Photoreflectance study of phosphorus passivation of GaAs (001)

We present a study of the effect of phosphorus passivation on the surface e lectric field of undoped GaAs using photoreflectance spectroscopy. Surface electric fields were determined in surface/intrinsic/n-type (s-i-n(+)) samp les prepared with various surface phosphorus treatments. A comparison with H2S passivated films and InGaP capped layers prepared in situ in the same g rowth equipment is also presented. Phosphorus surface passivation was achie ved by (1) exchange reaction of the GaAs surface under tertiarybutylphosphi ne vapor or (2) direct growth of GaP thin epitaxial layers. The total cover age of phosphorus has been estimated by x-ray diffraction techniques. We ob serve a maximum reduction of the surface Fermi level using epitaxially grow n 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 bu t reductions in the Fermi level and density of surface states are still qui te large after several months of air exposure. (C) 2000 American Institute of Physics. [S0021- 8979(00)01211-1].