Engineering the composition, morphology, and optical properties of InAsSb nanostructures via graded growth technique

Graded growth technique is utilized to realize the control over the composition, morphology, and optical properties of self-assembled InAsSb/InGaAs/InP nanostructures. By increasing the initial mole fraction of the Sb precursor during the graded growth of InAsSb, more Sb atoms can be incorporated into the InAsSb nanostructures despite the same Sb mole fraction averaged over the graded growth. This leads to a shape change from dots to dashes/wires for the InAsSb nanostructures. As a result of the composition and morphology change, photoluminescence from the InAsSb nanostructures shows different polarization and temperature characteristics. This work demonstrates a technologically important technique—graded growth, to control the growth and the resultant physical properties of self-assembled semiconductor nanostructures.Financial support from Australian Research Council is gratefully acknowledged

A revised checklist of Hawaiian mosses

A revised and updated literature-based checklist of Hawaiian mosses is presented. Geographic coverage includes the eight main Hawaiian Islands; the Northwestern Hawaiian Islands are excluded. The checklist is alphabetically ordered by scientific names; the family is noted for each genus. Synonyms and misapplied names are cross-referenced to the accepted names. A bibliography of supporting references is included

The drying of small drops of particulate slurries

The literature on the evaporation of drops of pure liquids, drops containing solids and droplet sprays has been critically reviewed. An experimental study was undertaken on the drying of suspended drops of pure water and aqueous sodium sulphate decahydrate with concentrations varying from 5 to 54. 1 wt. %. Individual drops were suspended from a glass filament balance in a 26 mm I.D. vertical wind tunnel, designed and constructed to supply hot de-humidified air, to simulate conditions encountered in commercial spray driers. A novel thin film thermocouple was developed to facilitate the simultaneous measurement of drop weight and core temperature. The heat conduction through the thermocouple was reduced because of its unique design; using essentially a single 50μ diameter nickel wire. For pure water drops, the Nusselt number was found to be a function of the Reynolds, Prandtl and Transfer numbers for a temperature range between 19 to 79°C.                  Nu = 2 + 0.19 (1/B)0.24 Re0.5 Pr0.33 Two distinct periods were observed during the drying of aqueous sodium sulphate decahydrate. The first period was characterised by the evaporation from a free liquid surface, whilst drying in the second period was controlled by the crust resistance. Fracturing of the crust occurred randomly but was more frequent at higher concentrations and temperatures. A model was proposed for the drying of slurry drops, based on a receding evaporation interface. The model was solved numerically for the variation of core temperature, drop weight and crust thickness as a function of time. Experimental results were in excellent agreement with the model predictions although at higher temperatures modifications to the model had to be made to accommodate the unusual behaviour of sodium sulphate slurries, i.e. the formation of hydrates

Controlling the morphology and optical properties of self-assembled InAsSb/InGaAs/InP nanostructures via Sb exposure

Engineering the surface energy, interface energy, and elastic strain energy in the system viaSb exposure is used to realize the control on the morphology and optical properties of self-assembled InP-based InAsSb/InGaAs nanostructures. By flowing trimethylantimony precursor over the surface of InGaAs buffer layer before the growth of InAsSbnanostructures, the surface/interface energy in the system is reduced, while the strain energy in the system is enhanced, which lead to a shape transition from dot to dash, and to wire for the InAsSbnanostructures. As a result of their morphology changes, the InAsSbnanostructures show different polarization characteristics in their photoluminescence emission.Financial support from Australian Research Council is gratefully acknowledged

Formation and shape control of InAsSb/InP (001) nanostructures

This paper presents a study on the formation and shape control of InAsSb/InP nanostructures on InP (001) substrates. For the formation of InAsSbnanostructures, incorporation of Sb atoms into InAs islands results in significant morphology change in the islands due to the surfactant effect of Sb atoms and the large strain in the system. And, shape control of InAsSb/InP nanostructures is achieved by optimizing their growth parameters. Low growth temperature and high growth rate will induce the formation of InAsSb elongated quantum dots, while high growth temperature and low growth rate will promote the formation of InAsSbquantum wires or dashes.Financial support from the Australian Research Council is gratefully acknowledged

Enhanced photoluminescence efficiency of mid-infrared InAsSb nanostructures using a carrier blocking layer

This paper presents a study on the emission efficiency enhancement of InAsSbnanostructures using a carrier blocking layer. InP is proposed to serve as the carrier blocking layer to suppress the thermal escape of carriers in InAsSbnanostructures and significantly enhance their emission efficiency at high temperature (good photoluminescence signal even at 330 K). However, this leads to a blueshift in their emission wavelength due to the significantly increased quantum confinement of the nanostructures. By inserting a thin InGaAs layer between InP blocking layer and InAsSbnanostructures, longer emission wavelength can be maintained. This provides an approach to achieve InAsSbnanostructures with both good high-temperature optical characteristics and long emission wavelength, which is very useful for fabricating mid-infrared emitters operating at room temperature.Financial support from Australian Research Council No. DP0774366 is gratefully acknowledged

Effect of matrix material on the morphology and optical properties of InP-based InAsSb nanostructures

This paper presents a study on the effect of matrix material on the morphology and optical properties of self-assembled InP-based InAsSbnanostructures. Due to the differences in surface roughness of the growth front, In 0.53 Ga 0.47 As matrix layer induces the formation of short quantum dashes (QDashes) and elongated quantum dots, while InP and In 0.52 Al 0.48 As matrix layers promote the formation of long QDashes and quantum wires, respectively. The shape anisotropy of InAsSbnanostructures on In 0.53 Ga 0.47 As , InP, and In 0.52 Al 0.48 As layers is further investigated with polarized photoluminescence measurements. The InAsSbnanostructures show a luminescence polarization degree of 8.5%, 14.3%, and 29% for In 0.53 Ga 0.47 As , InP, and In 0.52 Al 0.48 As matrixes, which corresponds well with the shape anisotropy observed with atomic force microscope. Furthermore, InAsSb/In 0.53 Ga 0.47 As nanostructures also show the longest, thermally stable emission wavelength, which serves as a promising material system for fabricating midinfrared emitters.Financial support from Australian Research Council is gratefully acknowledged. Facilities used in this work are supported by the Australian National Fabrication Facility

Study of intermixing in a GaAs/AlGaAs quantum-well structure using doped spin-on silica layers

The effect of two different dopants, P and Ga, in spin-on glass (SOG) films on impurity-free vacancy disordering (IFVD) in GaAs/AlGaAs quantum-well structures has been investigated. It is observed that by varying the annealing and baking temperatures, P-doped SOG films created a similar amount of intermixing as the undoped SOG films. This is different from the results of other studies of P-doped SiO₂ and is ascribed to the low doping concentration of P, indicating that the doping concentration of P in the SiO₂ layer is one of the key parameters that may control intermixing. On the other hand, for all the samples encapsulated with Ga-doped SOG layers, significant suppression of the intermixing was observed, making them very promising candidates with which to achieve the selective-area defect engineering that is required for any successful application of IFVD.One of the authors (H.H.T.) acknowledges a fellowship awarded to him by the Australian Research Council