Atomic hydrogen-cleaned GaAs(100) negative electron affinity photocathode:Surface studies with reflection high-energy electron diffraction and quantum efficiency

The quantum efficiency of a vicinal GaAs(100) negative electron affinity (N EA) photocathode is studied and correlated to the surface morphology. Clean ing of a GaAs(100) vicinal surface by atomic hydrogen and by heating are in vestigated using reflection high-energy electron diffraction (RHEED). After atomic hydrogen cleaning at 500 degrees C, the GaAs surface exhibits a str eaky (2x4)-reconstructed RHEED pattern. When the GaAs(100) surface is activ ated to NEA by the alternate deposition of cesium and oxygen, a quantum eff iciency of similar to 9% is measured. The photocathode quantum efficiency c orrelates with the out-of-phase RHEED intensity measured before activation. After the quantum efficiency decreases with operating time, further atomic hydrogen exposure also produces a (2x4) pattern. Surfaces prepared or revi ved by atomic hydrogen produce brighter out-of-phase electron diffraction p atterns and, when activated to NEA, higher quantum efficiency compared to t hose that are heat cleaned. (C) 2000 American Vacuum Society. [S0734-2101(0 0)03503-X].