Single particle and collective excitations of a two-dimensional electron gas at the Cs/InAs(110) Surface

The accumulation space-charge region at a semiconductor surface has been studied by a joint investigationof the plasmon excitation and the spectral density of the quasi-two-dimensional electron gas ~Q2DEG!. Theanalysis has been performed by means of high-resolution electron-energy-loss spectroscopy and highresolutionultraviolet photoemission, respectively. The accumulation layer was produced by depositing tinyamounts of Cs on the InAs~110! surface. By using a semiclassical dielectric model, the formation of theQ2DEG in the subsurface region was unambiguously proved by a satisfactory description of the coverage andprimary energy dependence of the collective excitations. The characteristic parameters of the Q2DEG, i.e.,charge density and width of the space-charge region, are determined. These results are in very good agreementwith the values deduced by self-consistently solving the Poisson and Schro¨dinger coupled equations, whichalso give the eigenvalue spectrum and spectral density as measured by photoemission.