Photoreflectance study of phosphorus passivation of GaAs (001)

Abstract

We present a study of the effect of phosphorus passivation on the surface electric field of undoped GaAs using photoreflectance spectroscopy. Surface electric fields were determined in $\mathrm{surface/intrinsic/}\mathrm{n-}\mathrm{type}$ $({\mathit{s-i-n}}^{+})$ samples prepared with various surface phosphorus treatments. A comparison with ${\mathrm{H}}_{\mathrm{2}}\mathrm{S}$ passivated films and InGaP capped layers prepared in situ in the same growth equipment is also presented. Phosphorus surface passivation was achieved by (1) exchange reaction of the GaAs surface under tertiarybutylphosphine vapor or (2) direct growth of GaP thin epitaxial layers. The total coverage of phosphorus has been estimated by x-ray diffraction techniques. We observe a maximum reduction of the surface Fermi level using epitaxially grown GaP with an effective coverage of two monolayers. Atomic force microscopy images of all passivation treatments exhibit excellent surface morphology without roughening. The passivation effects decreased somewhat over time but reductions in the Fermi level and density of surface states are still quite large after several months of air exposure.