[1 1 1]B-oriented GaAsSb grown by gas source molecular beam epitaxy

We report the GaAsSb bulk layers and GaAsSb/GaAs quantum wells (QWs) grown on (1 1 1)B GaAs substrates by gas source molecular beam epitaxy. We found that Sb composition in the GaAsSb epilayers is very sensitive to the substrate temperature. The composition drops from 0.35 to 0.16 as the substrate temperature increases from 450 to 550 °C. The [1 1 1]B-oriented GaAsSb epilayers show phase separation when the substrate temperature is lower than 525 °C. For a GaAsSb/GaAs multiple quantum wells (MQWs) structure composed of five periods of 5 nm GaAs_0.73Sb_0.27 QW and 30 nm GaAs barrier, the room temperature photoluminescence emission is located at 1255, 80 nm longer than the [1 0 0]-oriented sample with the same Sb composition. The peak wavelength shows significant blue shift as the excitation level increases, which evidences the type-II band alignment in this heterostructure.     

Specific features of electroluminescence in heterostructures with InSb quantum dots in an InAs matrix

The electrical and electroluminescence properties of a single narrow-gap heterostructure based on a p-n junction in indium arsenide, containing a single layer of InSb quantum dots in the InAs matrix, are studied. The presence of quantum dots has a significant effect on the shape of the reverse branch of the current-voltage characteristic of the heterostructure. Under reverse bias, the room-temperature electroluminescence spectra of the heterostructure with quantum dots, in addition to a negative-luminescence band with a maximum at the wavelength λ = 3.5 μm, contained a positive-luminescence emission band at 3.8 μm, caused by radiative transitions involving localized states of quantum dots at the type-II InSb/InAs heterointerface.     

Methods of controlling the emission wavelength in InAs/GaAsN/InGaAsN heterostructures on GaAs substrates

Studies of the properties of InGaAsN compounds and methods of controlling the emission wavelength in InAs/GaAsN/InGaAsN heterostructures grown by molecular beam epitaxy on GaAs substrates are reviewed. The results for different types of heterostructures with quantum-size InGaAsN layers are presented. Among those are (1) traditional InGaAsN quantum wells in a GaAs matrix, (2) InAs quantum dots embedded in an (In)GaAsN layer, and (3) strain-compensated superlattices InAs/GaAsN/InGaAsN with quantum wells and quantum dots. The methods used in the study allow controllable variations in the emission wavelength over the telecommunication range from 1.3 to 1.76 μm at room temperature.     

InAs/InGaAs/GaAs quantum dot lasers of 1.3 μm range with high(88%) differential efficiency

Multiple layers (up to 10) of InAs/InGaAs/GaAs quantum dots considerably enhance the optical gain of quantum dot lasers emitting around 1.3 μm. A differential efficiency as high as 88% has been achieved in these lasers. An emission wavelength of 1.28 μm, threshold current density of 147 A/cm², differential efficiency of 80%, and characteristic temperature of 150 K have been realised simultaneously in one device     

Room temperature operation of type-II GaAsSb/InGaAs quantum welllaser on GaAs substrates

A GaAsSb/InGaAs type-II quantum well laser diode on GaAs substrates was demonstrated for the first time. Threshold current density of 610 A/cm² was obtained from a 1.1 mm-long broad area laser with the emission wavelength of 1.2 μm     

Localization of holes in an InAs/GaAs quantum-dot molecule

Deep-level transient spectroscopy is used to study the emission of holes from the states of a vertically coupled system of InAs quantum dots in p-n InAs/GaAs heterostructures. This emission was considered in relation to the thickness of a GaAs interlayer between two layers of InAs quantum dots and to the reversebias voltage U_r. It is established that hole localization at one of the quantum dots is observed for a quantum-dot molecule composed of two vertically coupled self-organized quantum dots in an InAS/GaAs heterostructure that has a 20-Å-thick or 40-Å-thick GaAs interlayer between two layers of InAs quantum dots. For a thickness of the GaAs interlayer equal to 100 Å, it is found that the two layers of quantum dots are incompletely coupled, which results in a redistribution of the hole localization between the upper and lower quantum dots as the voltage U_r applied to the structure is varied. The studied structures with vertically coupled quantum dots were grown by molecular-beam epitaxy using self-organization effects.     

Self-organized InAs/GaAs quantum dots multilayers with growth interruption emitting at 1.3 μm

We have grown single, 10 and 20 InAs/GaAs quantum dots (QDs) multilayers by molecular beam epitaxy in Stranski-Krastanov growth mode with and without growth interruption. Multilayer structures of InAs QDs have been studied by photoluminescence (PL) and atomic force microscopy (AFM) techniques. Between 1 and 10 layers of QDs, 10 K PL shows a shift energy, and a PL linewidth reduction. Moreover, AFM image of the 10 layers sample shows that the InAs QDs size remains constant and almost uniform when the growth is without interruption. These effects are attributed to electronic coupling between QDs in the the columns. However, we show the possibility of extending the spectral range of luminescence due to InAs QDs up to 1.3 μm. Realisation of such a wavelength emission is related to formation of lateral associations or coupling of QDs (LAQDs or LCQDs) during InAs deposition when growth interruption (20 s) is used after each InAs QDs layer deposition. The growth interruption applied after the deposition of the InAs layer allows the formation of well-developed InAs dots (large dot size).     

Effect of a low-temperature-grown GaAs layer on InAs quantum-dot photoluminescence

The photoluminescence of InAs semiconductor quantum dots overgrown by GaAs in the low-temperature mode (LT-GaAs) using various spacer layers or without them is studied. Spacer layers are thin GaAs or AlAs layers grown at temperatures normal for molecular-beam epitaxy (MBE). Direct overgrowth leads to photoluminescence disappearance. When using a thin GaAs spacer layer, the photoluminescence from InAs quantum dots is partially recovered; however, its intensity appears lower by two orders of magnitude than in the reference sample in which the quantum-dot array is overgrown at normal temperature. The use of wider-gap AlAs as a spacer-layer material leads to the enhancement of photoluminescence from InAs quantum dots, but it is still more than ten times lower than that of reference-sample emission. A model taking into account carrier generation by light, diffusion and tunneling from quantum dots to the LT-GaAs layer is constructed.     

The effects of quantum dot coverage in InAs/(In)GaAs nanostructures for long wavelength emission

We present a study on the effects of quantum dot coverage on the properties of InAs dots embedded in GaAs and in metamorphic In_0.15Ga_0.85As confining layers grown by molecular beam epitaxy on GaAs substrates. We show that redshifted emission wavelengths exceeding 1.3 μm at room temperature were obtained by the combined use of InGaAs confining layers and high quantum dot coverage. The use of high InAs coverage, however, leads to detrimental effects on the optical and electrical properties of the structures. We relate such behaviour to the formation of extended structural defects originating from relaxed large-sized quantum dots that nucleate in accordance to thermodynamic equilibrium theories predicting the quantum dot ripening. The effect of the reduced lattice-mismatch of InGaAs metamorphic layers on quantum dot ripening is discussed in comparison with the InAs/GaAs system.     

Demonstration of 3.5 μm Ga1-xInxSb/InAssuperlattice diode laser

A demonstration of a semiconductor diode laser based on a type-II Ga _1-xIn_xSb/InAs superlattice active layer is reported. The laser structure uses InAs/AlSb superlattice cladding layers and a multiquantum well active layer with GaInAsSb barriers and Ga_1-xIn_xSb/InAs-superlattice wells. An emission wavelength of 3.47 μm for pulsed operation up to 160 K is observed     

Coupling of electron states in the InAs/GaAs quantum dot molecule

Deep level transient spectroscopy (DLTS) is used to study electron emission from the states in the system of vertically correlated InAs quantum dots in the p-n InAs/GaAs heterostructures, in relation to the thickness of the GaAs spacer between the two layers of InAs quantum dots and to the reverse-bias voltage. It is established that, with the 100 Å GaAs spacer, the InAs/GaAs heterostructure manifests itself as a system of uncoupled quantum dots. The DLTS spectra of such structures exhibit two peaks that are defined by the ground state and the excited state of an individual quantum dot, with energy levels slightly shifted (by 1–2 eV), due to the Stark effect. For the InAs/GaAs heterostructure with two layers of InAs quantum dots separated by the 40 Å GaAs spacer, it is found that the quantum dots are in the molecule-type phase. Hybridization of the electron states of two closely located quantum dots results in the splitting of the levels into bonding and antibonding levels corresponding to the electron ground states and excited states of the 1s ⁺, 1s ^?, 2p ⁺, 2p ^?, and 3d ⁺ types. These states manifest themselves as five peaks in the DLTS spectra. For these quantum states, a large Stark shift of energy levels (10–40 meV) and crossing of the dependences of the energy on the electric field are observed. The structures with vertically correlated quantum dots are grown by molecular beam epitaxy, with self-assembling effects.     

Photoluminescence of InAs quantum dots coupled to a two-dimensional electron gas

Self-assembled InAs quantum dots have been extensively studied by a variety of experimental techniques. Works have been done on the transport properties of the InAs dots located near a two-dimensional electron gas (2DEG). However, there have been few reports on the optical properties of the InAs dots located closely to 2DEG. In this work, InAs dots samples with 2DEG and without 2DEG growth by solid source molecular beam epitaxy were studied using photoluminescence measurements. Different photoluminescence behaviors between the InAs dots and the InAs dots near the 2DEG were observed. It was found that the emission efficiency of the InAs dots was significantly enhanced by the existence of the nearby 2DEG and the thermal activation energy of the InAs dots was decreased by the 2DEG. It was speculated that the 2DEG at the AlGaAs/GaAs interface worked as an electron reservoir to the InAs dots. As a result, the conduction band between the dots and 2DEG is lowered, and thus the thermal activation energy of PL is lowered. It was concluded that in this way the optical properties of the InAs quantum dots could be tailored for optical applications.     

Emission of electrons from the ground and first excited states of self-organized InAs/GaAs quantum dot structures

Capacitance- and conductance-voltage studies have been carried out on Schottky barrier structures containing a sheet of self-organized InAs quantum dots. The dots are formed in GaAs n-type matrices after the deposition of four monolayers of InAs. Quasi-static analysis of capacitance-voltage measurements indicates that there are at least two filled electron levels in the quantum dots, located 60 and 140 meV below the GaAs conduction band edge. The conductance of the structure depends on the balance between measurement frequency and the thermionic emission rate of carriers from the quantum dots. An investigation of the temperature-dependent conductance at different frequencies as a function of the reverse bias allows us to study separately the electron emission rates from the ground and first excited levels in the quantum dots. We estimate that the electron escape times from both levels of the quantum dots become comparable at room temperature and equal to about 100 ps.     

GaAs structures with InAs and As quantum dots produced in a single molecular beam epitaxy process

Epitaxial GaAs layers containing InAs semiconductor quantum dots and As metal quantum dots are grown by molecular beam epitaxy. The InAs quantum dots are formed by the Stranskii-Krastanow mechanism, whereas the As quantum dots are self-assembled in the GaAs layer grown at low temperature with a large As excess. The microstructure of the samples is studied by transmission electron microscopy. It is established that the As metal quantum dots formed in the immediate vicinity of the InAs semiconductor quantum dots are larger in size than the As quantum dots formed far from the InAs quantum dots. This is apparently due to the effect of strain fields of the InAs quantum dots upon the self-assembling of As quantum dots. Another phenomenon apparently associated with local strains around the InAs quantum dots is the formation of V-like defects (stacking faults) during the overgrowth of the InAs quantum dots with the GaAs layer by low-temperature molecular beam epitaxy. Such defects have a profound effect on the self-assembling of As quantum dots. Specifically, on high-temperature annealing needed for the formation of large-sized As quantum dots by Ostwald ripening, the V-like defects bring about the dissolution of the As quantum dots in the vicinity of the defects. In this case, excess arsenic most probably diffuses towards the open surface of the sample via the channels of accelerated diffusion in the planes of stacking faults.     

Study of the Structural and Luminescence Properties of InAs/GaAs Heterostructures with Bi-Doped Potential Barriers

The influence of Bi in GaAs barrier layers on the structural and optical properties of InAs/GaAs quantum-dot heterostructures is studied. By atomic-force microscopy and Raman spectroscopy, it is established that the introduction of Bi into GaAs to a content of up to 5 at % results in a decrease in the density of InAs quantum dots from 1.58 × 10¹⁰ to 0.93 × 10¹⁰ cm^–2. The effect is defined by a decrease in the mismatch between the crystal-lattice parameters at the InAs/GaAsBi heterointerface. In this case, an increase in the height of InAs quantum dots is detected. This increase is apparently due to intensification of the surface diffusion of In during growth at the GaAsBi surface. Analysis of the luminescence properties shows that the doping of GaAs potential barriers with Bi is accompanied by a red shift of the emission peak related to InAs quantum dots and by a decrease in the width of this peak.     

256×256 focal plane array midwavelength infrared camera based on InAs/GaSb short-period superlattices

An infrared camera based on a 256×256 focal plane array (FPA) for the second atmospheric window (3–5 μm) has been realized for the first time with InAs/GaSb short period superlattices (SLs). The SL detector structure with a broken gap type-II band alignment was grown by molecular beam epitaxy on GaSb substrates. Effective bandgap and strain in the superlattice were adjusted by varying the thickness of the InAs and GaSb layers and the controlled formation of InSb-like bonds at the interfaces. The FPAs were processed in a full wafer process using optical lithography, chemical-assisted ion beam etching, and conventional metallization technology. The FPAs were flip-chip bonded using indium solder bumps with a read-out integrated circuit and mounted into an integrated detector cooler assembly. The FPAs with a cut-off wavelength of 5.4 μm exhibit quantum efficiencies of 30% and detectivity values exceeding 10¹³ Jones at T=77 K. A noise equivalent temperature difference (NETD) of 11.1 mK was measured for an integration time of 5 ms using f/2 optics. The NETD scales inversely proportional to the square root of the integration time between 5 ms and 1 ms, revealing background limited performance. Excellent thermal images with low NETD values and a very good modulation transfer function demonstrate the high potential of this material system for the fabrication of future thermal imaging systems.     

Structural and optical properties of InAs quantum dots in AlGaAs matrix

Structural and optical properties of InAs quantum dots (QDs) grown in a wide-bandgap Al_0.3Ga_0.7As matrix is studied. It is shown that a high temperature stability of optical properties can be achieved owing to deep localization of carriers in a matrix whose band gap is wider than that in GaAs. Specific features of QD formation were studied for different amounts of deposited InAs. A steady red shift of the QD emission peak as far as ∼1.18 μm with the effective thickness of InAs in Al_0.3Ga_0.7As increasing was observed at room temperature. This made it possible to achieve a much higher energy of exciton localization than for QDs in a GaAs matrix. To obtain the maximum localization energy, the QD sheet was overgrown with an InGaAs layer. The possibility of reaching the emission wavelength of ~1.3 μm is demonstrated. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 37, No. 5, 2003, pp. 578–582. Original Russian Text Copyright ? 2003 by Sizov, Samsonenko, Tsyrlin, Polyakov, Egorov, Tonkikh, Zhukov, Mikhrin, Vasil’ev, Musikhin, Tsatsul’nikov, Ustinov, Ledentsov.     

Anomalous spin splitting of electrons in type-II InSb quantum dots in InAs

Magnetooptical studies of heterostructures with type-II InSb quantum dots in the InAs matrix grown by molecular beam epitaxy are carried out. Unusual behavior of magnetophotoluminescence from quantum dots measured in the Faraday geometry in the samples with multiple planes of quantum dots is found. Specifically, the peak with σ^? polarization, which corresponds to transitions of electrons with s = +1/2, has a higher energy than the σ⁺ peak corresponding to s = ?1/2, which contradicts the negative value of the electron g factor both in the InAs matrix and in the InSb quantum dot. The effect can be interpreted as the result of competition of two channels of radiative recombination, which differ by the initial states of electrons belonging either to the InSb quantum dots or to shallow-level donors in the InAs matrix.     

利用大周期光子晶体结构增强InAs/GaAs量子点的激发态发光

在该研究中,通过激光全息和湿法腐蚀的方法在InAs/GaAs量子点材料上制备光子晶体,研究了由激光二极管激发制备了光子晶体的InAs / GaAs量子点材料的光致发光光谱.发现具有光子晶体的量子点材料的光谱显示出多峰结构,光子晶体对短波长部分的发光增强和调制比对长波长部分的增强和调制更明显.InAs / GaAs量子点的光致发光光谱通过刻蚀形成的光子晶体结构得到了调控,并且量子点的激发态发光得到了明显增强.     

Structural and electrooptical characteristics of quantum dotsemitting at 1.3 μm on gallium arsenide

We present a comprehensive study of the structural and emission properties of self-assembled InAs quantum dots emitting at 1.3 μm. The dots are grown by molecular beam epitaxy on gallium arsenide substrates. Room-temperature emission at 1.3 μm is obtained by embedding the dots in an InGaAs layer. Depending on the growth structure, dot densities of 1-6×10¹⁰ cm^-2 are obtained. High dot densities are associated with large inhomogeneous broadenings, while narrow photoluminescence (PL) linewidths are obtained in low-density samples. From time-resolved PL experiments, a long carrier lifetime of ≈1.8 ns is measured at room temperature, which confirms the excellent structural quality. A fast PL rise (τ_rise=10±2 ps) is observed at all temperatures, indicating the potential for high-speed modulation. High-efficiency light-emitting diodes (LEDs) based on these dots are demonstrated, with external quantum efficiency of 1% at room temperature. This corresponds to an estimated 13% radiative efficiency. Electroluminescence spectra under high injection allow us to determine the transition energies of excited states in the dots and bidimensional states in the adjacent InGaAs quantum well