InAsSb Quantum Dots Research Articles

Nonequilibrium interplay between Andreev bound states and Kondo effect

Andreev bound states (ABSs), as a close resemblance and a prototype of Majorana bound states, attracted particular interest in semiconductor-superconductor hybrids. So far, ABSs were explored as an equilibrium behavior employing tunneling spectroscopy. Under nonequilibrium, theorists did predict that the local density of states (DOS) of the ABSs split and broaden. We investigated an InAsSb quantum dot coupled to two superconductors to explore the nonequilibrium dynamics of ABSs and their interplay with Kondo effect. Through tunneling spectroscopy, we demonstrated a full picture of the nonequilibrium dynamic splitting and broadening of ABSs, which interplays with the nonequilibrium Kondo DOS. Since the observed features might mimic those in the normal superconductor-topological superconductor or Majorana junctions, our discovery could provide a relevant comparison to benchmark the Majorana signal in future experiments.

Near thresholdless laser operation at room temperature

The development of a thresholdless laser operating above room temperature (RT) is key for the future replacement of electronics with photonic integrated circuits, enabling an increase of several orders of magnitude in computing speeds. Recently, thresholdless lasing characteristics at low temperature (4 K) have been demonstrated. However, for practical applications, RT laser emission becomes necessary. Here we report experimental evidence that is compatible with a laser based on InAsSb quantum dots embedded in a photonic-crystal microcavity that exhibits an ultralow-power threshold (860 nW) and high efficiency (β =0.85), thus operating in the near-thresholdless regime at RT in the 1.3 μm spectral window. The results open up a wide range of opportunities for RT applications of ultralow threshold lasers, such as integrated photonic circuitry or high sensitivity biosensors.

Fabrication of high quality factor GaAs/InAsSb photonic crystal microcavities by inductively coupled plasma etching and fast wet etching

The authors demonstrate high quality factor GaAs-based L9 photonic crystal microcavities (PCMs) with embedded InAsSb quantum dots with emission in 1.3 μm at room temperature. The fabrication process uses reactive ion beam etching with a CHF3/N2 gas mixture and reactive ion etching with a BCl3/N2 gas mixture to form PCMs on air-suspended slabs. An optimum N2 partial flux content of 0.65 and a successful removal of deposits formed during the membrane release by a fast wet etching in HF provide optical quality factors (Q-factors) as high as ∼30 000.

MOVPE GROWTH OF THE InP BASED MID-IR EMISSION QUANTUM DOT STRUCTURES

In this paper, semiconductor quantum dot structures for mid-infrared emission were self-assembled on InP substrate by using metal–organic vapor phase epitaxy growth. The InAs quantum dots grown at different conditions have been investigated. To improve the grown quantum dot's shape, the dot density and the dot size uniformity, a two-step growth method has been used and investigated. By changing the composition of the In x Ga 1-x As matrix layer of the InAs / In x Ga 1-x As / InP quantum dot structure, emission wavelength of the InAs quantum dot structure has been extended to the longest > 2.35 μm measured at 77 K. For the narrower bandgap semiconductor InAsSb quantum dots, the emission wavelength was measured at > 2.8 μm.

Growth and characterization of cooperative quantum dot chains in quaternary InAsSbP material system

The cooperative quantum dot chains (CQDCs) are grown from In-As-Sb-P quaternary liquid phase on InAs(100) substrate with a deviation of surface orientation from (100) of about 0.3° along [010] direction. The wet chemical etching is utilized to create an additional artificial disorientation of the substrate. AFM investigations show that CQDCs mainly consist of central coupled InAsSb quantum dot (QD) sub-chains surrounded by InAsP-leaf chains. Cooperative chains have a ∼120 nm total width, over 5 μm length and directed along [010]. The separation between QDs within sub-chains is about 40 nm. The red shift of CQDCs’ absorption edge is detected.

Mid-infrared emissive InAsSb quantum dots grown by metal–organic chemical vapor deposition

InAsSb islands/quantum dots (QDs) emitting at wavelength >2.8 μm were self-assembled on InP substrate by using metal–organic chemical vapor deposition (MOCVD). Instead of using arsine, the safer organic tert-butylarsine (TBAs) was used as the arsenic source in the growth process. Effects of the growth conditions, i.e. substrate temperature and the growth rate, on the InAsSb QD formations have been studied. A narrow temperature window from 450 °C to 470 °C was found for growing high quality InAsSb QDs. InAsSb rings instead of islands/dots were formed using the conventional Stranski–Krastanow (S–K) growth mode if the growth rate was low or if InAsSb was grown for a longer time. By increasing the V : III ratio for the InAsSb growth, InAsSb islands/dots were formed with the same growth rate. To reduce the dot size and increase the InAsSb QD density, an alternative interruption growth (AIG) method was proposed and investigated. Using the AIG growth method, much higher dot density of the InAsSb QDs has been achieved, about 3 × 109 cm−2, which is about 10 times of that of the QDs grown by using the conventional S–K growth method. Strong photoluminescence emissions of the InAsSb islands/dots were observed. At room temperature, the emission wavelength of the InAsSb islands/dots was measured at >2.8 μm.

Coexistence of type-I and type-II band alignments in antimony-incorporated InAsSb quantum dot nanostructures

Antimony-incorporated InAsSb quantum dots (QDs) are grown by molecular beam epitaxy on GaAs(001) substrates. The QD density increases ∼7 times while the QD height decreases ∼50% due to the increase of QD nucleation sites after Sb incorporation into the GaAs buffer layer and into the InAs QDs. These Sb-incorporated InAsSb QDs show red-shift in the photoluminescence (PL) spectrum and large energy separation between confined energy levels. More interestingly, besides the typical type-I QD transition, an additional peak from the recombination at wetting layer interface develops as the excitation laser intensity increases. This peak clearly exhibits type-II characteristics from the measurement of a large blue-shift of the PL peak and a long PL decay time. Finally, the mechanism of the coexistence of type-I and type-II band alignments is discussed.

Formation of InAs 1−xSb x quantum dots on vicinal InP(0 0 1) for 1.55-μm DFB laser applications

We have investigated the MOVPE growth of InAs 1− x Sb x quantum dots (QDs) on vicinal InP(0 0 1) substrate for DFB laser applications. Miscut orientation was adopted toward the [1 1¯ 0] direction in which InAsSb quantum wires elongate on normal InP(0 0 1) substrate. The interval between the QDs and the lateral size of the QDs in the [1 1 0] direction decreased as the Sb fraction was increased, which brought the density to as high as 1.1×10 11 cm −2 of InAsSb QDs. The InAsSb QDs were stacked with 30-nm-thick InGaAsP spacer layers for 10 periods without correlation, and had an emission of a wavelength at around 1.55 μm although the segregation of Sb atoms was slightly observed. A pn-buried-heterostructure-type DFB laser with InAsSb-QD active layer was fabricated. The lasing wavelength was 1540.6 nm at 25 °C, and CW, single-mode lasing operation was demonstrated up to 100 °C.

Abnormal optical behaviour of InAsSb quantum dots grown on GaAs substrate by molecular beam epitaxy

InAs(Sb) quantum dots (QDs) samples were grown on GaAs (001) substrate by Molecular Beam Epitaxy (MBE). The structural characterization by Atomic Force Microscopy (AFM) of samples shows that InAsSb islands size increases strongly with antimony incorporation in InAs/GaAs QDs and decreases with reducing the growth temperature from 520 °C to 490 °C. Abnormal optical behaviour was observed in room temperature (RT) photoluminescence (PL) spectra of samples grown at high temperature (520 °C). Temperature dependent PL study was investigated and reveals an anomalous evolution of emission peak energy (EPE) of InAsSb islands, well-known as “S-inverted curve” and attributed to the release of confined carriers from the InAsSb QDs ground states to the InAsSb wetting layer (WL) states. With only decreasing the growth temperature, the S-inverted shape was suppressed indicating a fulfilled 3D-confinement of carriers in the InAsSb/GaAs QD sample.

Optical Cavity Properties of Metal Mirror Microcavities with InAsSb Quantum Dots

The optical properties of metal mirror microcavities with InAsSb quantum dots (QDs) were studied. Metal mirror microcavities, consisting of InAsSb QDs and GaAs, were fabricated using lift-off methods and mounted on a (001) Si substrate. The micro-photoluminescence (µ-PL) spectra of these structures showed a modulation of emission properties at a resonance wavelength determined by µ-reflection measurement. The temperature dependence of cavity resonance wavelength was also investigated. The slope of the cavity resonance at approximately room temperature (RT) was found to be about 0.075 nm/K.

InAsSb/InGaAs quantum nanostructures on InP (100) substrate: observation of 2.35 µm photoluminescence

A theoretical and experimental study of the electronic properties of InAsSb quantum dots (QDs) grown on InP substrate is presented. Unstrained bulk InAsSb presents a direct gap between 0.1 eV to 0.35 eV, suitable for mid infrared emitters (3–5 µm). However, strain and quantum confinement effects may limit the extension of the emission spectrum of these nanostructures towards longer wavelengths. Various combinations of barrier materials are considered in the simulations. First photoluminescence spectroscopy experiments on molecular beam epitaxy (MBE) grown samples show promising results. Triple stacks of InAs QDs embedded in a GaInAsP alloy lattice matched to InP and grown by the Stranski-Krastanov mode exhibit room temperature (RT) luminescence at about 2 µm. Emission wavelengths as long as 2.35 µm have been observed at RT in a InAsSb/InGaAs/InP structure. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In As Sb ∕ In P quantum dots for midwave infrared emitters: A theoretical study

A theoretical study of the electronic properties of InAsSb quantum dots (QDs) deposited on InP substrate is presented. Unstrained bulk materials present a direct gap between 0.1and 0.35eV suitable for mid-infrared emitters (2–5μm). However, strain and quantum-confinement effects may limit the extension of the emission spectrum of these nanostructures towards the higher wavelengths. Various associations of materials in the barrier are considered. Among the possible associations, InAs0.5Sb0.5∕GaAs0.5Sb0.5 QDs may provide a low-energy emission with a material system similar to the well-known InAs∕GaAs system. Other materials associations such as InAsSb∕InGaAsP∕InP are also studied. Band lineups, optical transitions, optical losses, and effective masses are computed and discussed.

Room temperature continuous-wave operation of InAsSb quantum-dot distributed feedback lasers

InAsSb self-assembled quantum-dot (QD) distributed feedback (DFB) lasers based on (001) InP substrate have been grown by metalorganic vapor-phase epitaxy. A highly tensile-strained InGaAs was used as the barrier layer for InAsSb QDs. Single-mode emissions near 1.87μm have been demonstrated from narrow ridge waveguide DFB lasers in continuous-wave operation at temperatures up to 320K (47°C), with a characteristics temperature of 55K up to temperature of 310K.

Time-resolved photoluminescence and Raman scattering of InAsSb∕InP quantum dots

InAsSb quantum dots (QDs) grown by metalorganic vapor phase epitaxy on In0.53Ga0.47As∕InP under different TMSb∕AsH3 flow ratios have been characterized by means of continuous wave and time-resolved photoluminescence (PL) as well as Raman scattering. It was found that the flow ratio has a very strong influence on the QD composition, PL peak energies, and carrier recombination times. While the samples prepared using low TMSb∕AsH3 flow ratios show a bimodal character with both InAs and InAsSb QDs present, in the structures grown at high flow ratios the InAsSb QDs dominate, showing strong photoluminescence intensity, fast carrier capture and slow recombination.

Self-assembled InAsSb quantum dots on (001) InP substrates

Self-assembled InAsSb quantum dots (QD) on (001) InP substrates have been grown using metalorganic vapor phase epitaxy. The dot density and size are found to be strongly dependent on the presence of arsine. Direct deposition of InSb on InP and GaSb substrates formed large islands of InSb with low density of less than 5×109/cm2, however, InAsSb QDs of density as high as 4×1010/cm2 could be self-assembled by alternating group III and group V precursors, and high density almost pure InSb QDs were achieved on In0.53Ga0.47As/InP. The formation of high density InAsSb QDs is a result of a local nonequilibrium process and a reduction in mobility of In adatoms on the growth surface due to the presence of arsenic atoms, and in the case of high density almost pure InSb QDs on InGaAs/InP, the InAs interface layer is believed to be responsible. Photoluminescence shows that InSb QDs emit light at room temperature in the range of 1.7–2.2 μm.

Atomic Force Microscopy and Spectroscopy of Self-Assembled InAsSb Quantum Dots grown on InP Substrates by MOCVD

ABSTRACTInAsSb quantum dot (QD) lasers are promising light sources with emission wavelengths beyond 2μm as recently demonstrated. We report the first detailed atomic force microscope (AFM) characterization of uncapped InAsSb quantum dots self-assembled on GaAs/In0.53Ga0.47As layers. These quantum dot structures are grown on (100) InP substrates by metal organic chemical vapor deposition (MOCVD). Growth conditions are chosen to maximize photoluminescence intensity and to obtain high output powers from Fabry-Perot lasers with one stack of InAsSb QDs. Conductive AFM is employed to simultaneously study topography, current image, and current-voltage (I-V) characteristics from various InAs1-ySby QDs with y varied between 0 and 0.25. Typical dot density is 4–5×1010/cm2 and dots are estimated to have a lateral dimension at the base of ∼40nm and a height of 2–5nm. I-V characteristics measured from individual InAsSb QDs are compared to those from InAs QDs. Also reported are electronic properties including energy band gaps of InAs and InAsSb QDs.

Mid-infrared electroluminescence from InAsSb quantum dot light emitting diodes grown by liquid phase epitaxy

Mid-infrared electroluminescence is reported for the first time from InAs 0.75Sb 0.25 quantum dot (QD) light emitting diodes. The QDs were grown from the liquid phase at 590°C on an InAs(1 0 0) substrate and embedded within the undoped active region of an InAs homojunction pin diode. At 4 K and 250 mA injection current, a broad emission band was observed, centred at ∼4 μm , associated with transitions involving confined holes inside the InAsSb quantum dot. The QD emission band exhibits a blue shift with increasing injection current and the electroluminescence results indicate the presence of a phonon bottleneck in these devices. The QD electroluminescence was observed to persist up to room temperature.

Midinfrared photoluminescence of InAsSb quantum dots grown by liquid phase epitaxy

Photoluminescence in the 2–5 μm spectral region is reported from InAs1−xSbx quantum dots grown from the liquid phase at 580 °C on an InAs (100) substrate. Atomic force microscopy shows that coalesced quantum dots and then isolated quantum dots are formed with increasing Sb composition (x=0.2–0.3) and strain. The 4 K photoluminescence of the isolated and coalesced quantum dots was observed to peak in the midinfrared at 289 and 316 meV, (4.29 and 3.92 μm), respectively. These peaks are due to type II transitions and begin to quench at temperatures above 100 K as holes become thermally activated out of the quantum dot confinement potential.