RU2055948C1 - Cadmium sulfide film production method - Google Patents

Abstract

FIELD: inorganic chemistry. SUBSTANCE: method involves conducting thermal decomposition of low-toxic, noncombustible, sulfur-containing cadmium compound (o-phenanthroline) bis (diethyldithiocarbamate) on heated substrate at source temperature of 200-250 C. EFFECT: increased reproducibility of parameters of cadmium sulfide film production process, reduced consumption of basic volatile compound, improved safety conditions. 1 tbl

Description

 The invention relates to inorganic chemistry, in particular to the chemical technology of semiconductor materials, in particular to the production of cadmium sulfide (CdS) films, which can be used for the manufacture of optoelectronic devices: light-emitting diodes, optical switches, acoustic amplifiers.

For the synthesis of cadmium sulfide films, gas-phase methods of chemical deposition (GFHO) are widely used. Films prepared by co thermal decomposition of organometallic compounds, such as dimethylcadmium and hydrogen sulfide on the heated substrate at 600-800 ^{° C} [1]
Due to the toxicity and flammability of these compounds, the preparation of CdS films by the GFCS method using volatile sulfur-containing complex compounds as starting materials, for example, bis (diethyldithiocarbamato) cadmium [2], is an alternative direction having the following advantages over HFCS films from organometallic compounds:
safety of the process through the use of non-combustible and low toxic sulfur-containing complex compounds;
simplification of the technological process due to the use of instead of two initial substances one substance, which simultaneously contains metal and sulfur atoms;
lowering the temperature of the synthesis of CdS films to 400-500 ^about C.

A known method of producing CdS films by transferring a volatile sulfur-containing complex compound of bis (diethyldithiocarbamato) cadmium from the source zone to the zone of deposition of a carrier gas stream and thermal decomposition of the vapor of this compound on a heated substrate [3]
The disadvantages of the method using bis (diethyldithiocarbamato) cadmium are the poor reproducibility of the parameters for the synthesis of CdS thin films and the high consumption of complex compounds caused by the insufficient thermal stability of solid cadmium bis (diethyldithiocarbamato). At temperatures ^about 150-200 C partial decomposition of the complex compound in the source volume. This leads to a change in the composition of the gas phase in the growth zone of cadmium sulfide films that is uncontrolled from experiment to experiment, which leads to the irreproducibility of process parameters such as the growth rate and chemical composition of the synthesized films.

 The aim of the invention is to provide a method that improves the reproducibility of the parameters of the process for producing thin films of cadmium sulfide and reduces the consumption of the starting complex compound.

The goal is solved in that in the method for producing cadmium sulfide films by transferring a volatile sulfur-containing complex compound in a carrier gas stream and vapor thermolysis of this compound on a heated substrate, (o-phenanthroline) bis (diethyldithiocarbamato) cadmium Cd [ (C ₂ H _{5) 2} NCS _{2] 2} C ₁₂ H ₈ N _2, the process is conducted at a source temperature ^of 200-250 C and a substrate temperature of 450-600 ° ^C.

The distinctive features of the prototype are: use of a new compound (o-phenanthroline) bis (diethyldithiocarbamate), cadmium and higher thermal stability in the source zone at temperatures 200-250 ^C and at substrate temperatures of 450-600 ° ^C.

 These signs are significant and new, as they can improve the reproducibility of the parameters of the process for producing cadmium sulfide films and reduce the consumption of the initial complex compound. A method with such features was not found in the literature.

The addition of o-phenanthroline to the molecule of the complex compound of bis (diethyldithiocarbamato) cadmium leads to a significant increase in the thermal stability of the new molecule (o-phenyntroline) bis (diethyldithiocarbamato) cadmium. Thus, according to thermal analysis, the temperature began losing weight bis (diethyldithiocarbamate) of cadmium is 250 ^{° C} and associated with the decomposition of the molecule, while the temperature of onset of weight loss for the (o-phenanthroline) bis (diethyldithiocarbamate) of cadmium is 280 ^{° C} and associated with the sublimation of the complex compounds, which was shown by specially conducted experiments.

Good thermal stability (o-phenanthroline) bis (diethyldithiocarbamate), cadmium source operating conditions of 200-250 ^{° C} provides quantitative use of this compound for the starting integrated process of producing films, while when using bis (diethyldithiocarbamate), about half of the cadmium complex compound is subjected to decomposition at the source during the process.

 Thus, the use of volatile and more thermally stable (o-phenanthroline) bis (diethyldithiocarbamato) cadmium provides a more stable source operation, due to the absence of decomposition reactions. In addition, the use of this compound makes it possible to make the process of producing cadmium sulfide films more technologically advanced through the use of a non-combustible and low-toxic compound.

 The temperature of the source was chosen to be optimal and, on the one hand, ensures the absence of decomposition of (o-phenanthroline) bis (diethyldithiocarbamato) cadmium, and, on the other hand, provides a sufficient concentration of the complex compound in the gas phase necessary for the synthesis of СdS films with a growth rate of 15-20 mm / min. Since cadmium does not decompose (o-phenanthroline) bis (diethyldithiocarbamato) cadmium in this temperature range, the composition of the gas phase remains constant in the growth process, which ensures the stability of the growth rate and chemical composition of the films.

At a substrate temperature of 450-600 ^{° C} is stable expansion process which ensures a constant chemical composition of the formed films of CdS and the absence of contamination decomposition products (o-phenanthroline) bis (diethyldithiocarbamate) cadmium.

 Thus, the use of a thermally stable initial complex compound, optimal regimes of the source and growth zones makes it possible to carry out a reproducible process for producing films and to reduce the consumption of the initial complex compound. The results are shown in the table.

 In the course of experimental studies, it was found that a 1 g bis (diethyldithiocarbamato) cadmium sample is consumed for one experiment, and a similar cadmium bis (diethyl dithiocarbamato) sample is used for five experiments.

For the synthesis of CdS films, a vertical quartz reactor was used in which a source of the starting complex compound (o-phenanthroline) bis (diethyldithiocarbamato) cadmium and a support holder with local heating were sequentially placed. Process includes the transfer of a volatile starting compound complex from the source in a deposition zone helium stream under reduced pressure, and the decomposition of this compound in vapor heated to 450-600 ^{° C} substrate to form a CdS film. As substrates, polished, pretreated silicon, gallium arsenide, indium, quartz, sapphire arsenide plates were used. The chemical composition of the obtained CdS films was controlled by IR spectroscopy and X-ray phase analysis. The film thickness was determined by both weight and ellipsometric methods. An infrared spectroscopic study of the pyrolytic CdS films grown on the above types of substrates showed that they only contain cadmium sulfur bonds (ν _max = 240 cm ^-1 ). According to x-ray phase analysis and electron microscopy studies, the resulting films had a polycrystalline structure of hexagonal modification. CdS films have a high resistance (10 ¹³ Ohm · cm) and a refractive index of n = 2.8. Industrial applicability of the method is illustrated by examples.

EXAMPLE 1. 1 g of cadmium compressed into tablets (o-phenanthroline) bis (diethyldithiocarbamato) is placed in a source inside a reactor, a local heating furnace with a quartz substrate fixed on it is fixed in the growth zone, after which the reactor is compacted and pumped to residual pressure of 0.2 Pa. The flow of helium through the reactor is turned on, and it is set so that the working pressure inside the reactor is 13.3 Pa. It includes heating the reactor, and the source and substrate temperature is adjusted to predetermined values: _source T = 220 ^C, T = 500 ^to _substrate S. Toggle helium stream from position "in reactor" position "in the source" and the process is carried out for growing films 20 minutes. Then switch the helium flow past the source and turn off the heating of all furnaces, cool the reactor to room temperature. The film growth rate under these conditions according to the ellipsometric analysis is 0.664 ± 0.004 nm / min. The grown CdS films had weak photosensitivity, high resistance of 10 ¹³ Ohms.

EXAMPLE 2. Analogously to example 1, an experiment was conducted to obtain cadmium sulfide films on a quartz substrate at a higher synthesis temperature of 600 ^° C. The growth rate of СdS films was 24.61 ± 0.23 nm / min. As in the previous case, electron microscopy studies showed that the CdS film is polycrystalline, and an increase in the growth rate is associated with an increase in the number of small crystals and compaction of the layer.

 The cadmium sulfide films obtained by thermal decomposition of (o-phenanthroline) bis (diethyldithiocarbamato) cadmium and possessing the parameters listed above can be used in optoelectronics and as active elements of acoustic amplifiers.

Claims (1)

METHOD FOR PRODUCING CADMY SULPHIDE FILMS by transferring a volatile compound based on bis (diethyldithiocarbamato) cadmium from its source zone to the zone of deposition by a carrier gas stream and thermal decomposition of steam of this compound on a heated substrate, characterized in that (0-phenanthroline) is used as a compound bis (diethyldithiocarbamato) cadmium, the process is carried out at a source temperature of 200 - 250 ^o C and a substrate temperature of 450 - 600 ^o .

Images