Boron Phosphide Films by Reactive Sputtering: Searching for a P-Type Transparent Conductor

With an indirect band gap in the visible and a direct band gap at a much higher energy, boron phosphide (BP) holds promise as an unconventional p-type transparent conductor. This work reports on reactive sputtering of amorphous BP films, their partial crystallization in a P-containing annealing atmosphere, and extrinsic doping by C and Si. The highest hole concentration to date for p-type BP (5 x 10(20) cm(-3)) is achieved using C doping under B-rich conditions. Furthermore, bipolar doping is confirmed to be feasible in BP. An anneal temperature of at least 1000 degrees C is necessary for crystallization and dopant activation. Hole mobilities are low and indirect optical transitions are stronger than that predicted by theory. Low crystalline quality probably plays a role in both cases. High figures of merit for transparent conductors might be achievable in extrinsically doped BP films with improved crystalline quality.

Automated summary

This work reports on the reactive sputtering and annealing process of boron phosphide films, as well as the extrinsic doping to achieve p-type conductivity. The highest hole concentration to date for p-type boron phosphide has been achieved using carbon doping under boron-rich conditions. Furthermore, the feasibility of bipolar doping in boron phosphide has been confirmed.