Spectroscopic analysis of defects in chlorine doped polycrystalline CdTe

Abstract

The effects of Cl doping of thick polycrystalline CdTe layers grown by close space sublimation on their crystalline structure and the compensation and passivation processes have been investigated. From an extensive low temperature photoluminescence study, it is shown that, in polycrystalline CdTe:Cl, the main compensation processes are similar to those occurring in monocrystalline CdTe:Cl. However, specific compensation processes are also evidenced in polycrystalline CdTe: Defect complexes can be formed between Cl atoms and impurities in the vicinity of extended defects such as dislocations, twin boundaries, and grain boundaries. Furthermore, using low temperature cathodoluminescence imaging, chlorine induced passivation processes are proposed for defects such as double positioning twin boundaries within the grains. On the structural side, a bimodal distribution of the grain size is found: While small grains (5μm in diameter) are predominant at low Cl doping (around 2×1017at.cm−3), larger grains (40μm in diameter) prevail at higher doping levels (around 6.2×1017at.cm−3), with the proportion of small versus large grain decreasing as the doping level increases. Interestingly, while the radiative emission of small grains is mainly attributed to compensating complexes implying chlorine and Cd vacancies, in larger grains, the luminescence comes from deeper levels most probably associated with compensating complexes implying residual impurities.