Characteristic features of thermoluminescence in neodymium-doped gallium sulfide.

The thermoluminescence (TL) of neodymium-doped gallium sulfide (GaS:Nd) single crystals was measured from 10 K to room temperature with various heating rates between 0.2 and 1.0 K/sec. Two peaks centered at 70.9 K and 116.0 K were observed when using a heating rate of 0.8 K/sec. Initial rise and curve fitting methods were used to obtain information on trap activation energies. Activation energies of 94 and 216 meV were found for two analyzable peaks. The heating rate dependencies of TL intensities revealed that one of the observed peaks showed normal behavior according to the one trap-one recombination model, whereas the other model showed anomalous heating rate behavior. TL experiments were also carried out at different illumination temperatures from 10 to 32 K; maximum peak temperature remained almost the same at various illumination temperatures. This behavior indicated that the revealed trapping centers are single, discrete levels. The TL glow curves of undoped GaS crystals were also investigated and the effect of Nd doping on the TL characteristics of crystals is discussed in the manuscript.

Analysis of the Hall effect in TlGaTe(2) single crystals.

The electrical resistivity and Hall coefficient of p-type TlGaTe(2) crystals were measured in the temperature range of 110-320 K. The electrical resistivity, charge carrier density and Hall mobility data for the crystals have been analyzed by means of existing theories and models to determine the extrinsic energy levels, the carrier effective mass, the donor and acceptor concentrations and the dominant scattering mechanism in the crystal as well. The analysis of the temperature-dependent electrical resistivity recorded parallel and perpendicular to the crystal's axis (c-axis) reflected the existence of energy levels located at 0.26 and at 0.20 eV, respectively. The difference of these two energy levels is due to crystal anisotropy. The energy level at 0.26 eV was found to represent an acceptor level, as confirmed from Hall data analysis. The temperature dependence of the carrier density was analyzed by using the single-donor-single-acceptor model. The latter analysis revealed the carrier effective mass and the acceptor and donor concentrations as 0.73m(0),4.10 × 10(17) cm(-3) and 1.20 × 10(17) cm(-3), respectively. The Hall mobility of TlGaTe(2) is found to be limited by the scattering of hole-acoustic phonon interactions. The calculated theoretical mobility fits to the experimental one under the condition that the acoustic deformation potential is 11.0 eV, which is the energy position of the top of valence band maximum that is formed by the Te 5s states.

Temperature- and photo-excitation effects on the electrical properties of Tl(4)Se(3)S crystals.

The extrinsic energy states and the recombination mechanism in the Tl(4)Se(3)S chain crystals are being investigated by means of electrical and photoelectrical measurements for the first time. The electrical resistivity is observed to decrease exponentially with increasing temperature. The analysis of this dependence revealed three impurity levels located at 280, 68 and 48 meV. The photocurrent is observed to increase as temperature decreases down to a minimum temperature T(m) = 200 K. Below this temperature the photocurrent decreases upon temperature lowering. Two photoconductivity activation energies of 10 and 100 meV were determined for the temperature ranges below and above T(m), respectively. The photocurrent (I(ph)) versus illumination intensity (F) dependence follows the [Formula: see text] law. The value of γ decreases from ∼1.0 at 300 K to ∼0.34 at 160 K. The change in the value of γ with temperature is attributed to the exchange of roles between the monomolecular recombination at the surface near room temperature and trapping centers in the crystal, which become dominant as temperature decreases.

Visible photoluminescence from chain Tl(4)In(3)GaSe(8) semiconductor.

The emission band spectra of undoped Tl(4)In(3)GaSe(8) chain crystals have been studied in the 16-300 K temperature range and the 535-740 nm wavelength range. Two visible photoluminescence bands centred at 589 and 633 nm were observed at T = 16 K. Variations of both bands have been investigated over a wide range of laser excitation intensity (3 × 10(-4)-1.2 W cm(-2)). Radiative transitions with energies of 2.10 and 1.96 eV from two upper conduction bands to two shallow acceptor levels (0.03 and 0.01 eV), respectively, were suggested as being responsible for the observed bands in Tl(4)In(3)GaSe(8) crystal, which is non-transparent in the visible range.