Polycrystalline Boron Phosphide Semiconductor Electrodes

Thin films of polycrystalline boron phosphide (BP) are obtained by using conventional thermally activated chemical vapor deposition. BBr 3 and PBr 3 are used as reactants and BP is formed at 940°C in a H 2 environment. A rough black layer is obtained on alumina substrates. All films are n‐type with a high donor density. (Photo‐) current‐voltage curves are presented. The transient photocurrent response and the presence of a substantial photocurrent at subbandgap illumination strongly suggests the presence of a high density of surface states. Impedance spectra of the unilluminated electrode could be modelled adequately with an equivalent circuit. Numerical values of the space charge capacitance were obtained at anodic potentials. The flatband potential was determined from Mott‐Schottky plots, and appeared to depend strongly on the electrolyte pH. The flatband potential of BP is (+0.182 – 0.073 pH) V vs. SHE. This value is not concordant with reported theoretical predictions based on atomic electronegativities.