Optical Characterization of Hg_<1-x>Cd_xTe Layers Grown by Isothermal Vapour Epitaxy

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Hg_<1-x>Cd_xTe (0<x<0.3) forms a narrow gap semiconductor of II-VI group mixed compound between HgTe and CdTe. Hg_<1-x>Cd_xTe grown by Liquid Phase Epitaxy (LPE) is recently commercially available and utilized as a photodetector for the infrared region around 10∿15μm (x=0.2). However, LPE is rather complex method in the growth process. In the present experiments, Hg_<1-x>Cd_xTe layers are grown by Isothermal Vapour Phase Epitaxy (ISOVPE) method on CdTe (111) substrates. In the ISOVPE method, the process is very simple compared with the LPE method. Hg_<1-x>Cd_xTe layers which have graded band structures along growth direction are obtained. The wavenumbers of the absorption edge of Hg_<1-x>Cd_xTe layers are found to be changed with the growth condition. The change is caused by the fact that Fermi level in graded band shifts with the variation of growth condition. The growth condition for making wideband infrared detector is classified. The depth profile of graded gap Hg_<1-x>Cd_xTe is observed using Electron Probe Micro Analyzer (EPMA) method. The result indicates that Hg_<1-x>Cd_xTe structure is changed from a quasi two-layers type to a graded type and further to a inverted type in accordance with the increase in both growth temperature and time. These behaviours may be illustrated by using the inter-diffusion of HgTe and CdTe.
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