Surface passivation of GaAs with P2S5-containing solutions

Abstract

The surface chemistry of GaAs passivated with P2S5 solutions modified with sulfur and other sulfides has been studied with x-ray photoelectron spectroscopy, room-temperature photoluminescence, scanning Auger electron spectroscopy, and scanning electron microscopy. The degree of passivity achieved was measured by determining the intensity of room-temperature photoluminescence before and after passivation. An increase in luminescence intensity of up to 23 times was observed after a treatment by solutions containing P2S5 and (NH4)2S buffered with sulfur due to reduced surface nonradiative carrier recombination. Phosphorus oxides and sulfur bound to the Ga and As species were present on the passivated surface. In addition, all the surfaces treated with sulfide solutions were covered to a variable extent with crystallized residues, and a treatment was devised to eliminate these residues while still retaining a passivated surface. Exposure of passivated surfaces to room-temperature air increased the amount of gallium bound to oxygen, while simultaneously reducing the concentration of As on the surface. Arsenic oxide was absent from solution passivated surfaces, even after three weeks in air, but was detected on surfaces passivated in ultrahigh vacuum (UHV) by either evaporation of solid sulfur or adsorption of hydrogen sulfide. Upon exposure to air, the luminescence intensity decreased from all sample whether passivated in UHV or in aqueous solutions; however, the rate and degree of degradation was dependent upon whether passivation was done in vacuum (severe) or by solution (better) and depended upon the exact solution composition. However, the barrier height of Au/GaAs Schottky contacts with passivated interfaces was not changed by exposure to air for times up to one week.