Density of states of a two-dimensional electron gas at semiconductor surfaces

The formation of a two-dimensional ~2D! electron channel at semiconductor surfaces has been studied by high-luminosity and high energy-resolution ultraviolet photoelectron spectroscopy. A large variety of bandbending sources ~alkali metals, silver and antimony adatoms, cleavage defects! on different narrow-gap IIIV~ 110! substrates ~InAs, InSb! has been used. The measured photoemission spectral density in the semiconductor conduction band shows a steplike structure, consistent with the description of a jelliumlike 2D electron gas confined in a potential well, and it is independent of the band-bending sources. A self-consistent solution of the Poisson and Schro¨dinger equations gives the energy eigenvalues, the eigenstates, and the spectral density, in excellent agreement with the collection of photoemission results. Moreover, the accumulated charge density ranges between 331011 and 231012 electrons/cm2, consistent with previous experimental results on plasmon excitations.