The effect of vacuum heat treatment on the diamond surface conduction

Abstract

Monocrystalline epitaxial diamond layers were grown by microwave plasma CVD on (1 0 0) surfaces of high-temperature, high-pressure synthetic monocrystalline diamond bulk substrates. Electrical measurements were carried out using 2 and 4 point probes. Surface conductance was found to be in agreement with the boron doping level on as-grown layers. It is expected that the surface conductance is controlled by the hydrogen–carbon bonds on the surface. The hydrogen-influenced surface conductivity was changed by vacuum annealing at high temperatures: first 700 °C then ∼900 °C in a single two-step process. This process increased the surface resistance by about 8–9 orders of magnitude, which became as high as the measurement limit (>10 13 Ω) independent of the boron doping level. This effect was not observed on the bulk samples. Cathodoluminescence measurements showed small changes in the range of 450–500 nm wavelengths. Deuterium plasma treatments followed the vacuum annealing. The high surface resistance remained unchanged. Application of shallow alloyed Au contacts indicated that only a shallow surface region of the epitaxial layers was changed due to the annealing. The bulk crystals, however, did not show the same effects.