STRUCTURAL-ANALYSIS OF ALGAAS QUANTUM WIRES ON VICINAL (110)GAAS BY TRANSMISSION ELECTRON-MICROSCOPY AND ENERGY-DISPERSIVE X-RAY SPECTROSCOPY

Giant step structures consisting of coherently aligned multi-atomic steps were naturally formed during the molecular beam epitaxy growth of Al0.5Ga0.5As/GaAs superlattices (SLs) on vicinal (11O)GaAs surfaces misoriented 6 degrees toward (111)A. The growth of AlAs/AlxGa1-xAs/AlAs quantum wells (QWs) on the giant step structures realized Alx0Ga1-As-x0(x(0) < x) quantum wires (QWRs). We studied the giant step structures and the QWRs by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX). TEM observations revealed that the QWRs were formed at the step edges. The cross sections of the QWRs were as small as 10 nm x 20 nm and the lateral distances between them were about 0.15 mu m. We clarified the roles of the SLs to form the coherent giant step structures. From EDX analysis, it was estimated that the AlAs composition in the Al0.5Ga0.5As layers varied from 0.5 (terrace) to 0.41 (step edge). In the AlAs/AlxGa1-xAs/AlAs QWs, the AlAs compositional modulation and the confinement by the AlAs barriers led to the embedded Al(x0)Ga1(-x0)As regions. These results supported the existence of the Alx0Ga1x0As QWRs on the giant step structures.