Influence of hydrogen on hydrogenated cadmium telluride optical spectra

The presence of oxygen impurity in semiconducting materials affects the electrical properties of crystals and significantly limits their application. To remove oxygen impurity, ultrapure hydrogen is used while growing Te-containing crystals such as CdTe, CdZnTe, and ZnTe. The hydrogenation of CdTe crystals is a technological process that purifies the basic material from oxygen, mainly cadmium and tellurium oxide compounds incorporated in CdTe crystalline lattice. In the present work we analyses the deformations induced by hydrogen and oxygen atoms in CdTe crystals looking at their influence on the near fundamental band (NFB), middle infrared (MIR) and far infrared (FIR) reflectivity spectra as well as on cathodoluminescence (CL) spectra. Comparison of the hydrogenated CdTe phonon structure profiles confirms the presence of hydrogen atoms bounded inside the lattice. The possible localization of hydrogen and oxygen ions within the tetrahedron coordinated lattice is discussed in the framework of a model that shows a good agreement with recent NFB, MIR and FIR experiments carried out on hydrogenated CdTe crystals. Measured reflection spectra in the wavelength range 190-1400 nm (NFB) indicate the appearance in CdTe(HM) and CdTe(H L) of additional maxima at 966 nm related to the electron transitions from level about 0.2 eV above the valence band. The CL spectra confirmed existence of this electron level. We present a possible H2 alignment similar to the single H model i.e., over the face (at about 0.38 Å). For this model the angle from the central atom to the H atoms is equal to 64° which is also close to the bonding angle of CdH2 © 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim