Analysis of the 1.55 eV PL band of CdTe polycrystalline films

Photoluminescence (PL) spectra of CdTe at low temperatures usually show a narrow band at 1.55 eV, sometimes together with phonon replicas. It has been shown that this band is associated with a transition involving an acceptor level due to a cadmium vacancy; however, there is discrepancy about the high-energy level which causes this transition. It is assumed that this high-energy level comes from the bottom of the conduction band or arises from non-excited level due to a superficial donor. In order to clarify the origin of this level, we have carried out selective pair luminescence (SPL) studies at 10 K and also analyzed the temperature dependence of PL in CdTe polycrystalline samples. Our results allowed us to conclude that the 1.55 eV PL band arises from the overlap of two bands peaking at 1.550 and 1.556 eV, respectively. The first one is associated with a donor-acceptor pair transition and the second one (1.556 eV) is probably due to a transition involving excitons bound to a superficial acceptor of the type Cu_i⁺-V_Cd ^-.