Deep Levels in high resistive CdTe and CdZnTe explored by Photo-Hall Effect and Photoluminescence Spectroscopy
Abstract
The performance of CdTe and CdZnTe bulk radiation detectors is critically affected by deep levels (DLs), which capture photo-carriers and induce detector polarization. The deep level analysis thus constitutes an indispensable step at the material characterization and the optimization of the detector manufacture.
Various experimental methods were developed to determine properties of DLs in semi-insulating semiconductors, each of them having advantages and disadvantages. The principal problem of the most of techniques is their inability to distinguish the charge of captured carriers, i.e. the identification of electron and hole traps.
The obstacle may be solved by the measurement of the charge transport in thermal gradient or in magnetic field. While the DLs characterization by thermoelectric effect spectroscopy (TEES) belongs to routine methods used in laboratories, the measurement of galvanomagnetic properties of photo-excited samples remained out of focus of the researchers for decades.
In this presentation we fill in the gap in magnetic-field-based procedures at the research of DLs and report on the investigation of semi-insulating CdTe and CdZnTe by the Photo-Hall effect spectroscopy (PHES). The illumination in the wavelength range 1800 - 700 nm and dc electrical measurements are used.
We show on a set of samples, both n- and p-types, the typical features of spectra and deduce properties of DLs responsible for observed effects. The extensive collection of experimental data allow us to define both positive and negative sides of PHES.
Due to special character of the Hall voltage prioritizing more mobile electrons on holes the PHES appears particularly useful in p-types, where the character of principal DLs could be proven. In case of n-types the PHES does not enable us the unique interpretation and complementary investigation is necessary for explaining of observed transitions.