The photo-electronic properties of Hg1-xCdxTe grown by molecular beam epitaxy (MBE) or by liquid phase epitaxy (LPE) were investigated using Fourier transform transmission spectroscopy, Fourier transform photoluminescence measurements, spectroscopic ellipsometry (SE), as well as magneto-optics and magnetic-field-dependent Hall studies. The investigation was carried out from liquid helium to room temperatures in the infrared band up to 10 mum. Some important impurities and defects states, including As, Sb, Ag, Fe impurities and Hg vacancy as well as their complexes in Hg1-xCdxTe, were carefully studied. We obtained the energy levels of the impurity states and their optical, electric and magnetic behaviors. By SE measurement, a number of very useful parameters, such as the real and the imaginary part of dielectric constant, gap energies corresponding to important critical points, were extracted. Mobility spectra and multi-carrier fitting procedure were used to separate the contributions to the measured mobility from the light holes, heavy holes, and electrons. As a result, the sign change of transverse conductivity component with applied magnetic-field is explained according to multi-carrier process. Hg1-xCdxTe (MCT) is one of the most important infrared materials, which is subjected to intensive studies. Its optical and electrical properties are widely used for the fabrication of high performance photoconductive and photovoltaic detectors. Some of characteristics that directly affect device performance, such as impurities, defects, as well as the lifetime of the minority carriers, remain as the major concern. Recently, the quality of the MCT material grown by MBE and LPE has been improved and accurate control over the doping levels for several dopants have been realized [1-3]. Following the progresses made in material preparation and doping, we are able to study the material systematically. In this paper, we report the recent progress made on the investigation of the electrical and optical properties of both doped and undoped MCT in our laboratory using Fourier transform spectroscopy (FTIR), photoluminescence, magneto-photoconductivity, transport measurement, as well as SE. (C) 2002 Elsevier Science B.V. All rights reserved.