Electrical characterization of hole traps in p-type ZnSe and ZnSSe grown by molecular beam epitaxy

Abstract

Using deep-level transient spectroscopy (DLTS) and admittance spectroscopy we investigated nitrogen doped ZnSe and ZnSSe layers grown on p-type GaAs substrates by molecular beam epitaxy. Three major hole traps denoted T1, T2, and T3 were observed with energy levels at 0.11, 0.46, and 0.56 eV from the valence band, respectively. Similar energy levels were observed in nitrogen doped ZnSSe except that T1 was at 0.12 eV from the valence band. A crude estimation of the 0.11 eV trap concentration obtained from DLTS data shows correlation with the free carrier concentration due to nitrogen. We attribute T1 to a nitrogen acceptor which controls the p-type conduction in the materials. No other direct observations of this important acceptor level have been reported in the literature so far. The two remaining levels may originate from the nitrogen doping process. We also point out the effect of the series resistance observed in this kind of material.