Photoluminescent Properties of n-GaAs Electrodes: Simultaneous Determination of Depletion Widths and Surface Hole-Capture Velocities in Photoelectrochemical Cells

Steady-state photoluminescence measurements performed on n-GaAs electrodes used in photoelectrochemical cells (PEC's) employing a stabilizing, aqueous telluride electrolyte yield values for the electrode's depletion width W and surface hole-capture velocity S. Between -1.0 V (a potential near short circuit) and -1.5 V vs. an SCE reference electrode (a potential near open circuit at the photon flux of 1 x 10 to the 15th power photons/sq cm employed), the interface behaves ideally: virtually all of the applied potential appears in the semi-conductor space-charge region. Over this potential regime S is determined to be constant to within 10% and has a value, using literature values for hole lifetime and diffusion length, of approximately 200,000 cm/s for n-GaAs electrodes having carrier concentrations of (1 - 4) x 10 to the 17th power/cu cm. Similar values of S obtained in air and in the PEC suggest a common rate-limiting mechanism for hole consumption in the two media.