Vertical barrier layer formation during selective MBE growth of InGaAs ridge quantum wires on InP patterned substrates

Transmission electron microscope (TEM) observations and energy dispersive X-ray (EDX) analyses were carried out to investigate the microscopic structure and local variation of alloy composition in InGaAs/InAlAs ridge quantum wires (QWRs) grown by selective molecular beam epitaxy (MBE) on patterned InP substrates. In the QWR structure, formation of the vertical barrier layer having a width of 5–15 nm, which bisects whole InGaAs/InAlAs QWR structure including the QWR itself, was observed for the first time. Particularly, marked reduction of In composition down to xIn=0.45 was observed for the InGaAs layer grown at 500°C. The formation of the vertical barrier layer and temperature dependence of its composition can be explained in terms of a curvature-induced capillarity and a free energy of alloy mixing competing with the adatom diffusion effect.