Evolution of self-assembled InAs quantum ring formation

Abstract

The evolution of InAs quantum ring (QR) formation and the corresponding optical properties were investigated by atomic force microscopy (AFM) and photoluminescence (PL) spectroscopy. Just like a nanoscale volcanic eruption, the transformation from quantum dots (QDs) to QRs using the capping and annealing process depends on how much InAs is removed from the center of the dots to the surrounding areas. The final structure was found to depend on the annealing temperature and the cap layer thickness. We have investigated the QR formation at different stages using various growth conditions. The findings provided a clear picture on the mechanism of ring formation. We were able to obtain QRs with various geometries by controlling these growth parameters.

Quantum rings formed in InAs QDs annealing process

“…According to self-confinement effects of QDs, an optimum size value exists in the straininduced self organized growth of QDs. The new QDs can be formed with the further InAs deposition after the QDs reached the optimum size [9]. Thus, the bimodal size distribution QDs were formed, one part with optimum size, the other part without ripening.…”

“…There are mainly two factors resulting in the evolution of QDs and the formation of QRs. One is the effect of annealing temperature [9]; the other is the effect of capping layer thickness [8,9]. On the basis of the strain theory, the effect of the annealing temperature on the evolution process of QDs can be analyzed as follows.…”

GaSb quantum rings grown by metal organic molecular beam epitaxy

“…In Ref. [1][2][3][4][5][6][7], partial cap and annealing with As 2 provides the QRs. However, in our MOMBE case, the partial cap and annealing process does not provide the QRs, only the desorption of the top of the QDs happens.…”

“…According to the research on QDs, QRs have also been well investigated because of their unique shape, symmetry and physics related to a topological singularity. The typical scheme for the fabrication of QRs is the partial capping of QDs and annealing (growth interruption) processes [1][2][3][4][5][6][7] by molecular beam epitaxy (MBE). For example, InAs QDs grown on GaAs substrates are partially capped and then annealed under As 2 atmosphere.…”

Donor impurity states in elliptical quantum rings subjected to a magnetic field

“…The simplest model of the QR is the ideal circle QR (CQR) which has been studied by many groups [12][13][14][15][16][17][18]. However, some authors [19][20][21] have pointed out that the optical properties and electronic states of actual structures are strongly affected by both impurities and geometrical imperfections in the system, and that because imperfections occur in the growth and fabrication processes, an actual quantum ring may be closer to an elliptical QR (EQR) than a CQR.…”