Self-assembled vertically stacked InAs quantum dots

Abstract

In quantum dots (QDs) three-dimensional confinement of carriers lead to energy level discreteness to exhibit a rich spectrum of phenomena including quantum confinement, exchange splittings, Coulomb blockade, and multiexciton transitions. The 5-period vertically stacked samples with the size-controlled growth were grown by molecular-beam epitaxy (MBE) with solid sources of Al, Ga, In, and As in non-cracking K-cell. Measurements by reflection high-energy electron diffraction (RHEED), atomic force microscopy (AFM), and photoluminescence (PL) showed that the vertically stacked QDs was well-distributed, which can make the vertically stacked InAs QDs to exhibit the effects of the strong quantum confinement and coupling. The quantum dot, the behavior of which is to capture and emit carriers like a giant trap, is studied using a deep level transient spectroscopy (DLTS) technique, too. The electrons and holes in the QDs are respectively emitted from the relevant energy levels to the conduction and valence bands of the barrier layer with increasing measurement temperature, and the thermal emission energies from the QDs are related to their discrete energy levels. One of the attractive features of vertically stacked InAs/AlGaAs quantum dots, which were buried in AlGaAs high potential barrier and spacer epilayer, exhibits an unknown macroscopic quantum phenomenon (i.e., phase-change splitting of the ground state). In the vertically aligned QDs, due to many-body effect and quantum-mechanical renormalization, the electron ground state splits into series of peaks of which the intensity gradually, systematically decreases to redshift direction with a wavelength constant.