Growth, characterisation and electrical anisotropy in layered chalcogenides GaTe and InTe

GaTe and InTe are III-VI semiconductors with layered structures which have large anisotropy in electrical properties. Thermopower, resistivity and Hall effect have been studied in orthogonal directions in high quality single crystals grown by the Bridgman technique. The hole effective masses parallel and perpendicular to the layer plane were thus determined to be 0.46m(0) and 0.995m(0), respectively for GaTe and 0.125 m(0) and 0.765 m(0) for InTe. The carrier activation energies and hole mobilities were also anisotropic. Optical phonon scattering was dominant for GaTe with mu alpha T--n with n = 1.85-2.05 and 3.3-3.4 respectively along and perpendicular to the layer planes. InTe with higher carrier concentrations showed mu alpha T-m, characteristic of ionised impurity scattering with m = +1.43 in both directions. The optical band-gaps and anisotropy of the dielectric constants have also been measured.