Читать книгу All sciences. №8, 2022. International Scientific Journal - Ibratjon Xatamovich Aliyev - Страница 5

UDC 548

Yusupova Dilfuza Aminovna

Candidate of Physical and Mathematical Sciences, Associate Professor of the Faculty of Physics and Technology of Fergana State University

Ferghana State University, Ferghana, Uzbekistan

Аннотация: В работе приведены результаты исследования влияния лазерного излучения на кинетические характеристики поликристалли-ческих пленок узкозонных полупроводников халькогенидов свинца и висмута. Приведены результаты измерений проводимости, концентрации дырок и коэффициента термоЭДС в пленках под воздействием лазерных импульсов.

Ключевые слова: поликристаллическая пленка, лазерное излучение, халькогениды свинца и висмута, проводимость, концентрация носителей, коэффициент термо-ЭДС.

Abstract: The paper presents the results of a study of the effect of laser radiation on the kinetic characteristics of polycrystalline films of narrow-band semiconductors of lead and bismuth chalcogenides. The results of measurements of conductivity, hole concentration and thermal EMF coefficient in films under the influence of laser pulses are presented.

Keywords: polycrystalline film, laser radiation, lead and bismuth chalcogenides, conductivity, carrier concentration, thermo-EMF coefficient.

Laser processing of thin films deposited on a substrate is used to form film elements widely used in instrumentation and microelectronics. Laser processing of thin films is characterized by high accuracy and locality, non-contact, good controllability and in most cases sufficient performance. In the modern technology of semiconductor devices, methods of processing materials using ionizing radiation are becoming increasingly important [1]. Special attention is paid to the modification of the properties of layers under the action of short laser pulses, when, along with ordinary thermal heating of films, the influence of factors having a non-thermal nature is possible.

The physical mechanisms of action of laser radiation on thin films are in many ways similar to the effect of radiation on massive materials, but they have some features.

This paper presents the results of studies of the effect of g-radiation and laser irradiation on the kinetic coefficients of polycrystalline films of narrow-band semiconductors. The objects of research were polycrystalline layers of lead and bismuth chalcogenides and their compounds obtained by thermal vacuum condensation under various technological conditions. The substrates were quartz, polyimide (PM-1) and mica. The thickness of the obtained films was 0.34 microns. The films were irradiated with Co60 g-quanta and an industrial GIG-1M laser (D=15J, tim =50 ns) in air and in vacuum. Measurements of electrical conductivity, Hall coefficient and thermal EMF were carried out.

Electron microscopic studies have shown that with an increase in the condensation temperature, the size of the crystallites increases. When exposed to laser pulses of Pb0.8Sn0 films.2Te condensed at a temperature Tc = 373 K, it was found that at irradiation energies W > 0.15 J /cm2, there is a violation of the adhesion of the condensate with the substrate. In this regard, the irradiation energies were less than the specified value.

It should be noted that these energies are also less than the energy of the calculated value of the peak melting energy of films during laser processing in the nanosecond range, which is 02J/cm2 [1].

This paper presents studies of the effect of laser annealing (LO) on the kinetic properties of polycrystalline Pb0.8Sn0.2Te films obtained on polyimide and mica substrates by thermal vacuum technology at various condensation temperatures [2]. Irradiation was carried out in the modulated Q-factor mode with an industrial laser with a ruby emitter (l = 0.69 microns, tim = 50 ns). The energy density in the laser pulse was adjusted by focusing the light beam. The kinetic coefficients of the films were measured as a function of the number of laser pulse effects. At the same time, the structure of the initial and irradiated films was studied using scanning electron microscopy.

The conductivity s, the concentration of pH carriers and the coefficient of thermal emf a were measured depending on the number of laser pulses of films condensed at different substrate temperatures. The results of the conducted studies have shown that with an increase in Tc, the conductivity of films s increases, and the coefficient of thermal emf a decreases. When exposed to laser pulses, a decrease in s and a is observed in the films.

Electron microscopic studies of the films have shown that with an increase in Tc from 300K to 600K, the size of the crystallites increases from (5-6) 102 to 104 oA, and in these films with an increase in Tc, an increase in s and a decrease in a are observed.

Noticeable structural changes in LO were observed in films obtained on mica at Tc = 570K, i.e. at higher condensation temperatures. Here, the growth of single-crystal fragments is detected, the size of which was many times larger than the size of the crystallites in the original non-irradiated condensates.

The processes responsible for crystallization phenomena, in our opinion, are partial melting of condensates under laser irradiation (partial, since the energy in the pulse is less than the melting threshold) and shock crystallization (accelerated crystallization in the solid phase).

The nature of the change in the concentration of holes in Vi2SbxTe3 films at g-irradiation (Co60 source, intensity 103P/s) in freshly deposited films and a film pre-annealed in air at 420 K for 3 hours, in which the concentration of holes before annealing coincided with the initial concentration of holes, is given.

The following patterns were noted:

1. In samples with initial values of the concentration of holes p ~ 8 1018 cm-3, g – irradiation leads to their monotonous increase with an output at Fd > 108P for saturation (curve 1); at 1019 <p <(2-4) x 1019 cm-3, the concentration of holes decreases during irradiation. At Fd"108 P, a slight increase is observed and subsequently takes a constant value (curve 2). The constant value in both cases corresponds to the same concentration of holes p" 9 x 1018 cm-3 (dashed line in the figure).

2. At p> 5x1019 cm-3, with an increase in Fd, a decrease in concentration is observed with a decrease in the intensity of the process as the Fd increases (curve 3); in the same films, after thermal annealing, leading to a decrease in concentration, the process of decreasing concentration with an increase in Fd also slows down.

To explain the observed phenomena, it is necessary to accept the following. In technological regimes that provide a high concentration of holes, along with anti-structural defects, tellurium vacancies are formed in films [3]. Under g-irradiation, two processes are responsible for changes in the concentration of holes:

a) radiation-stimulated diffusion of antistructural atoms along vacancies with the displacement of the latter to the effluents – the boundaries of crystallites and dislocations;

b) displacement of tellurium atoms into internodes.

The intensity of the first process is proportional to the concentration of vacancies and is more energetically advantageous relative to the second process. The first process is accompanied by a decrease in the number of acceptors, and the second by an increase, therefore, depending on the initial concentration of tellurium vacancies in films, two types of changes in the concentration of holes at g – irradiation are possible, which is observed experimentally. The output of the p (Fd) dependence on saturation corresponds to the establishment of equilibrium in the course of both processes.

List of used literature

1. K.E.Anarkulov, M.M.Akhmedov, D.A.Yusupova, R. T. Rasulov, B. Duliev Kinetic processes in thin films of bismuth and lead chalcogenides under the influence of g- and laser irradiation. Uzbek Physical Journal, V. 4, No.2, 2002, pp. 113-116

2. S.H.Shamirzaev, D.A.Yusupova. Investigation of the electrophysical properties of polycrystalline films of bismuth-antimony tellurides containing nanogranule Khozirgi zamon fizikasining dolzarb muammolari. Republic of ilmiy konferentsiyasi materialari typlami Termiz 1- May, 2013 y.45-46 b.

3. D.A.Yusupova. Study of electrophysical properties of nanocrystalline films Bi2Te3 – Sb2Te3. «Integration of Sciences» International scientific and Practical journal. Moscow Issue No. 4 (19) (June, 2018), from 52—54