PREPARATION OF ZINC SULFIDE BY CVD METHOD

PREPARATION OF ZINC SULFIDE BY CVD METHOD

Liza Dudaeva

Master,  Higher School of Physics and Materials Technology Peter the Great Saint Petersburg University,

Russia, Saint Petersburg

Alexandr Semencha

Director, Higher School of Physics and Materials Technology Associate Professor, Department of Applied Chemistry Peter the Great Saint Petersburg University,

Russia, Saint Petersburg

ABSTRACT

The paper considers zinc sulfidization, consisting of two stages: by the method of preliminary deposition of zinc on substrates by physical vacuum deposition (PWD) on a magnetron installation, followed by vacuum chemical deposition on a CVD laboratory installation as part of the production technology of sulfur sulfide.

Keywords: ZnS, Zn, CD, PWD, KBr, laboratory installation, vacuum installation, zinc sulfidization, zinc deposition.

KBr and quartz substrates with pre-deposited zinc films were subjected to sulfidization according to the spent modes. The main maximum temperature was reached in the reactor zone with samples located in it at control points using a preheated furnace of a smaller size, containing a boat with a gray mass m = 3g. This amount of sulfur was chosen due to its high consumption in order to avoid shortages during spraying.[1]

1. Sulfidization process.

Table.1.

Modes of obtaining samples of zinc sulfide with numbering of samples according to the serial number of the experiment.

The oxidation reaction began after the interaction with the air of the samples of potassium bromide Zn, peaked after 72 hours, as shown in Fig. 1. The samples fell under experiment № 10.

Fig.1. Oxidized potassium bromide samples, white color – potassium bromide glass with Zn applied, silver glossy - quartz glass with Zn applied.

In the reactor zone in Fig. 2. samples were placed in certain areas, taking into account the temperature gradient.

А)B)

Fig.2. Assembly laboratory installation for CVD for obtaining ZnS, ErS. The view in the photo A,B includes the components of the installation

Initially, quartz glass was used to apply the material in a magnetron installation and a CVD reactor, but since the 7th experiment to obtain zinc sulfide, potassium bromide has also been added.[2]

For the next three, substrates with Zn deposited on a magnetron installation on two types of glass were selected: quartz and potassium bromide. Two glasses of different types with zinc pre-applied on them took part in each experiment.

The location of the samples was taken at two control points selected from the heat distribution graph inside the reactor [2] The location of the samples of experiments 1-6 is shown in Fig.3.

Fig.3. Control points of the location of the components of experiments 1-6;

1 – the distance from the beginning of the reactor to sample №. 1 in the experiment, 2 – the distance from the beginning of the reactor to the center of sample №. 2, 3 – the distance to the quartz boat with gray S, 4 – the distance to the inner quartz tube.

Before replacing one of the quartz glasses with Zn deposited in the magnetron chamber with potassium bromide glass with Zn deposited, the control points verified by the results of previous experiments[3] were changed, as shown in Fig. 4

Fig.4 Control points of the location of the components of experiments 1-6;

1 – the distance from the beginning of the reactor to sample №. 1 (potassium bromide sample) in the experiment, 2 – the distance from the beginning of the reactor to the center of sample №. 2 (quartz sample), 3 – the distance to the quartz boat with gray S, 4 – the distance to the inner quartz pipes.

In the last experiment, for the accuracy of the experiment, the samples of potassium bromide and quartz were replaced by each other's positions to understand whether small temperature deviations and the height of the samples affect the final result. The final distribution is shown in Fig. 5.

Fig.5. Control points of the location of the components of experiments 1-6;

1 – the distance from the beginning of the reactor to sample №. 1 (quartz sample) in the experiment, 2 – the distance from the beginning of the reactor to the center of sample №. 2 (potassium bromide sample), 3 – the distance to the quartz boat with gray S, 4 – the distance to the inner quartz pipe.

The argon cylinder was opened at the level of 10 l/min, which ensured a stable gas flow rate at the RRG BUIP[4] unit in accordance with the task of 2 l/min, taking into account the features of the equipment and a flow rate of 4 l/min.

2. Microscopy of ZnS.

Fig.6. Micrographs of samples 7-10 of the assumed ZnS. Background:potassium bromide

а)               b)      c)

Fig. 7. The elemental content of the samples of experiment No. 7-10 ZnS with a percentage and atomic ratio of values. Substrate: potassium bromide.[5]

Fig. 8 Micrographs of samples 7-10 of the assumed ZnS. Substrate: Quartz

а)     b)

Fig. 9. The elemental content of the samples of experiment No. 7-10 ZnS with a percentage and atomic ratio of values. Substrate: Quartz

Based on the data obtained, it can be concluded that a temperature of at least 450 °C[6] is necessary to overcome impurities[7] and obtain zinc sulfide.

In the sample in Fig. 8. b) -  pure zinc sulfide was obtained.

3. X-ray phase analysis.

X-ray phase[8-10] analysis of additional samples containing the assumed ZnS was carried out, they are displayed in the form of diffractograms in Fig.10.

Fig.10. Results of the analysis of samples according to the assumed ZnS obtained at 350, 450 and 550 degrees. a) – 350°C, b) – 450°C, c) – 550°C, d) general view

At a low deposition temperature (A), a mixture of zinc and zinc oxide, as well as pure zinc, prevails, from which it can be concluded that some areas on the substrate did not interact with sulfur in the reactor. With an increase in temperature on samples B and C of the stoichiometry of zinc sulfide in the wurtzite modification, there is also a tendency for the growth of monoclinic and hexagonal structures on the substrate surface.

As a result, thin films and ZnS were obtained at temperatures of 450 and 350 ⁰C, respectively, in the argon carrier gas flow at a speed of 2 l/min. The temperature of sulfur evaporation was in the range of 160-190 ⁰C. It should be noted that zinc sulfide films contained oxygen impurities.

Reference:

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