Anisotropic surface structure in ordered strained InGaP

Abstract

We have studied the surface structure of ordered In x Ga 1− x P organometallic vapour phase epitaxy (OMVPE)-grown layers using optical microscopy, atomic force microscopy (AFM), and synchrotron topography. The layers were intentionally lattice mismatched (0.388≤ x In≤0.552), and they exhibited a surface structure with three basic features. The first one is a fine island structure with the size of surface features in the range of 10 nm, which is very similar for all layers regardless of their misfit. This fine structure is superposed to surface undulations with lateral dimensions in the micrometer scale. The surface structure of the strained layers (tensile and compressed) follows the dislocation line pattern revealed by synchrotron topography. The change of the dominant misfit dislocation direction from [011] to [0−11] is observed for the layer still under tension with Δ a/ a=−3.28×10 −3. The best surface morphology and no misfit dislocations are observed for the slightly compressed layer with Δ a/ a=+9.42×10 −4. With increased compression in the layers, we observed at first the creation of large (probably metal) precipitates and then the formation of a misfit dislocation net. The third feature observed on the surface of ordered layers is the presence of hillocks. Their density, shape and orientation depend on lattice mismatch.