Structural, morphological, and band alignment properties of GaAs/Ge/GaAs heterostructures on (100), (110), and (111)A GaAs substrates

Abstract

Structural, morphological, and band offset properties of GaAs/Ge/GaAs heterostructures grown in situ on (100), (110), and (111)A GaAs substrates using two separate molecular beam epitaxy chambers, connected via vacuum transfer chamber, were investigated. Reflection high energy electron diffraction (RHEED) studies in all cases exhibited a streaky reconstructed surface pattern for Ge. Sharp RHEED patterns from the surface of GaAs on epitaxial Ge/(111)A GaAs and Ge/(110)GaAs demonstrated a superior interface quality than on Ge/(100)GaAs. Atomic force microscopy reveals smooth and uniform morphology with surface roughness of Ge about 0.2–0.3 nm. High-resolution triple axis x-ray rocking curves demonstrate a high-quality Ge epitaxial layer as well as GaAs/Ge/GaAs heterostructures by observing Pendellösung oscillations. Valence band offset, ΔEv, have been derived from x-ray photoelectron spectroscopy (XPS) data on GaAs/Ge/GaAs interfaces for three crystallographic orientations. The ΔEv values for epitaxial GaAs layers grown on Ge and Ge layers grown on (100), (110), and (111)A GaAs substrates are 0.23, 0.26, 0.31 eV (upper GaAs/Ge interface) and 0.42, 0.57, 0.61 eV (bottom Ge/GaAs interface), respectively. Using XPS data obtained from these heterostructures, variations in band discontinuities related to the crystallographic orientation have been observed and established a band offset relation of ΔEV(111)Ga>ΔEV(110)>ΔEV(100)As in both upper and lower interfaces.