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05.14.00 ЭНЕРГЕТИКА
05.14.01
ЭНЕРГЕТИЧЕСКИЕ СИСТЕМЫ И КОМПЛЕКСЫ
RESEARCH OF AHV-EFFECT IN FILMS AND CRYSTALS WITH THE EFFECT OF THE DOUBLE LUXURIFICATION
Kasimakhunova Anarkhan, professor, doctor of technical sciences, Fergana Polytechnic Institute. Fergana, Uzbekistan. E-mail: Kasimahunova@rambler.ru
Naymanbayev Raxmanali, associate professor, candidate of technical sciences, Fergana Polytechnic Institute. Fergana, Uzbekistan. E-mail: naymanbaev@mail.ru
Mamadalieva Lola, associate professor, candidate of technical sciences, Fergana Polytechnic Institute. Fergana, Uzbekistan. E-mail: Kasimahunova @rambler.ru
Nurdinova Raziyaxon, doctoral candidate, Fergana Polytechnic Institute. Fergana, Uzbekistan. E-mail: nurdinovar 2016@mail.ru
Olimov Shoirbek, doctoral candidate, Fergana Polytechnic Institute. Fergana, Uzbekistan. E-mail: shoirbek2015 @yandex.ru
Abstract. In this paper, the results of experimental studies of the AFN effect are carried out and its theory is developed. The nature of microprocesses leading to the occurrence of anomalously high photoelectric voltages (AHV effect) is formulated and determined. The energy parameters of the AHV films were studied.
Keywords: anomalous photovoltage (AFN), current-voltage characteristics, lux-volt characteristics, photovoltage spectra.
ИССЛБДОВАНИБ АФН-ЭФФБКТА В ПЛБНКАХ И КРИСТАЛЛАХ, ОБЛАДАЮЩИХ ЭФФБКТОМ ДВОЙНОГО ЛУЧБПРБЛОМЛБНИЯ
Касимахунова Анархан Мамасадиковна, профессор, доктор технических наук, Ферганский политехнический институт. Фергана, Узбекистан
Найманбаев Рахмонали, доцент, кандидат технических наук, Ферганский политехнический институт. Фергана, Узбекистан
Мамадалиева Лола Камилджановна, доцент, кандидат технических наук, Ферганский политехнический институт. Фергана, Узбекистан
Нурдинова Разияхон Абдихаликовна, докторант, Ферганский политехнический институт. Фергана, Узбекистан
Олимов Шоирбек Абдукоххорович, докторант, Ферганский политехнический институт. Фергана, Узбекистан
Аннотация. В данной работе проведены результаты экспериментальных исследований АФН-эффекта и развита его теория. Сформулировано и определено природа микропроцессов, приводящих к возникновению аномально высоких фотоэлектрических напряжений(АФН-эффект). Проведены исследования энергетических параметров АФН-пленок.
Ключевые слова: аномальное фотонапряжение (АФН), вольт-амперные характеристики, люкс-вольтовые характеристики, спектры фотонапряжения.
Performance of the task
In the middle of the last century Pensac and Goldstein [1] discovered in made thin films of cadmium telluride a photovoltage in hundreds of volts. This discovery aroused
great interest both in scientific terms and in terms of possible applications.
Practical aspects of this effect (the effect of anomalously big photovoltage-AHV) are related with the possibility of the direct
formation with the light of high voltages, the scientific interest names its anomalous character The impossibility of the formation photovoltages exceeding the width of the forbidden a semiconductor, it would seem from the general positions of solid state physics.
We have conducted extensive experimental researches of AHV-EFFECT and its theory has been developed [2]. It is shown that this effect is not specific for any particular class of substances and can be obtained from any semiconductor material. The researchers of crystalline structures showed that it is not a determining factor in AHV-EFFECT. This result is observed in both crystalline and polycrystalline, as well as amorphous, and in complex organic, inorganic, and polymer semiconductor structures.
According to the modern theoretical concepts, on the basis of the theory of AHV-EFFECT, it is possible to find the ideas of Adirovich [3], which were developed by his co-workers [4]. On the basis of these concepts, as well as the earlier model of AHV-EFFECT, the scientists could formulate and determine the nature of micro processes, which lead to the origin of anomalously high voltages (AHV-EFFECT). However, in the area of development of effective, the stable AHV-photodetectors., there are a lot of unresolved questions. As given above, considering the good perspective of these elements in the area of creating semiconductor devices we have made and conducted explorations on the energy parameters of AHV-Films.
Methods of making AHV-Films
We have received AHV-Films from different semiconductor materials with a wide and narrow forbidden area, using the method of vacuum evaporation. [2, 4] The technological way of the production AHV-Films depends on a large number of parameters such as the temperature of the evaporator and the substrate, the corner of deposition, the thickness of the film, the composition and pressure of the residual gases in the vacuum chamber, the conditions of thermal treatment after spraying. In this case, each semiconductor material corresponds to its optimal regime and often small deviations from it. Even one parameter leads to the disappearance of AHV-EFFECT in the manufactured films. Therefore, the development of the technology of receiving AHV-Films from another material will require a huge experimental labor, a big amount of test spraying with sequential changes, their combinations, and finding of parameters, specific for getting AHV-EFFECT on the films from the given semiconductor material.
The vacuum chamber where the performance of the films was representing a quartz cap, inside of which were located the substrates (glass, quartz, etc.) and a crucible made of aluminum oxide or beryllium oxide. The temperature of the substrate was set by means of a furnace, endowed outside on the vacuum cover.
Because of the difficulty of the technological regime (the process) of getting AHV-Films has not been learned well. The frequency of regime repeatability is very low. Anomalously-high voltage with time, there occurs so-called aging. The controllability of the regime is low, doping is insufficient. Heterogeneity in the composition and in the structure is uncontrolled.
During the labor, the given results of the research of AHV-EFFECT in the films and the crystals obtained doping with isovalent impurities and possessing the effect of double refraction.
The researches and the manufacturing have been conducted according to the special methodology and the setting
for getting AHV-Films from different semiconductor materials, which has been described in [4]. The developed method and the appropriate installation have provided in the film heterogeneity in the structure and in the composition. In the case of illumination of non-uniform a polycrystalline semiconductor can arise the vented photo-EDC, on the barriers of the different type. For instance, in the films CdTe, CdSe, ZnS and so on. It is observed so called AHV-EFFECT, consisting in the occurrence of anomalously-high voltages, exceeding the width of the forbidden area like a semiconductor. Turns out that the AHV-Film presents complex multi-layered structure (CMS) system, which consists of a number of microphotoelements (~105 cm-1 and more), each of them is associated with some structural feature of the film-microroughness, the presence of intercrystalline interlayers or grains, the boundaries of blocks, etc. Moreover, the vented photo-EDC, the effect may be conditioned with the diffusion (Demberevo) photo-EDC in the size of the microcrystal. In nonuniform CMS structures, the photo-EDC is determined by the intercrystalline substance. By the magnitude of photo-EDC and photoconductivity, it is possible to determine the mobility of charge carriers.
Polycrystalline and amorphous AHV-films (Sb2S3 and Sb2Se3) can have high effective volume resistivities (for example, (~1010-1011 Q • cm)) and low mobility of charge carriers. It is related with the presence of crystalline inclusions in the amorphous phase, where micro-heterojunctions are localized.
As the result of the research, AHV-EFFECT has been detected by us in copper and indium selenide, cadmium telluride with isovalent impurities (Cu, Ag and Au), germanium and silicon (Al, Ga and In), and in some equimolecular compositions (PbSe • Sb2Se3 or PbS • Sb2Se4). The polished glass, ceramic and ferroelectric plates are used as a substrate. It has been established that AHV-films are obtained only by oblique deposition on a substrate. Between the evaporator and the substrates in the vacuum chamber, a shutter was installed, moved by an electromagnetic drive parallel to the surface of the source. Changing the speed of movement, the inclination of the substrate inclination relative to the axis of the molecular beam, it was possible to independently control the angular anisotropy of the sputtering and the film thickness gradient. In this case, we obtain the films of constant thickness with oblique sputtering and wedge-shaped films when deposited along the normal. The films of both were received on all the studied semiconductor materials. From the experimental results, it can be noticed that AHV-Films form only inhomogeneous and anisotropic deposition, regardless of the presence or absence of a thickness gradient. The researches of the crystalline structure have shown that one of the factors of arising the AHV-EFFECT is heterogeneity in the structure and composition. In addition, in AHV films, the photodiffusion and photovoltaic mechanisms are performed:
VAHV = f (B R0).
(1)
The functional relationship is preserved if AHV-EFFECT can arise only in high-resistance films. The formula [1] shows: B is the intensity of the incident light; R0 is the dark resistance of the film.
In order to determine the scope and technical capabilities of AHV effect, the studies have been made of photoelectric, magnetoelectric, and photoelectret properties, newly obtained AHV-films and AHV-elements based on ferroelectrics.
Examining photovoltaic studies, experimental and theoretical studies of volt-ampere (VAC), lux-volt (LVCH) and spectral (SCH) characteristics of the AHV-films have been carried out.
Kasimakhunova A., Naymanbayev R., Mamadalieva L., Nurdinova R., Olimov Sh.
Volt-ampere characteristics
J • 10s, A
Basing on the submitted in the labor [1-5] of models the AHV-Films from cadmium telluride and considering the difficulties and also heterogeneity in the structure and composition of other AHV-Films and generalizing the results in [6] the VACH characteristic is obtained in a general form [7]. The dark I-V characteristic for the considered model is shown on the figure below.
a = 0,fi,(V)
a = 1, R. = <*>
a = 1, R, = <*>. /?.,, = <*>
a = 0, R, = <*>, fith = <x>
1 - W»Z.
2,3 -WCL
Fig. 1. Dark VACh for the considered model is shown on the fig. 1.
The volt-ampere information for interconnected (a = 1) non-interconnected (a = 0) CMS with p-n-junctions:
a - transfer coefficient; W - the thickness of the quasineutral transition regions;
L - diffusion length; R^ - leakage resistance of electron-hole junctions;
Rsh - the resistance of the photo shunt
In order to detect VACH, the fields predicted by theory, experimental researches of VACH characteristics have been conducted on various AHV-films (fig. 2). The dark VACH are linear to the values E = 5 • 103 V/cm, and at higher fields up to breakdown fields (E = 5 • 105 V/sm) are superlinear. The linear portion of VACH at the origin depends on the degree of shunting of the micro p-n-junctions. After a linear section, VACH has a superlinear region. However, according to the theory, when transitions of the displaced in the forward direction and displaced in the opposite direction, the effect of transferring the injected carriers (a) occurs, the transitions interconnected on VAX after the superlinear section should be again observed a linear portion that could not be detected in the experiment (see fig. 2). The physical meaning of superlinearity VACH is that while the recombination losses of the injection current in the p-n-regions constitute a small fraction of the saturation current of a single transition. Therefore, practically all the voltage applied to the transitions falls on the emitters. At sufficiently high currents, the shifted p-n-junctions begin to play the main role. VACH becomes sublinear. On the experimental VACH, the transition from the superlinear to the sublinear region was not detected.
20
15
10
VlC 5 4 3 2 1 0 10, A (
0,1 0,2 0,3 V, kV 0,4 0,5" J
2 4 6
Fig. 2. Experimental, dark VACH
8 V, kV
When illuminating samples, VACH is rectified and, under high illumination, the intensity of light becomes linear.
Rectification of VACH at high light illuminations is connected, apparently, with a decrease in the differential resistance of the reversely biased transitions and the voltage drop across the series resistance.
Lux-Volt characteristics
The most important characteristic of AHV-EFFECT is the dependence of photovoltage on light intensity. The research of LVCH has been made by attenuating the incident light flux by neutral light filters. The photovoltage was measured by an electrostatic voltmeter C-50, C-96, and the electrometer B2-5. Typical LVCH AHV films are shown on the same fig. 3.
150 200 B ■ 103, Ix
Fig. 3. Lux-volt characteristics of AHV-films:
1 - germanium; 2 - silicon; 3 - arsenide of halides; 4 - cadmium telluride
The lux-volt characteristics of samples of AHV-films doped with isovalent impurities do not pass through the zero of the coordinate system. It means that the given examples have dark electret voltage.
This voltage occurs during the process of oblique deposition of films, in the absence of a polarizing electric field. Interesting that the polarity of the electret voltage can coincide with the polarity of the anomalously high voltage generated by this film and it can be opposite. Some samples of the photovoltage equal to zero, while, the electret voltage is nonzero. The experiences on heating of the films in vacuum to a temperature of 1000 °C, also did not lead to the disappearance of the electret voltage.
The lux-volt characteristics of chalcogenides at room temperature are linear up to light intensity B = 0,35 W/cm2. In the case of the temperature of liquid nitrogen, the linearity of the LVCH remains only up to the excitation intensities B < 2 • 10-2 W/cm2. It is important that at 770 K the photoconductivity increases sharply in the region of low light intensities and even at B = 10-6 W/cm2 reaches values of the order of 1 V, and a further increase in the excitation intensity leads to an increase in the anomalous photovoltage up to several tens of thousands of volts, to B = 0,35 W/cm2.
Spectrums of the photovoltage
The results of measurements of the anomalous photovoltage spectra on semiconductors CdTe, Si, Ge, GaAs, Se, GaP, and chalcogenide alloys have shown that AHV effect is caused by light from the intrinsic absorption region. Typical spectra of AHV-films normalized to a unit of the incident light energy are shown on fig. 4. Along with the LVCH shown in the films of various substances, spectral dependences are observed with the inversion of the sign of the photovoltage.
400
X, mm
0,6
1,0
1,4
1,8
À, mm
Fig. 4. Typical spectrums of the photovoltage of the AHV-films: Si, Se, CdAs, Ge, CdP, CdTe (a); typical spectrums of VAHV of three GdTe films; c - spectrum of VAHV film of chalcogenide compound (b)
In the process of spectral studies, polar diagrams were made (the dependence of the photovoltage from the illumination corner of AHV films by monochromatic light). They make it possible to unequivocally determine the reasons for the onset of the onset of AHV in microphotoelements. The absence of sign inversion on the polar diagrams makes it possible to draw an unambiguous conclusion about the photovoltaic (p-n-transition) mechanism of AHV effect (fig. 5). If there is an inversion in the polar diagrams in the region of short monochromatic waves (near the deposition corner of the film), we can say that there is a diffusion mechanism (Dember).
Thus, the combination of polar and spectral measurements provides an answer to the question of the nature of the micro photoelements in AHV films.
In conclusion
According to the results of the developed special technology for obtaining anisotropic and heterogeneous (in terms of structure and composition) AHV films from the complex semiconductors optical compounds. It can be concluded that these structures were not studied and examined.
During the work, we could receive AHV-photodetector of the autonomous type with stable parameters and good degradation characteristics. With the help of AHV-Films,
a
b
Fig. 5. Dependence of the photovoltage from the corner of illumination of AHV-Flms (Ge) (a) and (TeCd) (b) by white light
Kasimakhunova A., Naymanbayev R., Mamadalieva L., Nurdinova R., Olimov Sh.
it is possible to get large photoelectrostatic fields with an intensity of the order of 105 V/cm and more. Such powerful fields are used in quantum electronics (for instance, as a source of high voltage in the circuits of the sorting system of a molecular generator), and also in robotics as a stimulator of electro-adhesive micro-grippers.
According to the results of researches (VACH , LVCH, SCH and electromagnetic measurements), it is possible to determine all the needed characteristics parameters and quantities for development of new optoelectronic devices based on AHV effect.
References
1. Pensak L, Goldstein B. // Phys.Rev., 1958. P. 109, 601.
2. Photoelectric phenomena in semiconductors and optoelectronics / under. Ed. E.I. Adirovicha. Tashkent: FAN, 1972. S. 143-229.
3. Adirovich E.I., Rubinov V.M., Yuabov Yu.M. // DAN SSSR, 1966. T. 168. P. 1037.
4. Kasimakhunova A.M., Nurdinova R.A. AHV elements with birefringence // Uzbek Jornal of Physics, 2017. Vol. 19, No 5. PP. 302-306.
5. Starkirkievich J., Sosnovski L., Simpson O. // Nature, 1946. Vol. 158. P. 28.
6. Stafeev V.I. // FIP, 1971. № 5. P. 408.
7. Yuabov Yu.M., Neymanbaev R. // FTP, 1978. № 12. P. 10.
