High-quality InAs Quantum Dots Research Articles

Impact of low-temperature cover layer growth of InAs/GaAs quantum dots on their optical properties

The effect of low-temperature InGaAs/GaAs cover layer growth of InAs quantum dots on their optical and structural properties was investigated. Photoluminescence intensity depended heavily on the growth temperature and thickness of the low-temperature cover layer and decreased as the number of dislocations formed directly above InAs quantum dots increased. These dislocations are formed at the initial stage of high-temperature GaAs growth, originating from pits that remain on the surface after the growth of the low-temperature cover layer and subsequent annealing. To ensure a high-quality InAs quantum dot structure free from dislocations, it is important to obtain a highly flat surface with suppressed pits after low-temperature cover layer growth and subsequent annealing.

Optical properties of bimodally distributed InAs quantum dots grown on digital AlAs0.56Sb0.44 matrix for use in intermediate band solar cells

High-quality InAs quantum dots (QDs) with nominal thicknesses of 5.0–8.0 monolayers were grown on a digital AlAs0.56Sb0.44 matrix lattice-matched to the InP(001) substrate. All QDs showed bimodal size distribution, and their optical properties were investigated by photoluminescence (PL) and time-resolved PL measurements. Power dependent PL exhibited a linear relationship between the peak energy and the cube root of the excitation power for both the small QD family (SQDF) and the large QD family (LQDF), which is attributed to the type-II transition. The PL intensity, peak energy, and carrier lifetime of SQDF and LQDF showed very sensitive at high temperature. Above 125 K, the PL intensity ratio increased continuously between LQDF and SQDF, the peak energy shifted anomalously in SQDF, and the longer carrier radiative lifetime (≥3.0 ns at 77 K) reduced rapidly in SQDF and slowly in LQDF. These results are ascribed to thermally activated carrier escape from SQDF into the wetting layer, which then relaxed into LQDF with low-localized energy states.

Temperature-Insensitive High-Speed Directly Modulated 1.55-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math> </inline-formula> Quantum Dot Lasers

Modulation properties and temperature stability of short cavity ridge waveguide lasers based on high-quality InAs quantum dots exhibiting a total modal gain of ~90 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> are reported. The 338-μm-long lasers show a threshold current of 20 mA at room temperature and an output powers of up to 36 mW. A maximum small signal modulation bandwidth of 15 GHz was obtained at 14 °C, which degrades to 13 GHz at 60 °C and 8 GHz at 80 °C. Digital modulation at 25 Gb/s between 15 °C and 50 °C was obtained with clear open eyes under constant drive conditions (dc and ac). The maximum data rates of 32 and 35 Gb/s were obtained for 338- and 230-μm-long lasers, respectively, at 14 °C.

Ultra-compact wavelength-tunable quantum-dot laser with silicon-photonics double ring filter

Compact, wavelength-tunable light sources are desired for the enhancement of information communication technology and bio-imaging applications. We propose a compact, wavelength-tunable laser diode with a wide wavelength-tunable range around 1230 nm consisting of a quantum-dot optical amplifier and a silicon photonic tunable filter. High-quality InAs quantum dots grown with the sandwiched sub-nano separator technique were used as the optical gain medium. The wavelength-tunable filter was constructed with ring resonators fabricated using silicon photonics. The single-mode laser oscillation was demonstrated with a 28.5-nm wavelength-tunable range.

High quality InAs quantum dots grown on patterned Si with a GaAs buffer layer

Ordered and dense InAs quantum dots grown on patterned Si(100) with a thin GaAs bufferlayer have been investigated by transmission electron microscopy and electron energy lossspectroscopy. {111} faceted InAs quantum dots with good crystallinity were observed on topof the underlying GaAs buffer layer. It was revealed that the GaAs buffer layer and thelateral expansion of InAs have played key roles in releasing the misfit strain between InAsand Si and suppressing the formation of lattice defects in InAs quantum dots. These resultssuggest a possible pathway for the strain relaxation in the formation of quantumdots.

Synthetic Scheme for High‐Quality InAs Nanocrystals Based on Self‐Focusing and One‐Pot Synthesis of InAs‐Based Core–Shell Nanocrystals

Paint by number: High-quality InAs quantum dots (QDs) for near-IR fluorescence (see picture) were synthesized by exploiting interparticle diffusion and self-focusing instead of using the traditional focusing of size distribution. InAs/CdSe core–shell QDs were grown and analyzed by a technique combining TEM and elemental analysis to determine the sizes and molar extinction coefficients of the extremely small InAs particles.

High Quality InAs Quantum Dots with an In(Ga,Al)AsSb Strain-Reducing Layer for Long Wavelength Photonic Devices

The effects of InGaAsSb and InAlAsSb strain-reducing layers on the optical properties of InAs/GaAs QDs are investigated. With these Sb-containing overgrown layers, InAs QDs exhibit much enhanced photoluminescence efficiency and thermal stability in the wavelength of 1.3 um and above, which is essential for long wavelength photonic devices.

High Quality InAs Quantum Dots with an In(Ga,Al)AsSb Strain-Reducing Layer for Long Wavelength Photonic Devices

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Selective growth of high quality InAs quantum dots in narrow regions using in situ mask

We have succeeded in selective formation of a self-assembled InAs quantum dot (QD) structure in a narrow region. The emission wavelength of the QDs was varied locally by a covered GaInAs layer grown with an in situ mask. This mask can be fitted to the sample holder and removed in an ultra-high-vacuum environment. The selectively grown QDs exhibited high optical quality with a photoluminescence peak at 1.29 μm and linewidth of 24 meV at room temperature. This technique provides greater latitude and design flexibility in fabricating optoelectronic and electronic devices with QD structures.

Self-Formation of High-Density and High-Uniformity InAs Quantum Dots on Sb/GaAs Layers by Molecular Beam Epitaxy

Self-assembled InAs quantum dots (QDs) grown on Sb/GaAs buffer layers by molecular beam epitaxy were investigated to achieve high-density and high-uniformity QDs. The density of InAs QDs on Sb/GaAs layers was markedly higher than that of InAs QDs on conventional GaAs layers. The high-density nucleation of three-dimensional (3D) InAs islands was attributed to the formation of two-dimensional (2D) wirelike structures prior to 3D islanding. QD density was controlled from 3×1010 to 1×1011 cm-2 by changing Sb supply amount. In addition, the density of very large dots due to coalescence increased with increasing Sb supply amount. On Sb (0.6 atomic layers)/GaAs buffer layers, we obtained high-density and high-quality InAs QDs, which revealed a narrow photoluminescence linewidth of about 30–35 meV.

Ordering of high-quality InAs quantum dots on defect-free nanoholes

We demonstrate a promising way for the fabrication of high-quality InAs quantum dot (QD) arrays by combining atomic force microscope (AFM) tip-induced nano-oxidation, atomic-hydrogen etching/cleaning (AHE/C), and droplet epitaxy method. The highly aligned defect-free nanoholes as nucleation sites were fabricated by using AFM tip-induced nano-oxidation and subsequent AHE/C. Using the droplet epitaxy on the artificially patterned nanoholes, we fabricated laterally arrayed InAs QDs with an interdot distance of 100nm. The photoluminescence from the InAs QD arrays showed strong emission at 1.22eV, even though the processed interface directly faced the base of the InAs QDs, indicating that the process can reduce the physical and chemical defects/contaminants at the nanoholes and interface.

Interband transitions and electronic properties of InAs/GaAs quantum dots embedded in AlxGa1−xAs/GaAs modulation-doped heterostructures

Abstract Reflection high-energy electron diffraction, atomic force microscopy, transmission electron microscopy, and double-crystal X-ray curves showed that high-quality InAs quantum dot (QD) arrays inserted into GaAs barriers were embedded in an Al0.3Ga0.7As/GaAs heterostructure. The temperature-dependent photoluminescence (PL) spectra of the InAs/GaAs QDs showed that the exciton peak corresponding interband transition from the ground electronic subband to the ground heavy-hole subband (E1–HH1) was dominantly observed and that the peak position and the full width at half maximum corresponding to the interband transitions of the PL spectrum were dependent on the temperature. The activation energy of the electrons confined in the InAs/GaAs QDs was 115 meV. The electronic subband energy and the energy wave function of the Al0.3Ga0.7As/GaAs heterostructures were calculated by using a self-consistent method. The electronic subband energies in the InAs/GaAs QDs were calculated by using a three-dimensional spatial plane wave method, and the value of the calculated (E1–HH1) transition in the InAs/GaAs QDs was in reasonable agreement with that obtained from the PL measurement.

Characterization of self-assembled InAs quantum dots with InAlAs∕InGaAs strain-reduced layers by photoluminescence spectroscopy

The optoelectronic characteristics of self-assembled InAs quantum dots (QDs) with strain-reduced layers (SRLs) were investigated using photoluminescence (PL) spectroscopy. Various SRLs that combine In0.14Al0.86As and In0.14Ga0.86As with the same total thickness were examined to ascertain their confining effect on carriers in InAs QDs. The emission wavelength is blueshifted as the thickness of InAlAs is increased. The energy separation between the ground state and the first excited state of QDs with InAlAs SRLs greatly exceeds that of QDs with InGaAs SRLs. Atomic force microscopic images and PL spectra of the QD samples demonstrated that high-quality InAs QDs with long emission wavelengths and a large energy separation can be generated by growing a low-temperature, thin InAlAs SRL onto self-assembled QDs.

Near room temperature droplet epitaxy for fabrication of InAs quantum dots

By using the droplet epitaxy method, we succeed in fabricating the InAs quantum dots (QDs) with the spatial density of 4×1010∕cm2 and an average lateral size of 20nm on GaAs (001) at the droplets deposition temperature of 50°C and subsequent annealing process under As4 flux. These QDs shows the intense photoluminescence even at room temperature indicating that high-quality InAs QDs can be fabricated by near room temperature droplets deposition and crystallization process by 400°C in situ annealing.

Growth of uniform InAs quantum dots on InGaAs surface structure modified superlattices on InP

We have developed a matrix layer structure, the InGaAs surface structure modified superlattice, to achieve high quality InAs quantum dots on (100) InP substrates. Formed by periodically repeating the group III- and group V-stabilized InGaAs layers, the InGaAs surface structure modified superlattice offers much greater advantages than the conventional InGaAs matrix layer for the growth of InAs quantum dots, where a thick InAs layer is required for the dot formation. By adjusting the number of period and the layer thickness of the superlattice structure, uniform InAs quantum dots are achieved even using an InAs deposition as thin as 2.5 monolayers. Photoluminescence measurements further verify a uniform size distribution of the achieved quantum dots.

High quality InAs quantum dots covered by InGaAs/GaAs hetero‐capping layer

Self-assembled InAs quantum dots with high performance were fabricated by molecular beam epitaxy via Stranski–Krastanov growth mode and InGaAs/GaAs hetero-capping growth. The size and shape of the dots were modified during the first GaAs capping layer, which plays an important role of a reduction in the inhomogeneous broadening. In particular, when the substrate temperature of the GaAs capping layer was 450 °C, the PL linewidth decreased to less than 20 meV. In order to reduce the residual strain in the InAs QDs and the capping layer, the InGaAs capping layer was additionally grown on the InAs dots covered by the first GaAs capping layer. As a result, the presented InGaAs/GaAs hetero-capping layer induced strong photoluminescence (PL) intensity, narrow PL linewidth and 1.3 μm light emission at room temperature.

Growth of InAs quantum dots on focussed ion beam implanted GaAs(100)

The growth of self-assembled InAs quantum dots on implantation doped GaAs was studied. Be and Si ions were implanted in a combined ion implantation/molecular beam epitaxy process to generate p- and n-type GaAs, respectively. The quality of the InAs quantum dots was investigated by photoluminescence spectroscopy and scanning electron microscopy. By employing an in situ annealing step before re-growth it was possible to fabricate high quality InAs quantum dots on ion doped GaAs for Be doses up to 1.4×10 14 cm −2. The sheet resistance of the Be doped GaAs was as low as 1 kΩ at 300 K and 0.6 kΩ at 4.2 K, respectively. Only for rather low Si doses up to 5×10 13 cm −2 acceptable photoluminescence could be detected. The sheet resistance for these doses was 1 kΩ at 300 K and 1.7 kΩ at 4.2K.