A study of recombination current in Schottky contacts by photovoltage measurements

Photovoltage measurements and internal photoemission measurements have been performed for Au/n-GaAs and Ag/n-GaAs contacts within the temperature range of 7 to 300 K. Reliable Schottky barrier heights (SBH) are determined from internal photoemission measurements which show that the SBH in both the contacts is independent of temperature, implying the interfacial Fermi level pinning relative to the conduction band minimum. It is found that the current transport processes such as thermionic emission, tunnelling and leakage current cannot be responsible for the observed photocurrent-photovoltage relationship for large photocurrent in the photovoltage measurements. The activation energies found for the current transport are actually the same in both the contacts, which are almost equal to half of the bandgap of GaAs, indicating that the recombination current is the dominant process. In addition, our results indicate that the equation currently used for the recombination current in Schottky contacts is generally over-simplified.