Испанский язык. Устные темы (A1-A2) 2-е изд., пер. и доп. Учебное пособие для академического бакалавриата
constant. Crystals have pronounced semiconductor properties, their photovoltaic properties are well studied [1].
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 mm2), when measuring Jz (z is the direction of spontaneous polarization) and illuminating the crystal in the x and y directions, POFT does not occur. The expression for the photovoltaic current Jz when illuminated in the x and y directions, respectively, has the form:
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 Jz (β) for λ=600 nm when illuminated along [100]. From the comparison of the experimental angular dependences of Jz (β) with (4) and (5), the numerical values of αιjκ or photovoltaic coefficients were estimated
Taking into account pleochroism and anisotropy of light reflection in SbSI [6], the following values were obtained:
K314*10—8; K323*10—8; K33 (2—3) *10—8A*cm* (W) -1. Thus, in SbSI, the photovoltaic coefficients K31, K32, K33 are more than an order of magnitude higher than the corresponding coefficients in LiNbO3: Fe.
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 Jx curve 2 was measured and the current Jz was measured in the long-wavelength region (λ=600nm, curve 1).The angular dependence of the measured current satisfies (5), while the Oh current in this region cannot be observed at all due to violation of condition (3) and spatial oscillation. Figure 2 shows the spectral Jz (curve 1), Jx (curve 2), attributed to the unit of incident energy, as well as the spectral dependence
constructed taking into account the dispersion of n0, pe and the absorption coefficient α* in the [010] direction.
Angular dependence Jx (β) in the form of curve 2, which agrees well with (7) at K15= (2—4) ·10—9A·cm· (W) -1 (λ=460nm).
Fig. 2. Spectral dependence of Jz (1), Jx (2) and L=l0a* (3).
While the spectral dependence measured earlier in is monotonic, the spectral dependence of Jx detects a sharp maximum near L1. Thus, the decline of Jx in the long-wave region, where L <<1, is due to POFT. The decline of Jx in the short wave region, where L> 1, is interesting.Since the AF effect is not related to the lifetime of nonequilibrium carriers, it is possible that this short-wave decline of Jx is due to a decrease in K15 and, consequently, mobility in the direction [100].
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 modification—cinnabarite 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].
It is shown that the optical activity of the α-HgS crystal has a stronger effect on the angular distribution of the photovoltaic current measured in linearly polarized light.
Fig. 3. shows the orientation dependence of the photovoltaic current Jx (β) in α-HgS. In accordance with (1) and the symmetry of the point group 32, the expression for Jx (β) when illuminated in the direction of the y axis has the form
where is the angle between the plane of polarization of light and the x—axis.
Comparison of the experimental angular dependence of Jx (β) with (2) gives
K11= (1—2) *10—9A* cm * (W) -1 (T=133 Κ, λ=500nm). The coincidence of the experimental angular dependence of Jx (β) with (2) shows that in the region of strong absorption (λ=500nm, α*>> 100cm-1), the effect of optical activity in the direction of the y axis on the angular distribution of Jx (β) is insignificant.The effect of optical activity in the z-direction was found when studying the angular dependence of Jx (β) in various spectral regions (Fig.1).The effect of optical activity in the z-direction was found when studying the angular dependence of Jx (β) in various spectral regions (Fig.1).The effect of optical activity in z- The angular dependence of Jx (β) in various spectral regions was discovered during the study of the angular dependence of Jx (β) in various spectral regions (Fig. 1).
In accordance with (1), the angular dependence of Jx (β) illumination in the z – direction (the z axis coincides with the axis of symmetry of the third order) has the form.
where β is the angle between the plane of light polarization and the y axis.
Figure 2 indicates a good correspondence between the experimental dependence of Jx (β) and (3) in the region of strong light absorption (λ= 400nm).The transition from the short-wave to the long-wave region, corresponding to a decrease in α*, changes the nature of the angular dependence of Jx (β) and its amplitude.The transition from the short-wave to the long-wave region, corresponding to a decrease in α*, changes the nature of the angular dependence of Jx (β) and its amplitude.
Fig.3.