Room-temperature photoluminescence at 1.55 μm from heterostructures with InAs/InGaAsN quantum dots on GaAs substrates

Room-temperature photoluminescence (PL) at 1.55 μm from heterostructures with InAs/InGaAsN quantum dots (QDs) grown by MBE on GaAs substrates is demonstrated for the first time. The effect of nitrogen incorporated into InAs/InGaAsN QDs on the PL wavelength and intensity was studied. The integral intensity of PL from the new structure with InAs/(In)GaAsN QDs is comparable to that from a structure with InGaAsN quantum wells emitting at 1.3 μm.     

Optical properties of strain-compensated InAs/InGaAsN/GaAsN superlattices

The optical properties of heterostructures comprising InAs/InGaAsN quantum wells in strain-compensated GaAsN/InGaAsN superlattices have been studied. It is demonstrated that, using such superlattices of various design and thickness and with additional InAs monolayer spacers, it is possible to control the wavelength of room-temperature emission from InGaAsN quantum wells within 1.3–1.6 μm without deteriorating the output radiation characteristics, which opens additional prospects for the development of lasers on GaAs substrates for telecommunication applications.     

Lasing properties of strain-compensated InAs/InGaAsN/GaAsN heterostructures in 1.3–1.55 μm spectral range

We have studied the radiative properties of heterostructures comprising InAs/InGaAsN quantum wells in strain-compensated GaAsN/InGaAsN superlattices, which are intended for the active regions of lasers operating at 1.3–1.55 μm. Using such superlattices and additional InAs monolayer insertions, it is possible to control the wavelength of room-temperature emission from InGaAsN quantum wells within 1.3–1.55 μm. The InAs/InGaAsN/GaAsN laser heterostructures are obtained, whose laser generation spectrum at 85 K corresponds to room-temperature lasing at ～1.5 μm.     

Effect of structural design on the optical properties of strain-compensated InAs/InGaAsN/GaAsN superlattices

We have studied the influence of structural design on the optical properties of heterostructures comprising InAs quantum wells (QWs) and quantum dots (QDs) in strain-compensated GaAsN/InGaAsN superlattices. It is established that, using such superlattices with various QW and barrier thicknesses and different numbers (from one to three) InAs inserts in the active region, it is possible to control the wavelength of room-temperature emission within 1.3–1.76 μ m without deteriorating the output radiation characteristics.     

Long-wavelength emission in InGaAsN/GaAs heterostructures with quantum wells

The properties of InGaAsN/GaAs heterostructures with quantum wells on GaAs substrates were studied. The GaAsN layers containing InGaAsN quantum wells with a high (exceeding 1%) nitrogen concentration were obtained. The long-wavelength emission in the InGaAsN quantum wells is obtained in the wavelength range up to 1.32 μm at room temperature. The effect of the InGaAsN quantum parameters on the optical properties of heterostructures is studied.     

Emission characteristics improvement in structures with InAs/GaAsN/InGaAsN superlattices

The influence of some parameters of nitrogen-containing heterostructures InAs/GaAsN/InGaAsN with strain-compensated superlattices (SCSL) on their emission characteristics has been studied. It is established that the net strain in the structure affects the photoluminescence (PL) linewidth, internal quantum efficiency, intensity, and wavelength. The maximum PL intensity and minimum full width at half maximum (FWHM) of the PL line were achieved with small strains (0–0.2%), whereas the maximum wavelengths (∼1.76 μm) observed for large strain (about +1%). By adding multilayer InAs inserts in the active InGaAsN quantum well in combination with using strain-compensated GaAsN/InGaAsN superlattices, it is possible to control the room-temperature emission wavelength in the range of 1.45–1.76 μm without significantly deteriorating the emissiion characteristics.     

Self-assembling InAs and InP quantum dots for optoelectronic devices

Stranski–Krastanov growth in molecular beam epitaxy allows the preparation of self assembling InAs and InP quantum dots on GaAs and Ga_0.52In_0.48P buffer layers, respectively. InAs dots in GaAs prepared by slow growth rates and low temperature overgrowth provide intense photoluminescence at the technologically important wavelength of 1.3 μm at room temperature. Strain induced vertical alignment, size modification and material interdiffusion for stacked dot layers are studied. A blue shift of the ground state transition energy is observed for the slowly deposited stacked InAs dots. This is ascribed to enhanced strain driven intermixing in vertically aligned islands. For very small densely stacked InP and InAs dots the reduced confinement shift causes a red shift of the ground state emission. The InP quantum dots show intense and narrow photoluminescence at room temperature in the visible red spectral range. First InP/Ga_0.52In_0.48P quantum dot injection lasers are prepared using threefold stacked InP dots. We observe lasing at room temperature in the wavelength range between 690–705 nm depending on the size of the stacked InP dots.     

Mid-Infrared Emission From InAs Quantum Dots Grown by Metal–Organic Vapor Phase Epitaxy

We have demonstrated mid-infrared emission from the self-assembled InAs quantum dots grown on InP substrate by metal-organic vapor phase epitaxy using low toxic tertiarybutylarsine and tertiarybutylphosphine as group V sources in pure nitrogen ambient. Emission wavelength of the InAs quantum dots has been extended to mid-infrared region by embedding the InAs quantum dots in graded In_xGa_1-xAs matrix layers. When compared with that of the InAs quantum dots grown on lattice matched In_0.53Ga_0.47As/InP matrix, emission wavelength of the InAs quantum dots red shifted by up to 370 nm when embedded the InAs quantum dots in graded In_0.53rarr0.8Ga_0.47rarr0.2As barriers. The longest emission wavelength of >2.35 mum from the self-assembled InAs quantum dot structure has been measured at 77 K. The full-width at half-maximum of the photoluminescence emission spectrum of the InAs quantum dots is as narrow as 25.5 meV. The results achieved would be promising to high performance mid-infrared quantum dot lasers on InP substrate     

Effect of high energy proton irradiation on InAs/GaAs quantum dots: Enhancement of photoluminescence efficiency (up to ∼7 times) with minimum spectral signature shift

We demonstrate 7-fold increase of photoluminescence efficiency in GaAs/(InAs/GaAs) quantum dot hetero-structure, employing high energy proton irradiation, without any post-annealing treatment. Protons of energy 3–5 MeV with fluence in the range (1.2–7.04) × 10¹² ions/cm² were used for irradiation. X-ray diffraction analysis revealed crystalline quality of the GaAs cap layer improves on proton irradiation. Photoluminescence study conducted at low temperature and low laser excitation density proved the presence of non-radiative recombination centers in the system which gets eliminated on proton irradiation. Shift in photoluminescence emission towards higher wavelength upon irradiation substantiated the reduction in strain field existed between GaAs cap layer and InAs/GaAs quantum dots. The enhancement in PL efficiency is thus attributed to the annihilation of defects/non-radiative recombination centers present in GaAs cap layer as well as in InAs/GaAs quantum dots induced by proton irradiation.     

Comparison of luminescence properties of bilayer and multilayer InAs/GaAs quantum dots

Coupled InAs/GaAs quantum dots have generated an interest for their longer emission wavelength and narrower line-width. However, a consensus has not been reached on the parameters of growth required to achieve a desired effect from coupling due to contradictory reports of shorter emission wavelengths. In this paper, we seek to compare the luminescence properties of bilayer quantum dots (BQDs) with those of multilayer quantum dots (MQDs), grown at a very low deposition rate, keeping all parameters constant. The BQD and MQD samples were grown by solid source MBE at a slow growth rate of 0.03 ML/s. A blueshift in the PL spectra for 11 layer coupled InAs/GaAs MQD heterostructure is observed compared to the BQDs for temperatures less than 180 K. This undesired blueshift is attributed to strain in the structure which overshadowed the usual redshift in emission wavelength in such structures due to electronic coupling. The variation in PL line-width with temperature in the MQD structure is found to be much lower than in the BQD. However the PL intensity of the MQDs fall at a faster rate with temperature compared to the BQD sample, due to strain generated non-radiative centers in the islands which favors in thermalization of carriers.     

Photoluminescence from multilayer InAs/GaAs structures with quantum dots in the 1.3–1.4 μm wavelength range

The optical properties of multilayer heterostructures with quantum dots were studied for InAs/GaAs systems obtained by the combined method of molecular-beam epitaxy and submonolayer migration-stimulated epitaxy. Using these structures, it is possible to obtain the room-temperature photoluminescence with maximum emission in the wavelength range from 1.3 to 1.4 μm.     

GaAsN/GaAs and InGaAsN/GaAs heterostructures grown by molecular beam epitaxy

Molecular beam epitaxy was used to fabricate GaAsN/GaAs and InGaAsN/GaAs heterostructures, and the influence of the growth regimes on their characteristics was studied. It is shown that implantation of nitrogen causes a substantial long-wavelength shift of the radiation. The possibility of obtaining 1.4 μm radiation at room temperature was demonstrated using In_0.28Ga_0.72As_0.97N_0.03/GaAs quantum wells. Pis’ma Zh. Tekh. Fiz. 24, 81–87 (December 12, 1998)     

InAs/GaAs nanostructures grown on patterned Si(001) by molecular beam epitaxy

The potential benefit from the combination of the optoelectronic and electronic functionality of III-V semiconductors with silicon technology is one of the most desired outcomes to date. Here we have systematically investigated the optical properties of InAs quantum structure embedded in GaAs grown on patterned sub-micron and nanosize holes on Si(001). III-V material tends to accumulate in the patterned sub-micron holes and a material depletion region is observed around holes when GaAs/InAs/GaAs is deposited directly on patterned Si(001). By use of a 60?nm SiO(2) layer and patterning sub-micron and nanosize holes through the oxide layer to the substrate, we demonstrate that high optical quality InAs nanostructures, both quantum dots and quantum wells, formed by a two-monolayer InAs layer embedded in GaAs can be epitaxially grown on Si(001). We also report the power-dependent and temperature-dependent photoluminescence spectra of these structures. The results show that hole diameter (sub-micron versus nanosize) has a strong effect on the structural and optical properties of GaAs/InAs/GaAs nanostructures.     

Site‐Controlled Single‐Photon Emitters Fabricated by Near‐Field Illumination

Many of the most advanced applications of semiconductor quantum dots (QDs) in quantum information technology require a fine control of the QDs' position and confinement potential, which cannot be achieved with conventional growth techniques. Here, a novel and versatile approach for the fabrication of site‐controlled QDs is presented. Hydrogen incorporation in GaAsN results in the formation of N–2H and N–2H–H complexes, which neutralize all the effects of N on GaAs, including the N‐induced large reduction of the bandgap energy. Starting from a fully hydrogenated GaAs/GaAsN:H/GaAs quantum well, the N? H bonds located within the light spot generated by a scanning near‐field optical microscope tip are broken, thus obtaining site‐controlled GaAsN QDs surrounded by a barrier of GaAsN:H (laterally) and GaAs (above and below). By adjusting the laser power density and exposure time, the optical properties of the QDs can be finely controlled and optimized, tuning the quantum confinement energy over more than 100 meV and resulting in the observation of single‐photon emission from both the exciton and biexciton recombinations. This novel fabrication technique reaches a position accuracy <100 nm and it can easily be applied to the realization of more complex nanostructures.     

Room-temperature photoconductivity in the 1–2.6 µm range in InAs/GaAs heterostructures with quantum dots

We have studied the room-temperature photoconductivity in the wavelength range 1–2.6 μm in InAs/GaAs heterostructures with quantum dots (QDs). Specific features of these heterostructures grown using the metalorganic vapor phase epitaxy (MOVPE) were an increase in the amount of InAs during the formation of a sheet of QDs and the use of alternating low-and-high-temperature regimes during their overgrowth with a GaAs barrier layer. For the first time, the MOVPE-grown multilayer InAs/GaAs heterostructures with quantum dots exhibited photoluminescence in a wavelength range of up to 1.6 μm and the photoconductivity up to 2.6 μm at room temperature. The heterostructures exhibited a room-temperature voltage sensitivity of 3 × 10³ V/W (within a Si-plate filter bandwidth) and a specific detectivity of 9 × 10⁸ cm Hz^1/2 W^?1.     

Quantum dots in InAs layers of subcritical thickness on GaAs(100)

Ensembles of InAs quantum dots formed at the GaAs(100) surface have been studied by the methods of reflection high-energy electron diffraction and photoluminescence. The amount of deposited InAs corresponds to a wetting layer thickness smaller than the critical value necessary for the transition from two-to three-dimensional growth. It is experimentally shown that, at a deposited film thickness of 1.5 and 1.6 monolayers, islands are formed after keeping the sample in a flow of As₄. The influence of the substrate temperature on the kinetic characteristics of the formation of InAs/GaAs islands has been studied.     

InAs/GaAs multiple quantum dot structures grown by LP-MOVPE

Structures with self-organised InAs quantum dots in a GaAs matrix were grown by the low pressure metal–organic vapour phase epitaxy (LP-MOVPE) technique. Photoluminescence and atomic force microscopy were used as the main characterisation methods for the growth optimisation. The properties of multiple-stacked quantum dot structures are influenced by the thickness of the GaAs separation layers (spacers) between quantum dot-containing InAs layers, by the InAs layer thickness, by arsine partial pressure during growth, and by group III precursor flow interruption time.     

Improved photoluminescence efficiency of patterned quantum dots incorporating a dots-in-the-well structure

InAs quantum dots embedded in InGaAs quantum well (DWELL: dots-in-the-well) structures grown on nanopatterned GaAs pyramids and planar GaAs(001) surface are comparatively investigated. Photoluminescence (PL) measurements demonstrate that the DWELL structure grown on the GaAs pyramids exhibits a broad quantum well PL band (full width at half-maximum ～ 90?meV) and a higher quantum dot emission efficiency than the DWELL structure grown on the planar GaAs(001) substrate. These properties are attributed to the InGaAs quantum well with distributed thickness profile on the faceted GaAs pyramids, which introduces a tapered energy band structure and enhances carrier capture into the quantum dots.     

Formation mechanism and optical properties of InAs quantum dots on the surface of GaAs nanowires

Formation mechanism and optical properties of InAs quantum dots (QDs) on the surface of GaAs nanowires (NWs) were investigated. This NW-QDs hybrid structure was fabricated by Au-catalyzed metal organic chemical vapor deposition. We found that the formation and distribution of QDs were strongly influenced by the deposition time of InAs as well as the diameter of GaAs NWs. A model based on the adatom diffusion mechanism was proposed to describe the evolution process of the QDs. Photoluminescence emission from the InAs QDs with a peak wavelength of 940 nm was observed at room temperature. The structure also exhibits a decoupling feature that QDs act as gain medium, while NW acts as Fabry-Perot cavity. This hybrid structure could serve as an important element in high-performance NW-based optoelectronic devices, such as near-infrared lasers, optical detectors, and solar cells.     

Growth of InAs Quantum Dots on GaAs (511)A Substrates: The Competition between Thermal Dynamics and Kinetics

The growth process of InAs quantum dots grown on GaAs (511)A substrates has been studied by atomic force microscopy. According to the atomic force microscopy studies for quantum dots grown with varying InAs coverage, a noncoherent nucleation of quantum dots is observed. Moreover, due to the long migration length of In atoms, the Ostwald ripening process is aggravated, resulting in the bad uniformity of InAs quantum dots on GaAs (511)A. In order to improve the uniformity of nucleation, the growth rate is increased. By studying the effects of increased growth rates on the growth of InAs quantum dots, it is found that the uniformity of InAs quantum dots is greatly improved as the growth rates increase to 0.14 ML s^?1. However, as the growth rates increase further, the uniformity of InAs quantum dots becomes dual‐mode, which can be attributed to the competition between Ostwald ripening and strain relaxation processes. The results in this work provide insights regarding the competition between thermal dynamical barriers and the growth kinetics in the growth of InAs quantum dots, and give guidance to improve the size uniformity of InAs quantum dots on (N11)A substrates.