Steady-state and time-resolved photoconductivity measurements of minority carrier lifetime in ZnTe

Abstract

Minority carrier lifetime in ZnTe has been determined from steady-state and time-resolved photoconductivity (PC) measurements. Three types of single crystal p-ZnTe(E_G = 2.26eV) grown by the Bridgman technique were studied: (i) as-grown, before and after hydrogen passivation, (ii) Zn annealed, and (iii) In-doped semi-insulating. Steady-state photoconductivity was studied between 80 and 300 K and showed that for as-grown samples, the lifetime went through a sharp maximum of 4.5× 10^-7s at 220 K, decreasing to 2.5× 10^-8s at 300 K. For hydrogen passivated samples, the low temperature behavior was similar but the lifetime remained high at 4.5× 10^-7s at 300 K, due to passivation of deep acceptors O_Te. Time-resolved photoconductivity measurements gave a value of 4.6× 10^-8s for as-grown ZnTe in reasonably good agreement and 3.2× 10^-7s for Zn annealed and 3.1× 10^-7s for SI-ZnTe. The radiative recombination constant B was thus found to be 1.4× 10^-9 and 4× 10^-10cm^3s-1, respectively, at 300 K for as-grown and Zn-annealed samples. PC spectral response studies showed a maximum at 2.41 eV at 300 K corresponding to the main valence-conduction band transition as well as a feature near 3.2 eV corresponding to the splitoff band. Slight shift in peak energy to 2.43 eV occurred on H surface passivation due to reduction of surface recombination velocity.