Some observations on Ge:GaAs(001) and GaAs:Ge(001) interfaces and films

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Abstract
Ge:GaAs(001) and GaAs:Ge(001) interfaces and thin films have been prepared by molecular beam epitaxy (MBE) and studied in situ by reflection electron diffraction (RHEED), angle-resolved photoemission spectroscopy (ARPES), and core level photoemission. The film structures have also been examined by transmission electron microscopy (TEM). Ge films grown on GaAs(001) substrates have a c(2×2) surface symmetry and are free of extended defects and domain structures. ARPES measurements of Ge(001)-c(2×2) surfaces in the photon energy range 20–50 eV show the presence of two surface states and dispersing bulk states. Valence bands along the ΓX symmetry direction are derived on the basis of a free-electronlike final state. The quality of the Ge–GaAs(001) interface however, is determined by the GaAs substrate reconstruction. Ge deposition on an intrinsic (2×4) reconstructed surface produces an abrupt interface, but when a c(4×4) chemisorption phase is used the distribution of arsenic across the interface region is diffuse. TEM examination of GaAs films on Ge(001) substrates has confirmed the presence of a domain structure in which the domains are distinguished by reversal of the polar axis.

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