Role of the charge state of deep vanadium impurities and associations of defects in photoelectric and optical properties of semi-insulating CdTe crystals

摘要

Photoexcited carrier and space charge field subnanosecond dynamicshas been investigated in bulk vanadium-doped and Cl- (or As-)co-doped CdTe crystals by using a degenerate four-wave mixingtechnique. Time-resolved measurements of picosecond grating decay atvarious illumination intensities revealed peculiarities of defecttransformation with doping or under illumination. Novel features incarrier generation and dynamics were observed for the first time andallowed parameters of the defects to be extracted. A fast electroncapture and its saturation with increasing intensity of illuminationwere observed in CdTe:V and attributed to a Cd divacancy, which isknown as a deep double acceptor Numerical modelling by using thetwo-deep-trap model allowed us to extract the concentration andrecombination activity of Cd divacancies. An enhanced electrongeneration rate by factor of 3- was found in Cl-co-doped CdTe:Vcrystals in spite of a decreased density of donor vanadium statesafter the co-doping. We attribute this additional channel of electrongeneration to photoexcitation of the DX centre, which activationenergy of 1-1.2 eV is close to a quantum energy of the YAG:Nd laserused (hν= 1.17 eV).