ELASTIC COEFFICIENTS IN TLGA(S1-XSEX)2 AND TLINXGA1-XS2 LAYER MIXED-CRYSTALS BY BRILLOUIN-SCATTERING

The compositional variation of the elastic coefficients C-11 and C33 for TlGa(S1-xSex) and TlInxGa1-xS2 layer mixed crystals are discussed using Brillouin scattering measurements. Clear anomalies are observed for the longitudinal phonons propagating parallel to the (00 1) plane (elastic coefficient C-11) at x(c) congruent-to 0.8 and x(c) congruent-to 0.3 in TlInxGa1-xS2 and TlGa(S1-xSex)2, respectively. These anomalies are explained by the formation of infinite clusters. A considerable difference in the rate of change of the elastic coefficient C33 with the composition for the mixed crystals TlGa(S1-xSex)2 and TlInxGa1-xS2 is observed. The temperature variation of C33 for a TlIn0.95Ga0.05S2 mixed crystals is also given and the results are discussed

single crystals grown by Bridgman technique

Structural, optical and electrical properties of Ge implanted GaSe single crystal have been studied by means of X-Ray Diffraction (XRD), temperature dependent conductivity and photoconductivity (PC) measurements for different annealing temperatures. It was observed that upon implanting GaSe with Ge and applying annealing process, the resistivity is reduced from 2.1x10(9) to 6.5x10(5) ohm-em. From the temperature dependent conductivities, the activation energies have been found to be 4, 34, and 314 meV for as-grown, 36 and 472 meV for as-implanted and 39 and 647 meV for implanted and annealed GaSe single crystals at 500 degrees C. Calculated activation energies from the conductivity measurements indicated that the transport mechanisms are dominated by thermal excitation at different temperature intervals in the implanted and unimplanted samples. By measuring photoconductivity (PC) measurement as a function of temperature and illumination intensity, the relation between photocurrent (I-PC) and illumination intensity (Phi) was studied and it was observed that the relation obeys the power law, I-PC alpha Phi(n) with n between 1 and 2, which is indication of behaving as a supralinear character and existing continuous distribution of localized states in the band gap. As a result of transmission measurements, it was observed that there is almost no considerable change in optical band gap of samples with increasing annealing temperatures for as-grown GaSe; however, a slight shift of optical band gap toward higher energies for Ge-implanted sample was observed with increasing annealing. temperatures. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA.C1 Middle E Tech Univ, Dept Phys, TR-06531 Ankara, Turkey.Pamukkale Univ, Dept Phys, Denizli, Turkey