Photocapacitance study of deep levels in thin CdTe PV devices

Steady state photocapacitance (PHCAP) was used to survey the deep levels in the energy range 0.73 eV to 1.38 eV with respect to the valence band in CdS/CdTe PV devices. The effect of the cadmium chloride treatment process on deep level densities is shown qualitatively. Estimates of the optical transition thresholds Epo for three deep minority type levels E1, E2, and E3 are given and a discussion of possible assignment to specific defects is presented. Preliminary results using deep level optical spectroscopy (DLOS) to measure the optical cross sections for holes σpo of the E2 and E3 levels are given. The thermal emission rates ent for electrons at 79 K are estimated for the E2 and E3 levels.