RU190137U1 - Complex for measuring the effect of light on the spectra of electric dipole relaxation times in semiconductors - Google Patents

Abstract

Use: to study the defective structure of semiconductor films, including those used to create solar cells. The essence of the utility model is that the device for measuring the effect of light on the spectra of electric dipole relaxation times in semiconductors consists of a monochromator with the possibility of varying the intensity and wavelength of illumination, an amplifier converter for varying the frequency of electric current and a temperature control system with an accuracy of 0, 01 K. Technical result: providing the ability to obtain data on the effect of light and temperature on the spectra of electric dipole relaxation times in semiconductors wide wavelength range, the electric field frequency and temperature. 3 il.

Description

The invention relates to devices for studying the properties of semiconductor films, including those used to create solar cells, radiation detectors and memory devices. More specifically, it relates to devices for studying the spectra of the times of electric dipole relaxation in semiconductors, including to determine the position of donor-acceptor energy levels created by defects in the structure of semiconductors.

Recently, thin-film solar cells based on CdTe, CuIn _x Ga _1-x Se ₂ (CIGS) or Cu _2-δ Zn _2-x Sn _x (S _1-y Se _y ) ₄ (CZTS, Se) have become popular. The advantage of these materials is that a film with a thickness of only a few microns is sufficient for effective absorption of sunlight, whereas using crystalline silicon requires a layer of about 200 microns. However, the efficiency of the batteries currently being created is noticeably lower than theoretically possible. This is due to insufficient research of a number of semiconductor materials, which in turn is associated with the imperfection of the technology used to study their properties.

Typically, optical spectroscopy, cathode luminescence, and temperature dependences of electrical conductivity and photoconductivity are used to study the position of levels. Despite the widespread use of these methods, they have certain limitations. The first method allows to obtain direct information only about the process of light absorption, the use of the second is limited to radiative processes, methods based on measuring the temperature dependences of electrical conductivity are effective only in a narrow range of donor-acceptor energy levels.

Another approach is to study the effect of light on the distribution of the times of electric dipole relaxation. This method allows one to study not only the processes of generation and recombination of free charge carriers associated with impurity levels in semiconductors, but also relaxation processes caused by the production under the action of light and the death of electric dipoles.

Our proposed utility model is a complex for measurements that makes it possible to obtain data on the effect of light and temperature on the spectra of electric dipole relaxation times in semiconductors in a wide range of wavelengths, frequencies of the electric field and temperatures.

The "photodielectric effect", as the phenomenon of an increase in the dielectric loss angle under the action of light of the electrical capacitance and the tangent of dielectric loss, was first observed by Goudnen and Paul in 1920. The first studies and attempts to explain the nature of the effect occurred mainly on ZnS, ZnO or CdS powders in the 50s of the last century. Some data were also obtained for single crystals [Roux J., Journ. phys. et rad., 15, 176 (1954).]. The magnitude of the effect is different and varies from a twofold or threefold increase in the dielectric constant for ZnS to a 7-100 fold increase in ZnO [Roux J., Compt. Rend., 236, 2492 (1953).]. The introduction of impurities that poison the luminescence of ZnS phosphors also weakens the photodielectric effect [Roux J., Journ. phys. et rad., 813 (1956).].

Known impedance meters such as [http://potentiostat.ru/product/%d0%bf%d0%be%d1%82%d0%b5%d0%bd%d1%86%d0%b8%d0%be%d1% 81% d1% 82% d0% b0% d1% 82% d1% 80-40% d1% 85% d1% 81% d0% bc% d0% be% d0% b4% d1% 83% d0% bb % d0% b5% d0% bc-% d0% b8% d0% b7% d0% bc% d0% b5% d1% 80% d0% b5% d0% bd% d0% b8% d1% 8f-% d1% 8d .

The impedance meter consists of a frequency analyzer module built into the potentiostat, a test equivalent and connecting cables. This device allows you to explore only the electrical conductivity, capacitance and the tangent of the dielectric loss angle of the studied sample in the dark. They do not provide the opportunity to explore the relaxation processes caused by the action of light.

The closest technical solution proposed utility model is a photoelectric spectrometer, described in [https://www.fotonowy.pl/products/photoelectric-spectrometer/?lang=en].

The known device consists of a potentiostat, a light intensity meter and a monochromator. This device allows you to study the electronic levels in semiconductors, however, since it operates at a constant current, as well as impedance meters, do not allow to obtain data on relaxation processes caused by the action of light. In addition, due to the absence of a temperature stabilization unit, it is impossible to investigate the temperature dependences of photoconductivity using such devices.

The objective of the proposed utility model is to create a device that allows one to obtain data on the effect of light and temperature on the spectra of electric dipole relaxation times in semiconductors in a wide range of wavelengths, frequencies of the electric field and temperatures.

The problem is solved using the proposed complex for measurements presented in FIG. 1, where:

1 - monochromator, λ = 0.22 ÷ 2.50 μm

2 - a light source (xenon lamp) with a power source, P _St. = 1000 W

3a - electric converter, frequency range of the electric field f = 10 ^-3 ÷ 10 ⁵ Hz

3b - amplifier, the frequency range of the electric field f = 10 ^-3 ÷ 10 Hz

4 - temperature control system, 77 ÷ 620 K with an accuracy of 0.01 K

5 - measuring cell

6 - computer with control board

The measuring cell 5 is shown in more detail in FIG. 2:

5a - mounting screw

5b - test sample

5c - dielectric substrate (sample carrier)

5g - nitrogen supply pipe

5d - nitrogen outlet pipe

5e - mounting spring

5g - top contact

5h - bottom contact

5i - electrical terminals

To maintain a constant temperature with high accuracy, the cell has double vacuum walls.

In this cell, in order to create the required working temperature from the temperature control system 4 (Fig. 1), the necessary nitrogen heated continuously through the nozzle 5d (Fig. 2) is fed through the nozzle 5g (Fig. 2). A feature of our complex is the supply of light from the monochromator to the sample through a stream of nitrogen coming out through the 5d tube (Fig. 2).

The advantages of the complex for measuring the effect of light on the spectra of electric dipole relaxation times in semiconductors over the above-described analogues are:

a.) use of a wide range of wavelengths (we used the ZMR-3 monochromator, 1 in Fig. 1) with the possibility of varying the intensity of illumination (DXSH-1000 lamp, 2 in Fig. 1),

b.) application of the frequency range of the electric field ν = 10 ^-3 ÷ 10 ⁵ Hz (converters from different companies can be used, we used the Novocontrol converter + Stanford Systems SR810 DSP amplifier, 3 in Fig. 1),

c.) temperature range 77 ÷ 620 K with an accuracy of 0.01 K (using the Novocontrol Qudro system, 4 in Fig. 1).

All this at the same time allows not only to investigate the photoconductivity of films, but also to study the relaxation times.

To study the characteristics of the sample on a dielectric substrate (usually glass) with sprayed electrical contacts is placed in the measuring cell and secured by means of a fixing screw 5a (Fig. 2) and springs 5e (Fig. 2). Its contacts 5g (fig. 2) and 5h (fig. 2) are connected to the terminals of the cell 5i (fig. 2). The sample is oriented in such a way that its back side is directed toward the nozzle 5d (Fig. 2). After connecting the contact cables to the cell, using the monochromator, set the required radiation wavelength. After that, using the computer with the control board, set the necessary range of frequencies and temperatures and record the spectra. Next, carry out the processing of the data using a mathematical apparatus.

The use of the proposed utility model is illustrated, but not limited to the following example.

Example 1. Investigation of the dielectric relaxation time spectra in CdS films.

To study glass substrates, a layer of CdS was applied by aerosol pyrolysis, copper contacts were applied by vacuum deposition. After that, the sample was fixed in the cell, as shown in FIG. 2

Further, at a fixed temperature T = 20 ° C in the frequency range 10 ^-3 -10 ⁵ Hz, information about the impedance was obtained on the basis of measuring the phase shift. In this case, monochromatic light with λ = 370, 520, 620 and 960 nm was applied to the sample.

Based on the obtained dependence of the phase shift on the frequency of the applied electric field, the frequency dependences of the complex dielectric constant ε * were constructed. In this example, Novocontrol WinFit 2.9 software was used for data analysis, but any other similar software is possible.

Based on the ratio

and

Were constructed relaxation time spectra (Fig. 3.) at different wavelengths (1 - λ = 370 nm, 2 - λ = 520 nm, 3 - λ = 620 nm, 4 - λ = 960 nm, 5 - in the dark)

From the spectra it can be seen that with an increase in the wavelength of light from 370 to 960 nm, the maxima shifted towards high relaxation times. At wavelengths longer than 960 nm, one maximum in the spectrum of G (τ) disappeared, and the second shifted to the dark value.

Thus, the complex for measurements proposed by us, in contrast to analogs, allows one to study not only electronic levels in semiconductors, but also to investigate relaxation times when exposed to light.

Claims (1)

A device for measuring the effect of light on the spectra of electric dipole relaxation times in semiconductors, consisting of a monochromator with the possibility of varying the intensity and wavelength of illumination, a converter with an amplifier for varying the frequency of electric current and a temperature control system with an accuracy of 0.01 K.

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