Low-resistance and nonalloyed ohmic contacts to plasma treated ZnO

Low-resistance and nonalloyed ohmic contacts to epitaxially grown n-ZnO were formed by exposing n-ZnO to an inductively coupled hydrogen and an argon plasma. Using Ti/Au, the specific contact resistivity of the ohmic contact was drastically decreased from 7.3×10−3 to 4.3×10−5 Ω cm2 by hydrogen plasma treatment. The photoluminescence spectrum of the hydrogen plasma treated ZnO showed a large enhancement in band-edge emission and a strong suppression in deep-level emission. These results suggest that the low contact resistivity can be attributed to an increase in carrier concentration on the ZnO surface. The specific contact resistivity of the Ar-plasma treated sample was also decreased to 5.0×10−4 Ω cm2, presumably due to the formation of shallow donor on the ZnO surface by ion bombardment.