RU2330352C1 - Method of obtaining photosensitive structure - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: method of obtaining photosensitive structure containing a plate of p-type monocrystal silicon with n-type front layer and p-n heterojunction involves joint heating of p-type monocrystal silicon substrate covered with target material, and synthesis of front layer with heterojunction. Target material is a solid porous carbonaceous material with porosity under 15% of volume, previously undergone thermal processing in contact with silicon at 1100-1350°C for 10-20 minutes; the synthesis is conducted at 1100-1250°C; a gap between carbonaceous material and p-type monocrystal silicon plate is not more than 8 micron.

EFFECT: allows obtaining heterostructure with high photosensitivity in the short-wave spectre range.

2 cl, 1 tbl, 8 dwg

Description

The invention relates to the field of production of materials of optoelectronics and solar technology, and more specifically photosensitive solid-state semiconductor heterostructures.

Known methods for producing photosensitive structures using chemical compounds, in particular, the method described in the article S. Fujiwara, T. Chikamura, M. Fakai. The heterojunction ZnSe - (Zn _1-x Cd _x Te) _1-y (In ₂ Te ₃ ) _y having hingh sensitivity in the visibe light range and its applications. Journal of Cristal Growth, 1983, v. 61, p. 567-575. The known method consists in sequential thermal spraying of ZnSe layers with a thickness of 0.1-0.3 μm and a solid solution (Zn _1-x Cd _x Te) _1-y (In ₂ Te ₃ ) _y with a thickness of (0.1-0.3) 10 ¹ μm on a glass substrate with a transparent electrode, heated to a temperature of 150-300 ° C, followed by annealing in vacuum for 2-20 minutes at a temperature of 500-550 ° C. However, obtaining high phototechnical parameters in this structure is associated with certain difficulties due to the need to obtain a relatively low-resistance layer of zinc selenide (ρ = 10 ⁷ Ohm · cm), which requires special technologies (for example, known from the monograph by A. Milns, D. Feucht. Heterojunctions and metal-semiconductor transitions, Moscow: Mir, 1975, p. 432), and therefore, complex technological equipment.

The prior art also knows a method for producing a television transmitting tube target (T. Ichibase, J. Yamamoto, F. Sakamoto major Photoconoluctive Processesin. Newcosvicon Target - National Technical Report, 1985, v.31, N1, p. 61-69), including sequential thermal spraying of ZnSe layers with a thickness of 0.1-0.3 microns, CdTe with a thickness of 0.5-2.0 microns and (ZnTe) _1-y (In ₂ Te ₃ ) _y with a thickness of 1.0-5.0 microns on a glass a substrate with a transparent electrode, heated to a temperature of 150-300 ° C, followed by annealing in vacuum for 2-20 minutes The disadvantage of this method is also the technological complexity associated with the relatively low resistivity of the zinc selenide layer.

Technologically simpler method that allows to reduce the cost of the photosensitive structure while maintaining its high lighting parameters, is known from RU 2046456, 6 H01L 31/18, publ. 10/20/2005. The method includes the steps of sequential thermal spraying of a ZnSe layer and CdTe layers 0.5-2.0 μm thick and (ZnTe) _1-y (In ₂ Te ₃ ) _y 1.0-5.0 μm thick on a glass substrate with a transparent electrode, heated to a temperature of 150-200 ° C, followed by annealing in vacuum at a temperature of 500-550 ° C for 2-20 minutes, while the ZnSe layer is sprayed with a thickness of 0.05-0.10 μm with an incident flux density of 10 ¹⁵ -10 ¹⁶ cm ^-2 s ^-1 .

It should be noted that for the implementation of the above methods use compounds of zinc, selenium, cadmium, which does not meet the increased requirements for the ecology of technological processes.

In this aspect, technologies using silicon and silicon carbide are very promising [Silicon carbide as a material of modern optoelectronics and semiconductor technology, M., 1984].

A known method of producing a heterostructure based on single-crystal silicon (US 6, 773,508, class C30B 25/04, C30B 25/04, publ. 08.010.2004). The method includes the following steps:

- Placing the silicon substrate in the reaction chamber.

- Passing a gaseous mixture containing hydrogen and hydrocarbon through the reaction chamber.

- Heating the reaction chamber to 1200-1450 ° C.

- Decomposition of a hydrocarbon with the deposition of pyrocarbon on a substrate, accompanied by the formation of a SiC film.

- Control over the formation of single-crystal SiC.

- Removing excess pyrocarbon by oxidizing it with oxygen (C + O ₃ = CO ₂ ) under the following conditions:

1. Displacement of hydrogen by a stream of argon.

2. Cooling the substrate with SiC to 550 ° C.

3. Processing by a stream of a mixture of argon and oxygen gases.

The method provides a heterostructure characterized by low photosensitivity and high cost.

The closest analogue of the claimed invention is the method disclosed in the article P. Shah, CDFuller (1976). Proc. 12 ^th IEEE Photovoltaic Specialists Conf., P.286, which consists in co-heating a p-type monocrystalline silicon substrate with a powder layer of phosphorus doped SiO ₂ oxide coated on the substrate to a temperature of 950 ° C and holding at this temperature for several minutes . As a result of the synthesis, a structure of p-type single-crystal silicon and an n-type Si frontal layer containing a pn heterojunction is obtained.

The method is more technological and can increase the integrated photosensitivity of the resulting heterostructure.

It should be noted, however, that the heterostructures obtained in a known manner have reduced photosensitivity in the short-wave part of the spectrum (see Fig. 1 [A. Farenbruch, R. Boub. Solar cells: Theory and experiment, Transl. From English under the editorship of M .M. Koltuna, M .: Energoatomizdat, 1987, 280 p.]).

The objective of the invention is to provide a method that allows to obtain a heterostructure with high photosensitivity to the short-wave part of the spectrum.

The technical result is achieved by the fact that in the method of obtaining a photosensitive structure containing a p-type single crystal silicon substrate, an n-type front layer and a pn heterojunction, including co-heating a p-type single crystal silicon substrate with the target material deposited on it and synthesis of the front layer and heterojunction of the aforementioned photosensitive structure, a solid, porous carbon-containing material preliminarily subjected to heat treatment in contact is used as the target material those with silicon at a temperature of 1100-1350 ° C for 10-20 minutes and said synthesis is carried out at a temperature of 1100-1250 ° C, the porosity of the carbonaceous material does not exceed about 15%.

The contact of the carbon-containing material and the p-type single crystal silicon substrate is achieved by placing the carbon-containing material on the substrate. Tight fit can be achieved by surface treatment of these elements.

It should be noted that the finished structure demonstrates the best characteristics in cases where the gap between the contacting surfaces does not exceed 8 microns. A decrease in the density of combination leads to the formation of a structure with properties that are inhomogeneous in area. This is due to the fact that silicon carbide of only one structural polytype is formed on the entire plane of the surface of the substrate. If the carbon-containing material is not pressed tightly against the silicon substrate, then, as a rule, the silicon carbide film will consist of different silicon carbide polytypes, such as 3C-SiC, 4H-SiC, 6H-SiC, which form twin crystal structures that degrade the quality of epitaxial layer. The photosensitivity of such a structure decreases sharply due to scattering of current carriers at the boundaries of twins.

The essence of the proposed method and the rationale for the selected parameters is illustrated in the graphic materials and examples presented in the table.

To implement the method on a plate made of silicon grade (KBD-1-KBD-10), the use of a particular grade of silicon (type CBD) depends on what magnitude the voltage must be at the output of the photosensitive element, a porous carbon-containing material is placed (for example, artificial fine-grained dense graphite MPG-6 brand in the form of a cylinder with a polished base, which provides a snug fit to the silicon surface under the influence of the weight of the cylinder), then the assembly is placed in a vacuum furnace or inert gas furnace. The furnace is heated to a temperature of 1100-1350 ° C, at which the assembly is maintained for 10-20 minutes. Then the furnace is cooled. The carbon-containing material is separated from the silicon wafer and transferred to the surface of a new p-type single crystal silicon wafer (KBD-1-KBD-10). The surface of the latter should be polished, etched and tightly aligned with the surface of the carbon-containing material that interacted at the first stage of the process with a silicon wafer, as described above.

Next, the new assembly is placed in a vacuum oven or inert gas furnace. The furnace is heated to a temperature of 1100-1250 ° C. The level of residual vapor of the atmosphere is maintained not lower than (1-10) Pa. The temperature is controlled by thermocouples with an accuracy of ± 20 ° C. The oven is held for several minutes at this temperature and then cooled. In the process of annealing in the contact area of silicon and carbon, they interact with the formation on the surface of the silicon wafer and the carbon-containing material of a multilayer carbide-containing film of complex composition.

The result is a structure containing a p-type monocrystalline silicon substrate of a given crystallographic orientation, an n-type front layer and a p-n heterojunction. The frontal layer has a complex composition: several SiC layers, of different polytypes penetrated by "ribbon" islands.

The invention is illustrated in graphic material, where:

Fig. 2a shows in a schematic form the complex structure of the front layer, which is formed by sublayers 1 and 2. The composition of sublayers 1 and 2 was obtained based on the analysis of patterns of film samples obtained using TEM (tunneling electron microscope). Samples were prepared as follows. The silicon substrate was etched in a solvent that did not dissolve the silicon carbide film. Further, silicon carbide layers were sequentially etched from a silicon carbide film by irradiating them with argon ions. In addition, each layer was analyzed by TEM. At the same time, both electron-microscopic images (magn. × 10,000-30000 times) of each layer and their microdiffraction patterns were taken. This allowed us to prove that the silicon carbide layer has a complex structure. Layers with photoconductive properties, as shown by the analysis, consist of three layers. The first layer is silicon carbide polytype 4H-SiC. It is covered with a layer of silicon carbide polytype 3C-SiC. Both layers must be epitaxial. In some cases, randomly spaced ribbon islands can penetrate them, which grow from the silicon substrate. Their presence is optional, but they do not impair the photosensitive properties of the heterojunction. This structure is shown in FIG. 2b.

Figure 3 shows typical current-voltage characteristics of structures, indicating the presence of a pn junction (curves 1, 3 were taken in the dark, and curves 2, 4 when irradiating structures from the front layer side with unfocused light from a 100 W incandescent lamp located at a distance of 20 cm from the surface).

Figure 4 presents the spectral characteristic of the heterostructure obtained in accordance with the claimed invention, indicating increased photosensitivity to the short-wave part of the spectrum. The indicated spectral characteristic was obtained at room temperature. The integrated photosensitivity of the heterostructure was obtained by irradiating unfocused light from a 100 W incandescent lamp located at a distance of 20 cm from the surface. To obtain it, we used a set of colored optical glasses No. 804 and a catalog of colored glasses (set of samples No. 535). The integrated photosensitivity characteristic corresponds to Examples 1, 2 of the Table.

It should be noted that heterostructures in which the SiC layer obtained by known methods (Silicon Carbide (Recent. Major Advances) Eds. WJ Choyke, H. Matsunami, G. Pensl. Springer. 2003) are not used in the short-wavelength layer as the front layer region of the spectrum with increased photosensitivity due to the low absorption of the thin-film front layer.

Heterostructures obtained using a carbon-containing material not previously treated by co-annealing with silicon, as well as heterostructures obtained using a carbon-containing material with porosity above 15% vol., Have low photosensitivity (Examples 3, 4, 5, 6 of the Table).

Heterostructures synthesized using a carbon-containing material pretreated by co-annealing with silicon, but at temperatures above 1350 ° C, have low integrated photosensitivity and an almost linear current-voltage characteristic (see examples 5, 6, 7, 8 of the Table).

At temperatures below 1100 ° C, a film does not form on the silicon surface during annealing.

Fig. 5a, Fig. 5b and Fig. 5c for comparison shows an electron micrograph taken by TEM and a diagram of the structure of the front layer of the heterostructure obtained without preliminary annealing of the carbon-containing material with silicon (a similar structure is also formed at synthesis temperatures above 1350 ° C as with pretreatment, and without pretreatment of carbon-containing material). Figure 5 indicate a deterioration in the crystalline properties of the film and a simplification of the structure of the front layer. The film in this case contains a large amount of polycrystalline phase and consists of only one polytype of silicon carbide 4H-SiC.

Heterostructures synthesized using a carbon-containing material of optimal porosity, but annealed for more than 20 minutes, possess similar properties (example 9 of the Table). An increase in the synthesis temperature of heterostructures reduces their integrated photosensitivity, increases the dark current, and leads to the formation of a frontal layer with the structure shown in Fig. 5 (Table 10, example).

The presented data prove that only if the proposed process conditions are observed, it is possible to obtain a photosensitive heterostructure with increased sensitivity in the short-wave part of the spectrum.

Properties of photosensitive heterostructures obtained under various synthesis conditions No. Carbon material The porosity of the carbon-containing material,% Annealing temperature, carbon-containing material, ° С Annealing time of carbon-containing material, min Synthesis temperature, ° С Short circuit current density *, μA / cm ² Spectral characteristic Volt-ampere characteristics Layer structure one PGM-6 fifteen 1100 twenty 1200 2500 Type 5 figure 4, curves 1, 2 type of figure 3 2 PGM-6 12 1350 10 1250 3000 Type 5 figure 4, curves 3, 4 type of figure 3 3 PGM-6 10 0 0 1200 400 - type of figure 4 type 6 four PGM-6 fifteen 0 0 1250 200 - type of figure 4 type 6 5 GM-3 26 0 0 1250 10 type of figure 4 type 6 6 GM-3 26 1350 twenty 1250 200 type of figure 4 type 6 7 PGM-6 fourteen 1450 fifteen 1250 0.1 - linear type 6 8 PGM-6 fifteen 1000 twenty 1340 0.15 - linear type 6 9 PGM-6 fifteen 1300 40 1250 0.5 - linear type 6 10 PGM-6 10 1250 fifteen 1400 800 - type of figure 4 type 6 * The short circuit current was measured when the heterostructure was irradiated from the front layer with unfocused light from a 100 W incandescent lamp located at a distance of 20 cm from the heterostructure

Claims (2)

1. A method of obtaining a photosensitive structure containing a p-type single crystal silicon wafer, an n-type front layer and a pn heterojunction, comprising co-heating a p-type single crystal silicon substrate with a target material deposited thereon and synthesizing a front layer and a heterojunction of said photosensitive structure characterized in that as the target material is used a solid, porous carbon-containing material, previously subjected to heat treatment in contact with silicon at a rate a temperature of 1100-1350 ° C for 10-20 min, and the aforementioned synthesis is carried out at a temperature of 1100-1250 ° C, while the porosity of the carbon-containing material does not exceed 15 vol.%, and the gap between the carbon-containing material and the p-type single-crystal silicon wafer is not exceeds 8 microns. 2. The method according to claim 1, characterized in that as the carbon-containing material using artificial fine-grained dense graphite grade MPG-6.

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