RELIABILITY OF THE ASPERITY CONTACT MODEL IN DETERMINING CHARGE INJECTION ACROSS INTERFACES

Current profiles across mechanically contacted materials usually diffe r from the ones obtained by corresponding evaporated contacts. The asp erity contact model has been brought up to cover such discrepancies. H owever, there is a lack of experimental evidence concerning its applic ability on electronic injection across the interfaces. The work presen ted in this paper uses I-V curves of a well-documented device, the met al-semiconductor contact, as a tool to examine the validity of the asp erity contact model and the implications of the interfacial layer, the axial contact force, the interfacial field and the relative permittiv ity of the surrounding space, on the injection process. Namely, the in fluence of interfacial layers has been studied in ultra-high-vacuum (U HV) environment (10(-10) mbar) using cleaved silicon samples, contacte d by hemispherical metal electrodes (Au, Cu, In, Al) covered insitu by fresh overlayers. The applied axial forces were controlled by electro magnets which displaced stainless steel electrodes to contact chemical ly prepared and cleaved [110] Si samples in a UHV environment. The imp ortance of the interfacial fields has been examined by using Si and Ga As samples having specific surface profiles, i,e., mesas with 10 mu m diameter and 1 mu m height, fabricated by plasma etching or wet chemis try processes. Finally, the effect of the relative permittivity of the surrounding space has been investigated by applying sinusoidal 50-Hz high current densities on metal-metal contacts in the laboratory and h igh vacuum (10(-6) mbar) environments. Utilizing the framework of the theory of the asperity contact model, the obtained results are in good agreement with the expected implications of the examined factors.