4 d transition-metal impurity rhodium in GaAs grown by metal-organic chemical vapor deposition

Abstract

Deep levels associated with 4d transition-metal impurity rhodium have been investigated in GaAs epitaxial layers grown by metal-organic chemical vapor deposition, using deep level transient spectroscopy (DLTS) technique. A comprehensive study of deep levels in the entire bandgap of GaAs has been carried out using both n- and p-type GaAs crystals over a wide temperature scan range, 12–470 K. In the n-type, Rh-doped material, two prominent broadbands of deep levels are found to be associated with Rh impurity; one in the upper-half and the other in the lower-half bandgap. In addition, one relatively small peak at the high temperature end of the majority-carrier emission spectra, corresponds to a deep level at Ec−0.92 eV, is also detected in the n-type Rh-doped samples. The minority carrier (hole) emission band in n-type material is found to consist of a doublet of hole emitting deep levels, labeled RhA and RhB, in the lower-half bandgap. This doublet is clearly observed to correspond to two Rh-related deep levels, labeled RhA and RhB, in the majority-carrier emission spectrum of p-type GaAs. In addition, a small hole emission peak, RhC, at the high-temperature end of the spectrum of p-type material corresponds to a deep level at Ev+0.87 eV. Data on directly measured carrier capture cross sections of deep levels are reported, wherever experimentally possible. Detailed double-correlation DLTS measurements are performed to investigate the characteristics of the observed Rh-related deep levels. The broad deep-level band in the upper-half bandgap, as well as the lower-half bandgap levels, RhA and RhB, are found to exhibit pronounced dependence of the thermal emission rates on electric field. While the former band cannot be resolved into component peaks, detailed data on the electric field dependence of hole emission rates are reported for the levels RhA and RhB over a range of measurement temperatures and analyzed in the light of the available theories. This analysis suggests the deep level RhB to be associated with a charged center while the deep level RhA is probably associated with an autolocalized self-trapping center.