DIRECT EVIDENCE OF LATERAL BANDGAP PATTERNING ON STEPPED STRUCTURES GROWN ON NONPLANAR, VICINAL GAAS-SURFACES BY CATHODOLUMINESCENCE INVESTIGATIONS

A novel technique for lateral bandgap patterning on non-planar GaAs substrates is introduced. When a grating is lithographically etched on a vicinal (100) GaAs substrate prior to organometallic chemical vapor deposition (OMCVD), growth results in a regular saw-tooth-type surface morphology consisting of macroscopic steps. These steps expose two distinct crystallographic orientations to the gas phase, i.e. (100) and (111)A. In this paper, we demonstrate that it is possible to take advantage of the selective deposition of reactants from the gas phase onto the two crystallographic facets to pattern the thickness and the corresponding effective bandgap of a quantum well. Spatially and spectrally resolved cathodoluminescence was employed to image directly the bandgap patterning, which was found to be in good agreement with transmission electron microscopy data on the structures. The ability to control the bandgap patterning with growth conditions is discussed. Finally, this study, which was first performed with 3.5-mu-m period gratings, was extended to submicron gratings where the step height become small enough to be in the range where confinement effects in two dimensions can be anticipated. This demonstrates that non-planar vicinal substrates can be used to grow lateral arrays of quantum wires by OMCVD.