Capping and decapping of MBE grown GaAs(001), Al0.5Ga0.5As(001), and AlAs(001) investigated with ASP, PES, LEED, and RHEED
1992; Elsevier BV; Volume: 56-58; Linguagem: Inglês
10.1016/0169-4332(92)90218-m
ISSN1873-5584
AutoresR. Bernstein, A. Borg, Hans Husby, Bjørn‐Ove Fimland, J. K. Grepstad,
Tópico(s)Electron and X-Ray Spectroscopy Techniques
ResumoArsenic capping and regeneration of MBE-grown GaAs(001), Al0.5Ga0.5As(001), and AlAs(001) epilayer surfaces were examined with Auger sputter profiling (ASP), synchrotron radiation and X-ray photoelectron spectroscopy (PES), LEED, and RHEED. It is found that clean, ordered surfaces of different As/Ga(Al) compositions and different surface reconstructions can be prepared in a controlled manner after long-term storage in air, by thermal desorption of the As cap at appropriate annealing temperatures. A protective film of amorphous arsenic was deposited in situ with both As2 and As4 molecular beams onto cold substrates. The recorded Auger depth profiles unveil capping layer thicknesses from 0.3 to 3 μm, the thicker for depositions using the As2 dimer source. The As3+ surface oxide, formed immediately upon exposure of the passivated wafers to air, remains on the order of 10Åthick, even after storage in atmosphere for several months. Core level photoemission shows selective desorption of this oxide upon annealing in UHV at 250°C. Further heating at 350°C evaporates the protective arsenic cap, and clean, As-terminated AlxGa1−xAs(001) surfaces with a regular arrayof chemisorbed excess AsAs dimers prevail. The recorded LEED and RHEED patterns show a c(4 × 4) surface reconstruction for GaAs(001) and Al0.5Ga0.5As(001), whereas this structural phase was observed with RHEED only for the highly reactive AlAs(001) surface. Subsequently annealing in UHV at 450°C causes desorption of the chemisorbed surface arsenic and a concurrent transition from c(4 × 4) to the (2 × 4)/c(2 × 8) surface of As stabilized MBE-grown AlxGa1−xAs(001). With AlAs(001), surface Al oxidation was observed immediately after annealing at 450°C, in spite of carefully controlled UHV environments
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