Ballistic electron emission microscopy studies of AurCaF rn-Si 111/ interfaces

We have performed ultrahigh-vacuum UHV. ballistic electron emission microscopy BEEM. measurements on AurCaF2rn-Si 111.into which calcium fluoride CaF2. about 2 monolayers ML..was introduced between Au and Si. A BEEM image clearly shows that a CaF2 intralayer deposited at 7008C induces the coexistence of two terrace types, each with a different BEEM I–V spectrum shape. A typical threshold voltage of the BEEM current for one type is about 0.75 V. In contrast, the other type shows a threshold voltage of about 3.6 V, which is much higher than that of the first type. Furthermore, the BEEM current on the second type is significantly reduced and saturates above approximately 6 V. Ca distributions measured by Auger electron spectroscopy AES.strongly suggest an inhomogeneous distribution of CaF2 coverage on 2 ML CaF2 deposited at 7008C.rn-Si 111.; there are two types of Si terraces, each of which has a different CaF2 coverage. Based on the AES measurements, we attribute the coexistence of the two terrace types in the BEEM image to the different degrees of coverage of the CaF2 intralayers. The second type of terrace has a Aur2 ML CaF2r1 ML CaFrSi 111.heterostructure. A 2 ML CaF2r1 ML CaF is an insulating intralayer which induces the threshold voltage of 3.6 V and the saturation of the BEEM current. In contrast, the first type has a Aur1 ML CaFrSi 111.heterostructure which has the threshold voltage of 0.75 V. q1998 Elsevier Science B.V. All rights reserved