The effect of chlorine doping concentration on the quality of CdTe single crystals grown by the modified physical vapor transport method

Undoped and Cl-doped CdTe crystals were grown by the modified PVT technique in a vertical configuration. Their structural quality as well as electrical and transport characteristics as a function of a doping concentration was analyzed by means of infrared (IR) spectroscopy, optical microscopy, secondary ion mass spectrometry (SIMS), photoelectrical and Hall effect measurements. In the investigated semi-insulating crystals with resistivity rho > 10(8)Omega x cm doped in the chlorine concentration range Nci = 10(18)-10(19)cm(-3) the best transport and structural characteristics were observed. The formation of precipitates and inclusions at higher values of Nc, results in worsening of crystalline quality as well as a decrease of resistivity in the doped samples. The IR transmission spectra in heavily doped samples are determined by the light scattering on these structural imperfections, whereas optical transitions between the heavy hole and light hole valence bands dominate spectra in undoped ones. The absorption peak caused by these transitions seems to be observed for the first time in undoped CdTe. (C) 2007 Elsevier B.V. All rights reserved.