The effect of vacuum heat treatment on the diamond surface conduction

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 (>1013 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.