Bo Xu

Electron Resonant Tunneling Through InAs ∕ GaAs Quantum Dots Embedded in a Schottky Diode with an AlAs Insertion Layer

Molecular beam epitaxy was employed to manufacture self-assembled InAs/GaAs quantum dot Schottky resonant tunneling diodes. By virtue of a thin AlAs insertion barrier, the thermal current was effectively reduced and electron resonant tunneling through quantum dots under both forward and reverse biased conditions was observed at relatively high temperature of 77 K. The ground states of quantum dots were found to be at similar to 0.19 eV below the conduction band of GaAs matrix. The theoretical computations were in conformity with experimental data. (c) 2006 The Electrochemical Society.

Room-temperature observation of electron resonant tunneling through InAs/AlAs quantum dots

Molecular beam epitaxy is employed to manufacture self-assembled InAs/AlAs quantum-dot resonant tunneling diodes. The resonant tunneling current is superimposed on the thermal current, and together they make up the total electron transport in devices. Steps in current-voltage characteristics and peaks in capacitance-voltage characteristics are explained as electron resonant tunneling via quantum dots at 77 or 300 K, and thus resonant tunneling is observed at room temperature in III-V quantum-dot materials. Hysteresis loops in the curves are attributed to hot electron injection/emission process of quantum dots, which indicates the concomitant charging/discharging effect. (c) 2006 The Electrochemical Society.

Carrier tunneling effects on the temperature dependent photoluminescence of InAs/GaAs quantum dot: Simulation and experiment

Considering the direct quantum tunneling of carrier, we propose a new carrier rate equation model to simulate the temperature dependent photoluminescence (TDPL) of InAs/GaAs quantum dots (QDs). The TDPL showed abnormal variations: the peak rapid redshift, linewidth shrinkage, and thermal activation energy all decreased with increasing tunneling strength. A criterion, which could be used to evaluate the tunneling strength, has been developed. That is, smaller tunneling strength coefficient α indicates higher carrier tunneling strength. Meanwhile, the criterion is also demonstrated via comparative experimental results of InAs QDs grown on different patterned GaAs substrates. It is found that, to some extent, the tunneling strength would be enhanced by decreasing the dot-dot distance for closely arranged QDs ensembles.

Quantum-dot growth simulation on periodic stress of substrate

InAs quantum dots (QDs) are grown on the cleaved edge of an In(x)Ga(1-x)AsGaAs supperlattice experimentally and a good linear alignment of these QDs on the surface of an In(x)Ga(1-x)As layer has been realized. The modulation effects of periodic strain on the substrate are investigated theoretically using a kinetic Monte Carlo method. Our results show that a good alignment of QDs can be achieved when the strain energy reaches 2% of the atomic binding energy. The simulation results are in excellent qualitative agreement with our experiments.

Temperature dependent photoluminescence of an In(Ga)As/GaAs quantum dot system with different areal density

We have systematically studied the temperature dependent photoluminescence of a self-assembled In(Ga)As/GaAs quantum dot (QD) system with different areal densities from similar to 10(9) to similar to 10(11) cm(-2). Different carrier channels are revealed experimentally and confirmed theoretically via a modified carrier equation model considering a new carrier transfer channel, i.e. continuum states ( CS). The wetting layer is demonstrated to be the carrier quenching channel for the low-density QDs but the carrier transfer channel for the high-density QDs. In particular, for the InGaAs/GaAs QDs with a medium density of similar to 10(10) cm(-2), the CS is verified to be an additional carrier transfer channel in the low temperature regime of 10-60 K, which is studied in detail via our models. The possible carrier channels that act on different temperature regimes are further discussed, and it is demonstrated that density is not a crucial factor in determining the carrier lateral coupling strength.

Optical identification of electronic state levels of an asymmetric InAs/InGaAs/GaAs dot-in-well structure

AbstractWe have studied the electronic state levels of an asymmetric InAs/InGaAs/GaAs dot-in-well structure, i.e., with an In0.15Ga0.85As quantum well (QW) as capping layer above InAs quantum dots (QDs), via temperature-dependent photoluminescence, photo-modulated reflectance, and rapid thermal annealing (RTA) treatments. It is shown that the carrier transfer via wetting layer (WL) is impeded according to the results of temperature dependent peak energy and line width variation of both the ground states (GS) and excited states (ES) of QDs. The quenching of integrated intensity is ascribed to the thermal escape of electron from the dots to the complex In0.15Ga0.85As QW + InAs WL structure. Additionally, as the RTA temperature increases, the peak of PL blue shifts and the full width at half maximum shrinks. Especially, the intensity ratio of GS to ES reaches the maximum when the energy difference approaches the energy of one or two LO phonon(s) of InAs bulk material, which could be explained by phonon-enhanced inter-sublevels carrier relaxation in such asymmetric dot-in-well structure.nPACS: 73.63.Kv; 73.61.Ey; 78.67.Hc; 81.16.Dn

Formation of AsxSb1-x mixing interfaces in InAs/GaSb superlattices grown by metalorganic chemical vapor deposition

Metalorganic chemical vapor deposition growth of InAs/GaSb superlattices is reported using an AsxSb1?x plane that connects the InAs and GaSb layers to compensate the tensile strain introduced by the InAs layers. The effects of gas switching sequences for growing the AsxSb1?x planes on the interface structure and crystalline quality of InAs/GaSb superlattices were investigated by Raman scattering spectroscopy and X-ray diffraction. It is found that uniform interfaces and high-quality superlattice can be obtained by growing the AsxSb1?x planes through the exchange interaction of As and Sb atoms at the surfaces of InAs or GaSb layers.

Metalorganic chemical vapor deposition growth of InAs/GaSb type II superlattices with controllable AsxSb1-x interfaces

InAs/GaSb type II superlattices were grown on (100) GaSb substrates by metalorganic chemical vapor deposition (MOCVD). A plane of mixed As and Sb atoms connecting the InAs and GaSb layers was introduced to compensate the tensile strain created by the InAs layer in the SL. Characterizations of the samples by atomic force microscopy and high-resolution X-ray diffraction demonstrate flat surface morphology and good crystalline quality. The lattice mismatch of approximately 0.18% between the SL and GaSb substrate is small compared to the MOCVD-grown supperlattice samples reported to date in the literature. Considerable optical absorption in 2- to 8-μm infrared region has been realized.PACS: 78.67.Pt; 81.15.Gh; 63.22.Np; 81.05.Ea

Effects of ultra-low Al alloying In(Al) As layer on the formation and evolution of InAs/GaAs quantum dots

We have introduced ultra-low Al composition at the two-dimensional to three-dimensional transition stage of InAs/GaAs quantum dots (QDs) formation. Two main effects of AlAs on the QDs are revealed: one is to lower the nucleation barrier so as to reduce the critical nucleation thickness of QDs, which is demonstrated by a surface kinetic nucleation model. The other is to facilitate the In atoms migration from wetting layer (WL) to QDs, which holds some signatures such as both increased QDs density and size with increasing AlAs composition, as well as the peak energy red-shift of photoluminescence spectra. The enhanced In atoms migration from WL to QDs is further confirmed via photo-modulated reflectance experiments and energy band calculation, which both demonstrate the reduction of effective WL thickness after AlAs insertion. The observed effects of AlAs on QDs formation and growth evolution could be explained by the Al-alloying effects of InAs wetting layer.

Scanning electron microscopy observation of in-device InAs/AlAs quantum dots by selective etching of capping layers

Self-assembled InAs/AlAs quantum dots embedded in a resonant tunneling diode device structure are grown by molecular beam epitaxy. Through the selective etching in a C6H8O7 center dot H2O-K3C6H5O7 center dot H2O-H2O2 buffer solution, 310 nm GaAs capping layers are removed and the InAs/AlAs quantum dots are observed by field-emission scanning electron microscopy. It is shown that as-fabricated quantum dots have a diameter of several tens of nanometers and a density of 10(10) cm(-2) order. The images taken by this means are comparable or slightly better than those of transmission electron microscopy. The undercut of the InAs/AlAs layer near the edges of mesas is detected and that verifies the reliability of the quantum dot images. The inhomogeneous oxidation of the upper AlAs barrier in H2O2 is also observed. By comparing the morphologies of the mesa edge adjacent regions and the rest areas of the sample, it is concluded that the physicochemical reaction introduced in this letter is diffusion limited.