Properties Of InGaAs Quantum Dots Research Articles

Исследование фотолюминесценции в системе InGaAs/GaAs с квантовыми точками спектрального диапазона 1100 нм

The results of studying the optical properties of InGaAs quantum dots are presented. Single-layer InGaAs quantum dots with a height of 5.3, 3.6 and 2.6 monolayers, as well as three-stacked layers of tunnel-uncoupled quantum dots with a height of 2.6 monolayers were formed by molecular–beam epitaxy according to the Stransky-Krastanov mechanism on GaAs substrates, using the partial capping and annealing technique. A decrease in the size of quantum dots makes it possible to carry out a blueshift of the photoluminescence spectrum maximum from 1200 nm to 1090 nm, and an increase in the number of QD layers makes it possible to compensate for the decrease in the peak intensity. It is shown that this type of quantum dots is suitable for creating the lasers active regions with a vertical microcavity for neuromorphic computing.

Investigation of photoluminescence in the InGaAs/GaAs system with 1100-nm range quantum dots

The results of studying the optical properties of InGaAs quantum dots are presented. Single-layer InGaAs quantum dots with a height of 5.3, 3.6 and 2.6 monolayers, as well as three-stacked layers of tunnel-uncoupled quantum dots with a height of 2.6 monolayers were formed by molecular-beam epitaxy according to the Stransky--Krastanov mechanism on GaAs substrates, using the partial capping and annealing technique. A decrease in the size of quantum dots makes it possible to carry out a blueshift of the photoluminescence spectrum maximum from 1200 nm to 1090 nm, and an increase in the number of QD layers makes it possible to compensate for the decrease in the peak intensity. It is shown that this type of quantum dots is suitable for creating the lasers active regions with a vertical microcavity for neuromorphic computing. Keywords: molecular-beam epitaxy, gallium arsenide, InGaAs, Stranski--Krastanow mode.

Influence of InGaAs cap layers with different In concentration on the properties of InGaAs quantum dots

InAs quantum dot (QD) layers grown by molecular-beam epitaxy were investigated by transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy. To achieve the highest possible In concentration in the QDs, InGaAs (instead of GaAs) cap layers with different In concentrations were deposited after the growth of the InAs QD layer. We combine different TEM techniques to determine the shape, size, and composition of the QDs. By applying a post-processing procedure, we are able to reconstruct the In concentration in the QDs which is measured too low in TEM due to the embedding of the QDs in material with lower In concentration and averaging along the finite TEM sample thickness. The determination of the composition of the layers on an atomic scale shows that the In concentration in the QDs increases in growth direction and reaches values up to 90%. Redistribution of indium during the InGaAs cap layer growth leads to a decrease of the In concentration in the cap layer with respect to the nominal In concentration. The observed redshift of the PL peak with increasing In concentration in the cap layer is attributed to the enlargement of island size and the change of the strain in the QD layers.

Controlling the properties of InGaAs quantum dots by selective-area epitaxy

Selective growth of InGaAs quantum dots on GaAs is reported. It is demonstrated that selective-area epitaxy can be used for in-plane bandgap energy control of quantum dots. Atomic force microscopy and cathodoluminescence are used for characterization of the selectively grown dots. Our results show that the composition, size, and uniformity of dots are determined by the dimensions of the mask used for patterning the substrate. Properties of dots can be selectively tuned by varying the mask dimensions. A single-step growth of a thin InGaAs quantum well and InGaAs quantum dots on the same wafer is demonstrated. By using a single-step growth, dots luminescing at different wavelengths, in the range 1150–1230nm, in different parts of the same wafer are achieved.

QUANTUM DOT OPTO-ELECTRONIC DEVICES

▪ Abstract Highly strained semiconductors grow epitaxially on mismatched substrates in the Stranski-Krastanow growth mode, wherein islands are formed after a few monolayers of layer-by-layer growth. Elastic relaxation on the facet edges, renormalization of the surface energy of the facets, and interaction between neighboring islands via the substrate are the driving forces for self-organized growth. The dimensions of the defect-free islands are of the order λB, the de Broglie wavelength, and provide three-dimensional quantum confinement of carriers. Self-organized In(Ga)As/GaAs quantum dots, or quantum boxes, are grown by molecular beam expitaxy (MBE) or metal-organic vapor phase epitaxy (MOVPE) on GaAs, InP, and other substrates and are being incorporated in microelectronic and opto-electronic devices. The use of strain to produce self-organized quantum dots has now become a well-accepted approach and is widely used in III–V semiconductors and other material systems. Much progress has been made in the area of growth, where focus has been on size control, and on optical characterization, where the goal has been the application to lasers and detectors. The unique carrier dynamics in the dots, characterized by femtosecond pump-probe spectroscopy, has led to novel device applications. This article reviews the growth and electronic properties of InGaAs quantum dots and the characteristics of interband and intersublevel lasers and detectors and modulation devices.

Self-organized InGaAs quantum dots on GaAs (311)B studied by conductive atomic force microscope tip

We have used conductive atomic force microscope (AFM) tips in order to probe the local electronic properties of InGaAs quantum dots (QDs) grown on GaAs (311)B and (001) substrates by atomic H-assisted molecular beam epitaxy. Highly doped Si and Si3N4 AFM tips coated with a metal such as Au and Ti which warrant electrical conductivity were used to measure the current–voltage (I–V) characteristics of QDs of varying sizes and of any other arbitrary positions on the surface such as the wetting layer. In the case of QDs formed on (001) substrates, it was found that the local surface potentials of larger QDs were lower than the small QDs due to the effect of surface states. On the other hand, noticeable differences were not observed for the QDs formed on (311)B substrates. The local surface potential was similar on each QD and in fact over the whole (311)B surface, and a complex phase separation and strain-relief mechanism were thought to be responsible the observed QDs assembly on (311)B. Last, a resonant tunneling characteristics through the quantized energy levels was studied with a small QD with ∼45 nm in diameter and ∼4 nm in height.

Influence of growth conditions on the formation and luminescence properties of InGaAs quantum dots in a Si matrix

The influence of the growth conditions during molecular-beam epitaxy and of the degree of lattice mismatch between the epilayer and the substrate on the formation of InGaAs islands on a Si(100) surface is studied. An increase in lattice mismatch (the InAs mole fraction) leads to an increase in the critical thickness corresponding to the onset of island growth, in contrast to the formation of InGaAs islands on GaAs(100). An increase in the deposition temperature also increases the critical thickness, whereas an increase in the arsenic pressure has the opposite effect. Structures containing an array of InGaAs islands in a Si matrix display a luminescence line in the range 1.2–1.3 µm, depending on the mole fraction of InAs.

Self-organized InGaAs quantum dots grown by molecular beam epitaxy on (100), [formula omitted], [formula omitted], [formula omitted], [formula omitted], and [formula omitted] oriented GaAs

In this paper, we report optical properties of InGaAs quantum dots grown by molecular beam epitaxy on GaAs (n11) A B , where n is 1, 2, 3, 5 and 7, and reference (100) substrates. A higher crystal quality of quantum dots has been detected on ( n11)B surfaces due to the strong integrated photoluminescence (PL) intensity, its value on (711)B orientation being 10 times larger than the QW one. Quantum dots grown on a (311)B surface showed a higher homogeneity in size. The quantum well PL peak position reveals a non-monotonical red-shift when the surface direction changes from (100) to (111).