Electronic properties of homoepitaxial (111) highly boron-doped diamond films

The use of diamond as a semiconductor for the realization of transistor structures, which can operate at high temperatures (≫700 K), is of increasing interest. In terms of bipolar devices, the growth of n-type phosphorus doped diamond is more efficient on the (111) growth plane; p-type boron-doped diamond growth has been most usually grown in the (100) direction and, hence, this study into the electronic properties, at high temperatures, of boron-doped diamond (111) homoepitaxial layers. It is shown that highly doped layers (hole carrier concentrations as high as 2×10²⁰ cm^-3) can be produced without promoting the onset of (unwanted) hopping conduction. The persistence of valance-band conduction in these films enables relatively high mobility values to be measured (∼20 cm²/V s) and, intriguingly, these values are not significantly reduced at high temperatures. The layers also display very low compensation levels, a fact that may explain the high mobility values since compensation is required for hopping conduction. The results are discussed in terms of the potential of these types of layers for use with high temperature compatible diamond transistors.