WORK FUNCTION, ELECTRON-AFFINITY, AND BAND BENDING AT DECAPPED GAAS(100) SURFACES

Work function and band bending measurements are performed on n- and p-type GaAs(100) surfaces prepared by molecular-beam epitaxy and As decapping. The band bending is almost independent of the decapping temperature and surface reconstruction [(1 x 1) --> C(4 X 4) --> C(2 X 8) --> (4 X 2)]. The work function and electron affinity undergo large and systematic variations of up to 400 meV which consistently establish maxima and minima of these quantities for the (2 X 4)-C(2 X 8) and (4 X 2)-C(8 X 2) structures, respectively. These variations are due to surface dipoles induced by charge exchanges between the cation and anion dangling bonds in the top two layers of the crystals. These charge exchanges are fully explained by applying a simple electron counting model to each reconstruction.