Nonstoichiometric deep levels in Mg-doped GaP epitaxial layers

Abstract

We have investigated the relation between deep levels in Mg-doped p-type GaP liquid phase epitaxy (LPE) layers and stoichiometry of the surface of the substrates by PHCAP measurement. Concentration of a deep donor level at E C−1.9–2.1 eV is higher in an n-type undoped GaP substrate annealed with applying phosphorus vapor pressure of 20 kPa than in sample annealed beneath a carbon cover. Next, Mg-doped LPE layers are grown on substrates that have been pre-annealed under phosphorus vapor pressure just before the growth. The densities of deep levels at E V+0.85 and E V+1.5 eV in long-time (2 h) pre-annealing sample are greatly decreased, but a deep level at E C−1.9–2.1 eV shows opposite tendency. The latter is thought to be identical to a deep level detected in the substrate, probably phosphorus interstitial atoms.