Studies on type-inversion of sulfide-treated p-InP

Abstract

The effects of various sulfide treatments on n- and p-InP and the stability of the sulfide-passivated surfaces have been studied by x-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS). When the sulfide treatments were performed at room temperature, a reduction of donor-type surface states was induced as indicated by a decrease of surface band bending on p-InP. However, such surface passivation deteriorated when annealed at 200–300 °C in vacuum, and a strong type inversion with band bending reaching 1.3 eV was observed on p-InP. XPS data from the annealed samples suggest that the presence of polysulfides plays an important role in the cause of the observed strong type inversion. However, SIMS analysis of the type-inverted samples indicated that the sulfur concentration at a depth of 7.5 nm from the surface was less than the SIMS detection limit for sulfur in InP (5×1016 atoms/cm3). In addition, XPS studies of the type-inverted samples showed that reversal of the type inversion occurred when the samples were immersed into water and/or a HF solution. Therefore, the observed type inversion of p-InP is probably caused either by the formation of surface sulfur-containing species, which contribute surface donor states near the conduction-band edge of InP, or by very shallow sulfur doping.