Spectroscopic analysis of defects in chlorine doped polycrystalline CdTe

The effects of Cl doping of thick polycrystalline $\mathrm{CdTe}$ 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 $\mathrm{CdTe}:\mathrm{Cl}$ , the main compensation processes are similar to those occurring in monocrystalline $\mathrm{CdTe}:\mathrm{Cl}$ . However, specific compensation processes are also evidenced in polycrystalline $\mathrm{CdTe}$ : 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 ($5\mathrm{\mu }\mathrm{m}$ in diameter) are predominant at low Cl doping (around $2\times {10}^{17}\mathrm{at}.{\mathrm{cm}}^{-3}$ ), larger grains ($40\mathrm{\mu }\mathrm{m}$ in diameter) prevail at higher doping levels (around $6.2\times {10}^{17}\mathrm{at}.{\mathrm{cm}}^{-3}$ ), 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.