Large terrace formation and modulated electronic states in (110) GaAs quantum wells

Interface roughness and local electronic states formed in GaAs quantum wells (QWs) grown on (110) cleaved surfaces were characterized by high-resolution microscopic photoluminescence (micro-PL) imaging and spectroscopy assisted by a solid immersion lens. From macroscopic PL spectra and micro-PL images, it was found that well width fluctuation of about 0.6 to 0.7 nm, which corresponds to 3 to 3.5 monolayers (ML), with laterally sub-$\mu \mathrm{m}$- to $\mu \mathrm{m}$-scale ML terraces existed in the (110) GaAs/AlAs QWs, and this was also supported by the results of atomic force microscopy measurements performed on the (110) GaAs surface. In high-resolution solid-immersion micro-PL spectroscopy, sharp PL peaks were observed at low excitation power and their temperature and excitation power dependence showed a localized quantum-dot-like (QD-like) nature in the (110) GaAs QWs. The spatial and spectral distribution of these sharp PL peaks indicated that the localized QD-like states were formed by short-scale roughness in the bottom GaAs-on-AlAs interface of the (110) GaAs/AlAs QWs on each $\mu \mathrm{m}$-scale large ML terrace in the top AlAs-on-GaAs interface.