Ballistic-electron-emission-microscopy studies on Au/SiO2 n-type Si(100) and Ir/SiO2 n-type Si(100) structures with very thin oxides

摘要

Ballistic electron emission microscopy (BEEM) has been used to study metal-oxide-semiconductor (MOS) structures such as Au/SiO2-type Si(100) and Ir/SiO2-type Si(100), with the thin SiO2 layer varying from 10 to 30 Angstrom. As expected, the presence of a 30-Angstrom oxide layer at the interface induces much higher electronic barriers than in the case of Schottky diodes. Samples with Au show a barrier height of similar to 4.1 eV, while those with Ir have a barrier as high as 5.6 eV. When the interface oxide-layer thickness is reduced to similar to 10 Angstrom, the BEEM spectra behavior is different. For Au/SiO2/Si junctions, although a clear threshold is always observed around 4 eV, showing that a high barrier is already formed at these small thicknesses, a leakage current is often detected below this threshold. In the case of Ir/SiO2/Si structures, the BEEM spectra display an anomalous behavior. Below the high-energy threshold around 5.5-6 eV, a first threshold (similar to 1.5 eV) and a broad peak (similar to 4 eV) are observed. These structures could result from a resonant tunneling effect through the oxide layer. A striking result is also observed in the reverse BEEM (RBEEM) mode. In contrast to what is normally observed, where the RBEEM current is much weaker than the BEEM current, for these ultrathin barriers we find a broad peak at 4 eV with approximately the same intensity in RBEEM as in BEEM. [References: 26]