Ultraviolet light emission from Si in a scanning tunneling microscope

Ultraviolet and visible radiation is observed from the contacts of a scanning tunneling microscope with Si(100) and (111) wafers. This luminescence relies on the presence of hot electrons in silicon, which are supplied, at positive bias on n- and p-type samples, through the injection from the tip, or, at negative bias on p-samples, by Zener tunneling. Measured spectra reveal a contribution of direct optical transitions in Si bulk. The necessary holes well below the valence band edge are injected from the tip or generated by Auger processes.