Photoinjection into SiO2: Use of Optical Interference to Determine Electron and Hole Contributions

Abstract

There is some ambiguity in the interpretation of internal photoemission experiments because of the possible contribution of hole emission from the anode in addition to the cathode electron emission. Furthermore, correction of the photocurrent spectra for optical intensity variations is essential to determination of photoelectric yields. Optical interference is useful as a tool in ascertaining current contributions from the two electrodes since wavelengths of intensity maxima at one electrode correspond approximately to minima at the other. In this work an analysis technique is presented whereby the absorbed intensities are accurately calculated, the absolute quantum yields are determined assuming no hole photocurrent contribution, and the resulting spectra are examined for evidence of such currents. Internal photoemission measurements have been made on Au–SiO₂–Si structures, and the technique has been applied to obtain quantum yields and look for evidence of hole emission. It is shown that hole photocurrents (if present) are negligible compared to electron currents and in particular for photoemission from Si into SiO₂ the quantum yield for holes must be at least two orders‐of‐magnitude smaller than the electron quantum yield. The first determination of absolute quantum yields for Si–SiO₂ and Au–SiO₂ emission is presented, and the barrier energies are found to be 4.30 and 4.15 eV respectively. The optical problem has been solved for a range of oxide thicknesses and it is shown that intensity variations are not negligible even for very thin (∼500 Å) films.