Steady-State and Time-Resolved Photoconductivity Measurements of Minority Carrier Lifetime in ZnTe

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 = 2.26 eV) 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^-7 s at 220 K, decreasing to 2.5 × 10^-8 s at 300 K. For hydrogen passivated samples, the low temperature behavior was similar but the lifetime remained high at 4.5 × 10^-7 s at 300 K, due to passivation of deep acceptors O_Te. Time-resolved photoconductivity measurements gave a value of 4.6 × 10^-8 s for as-grown ZnTe in reasonably good agreement and 3.2 × 10^-7 s for Zn annealed and 3.1 × 10^-7 s for SI-ZnTe. The radiative recombination constant B was thus found to be 1.4 × 10^-9 and 4 × 10^-10 cm³ s^-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.