Consideration of the Intricacies Inherent in Molecular Beam Epitaxy of the NaCl/GaAs System

Abstract

The high cost of substrates for III–V growth can be cost limiting for technologies that require large semiconductor areas. Thus, being able to separate device layers and reuse the original substrate is highly desirable, but existing techniques to lift a film from a substrate have substantial drawbacks. This work discusses some of the complexities with the growth of a water-soluble, alkali halide salt thin film between a III–V substrate and overlayer. Much of the difficulty stems from the growth of GaAs on an actively decomposing NaCl surface at elevated temperatures. Interestingly, the presence of an in situ electron beam incident on the NaCl surface, prior to and during GaAs deposition, affects the crystallinity and morphology of the III–V overlayer. Here, we investigate a wide range of growth temperatures and the timing of the impinging flux of both elemental sources and high energy electrons at different points during the growth. We show that an assortment of morphologies (discrete islands, porous material, and fully dense layers with sharp interfaces) and crystallinity (amorphous, crystalline, and highly textured) occur depending on the specific growth conditions, driven largely by changes in GaAs nucleation which is greatly affected by the presence of the reflection high energy electron diffraction beam.

Molecular Beam Epitaxy of Monocrystalline GaAs on Water-Soluble NaCl Thin Films

“…The NaCl layer (dark region) is significantly thicker (~55 nm) but still thinner than expected; some will still have sublimated during heating to the nucleation temperature and prior to achieving complete coalescence. Additional work has shown that the RHEED exposure increases the nucleation density of GaAs islands; 13 this would lead to faster coalescence of a full film, protecting the NaCl from further continuous desorption during the GaAs deposition.…”