Deep levels in high resistive CdTe and CdZnTe explored by photo-Hall effect and photoluminescence spectroscopy
Abstract
High resistive CdTe and CdZnTe single crystals were measured by photo-Hall effect spectroscopy (PHES) and photoluminescence spectroscopy (PL) with the aim of discovering the position of deep levels (DLs) in the band gap. Illumination in the range of 0.65-1.77 eV, room temperature, and DC electrical measurements were used in the case of PHES.
Low temperature (4K) photoluminescence spectra were recorded in the spectral range above 0.47 eV. Eight samples, both n-type and p-type, were studied and typical shapes of spectra were collected, compared and interpreted for both spectroscopy methods.
It was shown that a simple single-level model of PHES often fails in the interpretation of DLs distant from the midgap. Eight DLs with the energy E-c - 0.65 eV, E-c - 0.8 eV, Ec - 0.9 eV, E-c - (1.10-1.15) eV, E-v + 0.70 eV, E-v + 0.85 eV, E-v + 1.0 eV, and E-c - 1.25 eV were interpreted.
A memory effect characterized by a relaxation time of about 60 s was observed at the 0.8 eV level and allowed us to determine the 1.7. x. 10(-17) cm(2) capture cross-section of electrons on this level. It is argued that PHES is a convenient complementary method to identify and characterize DLs, including DLs inaccessible by thermal emission techniques.
DLs observed by PHES were consistently verified by PL.