Effects of island coalescence on the compensation mechanisms in chlorine doped polycrystalline CdTe

Combined structural, chemical, and spectroscopic analyses have been carried out on chlorine (Cl) doped polycrystalline CdTe before, upon, and after coalescence of the initial isolated islands in order to investigate the effects of the formation of grain boundaries on Cl incorporation and on the related compensation mechanisms. From 4 K cathodoluminescence measurements, coalescence is found to be associated with a change in the Cl related compensation mechanisms in particular with the appearance of shallow acceptor complexes noted β. Simultaneously, the donor acceptor pair transitions involving A centers shift toward higher energies, indicating a decrease of the donor to acceptor separation. These observations are tentatively assigned to the segregation of Cl atoms in the vicinity of grain boundaries, upon coalescence, as directly shown by time-of-flight secondary ion mass spectroscopy imaging. Furthermore, long after coalescence, on thick polycrystalline CdTe, the density of β acceptor complexes is even larger due to twinning deformation processes suggesting further segregation phenomena within grains.