Band gap of the Ge(111)2×1 and Si(111)2×1 surfaces by scanning tunneling spectroscopy

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The scanning tunneling microscope is used to measure the spectrum of states for the Ge(111)2×{}1 and Si(111)2×{}1 surfaces. Detailed spectra, revealing the entire empty and filled state bands for both surfaces are obtained. Band gaps of 0.65±{}0.09 eV and 0.50±{}0.05 eV are found for the Ge and Si surfaces, respectively. The results are compared with values for the band gaps obtained from recent quasiparticle calculations.