Electron injection into $\sim 25\mathrm{nm}$ thick Si${\mathrm{O}}_2$ films in Pt/Si${\mathrm{O}}_2$/Si structures using ballistic electron emission microscopy (BEEM) is found to produce a local suppression in the BEEM current, which is at least partly due to electron trapping in the Si${\mathrm{O}}_2$ film. Measured variations in the BEEM threshold voltage with the voltage applied across the Si${\mathrm{O}}_2$ film can be used to estimate the local trapped electron density and the centroid location, which agree with macroscopic measurements. Our measurements indicate that BEEM can be sensitive to very small numbers of electrons trapped in buried Si${\mathrm{O}}_2$ films.

• Received 8 November 1995

DOI:https://doi.org/10.1103/PhysRevLett.77.91