Ballistic electron emission microscopy studies of the temperature dependence of Schottky barrier height distribution in CoSi 2/n-Si(1 0 0) diodes formed by solid phase reaction

Abstract

Ballistic electron emission microscopy (BEEM) and ballistic electron emission spectroscopy have been performed on polycrystalline and epitaxial CoSi 2/n-Si(1 0 0) contacts at temperatures ranging from −144°C to −20°C. The ultra-thin CoSi 2 films (∼10 nm) were fabricated by solid state reaction of a single layer of Co (3 nm) or a multilayer of Ti (1 nm)/Co (3 nm)/amorphous-Si(1 nm)/Ti (1 nm) with a Si substrate, respectively. The spatial distribution of barrier height over the contact area obeys a Gaussian function at each temperature. The mean barrier height increases almost linearly with decreasing temperature with a coefficient of −0.23±0.02 meV/K for polycrystalline CoSi 2/Si diodes and −0.13±0.03 meV/K for epitaxial diodes. This is approximately equal to one or one-half of the temperature coefficient of the indirect energy gap in Si, respectively. It suggests that the Fermi level is pinned to different band positions of Si. The width of the Gaussian distribution is about 30–40 meV, without clear dependence on the temperature. The results obtained from conventional current–voltage and capacitance–voltage ( I– V/ C– V) measurements are compared to BEEM results.