Deep electron states in chlorine-doped ZnSe films grown by molecular beam epitaxy

Deep level transient spectroscopy (DLTS) was used to investigate defect centers in chlorine-doped ZnSe epitaxial films grown by molecular beam epitaxy on (100) n⁺-GaAs substrates. The resulting carrier concentrations were in the range from 8×10¹⁵ to 3.8×10¹⁸ cm^-3. In low and moderately doped samples two isolated point defects are found, with energy levels at 0.30 and 0.51 eV below the conduction band. The concentration of the dominant trap (at 0.51 eV) is relatively low - of the order of 10¹⁵ cm^-3 - and does not depend on the Cl-doping level. The trap exhibits a strong electric field dependence, indicating its donorlike character. Heavily doped samples reveal a single thermal emission peak. The DLTS amplitude of this peak changes as a logarithm of the filling pulse duration, suggesting that the emission originates from spatially extended defects. We compare the DLTS behavior observed on ZnSe:Cl to earlier studies of Ga-doped ZnSe. Our results clearly indicate that Cl is far superior to Ga as an n-type dopant, because - unlike Ga - Cl does not of itself introduce any detectable deep defects into ZnSe.