Two levels of the Schottky barrier in CVD diamond/silicon heterojunctions at low temperature

The I–V characteristics of some CVD diamond/silicon heterojunctions measured in the temperature range of 129–295 K showed an abnormal increase in current at low voltage and temperature. The devices show a bend in reverse and forward currents due to extra current, suggesting that there are two independent contributions to the thermionic current, corresponding to two levels of the Schottky barrier. When the temperature increases, the influence of the Schottky barrier height at small voltages decreases and normal current behaviour is observed at high temperatures. Conductance curves measured at a test frequency of 200 Hz also present a bend for low voltage and temperature. To explain the atypical current behaviour, an electrical equivalent circuit model composed of two diodes in parallel with different barrier heights was proposed. The results show that lowering of the barrier height in specific areas explains the excess current at low voltage and the origin of this effect is possibly related to non-uniformity in specific regions of the material.