InGaAs quantum disk: fabrication via self-organization and spectroscopies

Abstract

We have examined the spontaneous rearrangement of a strained InGaAs/AlGaAs heterostructure, on a (311)B, substrate into naturally ordered array of InGaAs disks automatically buried in Al-rich alloy. Unlike nano-islands formed via Stranski-Krastanov mechanism, it serves as a strong tendency to align themselves. We have stressed important interplay of islanding of the material with lattice mismatch, atomic diffusion across the interface between unstrained and strained materials, lateral mass transport, and development of the surface into low index surfaces with low surface energies: all these seek to lower the total energy. Because of the damageless fabrication, these quantum disks showed excellent optical properties, which facilitated single-dot spectroscopy. Such spectroscopy revealed that lateral together with vertical confinement of exciton motion discretizes the exciton density-of-states resulting in sharp and distinct photo emission/absorption spectra despite their mesoscopic confinement. These characterize optical properties which are specific only to zero-dimensional system, thereby proving quantum dot characteristic. As for future device application, we undertook an attempt to artificially position the self-organized structure more accurately by periodic seeding on the virgin (311)B substrate. The results show that it is feasible to further improve the ordering of the array of quantum disks.