InAs Material Research Articles

Atomic structure of InAs and InGaAs quantum dots determined by cross-sectional scanning tunneling microscopy

In this work we present a comparative cross-sectional scanning tunneling microscopy study of different InAs and InGaAs quantum dot structures grown by metalorganic vapor phase epitaxy. The varying growth conditions lead to completely different spatial structures, as distinctive quantum dots, intermixed layers, and intermixed dots. Especially the overgrowth procedure and the arrangement of growth interruptions are responsible for segregation of the InAs material.

Study of the spontaneous alignment of InAs quantum dots along the surface steps as a function of the InAs coverage

The evolution of InAs quantum dots (QDs) deposited on GaAs (001) was investigated in a continuous and unambiguous way as a function of the InAs coverage. Taking advantage of the intrinsic non-uniformity of the In flux in the molecular beam epitaxy system, a single sample was grown where the amount of InAs material varied in a monotonic way along the sample area. High-quality atomic force microscopy (AFM) images showed a saturation of the number of QDs nucleated out of the surface steps as the system evolved and confirmed that QDs can be effectively aligned along the surface steps up to the highest densities, which is an important subject for device application.

Monte Carlo calculation of electron drift characteristics and avalanche noise in bulk InAs

Field dependent drift velocity results are presented for electron transport in bulk indium arsenide (InAs) material based on a Monte Carlo model, which includes an analytical treatment of band-to-band impact ionization. Avalanche multiplication and related excess noise factor (F) are computed as a function of device length and applied voltage. A decrease in F with increases in device length is obtained. The results suggest an inherent utility for InAs-based single-photon avalanche detectors, particularly around the 2 μm region of interest for atmospheric remote sensing applications.

Maximization of the InAs quantum-dot density through the growth of an intentionally non-homogeneous sample

We investigated the maximum density of InAs quantum dots grown by molecular beam epitaxy on GaAs(0 0 1) substrates. Different from most current work, we took advantage of the non-uniformity of the molecular beams to produce a sample in which the amount of InAs material was continuously varied across the surface in order to analyze the evolution of the QDs as a function of the film thickness. A density of structures as high as 1800 μm −2 could be observed by atomic force microscopy and is around twice the maximum value typically reported in the literature. No loss of size uniformity was detected for such a high density.

Transport properties of two-dimensional electron gases containing linear ordering InAs self-assembled quantum dots

We present a study of the anisotropic properties of two-dimensional electron gases formed in GaAs/AlGaAs heterostructures in which InAs self-assembled quantum dots have been inserted into the center of a GaAs quantum well. We observe an anisotropic mobility for the orthogonal [1̄10] and [110] directions. The mobility in the [1̄10] direction was found to be up to approximately twice that in the [110] direction. It is suggested that the interface roughness scattering due to the inserted InAs material could be a cause for the large anisotropies in mobility.

Effect of V/III ratio and PH 3 annealing on InAs dots grown by MOVPE on InP(0 0 1) step-bunched surfaces

The self-organisation of InAs nanostructures grown by MOVPE on 0.2° misoriented (0 0 1)InP substrates has been studied as a function of growth parameters. The surface morphology of thin layers has been observed by atomic force microscopy for nominal thicknesses of about 3 and 6 ML. The InAs material was deposited at 500°C with V/III flux ratios ranging from 50 to 240. We observed that InAs dots were self-aligned along the bunched steps of the surface forming strips of several micrometers length, regularly spaced every 3–4 terraces. The surface distribution of the strips could be varied with the growth conditions, i.e. V/III flux ratio. The influence of the cooling atmosphere was also studied for samples cooled down from 500°C to 350°C during 6 min under either arsine or phosphine flux. This step has been found to largely determine the surface morphology of the InAs nanostructures. Under phosphine atmosphere, we will take into account the strong As→P exchange which takes place.

Effect of thin GaAs tensile-strained layer on InAs quantum dots on InP (001) substrate grown by LP-MOVPE

The InAs quantum dots on thin tensile-strained GaAs layer on InP (001) substrate are grown by LP-MOVPE. Approximately 2 nm GaAs tensile-strained layer is first grown on InP substrate, then 2 monolayer (ML) InAs for sample A, 4 ML for sample B, 6 ML for sample C and 8 ML for sample D are deposited. An atomic force microscope (AFM) is used to study the behavior of the InAs quantum dots. For sample A, two types of InAs islands are observed. Strain-induced grooves appear on the surface. For the other three samples, the InAs islands arrange along two orthogonal directions and the island density decreases with an increase in the amount of InAs material. The density of sample B is as high as 1.9×10 10 cm −2 , the densities are 1.39×10 10 and 0 .79×10 10 cm −2 for samples C and D, respectively. Furthermore, the base shape changes for different samples. For samples A and B, the base shapes are round; for sample C, the base changes into ellipsis; but for sample D, the base changes into triangle. The base area increases with an increase in the deposition of InAs. We also investigate the PL spectrum of InAs QDs with GaAs and with it and find that the QDs quality is higher with GaAs layer.

Effects of growth interruption on self-assembled InAs/GaAs islands

The effect of growth interruption on the InAs deposition and its subsequent growth as self-assembled island structures, in particular the material transport process of the InAs layers has been investigated by photoluminescence and transmission electron microscopy measurements. InAs material in structures with only coherent islands transfers from the wetting layer to the formed islands and the growth interruption causes a red shift of PL peak energy. On the other hand, the PL peak shifts to higher energy in structures containing simultaneously coherent and noncoherent islands with dislocations. In this case, the noncoherent islands capture InAs material from the surrounding wetting layer as well as coherent islands, which casues a reduction in the size of these islands. The variations in the PL intensity and line width are also discussed.

Magnetoexcitons in a GaSb-AlSb-InAs quantum-well structure.

We study theoretically the magnetoexcitons in a GaSb-AlSb-InAs quantum-well structure. Two numerical approaches, a variational and an expansion method, have been proposed to study the exciton ground state. The exciton binding energy has been found to increase with increasing applied magnetic field and with decreasing layer thicknesses of the GaSb, AlSb, and InAs materials. The strength of the applied magnetic field, along with quantum-well structure parameters, determines the condition under which the system undergoes transition from semiconductor to excitonic phase. The excited states of the magnetoexcitons have also been studied with the application of the expansion method.