The p-Inp semiconductor / electrolyte contact under depletion conditions: Impedance, reverse currents and photopotentials

Abstract

Current—voltage and impedance spectroscopic measurements were made at the p-InP < 100 >H 2SO 4 contact. Small reverse saturation current densities (ca. −1 nA cm −2) at low doped samples allowed measurement of the space-charge capacity C sc over more than seven frequency decades (20 mHz–30 kHz). An extremely low and potential-independent frequency dispersion of C sc of 0.4% per frequency decade was obtained (20 Hz–20 kHz). Results obtained from capacitance data for the semiconductor—surface energy barrier height φ B with and without platinum coating and for different doping densities are compared with data from photentials. Larger variations of φ B (0.7–1.0 eV) than those typically achieved at solid state p-Inp—metal contacts are verified. Flatband potentials and photopotentials are used to estimate the band-bending under illumination which, at bare and Pt-coated p-InP—electrolyte contacts, turns out to be 70–240 mV lower than at ideal Schottky contacts.