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 1020 cm amp; 8722;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 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 qualit