Refractive indices of layered semiconductor ferroelectrics TlInS2, TlGaS2, and TlGaSe2 from ellipsometric measurements limited to only layer-plane surfaces

Abstract

The ternary layered Tl-contained semiconductor ferroelectrics TlInS2, TlGaS2, and TlGaSe2, exhibiting an incommensurate phase and a relaxor state with temperature, were approached down to 0.76eV at room temperature by spectroscopic phase modulated ellipsometry in a region below the energy gap of each material. By using both coherent and incoherent reflection modes on only the layer-plane surfaces, the refractive indices in the parallel- and perpendicular-to-the-layers directions of the light propagation were determined. Sellmeier single-oscillator form was used to fit the model data to the experimental intensities. The discrepancy between the model and experimental data was shown to be negligible. Besides, a self-consistent picture of the obtained refraction indices was emerging after the discussion based on the available data for the studied materials. The applied experimental approach was thus found to be quite effective for layered materials, and the obtained refractive indices might be used for database with high degree of confidence.

Effect of isomorphic atom substitution on the refractive index and oscillator parameters of TlInS2xSe2(1‐x) (0.25 ≤ x ≤ 1) layered mixed crystals

“…The oscillator energy E so is an "average" energy gap and it is approximately equals to two times of the lowest direct band gap E gd (E so ≈ 2.0 E gd ) [14][15][16][17]. In this study, the [18,19]. In our study, the determined value of the refractive index, corresponding to the λ = 600 nm (the common wavelength chosen for the comparison with the results of the other studies), were found to be 2.79.…”

“…In our study, the determined value of the refractive index, corresponding to the λ = 600 nm (the common wavelength chosen for the comparison with the results of the other studies), were found to be 2.79. The values of the refractive indices obtained in literature for the same wavelength were equal to 2.62 [18] and 2.81 [19].…”

Диэлектрические потери и перенос заряда в легированном сурьмой монокристалле TlGaS-=SUB=-2-=/SUB=-

“…Квазидвумерность, широ-козонность, структурная анизотропия, фазовые перехо-ды, оптические и фотопроводящие свойства и другие особенности привлекают исследователей для лучшего понимания физики TlGaS 2 . Оптическая активность, вы-сокая фоточувствительность в широком спектральном диапазоне [1,2] отличают TlGaS 2 от других полупровод-ников и делают его перспективным с практической точки зрения [3][4][5][6]. На основе TlGaS 2 были предложены види-мые и инфракрасные датчики света [7], а также высоко-чувствительные детекторы лазерного излучения [8][9][10][11].…”

Faraday effect in TlInS2 crystals

“…For example, the studies of the electrical properties have indicated that the crystals are very promising for creating solid-state electronic devices [4]. Moreover, one can mention possible applications of the TlInS 2 crystals in optoelectronics associated with their high photosensitivity in the visible spectral range (the two-photon absorption coefficient being β = (9.4±1.5)×10 −9 cm/W [5]), high optical birefringence [3] and peculiar photoinduced phenomena that enable memory effects [6]. A specific feature of thermal expansion, the existence of elliptical conical surface of zero thermal expansion, whose orientation does not depend on the temperature in the wide interval (160-280 K) [7], can also stimulate some practical applications of TlInS 2 .…”

“…TlInS 2 is transparent in the spectral range from 500 to 12500 nm [2]. From the ellipsometric measurements limited to layer-plane surfaces, it is known that the refractive indices at the wavelength 632.8 nm   are equal to 2.594 and 2.744 respectively for the parallel-to-layer and perpendicular-to-layer directions of light propagation [3].…”