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SPATIALLY OSCILLATING PHOTOVOLTAIC CURRENT IN AN OPTICALLY ACTIVE FERROELECTRIC SbSI
Karimov Sherzod Bahodirovich
Candidate of the Faculty of Physics and Technology of Fergana State University
Aliev Ibratjon Khatamovich
2nd year student of the Faculty of Mathematics and Computer Science of Fergana State University
Karimov Bahodir Khoshimov
Candidate of Physical and Mathematical Sciences, Faculty of Physics and Technology, Fergana State University
Ferghana State University, Ferghana, Uzbekistan
Аннотация. В настоящей работе обнаружен и исследованы пространственно-осциллирующей фотовольтаический ток (ПОФТ) в направлении [100] в сегнетоэлектрике SbSJ при освещении поляризованным светом в направлении [010] и образованию от оптической зависимости в [001] направлении структуры пространственного осциллирующего фотовольтаического тока J
x
Ключевые слова: сегнетоэлектрик, поляризация, оптически-активный кристалл, пространственно-осциллирующий фотовольтаический ток, тензор 3-ранга.
Annotation. In this paper, the spatially oscillating photovoltaic current (POFT) in the direction [100] in the SbSJ ferroelectric is detected and investigated when illuminated with polarized light in the direction [010] and the formation of the structure of the spatial oscillating photovoltaic current Jx from the optical dependence in the direction [001]. Some experimental and physical bases of spatially oscillating photovoltaic current are discussed.
Keywords: ferroelectric, polarization, optically active crystal, spatially oscillating photovoltaic current, rank 3 tensor.
In recent years, it has become clear that in thermodynamic nonequilibrium conditions, currents of a different nature are possible due to the absence of a center of symmetry medium. The most important of this class of effect is the anomalous photovoltaic effect (AF effect).
The AF effect is that with uniform illumination of a short-circuited ferroelectric, a stationary current flows through it, which in [1,2] was called photovoltaic. It has been shown that it is the photovoltaic current that leads to the anomalous photovoltaic effect (AF effect) in ferroelectrics.
The anomalous photovoltaic effect discovered for ferroelectrics for the first time in [1,2] is a special case of a more general AF effect described for crystals without a center of symmetry by the third rank aijk tensor [3].
According to (1), with uniform illumination by linearly polarized light of homogeneous crystals without a center of symmetry (ferroelectric or piezoelectric crystal), a photovoltaic current Ji arises in it, the sign and magnitude of which depend on the orientation of the polarization vector of light with projections Ej, Ek*.
The components of the aijk tensor are nonzero for 20 acentric symmetry groups. If the electrodes of the crystal are opened, the photovoltaic current Ji generates photovoltaic voltages
where σ
t
f
g
In accordance with (1) and the symmetry of the point group of the crystal, expressions can be written for the photovoltaic current Ji. Comparison of the experimental angular dependence of J
i
ijk
a* is the light absorption coefficient.
As shown by Belinicher [4], depending on the shape of the optical indicatrix and the direction of propagation of plane polarized light in the crystal, there may be directions for which the photovoltaic current (1) is spatially oscillating. In this case:
where n
e
0
e
0
In this case, the photovoltaic current (2) oscillates in the crystal with a period of
As indicated in [4] and as can be seen from (2), a spatially oscillating photovoltaic current (SWEAT) can be experimentally observed under conditions of strong light absorption.
where α* is the absorption coefficient.
1. SPATIALLY OSCILLATING PHOTOVOLTAIC CURRENT IN SbSi FERROELECTRIC
In this paper, a spatially oscillating photovoltaic current (POFT) in the direction [100] in the SbSI ferroelectric is detected and investigated when illuminated with polarized light in the direction [010].
Antimony sulfoiodide (SbSI) belongs to the class of chalcogenides of metals of the fifth group A
V
VI
II
x
1-x
c
0
The phase transition at 22
0
Measurements were carried out for SbSI single crystals in the ferroelectric phase at a temperature of T = 133 K. The crystal was illuminated by plane polarized light using a xenon lamp and a ZMR monochromator. The stationary photovoltaic current J was measured by the method previously described [1]. In accordance with the SbSI symmetry (point group mm
2
z
where I is the light intensity, β is the angle between the plane of polarization of light and the z axis. In Fig.1, curve 1 represents the experimental angular dependence of J
z
z
Taking into account pleochroism and anisotropy of light reflection in SbSI [6], the following values were obtained:
K
314
8
323
8
33
8
-1
31
32
33
Fig.1. Dependence of the photovoltaic current Jz (1) at l = 600 nm and Jx (2) at l = 460 on the orientation of the plane of polarization of light in SbSI.
According to (2), for SbSI, the photovoltaic current components are spatially oscillating. However, when the crystal is illuminated in the region of strong absorption in the direction of the x or y axes and when condition (3) is met, currents flow along the surfaces (100) and (010), respectively.
where β is the angle between the plane of polarization of light and the z axis. According to [1,7] for SbSI, the strong absorption condition (3) should be fulfilled already at λ470 nm. To observe the POFT under conditions of strong absorption, silver electrodes in the form of bands parallel to the axis of spontaneous polarization z were sprayed onto the face of the cinacoid (010). Using these electrodes, when the crystal was illuminated in the direction [010] by polarized light with λ=460 nm, the current J
x
z
z
x
constructed taking into account the dispersion of n0, pe and the absorption coefficient α* in the [010] direction.
Angular dependence J
x
15
9
-1
Fig. 2. Spectral dependence of J
z
x
0
While the spectral dependence measured earlier in is monotonic, the spectral dependence of Jx detects a sharp maximum near L
1
x
x
15
2. SPATIALLY OSCILLATING PHOTOVOLTAIC CURRENT IN A FERROELECTRIC α-HgS
The paper considers photovoltaic effects in optically active α-HgS crystals. Some experimental and physical bases of the photovoltaic effect in active crystals are discussed.
Mercury sulphide HgS exists in two modifications: the black modification metacinnabarite (β-HgS) crystallizes in a cubic system (point group 3m), the red modificationcinnabarite or cinnabar (α-HQs) crystallizes in a trigonal system (point group 32).
Red cinnabar crystals with a particularly large specific rotation along the optical axis for the red rays transmitted by them r= 2350/mm were studied in this work. Α HgS crystals grown by the hydrothermal method in the Laboratory of Hydrothermal Synthesis at the Institute of Crystallography of the Russian Academy of Sciences were studied. The starting materials for the manufacture of cinnabarite were pure mercury in sulfur. Electrical, electro-optical properties of α-HgS crystals and photoelectric properties of crystals were studied in [5,6].