Reversible conductivity control and quantitative identification of compensating defects in ZnSe bulk crystals

Donor compensation by associates of donor impurities and cation vacancies i s investigated in vapor grown ZnSe: I and Al diffused melt grown bulk cryst als. Both the (I-Se V-Zn) and the (Al-Zn V-Zn) A-centers could be identifie d by electron paramagnetic resonance (EPR) spectroscopy. The concentrations of the compensating defects can be reversibly changed by vapor-phase equil ibration and a reproducible adjustment of room temperature (RT) carrier con centrations n(e) up to 1.4 x 10(18) cm(-3) (ZnSe : I) and 2.7 x 10(18) cm(- 3) (ZnSe : Al) is possible. The results are explained in tenns of a defect chemical model. The supposed high concentrations of one type of vacancy ass ociated defects are confirmed using positron annihilation (PA). Lowered com pensation leads to an increase of carrier mobility mu(e) with increasing n( e). In low doped systems mobilities of 500 cm(2)/Vs can be obtained. A simi larly drastic shift of the absorption edge to lower photon energies is obse rved for both I- and Al-doped crystals. (C) 2000 Published by Elsevier Scie nce B.V. All rights reserved.