In Situ, Real-Time Diffuse Optical Reflectivity Measurements During GaAs Cleaning and Subsequent ZnSe/GaAs Heteroepitaxy

Real-time diffuse optical reflectivity measurements were performed during conventional in situ thermal cleaning and while employing a combined thermal/H-atom treatment of GaAs substrates, the H-atom flux being derived from a rf plasma discharge, hydrogen free-radical source. The diffuse optical reflectivity technique was subsequently employed to monitor heterointerface roughening during molecular-beam epitaxial growth of ZnSe on GaAs substrates which were cleaned in situ using the combined thermal/H-atom treatment. Atomically clean GaAs surfaces were found to be specular when prepared in situ using the combined thermal/ H-atom treatment in contrast to conventional thermally treated GaAs surfaces which are considerably rough on the atomic level, surface roughening in this case being associated with the oxide desorption process. A further benefit associated with the specular nature of the thermal/ H-atom treated GaAs surfaces is that heterointerface roughening occurring as a consequence of plastic deformation could be detected upon attainment of the critical thickness in the case of the ZnSe/GaAs heteroepitaxial system by monitoring diffuse optical scattering as a function of deposition time. In addition to providing critical thickness data, this real-time monitoring technique also revealed that the degree of heterointerface roughening mirrors the strain relaxation process as a function of increasing film thickness, being complete at a ZnSe film thickness around 0.5 μn.