Photo-electronic phenomena in narrow gap Hg 1x Cd x Te q N. Dai * , Y. Chang, X.G. Wang, B. Li, J.H. Chu National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai 200083, China Received 19 April 2002; accepted 26 August 2002 Abstract The photo-electronic properties of Hg 1x Cd x Te grown by molecular beam epitaxy (MBE) or by liquid phase epitaxy (LPE) were investigated using Fourier transform transmission spectroscopy, Fourier transform photoluminescence measurements, spectro- scopic 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 lm. Some important impurities and defects states, including As,Sb,Ag,FeimpuritiesandHgvacancyaswellastheircomplexesinHg 1x Cd x Te, 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 pa- rameters,suchastherealandtheimaginarypartofdielectricconstant,gapenergiescorrespondingtoimportantcriticalpoints,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. Hg 1x Cd x Te (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. Ó 2002 Elsevier Science B.V. All rights reserved. PACS: 71.20.Nr; 71.55.Eg; 72.20.My; 73.20.At Keywords: Photoluminescence; Mobility; Impurity; Vacancy 1. Introduction Impurity states in MCT have strong impact on the optical and electrical properties of the material used for device purposes [4–7]. Most of the studies on impurities focus on the observation of luminescence emissions as- sociated with the impurity levels. However, due to the strong Auger recombination in materials with narrow band gaps, the photoluminescence can only be observed on the materials with relatively high Cd concentrations. Thus,far-infraredtransmission(FIRT)appearstobethe only option for optical characterization of those with narrow band gaps. However, FIRT measurement could be difficult due to the fact that the ionized energies of acceptorsthatareCd-concentrationdependentareinthe range from 2 to 30 meV. This range overlaps with the reststrahlen band (10–21 meV for bulk materials with over100 lmthickness)aswellassomelocalizedphonon modes associated with structural disorders [8,9]. This was overcome in our experiments by the use of thin epitaxial layers grown by MBE and liquid phase epitaxy (LPE), where the interference is significantly suppressed. Thecarrierdensitiesofthematerialsarekeptlowenough for those impurity transitions to be clearly identified. Current Applied Physics 2 (2002) 365–371 www.elsevier.com/locate/cap q Original version presented at the 2001 Korea–China Joint Sym- posium on Semiconductor Physics and Device Applications, Dongguk University, Seoul, Korea, 5–9 December 2001. * Corresponding author. E-mail address: ndai@mail.sitp.ac.cn (N. Dai). 1567-1739/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII:S1567-1739(02)00141-4