The influence of calcium fluoride (CaF2) [about two monolayers (ML)] in Au/CaF2/Si(111) heterostructure on hot-electron transport across the CaF2 intralayers has been studied using ballistic electron emission microscopy (BEEM) and Fourier transform infrared spectroscopy (FTIR). The BEEM current-voltage spectra show that the electron transport property is strongly affected by the CaF2 intralayers. The threshold voltage V0 for the onset of the BEEM current for an insulating CaF 2 intralayer, which is about 3.6 V, is obtained only for the sample in which CaF2 was deposited at 700°C. In contrast, the threshold voltage of the sample in which CaF2 was deposited at 550°C .is determined to be about 0.74 V. The FTIR spectra of these CaF2 layers show that Ca-Si-F bonds exist in the latter, but not in the former. The existence of Ca-Si-F bonds implies that the CaF2 heteroepitaxial growth at 550°C is unsuccessful in obtaining a high-quality CaF2 layer and will induce many defects in the CaF2 layer and/or at the interface. The defect-induced states in the CaF2 intralayers allow hot electrons to travel through the intralayers even below 3.6 eV and lie in a position of the threshold voltage for the onset of the BEEM current to be about 0.74 V.
ASJC Scopus subject areas
- Physics and Astronomy(all)