Self-Ordering Mechanism of Quantum Wires Grown on Nonplanar Substrates

The self-ordering mechanism of GaAs/AlGaAs quantum wires grown by MOCVD on V-grooved substrates was studied using cross-sectional transmission electron microscopy. Structures with barriers composed of different AlGaAs alloys as well as short period AlGaAs/GaAs superlattices were investigated for different growth temperatures. The boundaries of these crescent shaped wires can be approximated by hyperbolic profiles. The radius of curvature at the bottom of the grooves increases with increasing growth temperature and decreases with increasing Al mole fraction in the AlGaAs barriers. Deposition of the GaAs wire induces a linear increase of the radius, while subsequent deposition of AlGaAs barriers leads to exponential recovery to its self-limiting value. The self limiting nature of the growth allows the reproducible formation of wires with dimensions in the 10 nm range and less than +/-5% variations in shape. Vertically stacked quantum wire arrays formed in this way show quasi-one-dimensional subband structure with 40-50 meV subband separation and strong polarization anisotropy in photoluminescence excitation spectra.