Combined LEED, AES, and work function studies during the formation of Ge : GaAs(110) heterostructures

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Abstract
On clean, cleaved GaAs(110) surfaces Ge was deposited by MBE up to a thickness of 100 monolayers at different growth temperatures. At the interface Ge reacts with the GaAs. As measured by AES (0.65±0.25) monolayers of arsenic are dissolved and mainly segregated at the surface of the growing film. At a growth temperature of 295 °C the interface is abrupt, but broadened by diffusion for growth at 395 °C. With Ge films thicker than 5 monolayers a well developed 3×1 LEED pattern is observed which converts to a 2×1 pattern during an anneal above 400 °C. The LEED patterns are interpreted by surface segregation of GeAs2 and GeAs layers, respectively, one to two monolayers thick. The observed increase of the work function in the submonolayer coverage range is explained by band bending due to chemisorption induced surface states at Ess−Ev=0.89 eV and with a charge transfer of −(0.2±0.1) e0 per Ge atom. Therefore it is concluded that the Ge atoms bond to As atoms in the initial growth stage. The band scheme of the heterostructure is discussed, and the conduction band discontinuity of the Ge:GaAs(110) heterstructure is estimated as ΔEc?0.12) eV.

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