Changes in the photoluminescence spectrum near twin boundaries in ZnTe crystals produced by rapid crystallization

Abstract

{111} ZnTe crystals with various densities of twin boundaries in the growth direction were produced at ∼670°C by the chemical vapor deposition method with the vapor environment offset toward an excess of Zn. Defects are formed in conical crystallites (up to 5 mm in height and with lateral dimensions of 10–500 μm at the bottom and up to 2 mm at the top) due to instabilities in the crystallization front, which arise because of convection-type heat and mass exchange in the oversaturated vapor medium. The influence of twin boundaries on the distribution of chemical impurities and the electronic spectrum of ZnTe was studied using x-ray diffractometry, scanning electron microscopy, and low-temperature photoluminescence (PL). It is found that rapid low-temperature growth of [111] ZnTe polycrystals from the vapor phase with an excessive Zn content favors the intensive formation of rotation and reflection twins. The incoherent [111] boundary of reflection twins is conductive to the separation and accumulation of impurities. In the regions of a crystal with a high density of reflection twins, exciton-impurity complexes (I C , I X ) and a Y strip, which is usually related to extended defects (dislocations, twins, crystallite boundaries), are found in the low-temperature PL spectra. Additional studies show that I X is related to excitons trapped by neutral isoelectronic or charged defects and that I C is probably due to an impurity of group IV of the Periodic Table.