Optical properties of In/sub 0.8/Ga/sub 0.2/As self-assembled quantum dots on SiO/sub 2/-patterned [001] vicinal GaAs substrates
In this study, we investigated the optical properties of InGaAs SAQD on SiO/sub 2/-patterned exact and 5 /spl deg/-off [001] GaAs substrates. Also, we compared the discrete nature of the density of states in SAQDs for both starting materials.
Fabrication of wirelike InAs quantum dots on 2°-off GaAs (100) substrates by changing the thickness of the InAs layer
Wirelike InAs quatum dots (QDs) grown on 2°-off (100) GaAs substrates by changing the thickness of the InAs layer were successfully fabricated. The sizes of the InAs QDs along the step lines increased with increasing the thickness of the InAs layer, and their increases were attributed to transform of the InAs QDs into the wirelike InAs QDs. The optimal thicknesses of the InAs layers for the wirelike QDs and the interval of the wirelike QDs were significantly affected by the terrace width resulting from the bunching effect due to the thickness variations of the GaAs buffer layers grown on 2°-off (100) GaAs substrates. These results indicate that these wirelike InAs QDs are useful for applications in nanoelectronic devices, such as wrap gate single electron transistors.
Multiphonon-assisted tunneling through deep levels: A rapid energy-relaxation mechanism in nonideal quantum-dot heterostructures.
The presence of a deep-level trap coupled to a quantum-dot heterostructure is shown to provide a rapid energy-relaxation pathway through which electrons may thermalize. A capture process is considered whereby a free conduction-band electron is captured into the ground conduction-band state of a quantum dot by multiphonon-assisted tunneling through the trap. As an example calculation, transition rates for a 5 nm radius ${\mathrm{In}}_{0.5}$${\mathrm{Ga}}_{0.5}$As/GaAs quantum dot coupled to the defect M1 are calculated as a function of separation between the quantum dot and the deep level. For separations less than \ensuremath{\approxeq}10 nm these rates are found to be in excess of ${10}^{10}$ ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$ at 4.2 K. The result suggests that the presence of point defects may serve to enhance the luminescence efficiency of quantum-dot material. The physical situation described in this paper could only arise if the spatial distribution of defects were strongly correlated with that of the quantum-dot structures, e.g., through formation of interface states or point defects as a consequence of the growth process. With this caveat, the proposed mechanism may possibly explain the failure to observe a significant phonon bottleneck effect in recent work on ${\mathrm{In}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ga}}_{\mathit{x}}$As quantum-dot structures [e.g., Appl. Phys. Lett. 64, 2815 (1994)].