Control of InAs∕GaAs quantum dot density and alignment using modified buffer layers

Abstract

We have investigated the patterning effects of GaAs buffers during the growth of InAs∕GaAs quantum dot (QD) superlattices (SLs). One-, five-, and ten-period QD SLs were deposited on GaAs buffer layers grown at 580°C and/or 500°C, with various annealing steps. High-temperature-grown buffers consist of relatively flat surfaces, while low-temperature-grown buffers contain “mound-like” features elongated along the [11¯0] direction. Isotropic distributions of QDs are observed for QD growth on flat buffers. Interestingly, QD alignment along the [11¯0] direction is observed for QD SL growth on buffers containing mounds. This anisotropic QD alignment is enhanced as the number of QD SLs increases and is dependent on the density of mounds. For flat buffers, the density of QDs decreases with stacking, consistent with the model of Tersoff [J. Tersoff, C. Teichert, and M. G. Lagally, Phys. Rev. Lett. 76, 1675 (1996)]. However, for buffers containing mounds, this effect is compensated by an increase in QD density. We propose a mechanism for QD nucleation, based upon buffer layer patterning leading to an undulated In-enriched GaAs spacer layer following the initial layer of QDs.