CHARACTERIZATION OF THE Z LUMINESCENCE SYSTEM IN HIGH-PURITY CDTE

4.2 K Photoluminescence (PL) bands with unusual spectral properties have been observed and identified in high purity low-temperature-grown bulk polycrystalline CdTe. Two sharp bands dominate at about 1.300 and 1.355 eV in p- and n-type samples respectively (Z centre). Detailed PL studies including time-resolved measurements are used to define the precise Z0/+ energy level in the gap: E(c) - 251 meV or E(v) + 1.355 eV. By varying the excitation wavelength we find a strong transformation of the PL spectrum which allows us to compare the shape of the two spectral regions: 1.24-1.36 eV and 1.45-1.57 eV associated with Z-acceptor and conventional donor acceptor recombination respectively. In this way we defined the second level (Z-/0 transition): E(c) - 206 meV or E(v) + 1.400 eV. The PL properties of the Z centre, a laser microprobe mass analysis investigation and correlation with a spin-polarized tight-binding model allow us to suggest that the Z centre originates from a 3d impurity on a Cd site, most probably Cu.