Study on the accumulated impurities at the epilayer/substrate interface and their influence on the leakage current of metal-semiconductor-field effect transistors

Abstract

Carrier impurities accumulated at the interface of a molecular beam epitaxial (MBE) grown GaAs layer-substrate have been studied in connection with substrate surface preparation just prior to MBE growth. Although the accumulated impurity density of silicon (higher than 7 × 10 17 cm -3) at the interface is the same for both H 2SO 4- and HF-treated samples, the oxygen level is much higher for the H 2SO 4-treated (higher than 1 × 10 19 cm -3) than for the HF-treated sample (less than 2 × 10 18 cm -1). High density of carriers (higher than 7 × 10 17 cm -3 is found to be accumulated at the interface only for the HF-treated sample. Further, absorbances at 1080 and 1260 cm -1 in FTIR spectra, which correspond to Si-O bonds, are observed only for the H 2SO 4-treated sample. The accumulated carrier concentration obtained in the HF-treated sample is thought to originate from the accumulated silicon which is not inactivated by making Si-O bonds. The accumulated impurities depend upon the initial surface condition of GaAs substrate before growth. The arsenic passivation layer has a good effect on reducing the accumulated impurities, which causes the carrier accumulation.