated volume. The introduction of a sample of selenium powder, which is characterized by significant vapor pressure at heat treatment temperatures, will lead to the elimination of a significant number of vacancies in the PbSe lattice due to diffusion processes. It was found that when the ratio of the hermetically sealed volume (V _neger ) to the area of the activated films (S _PL ) equal to 20-40, the optimum level of oxidation of the films is observed, and they are highly photosensitive. At

the oxygen content is insufficient to provide the required degree of oxidation of PbSe and to obtain high sensitivity of the layers. With the ratio

films reduce their photosensitivity level compared to optimal conditions due to their oxidation. Films processed by

possess a dark resistance of 0.2-1.0 MΩ, a volt sensitivity at a modulation frequency of 1200 Hz and a bias voltage of 10 V / mm from 800 to 1800 μV. This makes it possible to have a detection ability of samples at 293 K

(573 K, 1200 Hz) = (0.5-1.1) · 10 ¹⁰ cm · W ^-1 · W ^1/2 . The introduction of a weighed sample of selenium powder additionally increases the photosensitivity level by 20-30% while reducing the optimal heat treatment temperature by 20-30 ° C. The detection ability of PbSe layers at 293 K increases to (1.2-1.3) · 10 ¹⁰ cm · W ^-1 · Hz ^1/2 . The time constant in this case is 3-5 μs, the maximum spectral sensitivity is 3.5-3.8 μm. Cooling the layers to 195 K allows one to increase the detection ability for the best samples to (5-6) · 10 ¹⁰ cm · W ^-1 · Hz ^1/2 .

A comparative analysis of the results obtained with the prototype allows us to conclude that the claimed method differs from the known one by sensitizing to infrared radiation in an unpressurized closed volume with a certain ratio between the volume and the surface area of activated films with heating in the presence of selenium powder. Thus, the claimed technical solution meets the criterion of "novelty." It leads to an increase in the photosensitivity level of PbSe films, i.e. gives them a new quality, which allows us to conclude that the proposed method meets the criterion of "significant difference".

до

см², что соответствует 2-4 стандартным подложкам размерами 24×24 мм. Дополнительно в емкость для термообработки вводится навеска металлического селена массой 0,7-1,2 г. Емкости помещаются в печь и подложки нагреваются в присутствии селена до 330-390°С, затем нагрев отключается, и подложки извлекаются из печи при снижении ее температуры до 50-60°С.The thermosensitization method is implemented as follows: lead selenide films 0.6-1.0 μm thick chemically deposited on dielectric substrates from glass, quartz, glass, and oxidized silicon are placed in a bottle, Petri dish, crystallizer, etc., are closed from above by simple application glass plate. The number of substrates with a film for heat treatment is selected in such a way that the ratio of the free volume of the used container to the surface area of activated films is 20-40, for example, when processing in a container with a volume of 480 cm ³ , films with a surface area of

before

cm ² , which corresponds to 2-4 standard substrates with dimensions 24 × 24 mm In addition, a sample of metallic selenium weighing 0.7-1.2 g is introduced into the container for heat treatment. The containers are placed in a furnace and the substrates are heated in the presence of selenium to 330-390 ° С, then the heating is turned off and the substrates are removed from the furnace when its temperature drops to 50-60 ° C.

Combinations of thermosensitization conditions for chemically precipitated lead selenide films are shown in Table 2.

table 2 Combinations of heat treatment conditions for PbSe films Parameter Name Options one 2 3 four 5 6 7 8 Processing temperature, ° С 330 360 350 350 380 380 360 360

The ratio of the volume of the tank for heating to the surface area of the films,

twenty 26 thirty thirty 40 10 fifty fifty Introduction of selenium + + + +

The photoelectric parameters of lead selenide films, depending on the combination of thermosensitization conditions at 293 K, are shown in Table 3.

Table 3 The photoelectric parameters of PbSe films at 293 K. The measurements were carried out in accordance with GOST 17772-72. Acht source 573 K, irradiation 10 ^-4 W / cm ² , bias voltage 10 V / mm, modulation frequency 1200 Hz. Parameter Name Combinations of heat treatment conditions Prototype [4] one 2 3 four 5 6 7 8 Dark resistance, megohms 0.28 0.38 0.41 0.66 0.92 0.81 1,0 1,1 0.49 Volt sensitivity, μV 720 1340 2100 1820 750 380 690 350 360

, см·Вт^-1·Гц^1/2 Detection ability

, cm · W ^-1 · Hz ^1/2 3.8 8.2 12.1 5,4 3.9 1.9 3,7 1.8 1.9 Time constant, μs four four 5 5 3 3 four 3 four Maximum spectral sensitivity, microns 3.6 3,7 3.6 3.8 3.6 3,5 3,7 3,7 3,7

, близкие прототипу.As can be seen from table 3, the maximum values of the detecting ability of the film are processed in the claimed conditions (options 2-4). They exceed the same parameter for layers heat-treated according to the prototype in 3.5-6.0 times. PbSe films sensitized during the creation of transcendental conditions (options 6, 8) have the meanings

close to the prototype.

The higher value of the detection ability of the films processed according to option 7, compared with the conditions of option 8 is explained by their heating in the presence of selenium powder.

Literature

1. Bob V. Ms. Lean. Method of production of lead selenide photodetector ctlls. Pat. USA No. 2997409 cl. 117-201 from 08.23.61.

2. Martin Y.M., Hermandez Y.L. Arrays of termally evaporated PbSe infrared on sisubstrates operating at room temperature // Semicond. Sci. Technol. 1996. V.11. P.1740-1744.

3. Thomas H. Johnson. Solutions and methods for depositing lead selenide. Pat. USA No. 3.178.312. cl. 117-201 from 04/13/65.

4. Butkevich V.G., Bochkov V.D., Globus E.R. Photodetectors and photodetectors based on polycrystalline and epitaxial layers of lead chalcogenides // Applied Physics. 2001. No.6. S.66-112.

5. Rarenko I.I. et al. Physical properties of layers A ^IV B ^VI deposited under activated conditions. On Sat Reliability of microelectronic circuits and elements. Kiev: Naukova Dumka. 1982. S. 101-119.

6. Ravich Yu.I., Efimova B.A., Smirnova I.A. Semiconductor research methods as applied to lead chalcogenides PbTe, PbSe, PbS. M .: Science. 1968.383 s.

7. Briones F. Golmayo d. Ortiz G. The role of oxygen in the sensitization of photoconductive PbSe films // Thin Solid Films. 1981. V.79. Number 4. P.385-395.

Claims (1)

A method of sensitizing chemically deposited films of lead selenide to infrared radiation, which consists in heating the films in an atmosphere of air in an airtight container, characterized in that the heat treatment is carried out at a ratio of the volume of the container and the surface area of the processed films equal to 20-40, and the heating is carried out in the presence of selenium powder.