Surface electronic structure of H/InAs(001)-4×2 studied by synchrotron radiation

The free surface electronic structure of undoped and n-type InAs(001) is well-known to exhibit electron accumulation while p-type InAs(001) shows an inversion layer on the surface. We report a high-resolution synchrotron radiation (hv = 40 - 160 eV) photoemission study to clarify effects of hydrogenation on the electronic structure of undoped, n-type, and p-type InAs(001). Chemically treated surfaces annealed at 420°C show a clear 4×2 reconstruction. In 4d/As 3d core levels reveal a single component surface contribution with surface core-level shifts of ~200 meV. They appear at higher/lower binding energy (BE) than the bulk, suggestive of a charge redistribution of surface In and As atoms as in InGaAs(001)-4×2. Upon exposure to atomic hydrogen (H⁺ and H^-) generated by a UHV cracker, the valence band maximum shifts to higher BEs, suggestive of n-type doping. Concurrently, the In 4d and As 3d surface components show reduced intensity with appearance of Hydrogen-induced components. The induced In 4d/As 3d component occurring at low/high BE is associated with H^-/H⁺, respectively. The results suggest surface In atoms get charge enriched upon H bonding, and most likely cause the re-transformation from the (4×2) to the original (1x1) structure as confirmed by LEED measurements.