Direct measurement of quantum-state dispersion in an accumulation layer at a semiconductor surface

We use high-resolution photoemission spectroscopy to measure the dispersions of quantized energy levels located in an accumulation two-dimensional electron channel created in the subsurface region of a semiconductor. The experiments are performed for InAs(110) covered by about 10^-2Cs monolayer. From the band dispersion, the average effective mass of the carriers in the channel is determined. Our findings are further supported by self-consistent calculations and model-function curve fitting.