Abstract

Quantum-wire photonic structures in which active electrons occupy only the lowest quantum state of the wire require that wire widths be smaller than those obtainable by currently available lithographic techniques. An alternative approach to obtain the requisitely small dimensions for quantum-wire widths is to use the periodicity provided by atomic steps on a slightly off-axis crystal surface (i.e., the steps on a crystal surface misoriented by a small angle with respect to a principal crystal axis) as a basis for small lateral structures. Microstructures with such lateral compositional features have recently been produced by alternate fractional monolayer epitaxy on atomically stepped surfaces. The structures, which consist of superlattices, tilted or normal with respect to the crystal surface, are produced by depositing alternately half-monolayer coverages of GaAs and AlAs by either molecular-beam epitaxy or metal organic chemical vapor deposition. When enclosed between barrier layers grown before and after the tilted superlattice, the superlattice becomes an array of quantum wires. The tilt angle of the superlattice and the uniformity of the superlattice period are determined by flux exposures and surface smoothness and are sensitively dependent on growth conditions. In situ electron diffraction, postgrowth examination of cross sections by transmission electron microscopy, and observation of superlattice surfaces by atomic force microscopy after oxidation and etching will be presented. These studies permit us to assess the grown structures and to correlate their properties with observed optical properties.

© 1990 Optical Society of America