Distinguishing between buried semiconductor/metal contacts and hybrid semiconductor/metal/liquid contacts at n-gallium arsenide/potassium hydroxide-selenium (Se-/2-)(aq) junctions

Abstract

The current-voltage properties of n-GaAs photoanodes have been evaluated in KOH-Se[sup [minus]]/2[minus]/(aq), CH[sub 3]CN-Fe[sup +]/0, and CH[sub 3]CN-MV[sup 2+]/+ solutions. Chemisorption of transition-metal ions (Rh[sup III], Co[sup III], Ru[sup III], Os[sup III]) onto n-GaAs has been shown previously to effect improved photoanode behavior for n-GaAs/KOH-Se[sup [minus]]/2[minus](aq) contacts, but it is not clear whether the chemisorbed metal forms a buried semiconductor/metal junction or results in a hybrid semiconductor/metal/liquid contact. After chemisorption of transition-metal ions, n-GaAs photoanodes displayed different open circuit voltages in contact with each electrolyte solution investigated. The role of the chemisorbed metal in the n-GaAs/M/KOH-Se[sup [minus]]/2[minus](aq) system is, therefore, best described as catalyzing interfacial charge transfer at the semiconductor/liquid interface, as opposed to establishing a semiconductor/metal or semiconductor/insulator/metal contact that is exposed to, but not influenced by, the electrolyte solution. 65 refs., 6 figs., 2 tabs.