Long-Wavelength Photoluminescence from Stacked Layers of High-Quality Type-II GaSb/GaAs Quantum Rings

Abstract

We report the successful molecular-beam epitaxial growth of 10 stacked layers of GaSb/GaAs quantum rings using a new procedure. Exact control of the arsenic flux during capping helps to reduce the strong group-V As−Sb exchange reactions, enabling the rings to be capped at the same growth temperature (480 °C) without dissolution. X-ray diffraction and transmission electron microscopy indicate excellent structural quality and uniformity with no threading dislocations. This is due to the reduction in the average strain through the quantum-ring formation. The total ring density in the stacks is 1 × 10 11 cm −2 . An unusually long-wavelength quantum-ring photoluminescence peak of 1.3 μm is observed at low temperature, which is attributed to a reduction in the quantum-ring charging due to lower unintentional p-doping in the GaAs cap layer. The impact that this effect will have on future device designs in solar cells and lasers is also discussed.

Blueshifts of the emission energy in type-II quantum dot and quantum ring nanostructures

“…These holes are believed to originate from unintentional background doping and act to increase the ground-state transition energy compared with an uncharged dot. Sample J has the lowest E 0 value reported for any GaSb/GaAs QD/QR sample 37 and, during growth, this sample was exposed to high temperatures for the longest time, due to the hot GaAs cap temperature and 10 layers of QR growth. It has been shown that higher temperature MBE growth of GaAs decreases the incorporation of unintentional p-dopants.…”

Photoluminescence studies of individual and few GaSb/GaAs quantum rings

“…For light generation purposes, however, the reduction in electron-hole overlap could be detrimental to operating performance. Fabrication of GaSb/GaAs nanostructures by molecular beam epitaxy (MBE) has been shown to result in the formation of nano-rings, [8][9][10] rather than dots, under specific growth conditions. GaSb quantum rings [ Fig.…”

“…GaSb quantum rings [ Fig. 1(a)] have recently been studied in bulk optical measurements, [9][10][11][12] and found to have some surprising optical properties. Cross-sectional scanning tunnelling microscopy (x-STM) has revealed that the ring geometry can confine the electron's wavefunction in its centre, 13 as illustrated in the band diagram in Fig.…”

The structural, electronic and optical properties of GaSb/GaAs nanostructures for charge-based memory

“…Indeed, the growth of defect-free 10-fold stacks of GaSb/GaAs QRs has recently been demonstrated. 40 The disadvantage of QRs (compared to QDs) is that the reduction in volume due to their geometry increases the capacitive charging energy, and hence the amount of charge that can be stored: here we report a charging energy of 24 meV for MBE-grown GaSb QRs compared to 13 meV for GaAsSb QDs grown by MOCVD 17,41 . However, given that we are now considering GaSb nanostructures as a basis for SV-RAM, which implies a single bit per cell (programming of multi-bit cells is slow), it may be that only a few holes need to be stored, in which case capacitive charging energy becomes less important.…”