AlSb Quantum Dot Research Articles

Colloidal Aluminum Antimonide Quantum Dots

AlSb is a less studied member of the III–V semiconductor family, and herein, we report the colloidal synthesis of AlSb quantum dots (QDs) for the first time. Different sizes of colloidal AlSb QDs (5 to 9 nm) were produced by the controlled reaction of AlCl3 and Sb[N(Si(Me)3)2]3 in the presence of superhydride. These colloidal AlSb quantum dots showed excitonic transitions in the UV-A region and a tunable band-edge emission (quantum yield of up to 18%) in the blue spectral range. Among all III–V quantum dots, these quantum dots show the brightest core emission in the blue spectral region.

Structural and optical characterization of GaSb on Si (001) grown by Molecular Beam Epitaxy

GaSb epilayers were grown on Si (001) using molecular beam epitaxy via AlSb quantum dots as an interfacial misfit (IMF) array between the Si substrates and GaSb epilayers. The effect of IMF array thickness, growth temperature and post annealing on the surface morphology, structural and optical properties of the GaSb on Si were investigated. Among five different IMF array thicknesses (5, 10, 20, 40 and 80 ML) that were used in this study, the best result was obtained from the sample with a 20 ML AlSb IMF array. Additionally, it was found that although the full width at half maximum (FWHM) and threading dislocation (TD) densities obtained from high resolution x-ray diffraction curves can be improved by increasing the growth temperature, a decrease in the photoluminescence (PL) signal and an increase in the surface roughness (RMS) emerged. On the other hand, the results indicate that by applying post annealing the GaSb epilayer crystal quality can be improved in terms of FWHM, TD density, PL signal or RMS depending on the post annealing temperature. By applying post annealing at 570 °C for 30 min we achieve a FWHM value of 260 arcsec for a 1 μm thick GaSb epilayer on Si (001) and improve the PL signal intensity without worsening the RMS value.

Growth of GaSb and AlSb quantum dots on high-index GaAs substrates

We investigate the growth of GaSb and AlSb quantum dots (QDs) on high-index GaAs substrates at various substrate temperatures (Ts). The GaSb QD density on GaAs(311)A is about 1.5–2 times larger than that on GaAs(100) substrates. Small and dense AlSb QDs are formed by AlSb deposition on GaAs(311)A substrates at relatively high temperatures (Ts ≥ 430 °C) with QD densities as high as 29 × 1010 cm−2. In contrast, no QDs are observed for low-temperature AlSb deposition (Ts ∼ 410 °C). In contrast to InAs QDs, GaSb and AlSb QDs are easily formed even on GaAs(111)A surfaces. We use a rate equation to analyze the experimental data and discuss QD density and size and their Ts dependences.

GaAs Based InAs/GaSb Superlattice Short Wavelength Infrared Detectors Grown by Molecular Beam Epitaxy

InAs/GaSb superlattice (SL) short wavelength infrared photoconduction detectors are grown by molecular beam epitaxy on GaAs(001) semi-insulating substrates. An interfacial misfit mode AlSb quantum dot layer and a thick GaSb layer are grown as buffer layers. The detectors containing a 200-period 2 ML/8 ML InAs/GaSb SL active layer are fabricated with a pixel area of 800×800 μm2 without using passivation or antireflection coatings. Corresponding to the 50% cutoff wavelengths of 2.05 μm at 77 K and 2.25 μm at 300 K, the peak detectivities of the detectors are 4 × 109 cm·Hz1/2/W at 77 K and 2 × 108 cm·Hz1/2/W at 300 K, respectively.

Comparison of short period InAs/GaSb superlattices on GaSb and GaAs substrates

Type II superlattices (SLs) short period InAs(4ML)/GaSb(8ML) were grown by molecular-beam epitaxy on lattice-mismatched GaAs substrates and on GaSb substrates. A smooth GaSb epilayer was formed on GaAs substrates by inserting mulit-buffer layers including an interfacial misfit mode AlSb quantum dot layer and AlSb/GaSb superlattices smooth layer. SLs grown on GaAs substrates (GaAs-based SLs) showed well-resolved satellite peaks in XRD. GaSb-based SLs with better structural quality and smoother surface showed strong photoluminescence at 2.55 μm with a full width at half maximum (FWHM) of 20 meV, narrower than 31 meV of GaAs-based SLs. Inferior optical absorption of GaAs-based SL was observed in the range of 2–3 μm. Photoresponse of GaSb-based SLs showed the cut-off wavelength at 2.6 μm.

Growth mechanisms and structural properties of self-assembled AlSb quantum dots on a Si(1 0 0) substrate

The growth of AlSb quantum dots (QDs) on Si(1 0 0) substrates by molecular beam epitaxy (MBE) was investigated using reflection high-energy electron diffraction and atomic force microscopy (AFM), with varying the growth rate and Sb 4/Al flux ratio. The thickness of the AlSb wetting layer (WL) was found to be independent of the Sb 4/Al flux ratio and AlSb growth rate. At 540 °C, the thickness of the AlSb WL was about 0.3 monolayer regardless of the growth rate and flux ratio. AFM images showed that the size and density of AlSb QDs strongly depended on the growth rate and flux ratio. These results provide important information on the formation process of AlSb QDs on Si substrates.

High quality AlSb bulk material on Si substrates using a monolithic self-assembled quantum dot nucleation layer

We report and characterize the growth of defect-free AlSb bulk material on Si (001) substrates using a monolithic self-assembled AlSb quantum dot (QD) nucleation layer. During the first few monolayers of AlSb growth on Si, highly crystalline QDs form. With continued deposition, the islands coalesce into a planar material with no detectable defects. The QD nucleation layer facilitates a completely relaxed AlSb within ∼100 ML of deposition according to x-ray diffraction. We attribute the success of AlSb growth on Si to both the large AlSb∕Si lattice mismatch (Δa0∕a0=13.5%) in combination with the strong AlSb atomic bond. We also demonstrate room temperature photoluminescence from an InGaSb QW grown on the AlSb bulk layer.

Room-temperature optically-pumped GaSb quantum well based VCSEL monolithically grown on Si (100) substrate

Room-temperature optically-pumped In/sub 0.2/Ga/sub 0.8/Sb quantum well lasers on Si are reported. The defect-free monolithic epistructure growth on a Si(100) substrate is initiated by an AlSb quantum dot nucleation layer followed by an AlSb/GaSb superlattice. The 13% mismatch between the AlSb and Si lattice is accommodated by misfit dislocations and associated crystallographic undulations in the AlSb buffer. The nucleation layer and buffer are characterised by atomic force microscopy and transmission electron microscopy. The lasing spectrum is characterised as a function of pump power and polarisation analysis.

Photoluminescence studies of self-assembled InSb, GaSb, and AlSb quantum dot heterostructures

Photoluminescence (PL) spectroscopy has been performed on a set of self-assembled InSb, GaSb, and AlSb quantum dot (QD) heterostructures grown on GaAs. Strong emission bands with peak energies near 1.15 eV and linewidths of ∼80 meV are observed at 1.6 K from 3 monolayer (ML) InSb and GaSb QDs capped with GaAs. The PL from a capped 4 ML AlSb QD sample is weaker with peak energy at 1.26 eV. The PL bands from these Sb-based QD samples shift to lower energy by 20–50 meV with decreasing excitation power density. This behavior suggests a type II band lineup. Support for this assignment, with electrons in the GaAs and holes in the (In,Ga,Al)Sb QDs, is found from the observed shift of GaSb QD emission to higher energies when the GaAs barrier layers are replaced by Al0.1Ga0.9As.

Phonons in self-assembled (In,Ga,Al)Sb quantum dots

Quantum dots of InSb, GaSb, and AlSb were grown on GaAs substrates by molecular beam epitaxy and characterized by atomic force microscopy and Raman spectroscopy. There is a clear correlation between the observation of quantum dots by atomic force microscopy and a phonon mode at an energy a few wavenumbers below the longitudinal optic phonon energy for thick (In,Ga,Al)Sb layers. In the case of nominally AlSb quantum dots, a two-mode behavior is observed and attributed to the segregation of Ga into the AlSb during growth.