New method of preparing (100) InP surfaces for schottky barrier and ohmic contact formation
The electrical behaviour of metal contacts to the (100) InP surface is examined and shown to be critically dependant on the surface pretreatment. Ag and Al contacts were deposited onto surfaces under ultrahigh vacuum conditions with particular emphasis being placed on surface preparation. The chemical composition of the InP surface during preparation was monitored using Auger electron spectroscopy. The results indicate that the electrical behaviour of the contact is dominated by the compositional and morphological features of the interface. Surfaces prepared by low energy Ar+ ion bombardment are highly disordered and non-stoichiometric. This damage is only partly removed by annealing. Small In islands remain which are a consequence of selective sputtering and In atom migration. These islands are shown to be a key factor in the production of ohmic contacts using metals previously considered to be inert. H+ ion bombardment is shown to be effective in cleaning the surface without introducing In precipitation, enabling barrier contacts to be formed using Au and Ag. Chemical interactions at the interface which would normally prevent a reactive metal such as Al from forming a barrier contact can be overcome by means of a passivating layer of oxide approximately 30A0 thick formed by low temperature plasma oxidation. The existence of a thin interfacial oxide is shown not to influence the electrical behaviour of a barrier contact provided the layer occurs within the range of tunnelling electrons. The thermal stability of the Al Schottky barrier contact is shown to be superior to that of other metallizations on plasma oxidized surfaces.