An in-situ laser-light scattering study of the development of surface topography during GaAs and In xGa 1 − xAs chemical beam epitaxy

Abstract

The development of surface topography during the annealing of epi-ready (001) GaAs wafers and the subsequent CBE growth of GaAs and In x Ga 1 − x As layers were investigated using laser-light scattering (LLS) from a rotating substrate. The change in scattered light intensity during the pre-growth anneal is usually attributed to oxide desorption. However, we have found that a wide range of behaviour is possible depending on the growth history of the chamber. We suggest that this is due to the desorption of previously deposited species from the cryopanel as a result of radiant heating from the substrate, leading to contamination of the wafer surface. Procedures to minimise this contamination are outlined. LLS was used to study the changes in surface topography during growth, particularly the development of elliptical islands during the growth of GaAs and the onset of the “cross-hatch” pattern during the growth of InGaAs. It has recently been established that the ridges of the cross-hatch pattern are associated with dislocations which lie parallel to the surface. The development of these ridges parallel to 〈110〉 is related to the critical thickness of the layer. Interference oscillations in scattered light intensity during the growth of multilayer structures are also shown to be observable using LLS.