OPTICAL-PROPERTIES OF UNDOPED AND IODINE-DOPED CDTE

A comprehensive study of the properties of undoped and iodine-doped CdTe structures by photoluminescence (PL) and photoreflectance (PR) is reported. Undoped bulk CdTe and iodine-doped CdTe layers grown by metalorganic molecular beam epitaxy on (100)-oriented CdTe and (211)B-oriented GaAs substrates with electron concentrations ranging from 10(14) to mid- 10(18) cm(-3) were included in this study. Lineshape modeling of 80K PL and PR spectra indicated the presence of both free exciton and donor-hole transitions at the higher doping levels. Strong PL and PR signals were also observed at room temperature. If only a single transition is considered for the analysis of the 300K spectra, the PL emission peak and the PR transition energy both exhibit a strong dependence on electron concentration for doped layers. However, Lineshape modeling of the room-temperature spectra indicated the presence of multiple transitions consisting of free exciton and direct band-to-band transitions. The use of two transitions resulted in a constant value of bandgap over the entire range of conductivities studied. A strong correlation remained between the broadening of the PR and PL spectra and excess carrier concentration N-D-N-A. In addition, the E(1) transition energy measured by PR was found to vary dramatically with growth conditions.