Читать книгу All sciences. №6, 2022. International Scientific Journal - Ibratjon Xatamovich Aliyev - Страница 7

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 J_x (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 J_x (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 J_x (β) is insignificant.The effect of optical activity in the z-direction was found when studying the angular dependence of J_x (β) in various spectral regions (Fig.1).The effect of optical activity in the z-direction was found when studying the angular dependence of J_x (β) in various spectral regions (Fig.1).The effect of optical activity in z- The angular dependence of J_x (β) in various spectral regions was discovered during the study of the angular dependence of J_x (β) in various spectral regions (Fig. 1).

In accordance with (1), the angular dependence of J_x (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 J_x (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. Orientation dependence of the photovoltaic current Jx (β) in a-HgS (T=133⁰K).

Figure 4 shows the spectral-angular diagram of the photovoltaic current Jx. Obviously, its shape is determined by its optical activity in the z-direction, its spectral dispersion, as well as the spectral distribution of the photovoltaic effect in α-HgS.

The optical dependence in the z – direction thus leads to the formation of the structure of the spatial oscillating photovoltaic current Jx. The photovoltaic current oscillates in the z-direction with a period of

Where χ is the optical activity coefficient.

The angular dependence of J_x (β) coincides with (3) only under the condition of strong light absorption

where α* is the light absorption coefficient.

Fig. 4. Spectral – angular diagram of photovoltaic current in a-HgS (T=133⁰K). The direction of light propagation is indicated in the upper part of the figure.

Note: The Board of Authors thanks V. A. Kuznetsov for providing the crystals and V. M. Fridkin for the discussion.