Application of two- and four-point contact probes to various monocrystalline diamond surfaces

Abstract

Point contact methods using metallic needles are widely applied for electrical measurements on the diamond semiconductor surfaces because of the difficulties of alloyed ohmic contact preparation. Contradictions and discussions in the literature concerning the resistance values and the shape of I–V characteristics made necessary a detailed study of the point contact measurements. In this work two- and four-point methods were applied to HPHT bulk crystals and MPCVD monocrystalline epitaxial layers in order to evaluate the applicability of these methods, to estimate the current conductivity character of such metal tip–diamond junctions, and to measure the electrical resistance of these crystals. Some samples underwent various treatments: annealing in vacuum; hydrogenation in molecular hydrogen; deuteration in RF and MW plasmas. Conductivity character of the contacts was determined and the applicability of point contacts was demonstrated. In contrast to some earlier results, only linear I–V characteristics were found. Conducting superficial layer connected with the presence of hydrogen was not observed. After the microwave deuterium plasma treatment, just the contrary, a highly resistive superficial layer posed obstacles before the measurements.