RU2533888C1 - Solution for hydrochemical sedimentation of semi-conductor films of indium sulphide - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: solution contains indium (III) salt, tartaric acid, thioacetamide, hydroxylamine hydrochloride with the following reagent concentration, mol/l: indium(III) salt - 0.01-0.2; thioacetamide - 0.01-0.5; tartaric acid - 0.005-0.2; hydroxylamine hydrochloride - 0.005-0.15.

EFFECT: invention makes it possible to obtain films of indium sulphide, which are characterised by higher values of thickness with the simultaneous preservation of high quality of the film surface.

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Description

The invention relates to the field of semiconductor materials science, and in particular to a technology for producing optoelectronics and solar energy products, and can be used in the manufacture of photodetectors and solar radiation converters. The technical result of the invention is the production of thin semiconductor films of indium (III) sulfide by the method of chemical deposition from aqueous solutions, characterized by higher productivity and simplicity of hardware design.

Due to its properties, indium (III) sulfide is widely used in optoelectronics, in particular, when creating solar radiation converters as an upper buffer layer, thus replacing environmentally unsafe cadmium sulfide, and when producing such a promising material as copper (I) disulfide - Indium sulfide CuInS ₂ (CIS), it acts as the basis of this compound.

Particularly relevant is the problem of increasing the efficiency of solar cells. One of the ways to solve it is to ensure more complete absorption of radiation, primarily due to an increase in the thickness of the semiconductor layer. Shown [Kosyachenko L.A., Grushko E.V., Mikityuk T.I. Absorption capacity of semiconductors used in the manufacture of solar panels. FTP. 2012.V. 46. No. 4. P. 482-486], that almost complete absorption of CIS photons in solar radiation is achieved at a layer thickness of 1 to 2-3 microns.

The layer thickness of the functional element based on indium (III) sulfide has a direct effect on the efficiency solar transducer and providing efficient heat transfer. To obtain high-quality CIS structures, it is technologically simpler and more economical to apply a layer of indium (III) sulfide in one technological stage.

Several non-solvent, inefficient technological methods for producing thin films of indium (III) sulfide are known. These include: spraying a solution of a thiourea complex of indium (III) salt followed by pyrolysis on a heated substrate [John TT et. al. Modification in cell structure for better performance of spray pyrolysed CuInS ₂ / In ₂ S ₃ thin film solar cell. Appl. Phys. A. 2006. V. 82. P. 703-707], production of indium (III) sulfide with sulfidization of a metal layer in an atmosphere of hydrogen sulfide H ₂ S [Yoosuf R., Jayaraj MK Optical and photoelectrical properties of β-In ₂ S ₃ thin films prepared by two-stage process. Solar Energy Materials and Solar Cells. 2005. V. 89. P. 85-94], chemical vapor deposition and layered atomic epitaxy [Sterner J., Malmstrom J., Stolt L. Study on ALD In ₂ S ₃ / Cu (In, Ga) Se ₂ interface formation. Prog. Photovolt: Res. Appl. 2005. V. 13. P. 179-193]. But the technologically simple, not requiring high temperatures and vacuum is the hydrochemical deposition of films [Markov VF, Maskaeva LN, Ivanov PN Hydrochemical deposition of metal sulfide films: modeling and experiment. Ek .: Ural Branch of the Russian Academy of Sciences. 2006.218 p.].

The solution for the hydrochemical synthesis of indium (III) sulfide layers includes an indium (III) salt, which plays the role of a supplier of In ³⁺ ions, a chalcogenizer as a source of S ^2– sulfur ions, and various additives that control the deposition rate of the layer. The greatest difficulty is the selection of the working formulation of the reaction mixture and the content of its components in it.

Several analogues of the invention are known, which are based on the method of hydrochemical deposition of thin films of indium (III) sulfide. So, for example, in [EPO Patent No.EP 2216824 B1, cl. H01L 31/0749, H01L 31/18, publ. 2012] the precipitation solution contains indium (III) chloride and a chalcogenizer - thioacetamide CH ₃ CSNH ₂ (TAA). The pH of the reaction mixture is controlled by the addition of hydrochloric acid and sodium hydroxide in the aisles from 1 to 12 at a deposition temperature of 60 ° C. The authors of the patent note a strong influence of the acidity of the medium on the process of obtaining high-quality layers of indium (III) sulfide and indicate that the optimal pH range is from 1 to 3.5 units.

In [Kale SS et. al. A comparative photo-electrochemical study of In ₂ O ₃ / In ₂ S ₃ multilayer thun films. Materials Science and Engineering B. 2006. V. 133. P. 222-225] the preparation of thin films of In ₂ S ₃ is also carried out in a slightly acidic environment due to the precipitation of indium hydroxide at pH above 3.6, which complicates the process of formation of a sulfide film. TAA was also used as a chalcogenizer in the work. To reduce the pH of the reaction mixture to 2.35-2.45 units, an addition of acetic acid was introduced into the solution. Under acidic conditions (at pH <3), the acid-catalytic process of hydrolysis of thioacetamide proceeds to the formation of acetamide, which is then also hydrolyzed, and hydrogen sulfide. In this case, the hydrolysis rate strongly depends on temperature, the concentration of acid and thioacetamide in solution, as the authors of the work indicate. Hydrolysis of hydrogen sulfide proceeds stepwise with the formation of sulfide ions, which, when reacted with indium (III) ions, form indium (III) sulfide.

For the deposition of a semiconductor layer of indium (III) sulfide in [Yahmadi B. et. al. Structural analysis of indium sulphide thin films elaborated by chemical bath deposition. Thin Solid Films. 2005. V. 473. P. 201-207] used a solution containing indium (III) chloride, acetic acid and thioacetamide. Precipitation was carried out at 70 ° C for 90 min. The processed glass substrates were vertically mounted in sealed reactors, which were placed in a thermostat. The resulting indium (III) sulfide films were light yellow in color. It should be noted that the thickness of the deposited layers did not exceed 680 nm with a significant synthesis time and relatively high concentrations of the chalcogenizer in the mixture.

Closest to the proposed invention is a solution of deposition of a semiconductor layer of indium sulfide (III), taken by the authors as a prototype [US Patent No. 201330017322, class. С23С 18/1233, С23С 18/125, С23С 18/1241, С23С 18/1245, С23С 18/1204, publ. 2013]. In the prototype, the following composition of the In ₂ S ₃ deposition solution was used:

- indium (III) salt - 0.025-0.1 M;

- complexing agent (tartaric acid) 0.01-0.5 M;

- thioacetamide - 0.01-1.0 M.

Deposition was carried out on glass, metal, and polymer substrates in the temperature range from 25 to 65 ° C for 30–105 min. Solutions were prepared on the basis of deionized water by sequential dissolution of the complexing agent and indium salt. Then a solution of thioacetamide was poured. The pH of the solution was set from 1 to 3 in order to avoid the formation of indium (III) hydroxide. The authors of the patent assign an important role to a complexing agent, which may be tartaric, succinic, citric and malonic acids, which form chilate complexes with indium of various strengths depending on the distance between carboxyl groups. Accordingly, the smaller it is, the stronger the complex with metal ions, and, therefore, film growth slows down.

Glass substrates for the deposition of indium (III) sulfide were pretreated, after which they were installed face down in sealed reactors, which were placed in a water thermostat.

The light yellow colored indium (III) sulfide films obtained on the substrates had a thickness of 30 to 130 nm. As such, the mechanism of the formation of In ₂ S ₃ is not described in the patent, but presumably it was carried out as follows taking into account the reaction (where InL _x is a chilate complex with indium):

3CH ₃ CSNH ₂ + 2InL _x + 6H ₂ O → In ₂ S ₃ + 2xL + 3CH ₃ COO ^- + 3NH ₄ ⁺ + 6H ⁺

CH ₃ CSNH ₂ + 2H ₃ O ⁺ ↔CH ₃ CONH ₂ + H ₂ S + 2H ₂ O

CH ₃ CONH ₂ + H ₂ OCHCH ₃ COO ^- + NH ₄ ⁺

H ₂ S + H ₂ OHS ^- + H ₂ O ⁺

InL _x ↔In ³⁺ + xL

2In ³⁺ + 3HS ^- + 3H ₂ O → In ₂ S ₃ + 3H ₃ O ⁺

It should be noted that the obtained In ₂ S ₃ layers had good uniformity and surface quality with a significant synthesis time of up to 105 min. The thickness of the deposited layers did not exceed 130 nm.

The objective of the invention is to obtain films of indium sulfide (III), characterized by higher thicknesses while maintaining high surface quality of the films.

The problem is achieved by the fact that for the manufacture of films of indium (III) sulfide, a solution of the reaction mixture is proposed, which in addition to indium (III) salt, tartaric acid and thioacetamide additionally contains hydroxylamine hydrochloride. The deposition of indium (III) sulfide films is carried out on substrates of dielectric materials (glass, glass) from a solution, the concentration of components of which are in the following concentration ranges, mol / l:

indium (III) salt 0.01-0.2;

thioacetamide 0.01-0.5;

tartaric acid 0.005-0.2;

hydroxylamine hydrochloride 0.005-0.15.

The process is conducted in a slightly acidic solution at a temperature of 60-95 ° C for 30-180 minutes. The resulting indium (III) sulfide layers have good adhesion to substrates and a mirror surface. Their thickness significantly exceeds the values characteristic of the used solution of the prototype, and ranges from 0.4 to 2.2 microns.

The essence of the present invention lies in the fact that the introduced additives of hydroxylamine hydrochloric acid and tartaric acid in comparison with the prototype change the kinetics of the deposition process in the direction that provides an increase in the thickness of the deposited layers. Hydroxylamine, being a strong reducing agent, accelerates the deposition process, affecting the rate of hydrolysis of thioacetamide. Tartaric acid has a double role: firstly, it is a complexing agent for In ³⁺ ions with the following instability constants of the InTart ⁺ complexes (pk _n = 4.5), InTart ^- (pk _n = 7.58), and secondly Being a relatively weak acid, due to the hydrolysis process, it increases the buffer capacity of the reaction mixture, maintaining the pH of the solution at a certain level throughout almost the entire deposition process.

Studies have been conducted proving the receipt of the specified technical result of the claimed method.

Example 1

The substrate (made of dielectric or conductive material) was thoroughly wiped with a cotton swab dipped in a solution of soda ash, washed with water, etched in a 2-8% solution of hydrofluoric acid for 7-10 seconds, washed with distilled water. Then the substrate is treated in a chromium mixture for 20 min at 70 ° C, washed thoroughly with distilled water. The prepared substrate is placed in a bath (reactor) with a solution for the chemical deposition of an indium (III) sulfide film prepared as follows.

To 1.5 ml of a 1.25 M solution of indium (III) nitrate, 1 ml of a 1 M solution of tartaric acid is poured, the required amount of water is added, 0.5 ml of a 4.66 M solution of hydroxylamine hydrochloric acid are added, and finally 2 ml of a 1 M solution are added thioacetamide. The deposition process is carried out at 80 ° C for 60 minutes The result is a yellow-orange film with a thickness of 1.1 μm. X-ray data and elemental analysis of the films showed that the composition and structure of the obtained layers corresponds to the phase of indium (III) sulfide.

Example 2

The preparation of the substrate was carried out in accordance with Example 1. Next, 2 ml of a 1 M solution of tartaric acid were added to 2 ml of a 1.5 M solution of indium (III) chloride, the required amount of water was added, 1 ml of a 4.66 M solution of hydroxylamine hydrochloric acid was added, and finally pour 4 ml of a 1 M solution of thioacetamide. The deposition process is carried out at 80 ° C for 120 minutes The result is a yellow-orange film with a thickness of 1.5 μm. X-ray data and elemental analysis of the films showed that the composition and structure of the obtained layers corresponds to the phase of indium (III) sulfide.

The obtained thicknesses of the In ₂ S ₃ films synthesized from the inventive reaction mixture by varying its component composition and deposition conditions are shown in the table:

It can be seen from the table that the largest film thickness was obtained under deposition conditions corresponding to example a. In this case, the thickness of the deposited layer is 15-70 times greater than the thickness of the films of the prototype (prototype). The maximum layer thicknesses can be achieved by increasing the deposition time. An increase in the concentration of thioacetamide to 0.6 mol / L or a decrease in the concentration of indium salt and tartaric acid to 0.001 mol / L in the reaction mixture negatively affects the thickness of the layers (examples b, d, g). An increase in the concentrations of the last two reagents can lead either to an abundant precipitation of indium sulfide without the formation of a film, or to the absence of the formation of a solid phase. A decrease in the synthesis temperature significantly slows down the process (example c), while its increase accelerates the process (example d). This affects both the thickness of the layers and the quality of their surface. An increase in the concentration of hydroxylamine hydrochloride (example e) makes it difficult to form a film on a substrate.

Thus, the inventive solution for hydrochemical deposition allows in one technological stage to obtain films of indium sulfide (III), the thickness of which significantly exceeds the layers deposited by the prototype.

Claims (1)

A solution for the hydrochemical deposition of semiconductor films of indium (III) sulfide, containing an indium (III) salt, tartaric acid and thioacetamide, characterized in that the solution additionally contains hydrochloric acid hydrochloramine at the following reagent concentrations, mol / l:
indium (III) salt 0.01-0.2 thioacetamide 0.01-0.5 wine acid 0.005-0.2 hydroxylamine hydrochloride 0.005-0.15