The formation of a two-dimensional ͑2D͒ 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 defects͒ on different narrow-gap III-V͑110͒ substrates ͑InAs, InSb͒ 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 Schrödinger 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 3ϫ10 11 and 2ϫ10 12 electrons/cm 2 , consistent with previous experimental results on plasmon excitations.

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Because of a typing error, we wrote that the SBZ of the Cu͑100͒ surface is a square with a side of length 2.55 Å Ϫ1 . The correct value is 2.46 Å Ϫ1 . This error is irrelevant to the results.

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