Study on the low temperature photoluminescence spectra of II-VI group telluride bulk crystals

The dominant point defects in II-VI group telluride bulk crystals grown from melt usually varied due to different growth conditions and cooling history, in turn affect the electrical and optical behaviors of corresponding single crystals and devices. Low temperature photoluminescence (PL) spectra acts as a contact-less and non-destructive technique, can be used to evaluate the behaviors of point defects and impurities in the as-grown telluride bulk crystals. With the purpose of comparing the defect structures in un-doped ZnTe and CdTe crystals grown under Te-rich condition, 8.6 K PL spectra were obtained. The conductivity type and resistivity were investigated by Hall-effect measurements at room temperature (RT). For p-type low resistivity ZnTe crystal, the intensity of free electron to neutral acceptor (e, A⁰) transition is higher than the donor-acceptor pair (DAP) transition, which predominates in the PL spectra. However, in the contrary, DAP peak dominates the PL emissions for n-type high resistivity CdTe. This difference is mainly attributed to the distinct properties of the grown-in point defects due to different growth velocities and cooling processes. In terms of the un-doped CdZnTe crystal grown under stoichiometry, neutral donor bound exciton (D⁰, X) emission is predominated in the 9.2 K PL spectra, with the intensity of (e, A⁰) peak is higher than DAP peak, which then overlaps to each other when the temperature higher then 15 K. In the case of In-doped CdZnTe crystal grown by Te-rich situation, A-center emission is clearly observed, which introduces an energy level approximately of 0.15 eV, with the intensity proportional to the concentration of indium dopant. This defect is seemingly related to the complex of [In_Cd⁺V_Cd^2-]^- formed by a shallow donor In_Cd and Cd vacancy.