Ballistic electron emission microscopy studies on Au/CaF2/n-Si(111) heterostructures

Electron transport phenomena across Au/CaF2/n-Si (111) heterostructures, in which calcium fluoride (CaF2) [about two monolayers (ML)] was introduced into the interface at room temperature (RT), 550 degrees C, and 700 degrees C, have been studied by ballistic electron emission microscopy (BEEM) and ballistic electron emission spectroscopy (BEES). Not only the Au growth but also the electron transport properties strongly depend upon the growth temperatures of CaF2 intralayers. In the case of CaF2 growth at RT, CaF2 molecules will exist on the surface of the 50 ML Au/2 ML CaF2(RT)/n-Si (111) sample. BEES clearly shows that the Schottky barrier of the intermixed layer on Si (111) is about 1.06 V which is higher than the value of 0.73 V for Au/Si (111). At 550 and 700 degrees C, thin, flat Au islands, each about 0.15 nm thick, grow in stacks on the CaF2 layer. The threshold voltage of the BEEM current for an insulating CaF2 intralayer, which is about 3.58 V, is obtained only in the sample in which CaF2 was deposited at 700 degrees C. Furthermore, it was found that an inhomogeneous coverage of CaF2 exists on the sample. By using the CaF2 intralayer formed at 700 degrees C, we modified the electronic potential barrier on the nanometer scale. (C) 1998 American Vacuum Society. [S0734-2101(98)04204-3].