Electron-phonon scattering in transport properties of InSe single crystals

Summary The electron-phonon scattering in indium selenide single crystals has been investigated by Hall-mobility and Raman-spectroscopy measurements. The experimental data have been interpreted according to the Fivaz and Schmid model for homopolar optical scattering. The best fit of the experimental results is obtained by assuming the bidimensional behaviour of the interaction involving anA ₁ phonon with energy 14.5 meV. The bidimensional character is probably due to the presence of a large number of planar defects, confirmed by electron microscope observations, which strongly localize the carriers within the layers.

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Riassunto In questo lavoro è riportato uno studio dell'interazione elettrone-fonone in monocristalli di seleniuro di indio, condotto mediante misure di effetto Hall e spettroscopia Raman. I dati sperimentali sono stati interpretati secondo il modello di Fivaz e Schmid, per lo scattering da fononi ottici omopolari. L'approssimazione migliore delle curve sperimentali è ottenuta assumendo un carattere bidimensionale per l'interazione tra gli elettroni ed i fononi, nel modoA ₁, con energia 14.5 meV. Il carattere bidimensionale delle proprietà di trasporto è probabilmente dovuto alla presenza di difetti planari che localizzano i portatori di carica all'interno degli strati.

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Резюме Исследуется электрон-фононное рассеяние в монокристаллах InSe, используя измерения подвижности Холла и спектроскопии комбинационного рассеяния. Экспериментальые данные интерпретируются в соответствии с моделью Фиваца и Шмидта для гомополярного оптического рассеяния. Наилучшая подгонка экспериментальных результав получается в предположении двумерного характера взаимодействия между электронами и фононами, модыA ₁ , с энергией 14.5 мэВ. Двумерный характер, по-видимому, обусуовлен наличием большого числа плоских дефектов, которые сильно локализуют носители внутри слоев, что подтверждается наблюдениями электронной микроскопии.

     

Effect of annealing on the photoelectric properties of single crystals of InSe

The effect of different heat-treatment regimes on recombination processes in n-In_1.03Se_0.97<0.5Zn> was studied by the method of square-wave modulation of light intensity, with subsequent analysis of the experimental data by the least squares method on a computer. The specimens were annealed at a temperature of 360–400°C in a vacuum [1] or Zn vapors [11] for different periods of time. They were then slowly cooled at a rate of 2 deg/min (A) or quenched (B). It was established the lifetime of the nonequilibrium carriers increases by nearly an order of magnitude in case IB, while the ratio of s- and r-centers remains nearly the same. In case IIA, _s decreases roughly by a factor of two, while in the best specimens it reaches 2.3·10^–5 sec. Annealing for 20 h in regime IA leads to a large increase (by about 25%) in the density of s-centers.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 61–64, November, 1990.     

Mass attenuation coefficients for n-type InSe, InSe:Gd, InSe:Ho and InSe:Er single crystals

Measurements have been made to determine the mass attenuation coefficients of undoped n-type InSe, and Gd, Ho, Er doped n-InSe single crystals using a Si(Li) detector in the energy region 15.746–40.930 keV X-ray energies with energy dispersive X-ray fluorescence systems. InSe, InSe:Gd, InSe:Ho and InSe:Er single crystals were grown by using the stockbarger method. The measured values are graphically compared with the theoretical ones obtained using WinXcom.     

Structure and magnetic properties of cobalt-intercalated layered InSe crystals

We study the structure and magnetic properties of Co _x InSe layered crystals electrochemically intercalated by cobalt in a constant magnetic field. It is found that impurity clusters consisting of cobalt nano-particles with the fcc structure are formed in the intercalates under investigation on the Van der Waals planes in the space between the layers. Intercalates Co_0.1InSe obtained by implantation in a magnetic field exhibit a change in their magnetic properties (dependence of the magnetic moment in the magnetic field strength has the form of a hysteresis loop, which is typical of ferromagnetic materials).     

Effects of exposure temperature on thermally stimulated currents in InSe single crystals

The thermally stimulated currents (TSC) in InSe single crystals are investigated as a function of initial temperature T₀ at which the samples examined are excited. In particular, experiments show that the peak at low temperature increases considerably in height and shifts markedly to lower temperatures as T₀ is reduced. A kinetic model is proposed for the interpretation of the results.     

Effective mass calculation for InSe, InSe:Er crystals

Undoped indium selenide (InSe) and Er doped InSe single crystals were grown by Bridgman–Stockberger method. The InSe crystals both undoped and doped Er had no cracks or voids on the surface. No polishing or cleaning treatments were carried out on the cleaved faces of these samples because of the natural mirror-like cleavage faces. The absorption measurements were carried out in the temperature range 10–320 K and the external electric field effect on the absorption measurements is investigated. The absorption edge shifted towards to the longer wavelengths under an electric field as 6 kV/cm. Using the electric field shifting, effective mass values are calculated.     

Electron diffraction study of melt-grown InSe crystals

Summary Electron diffraction has been performed on thin crystals of indium selenide, cleaved from ingots grown from stoichiometric and nonstoichiometric melt by the Bridgman-Stockbarger method. The analysis of the selected area diffraction patterns has shown the presence of two phases, whose lattice parameters have been calculated. The stacking sequence of the polytypes has been observed through the moiré patterns.

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Riassunto è stata effettuata la diffrazione elettronica su cristalli di seleniuro di indio, clivati da lingotti cresciuti col metodo di Bridgman-Stoekbarger parterdo dagli elementi puri, presi sia in rapporto stechiometrico che in rapporti diversi. L’analisi delle figure di diffrazione ottenute in area selezionata ha permesso d’individuare la presenza di due politipi, i cui parametri reticolari sono stati calcolati. L’impilamento dei due politipi è stato osservato mediante le frange moiré.

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Резюме Исследуется дифракция электронов на тонких кристалах InSe, выращенных из стехиометрического и нестехионетрического расплавов, с помощью метода Бридгмана-Стокбаргера. Анализ дифракдионных картин обнаруживаеет наличне двух фаз, для которых вычисляются параметры решетки. С помощью наблюдения муаровых полос исследуется поспедовательность группирования политипов.

     

Scintillation properties of BeO single crystals

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 49, No. 2, pp. 286–291, August, 1988.     

Electrical properties of molybdenite single crystals

Molybdenite crystals used in the present work were grown by direct vapour transport or sublimation method. The electrical resistivities and I-V characteristics were measured at different temperatures in the symmetry plane. The room temperature resistance of a specimen annealed for different periods has also been measured. These results are described and discussed.     

Luminescent properties of LiCl-Cu single crystals

The absorption, photoluminescence, x-ray luminescence, and thermoluminescence spectra, and the photoluminescence excitation spectra of LiCl-Cu single crystals with different activator concentration were investigated at temperatures of 79–450°K. The absorption spectrum at room temperature has two bands with maxima at 237 and 259 nm. The absorption coefficient of the 237 nm band is proportional to the copper concentration in the crystal (C_Cu ≤ 7·10^?4 mole %). The photoluminescence and x-ray luminescence spectrum at room temperature consists of one emission band at 324 nm, which conforms with the Mollwo-Ivey rule in the homologous series RbCl → KCl → NaCl → LiCl. The copper ions create trapping levels for electrons and holes at different depths in the forbidden band of the LiCl crystal. The correlation between the thermoluminescence peaks and the recombination-luminescence excitation bands (infrared stimulation) is investigated.     

Surface properties of GaTe single crystals

Surface properties of gallium telluride were studied. It was found that the surface after vacuum cleavage is partly reconstructed from monoclinic to hexagonal. Peculiarities of the surface topology are also discussed.     

Optical properties of InBr single crystals

Single crystals of orthorhombic InBr were grown by the sublimation technique. Two of the three principal refractive indices were determined by measuring interference due to multiple reflection. The absorption curve near the band edge was measured at 295,80 and 10°K for different polarisation vectors of the incident light. At low temperatures large exciton absorptions could be seen which enabled us to determine accurate values of the band gap energy.     

Electrical properties of neutron-transmutation-doped InSe

Neutron-transmutation-doping (NTD) has been used to introduce a controlled amount of tin-related shallow donors with a uniform distribution into the layered semiconductor InSe. The electrical properties of transmutation-doped (TD) InSe, between 30 and 300 K have been measured and compared with those of InSe conventionally tin-doped during growth. After annealing at 450°C, the lattice damage associated with NTD is removed and the donor centres become electrically active. For concentrations of transmutated Sn bigger than 10¹⁷ cm^-3 the free-electron concentration saturates and this is interpreted as a result of segregation determined by the Sn solubility limit in the host lattice. The Hall mobility at room temperature is higher in TD samples than in conventionally tin-doped ones for the same electron concentration.     

Optical detectors on GaSe and InSe layered crystals

Fast uncooled GaSe and InSe detectors that can record ultrashort (10^?12–10^?9 s) laser pulses in the visual and near-IR ranges are developed. The quick response of the detectors is due to rapid recombination channels with a high capture cross section present in the crystals.     

Optical properties of Tm-doped GaSe single crystals

Optical properties of Tm-doped GaSe single crystals were investigated by measurements of optical absorption and photoluminescence. The single crystals were grown by the Bridgman technique. The X-ray diffraction analysis revealed that the single crystals were in the ε-type GaSe phase. The optical absorption spectra showed a sharp absorption peak at 582 nm near the band edge, which is due to direct free exciton. The temperature dependence of the energy of the exciton absorption peak was well fitted by the Varshni relation. In the photoluminescence spectrum at 10 K, we observed a very weak emission peak at 586 nm, a relatively strong emission peak centered at 613 nm, and several sharp and narrow emission peaks in the 790-840 nm region. The two emission peaks at 586 and 613 nm were associated with intrinsic emission lines due to direct free exciton and indirect bound exciton. The emission peaks in the 790-840 nm region, which were related to extrinsic emission, were assigned as due to the ³F₄→³H₆ transition of Tm³⁺ ions with a low symmetry of D₃ in the host lattice.     

Phonon properties of CoSb2 single crystals

The phonon properties of CoSb(2) have been investigated by Raman scattering spectroscopy and lattice dynamics calculations. Sixteen out of eighteen Raman active modes predicted by factor-group analysis are experimentally observed and assigned. The calculated and measured phonon energies at the Γ point are in very good agreement. The temperature dependence of the A(g) symmetry modes is well represented by phonon-phonon interactions without contribution from any other phonon or electron related interactions.     

Laser properties of praseodymium pentaphosphate single crystals

PrP₅O₁₄, Pr_xLa_1−xP₅O₁₄, and Pr_xY_1−xP₅O₁₄ (0≦x≦1) single crystals of laser quality were synthesized and their crystallographic and optical parameters measured. Laser emissions in the visible (λ=637.4 nm) with no mirrors in place (superradiance) and also in various optical resonators have been observed.