Energy-dependent conduction band mass of SiO2 determined by ballistic electron emission microscopy

Quantum interference oscillations in ballistic electron emission microscopy (BEEM) spectra were observed for metal-oxide-semiconductor structures with 23 and 30 Angstrom SiO2 interlayers. Maxima in the transmission coefficien ts, obtained from solutions of the one-dimensional Schrodinger equation tha t included image force corrections, could be matched to the spectral maxima provided that the effective electron mass m(ox), an adjustable parameter, was increased at each of the consecutive higher energy maxima. The resultin g energy dependence or dispersion of m(ox)(E) showed a dependence on the ox ide thickness. The 23 and 30 Angstrom oxides exhibit initial (zero kinetic energy) m(ox) values of 0.52 m(0) and 0.45 m(0), respectively, that dispers e upward with energy by approximate to 0.3 m(0) over a 0-2.5 eV range in ki netic energies. The range of m(ox) values observed is substantially lower t han the average m(ox) values deduced from quantum interference in Fowler-No rdheim tunneling experiments. The origin of these differences are discussed , and it is argued that BEEM is an inherently simpler and less error prone technique to evaluate m(ox). (C) 1999 American Vacuum Society. [S0734-211X( 99)05004-0].