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Institute of Nuclear Physics
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EFFECT OF Yb-DOPED GaS SINGLE CRYSTALS ON THE PHOTOELECTRIC PROPERTIES

Not scheduled
20m
Institute of Nuclear Physics

Institute of Nuclear Physics

Ulugbek town, Tashkent, 100214, Uzbekistan
Oral Radiation physics and radiation materials science

Speaker

Aydan Khaligzade (Institute of Radiation Problems Ministry of Science and Education Republic of Azerbaijan)

Description

AIIIBVI group compound semiconductors are typical layered materials with wide band gaps, and GaS single crystals are of particular interest for visible and near-UV optoelectronic applications. GaS has a hexagonal structure (a = 0.359 nm, c = 1.549 nm) with an S–Ga–Ga–S sequence, where each Ga atom is bonded to one Ga and three S atoms. The bonding is strongly ionic–covalent within the layers, while the interlayer interaction is governed by weak Van der Waals forces. With a room-temperature band gap of 2.5 eV and pronounced anisotropy along the c-axis, GaS exhibits useful properties for optoelectronic devices, electrical sensors, and nonlinear optical applications.[1,2,3].
The photoelectric properties of Yb-doped GaS layered single crystals are of significant scientific and practical interest, as Yb is introduced during growth and sulfur deficiency—caused by its volatility—is compensated by thermal treatment in sulfur vapour. The studied crystals, which exhibit p-type conductivity, were contacted with silver paste along the c-axis and irradiated at 300 K using a Co⁶⁰ source under cryostat vacuum conditions. Their photoelectric characteristics were investigated with a setup comprising an SF-4 monochromator, B7-30 electrometric amplifier, F136 nano-microammeter, B7-21 voltmeter, and TEC-9 current source.
As seen in Figure 1, the long-wavelength edge in the spectral distribution of photocurrent shifts from 660 nm to 700 nm upon the introduction of Yb dopant atoms. This shift is associated with the ionisation of the energy levels created by Yb atoms in the band gap of the GaS crystal. In the GaS(Yb) crystal (Figure 1, curve 2), the maximum photocurrent corresponds to a wavelength of λmax = 475 nm. Based on literature results, the width of the band gap of the crystal was estimated (according to λ1/2) as ~∆Eλ1/2 ≈ 2.3 eV.
As can be observed from the figure, the introduction of Yb atoms does not alter the wavelength corresponding to the maximum photocurrent in GaS single crystals, and the photocurrent value at this wavelength changes only slightly.
Figure 2 presents the spectral distribution of the photocurrent in pure and ytterbium-doped GaS single crystals at T = 110 K. According to Bube’s theory of photoconductivity, the decrease in crystal temperature results in the shift of the photocurrent maximum in the spectrum toward the shorter-wavelength region. From the graph, it can be seen that in the GaS single crystal (Figure 2, curve 1), a maximum is observed near the intrinsic absorption edge (λ = 472 nm).

Figure 1. Spectral distribution of photocurrent of 0.1 at% GaS and GaS(Yb) single crystals at room temperature (U=50V)

Figure 2. Spectral distribution of photocurrent of GaS and GaS(Yb) 0.1 at% single crystals at T=110K (U=50V)

When the GaS single crystal is doped with Yb (curve 2), the photocurrent increases, while the maximum photocurrent (λ = 476 nm) remains very close to the wavelength region observed in the pure GaS single crystal. Similarly, in the impurity region of the GaS(Yb) single crystal, an increase in photocurrent is observed. The enhancement of photocurrent upon Yb doping of GaS is attributed to the partial compensation of gallium vacancies.

From the comparison of the graphs in Figures 1 and 2, it can be concluded that the incorporation of Yb atoms into the GaS single crystal leads to a shift of the spectral characteristics toward the longer-wavelength region and to an increase in photocurrent at low temperatures. According to considerations reported in the literature, the application of a constant and homogeneous electric field to the crystal affects the charge carrier transport mechanism, thereby altering the absorption spectrum. In particular, in the region where hν < Eg, the absorption coefficient depends on the intensity of the applied electric field, which in turn influences the electronic transitions.

Primary author

Aydan Khaligzade (Institute of Radiation Problems Ministry of Science and Education Republic of Azerbaijan)

Co-authors

Ms Narmin Mammadova Prof. Rahim Madatov (Head of Department) Dr Rakhshana Mamishova (Leader researcher) Dr Teymur Tagiev (Leader researcher)

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