Two levels of Ni/n-GaAs Schottky barrier heights formed on a wafer by controlling pH of pretreatment chemicals: Effect of oxygen adsorption

Schottky barrier heights of Ni/n-GaAs junctions were controlled by changing the pH of pretreatment chemicals. An effective barrier height of 0.8 eV wa s obtained by treatment with dilute HCl liquid (pH = l). and 0.6 eV by trea tment with dilute NH4OH liquid (pH = 13). Surface analysis by an x-ray phot oelectron spectroscopy indicated the existence of about twice the density o f oxygen at the surface of the HCl-treated wafer as compared with that pret reated by the NH4OH liquid. The former shows nearly linear C-2-V characteri stics, while the latter shows larger but less frequency dependent capacitan ces. Two levels of Ni/n-GaAs Schottky barriers were formed on a wafer by su ccessive pretreatments and selective Ni evaporations.