Abstract
Thin film heteroepitaxial silicon and GaAs grown on sapphire (Al2O3) were studied in an MIS configuration using a photoelectric technique. The Al2O3 substrate layer serves as the insulator and an aluminum film deposited on the other side of the substrate serves as the metal electrode. The results demonstrate that it is possible to transport photoexcited electrons across Al2O3 layers of several mils thickness. The photoelectric threshold energy value for the Al–Al2O3 is measured to be 3.85±0.05 eV while for the Si–Al2O3 and GaAs–Al2O3 interfaces, the values of the threshold energy are 4.5 and 4.4 eV, respectively. The electron affinity of the sapphire is found to be 0.42±0.07 eV. The amount of band bending in the semiconductor is obtained from the experimental results. It is also shown that the escape length of photoelectrons in heteroepitaxial semiconductor films is at least several microns in contrast with the low values (of the order of a few angstroms) quoted in the literature for bulk materials.
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