AN IMPEDANCE STUDY OF BORON PHOSPHIDE SEMICONDUCTOR ELECTRODES

Impedance spectroscopy is employed in a study on the electrical and optical properties of boron phosphide (BP) electrolyte interfaces. With this technique both the space charge capacitance can be determined and the charge trapping in surface states can be investigated. The flatband potential of boron phosphide and the corresponding band-edge positions are found to be considerably more positive than the related III-V semiconductors GaP, GaAs, and InP. As a consequence, BP is found to be more stable for photo-etch reactions than any of these materials. It is shown that the band positions of GaP, GaAs, InP, and BP can be predicted from the atomic electronegativities fairly accurately. In neutral and alkaline electrolytes the surface of BP is free of native oxide and the surface state density is low. In acid electrolytes, however, a native oxide is present on the surface of BP. This oxide is probably hexagonal B2O3 and is observed to be able to cause a large shift of the bandedges. In the latter electrolytes the Mott-Schottky plots of BP are heavily distorted by the presence of additional surface state capacitances.