Analysis of optical gain and threshold current density of 980 nm InGaAs/GaAs compressively strained quantum well lasers

The valence hole subbands, optical gain spectra and threshold current density of InGaAs/GaAs compressive-strained quantum wells (QWs) were studied using a numerical approach. We found that a higher In composition in the quantum well and a thicker well give longer emitting wavelength; a narrower well and higher In composition lead to higher TE mode peak gain. The result also shows a suitable combination of In composition, QW thickness and number of QWs should be selected to achieve low threshold current density.     

The effect of ferromagnetic Mn-delta-doped layer on the emission properties of GaAsSb/GaAs and InGaAs/GaAsSb/GaAs heterostructures

We have studied the emission characteristics and circularly polarized electroluminescence of light-emitting diodes based on heterostructures with a single (GaAs/GaAsSb/GaAs) or two-layer (GaAs/InGaAs/GaAsSb/GaAs) quantum well (QW) and a Mn-delta-doped layer in the GaAs barrier. The ferromagnetic effect of the delta-layer of Mn on the spin polarization of carriers in QWs based on type-II heterostructures has been observed and studied for the first time. The observed phenomena are described using a model of the exchange interaction of Mn ions in the barrier and holes in the QW.     

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.     

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.     

Self-assembled InAs/GaAs quantum dots covered by different strain reducing layers exhibiting strong photo- and electroluminescence in 1.3 and 1.55 microm bands

The effect of different InGaAs and GaAsSb strain reducing layers on photoluminescence and electroluminescence from self-assembled InAs/GaAs quantum dots grown by metal-organic vapour phase epitaxy was investigated. The aim was to shift their luminescence maximum towards optical communication wavelengths at 1.3 or 1.55 microm. Results show that covering by InGaAs strain reducing layer provides stronger shift of photoluminescence maximum (up to 1.55 microm) as compared to GaAsSb one with similar strain in the structure. This is caused by the increase of quantum dot size during InGaAs capping and reduction of quantum confinement of the electron wave function which spreads into the cap. Unfortunately, the weaker electron confinement in quantum dots is a reason of a considerable blue shift of electroluminescence from these InGaAs structures since optical transitions move to InGaAs quantum well. Although strong electroluminescence at 1300 nm was achieved from quantum dots covered by both types of strain reducing layers, the GaAsSb strain reducing layer is more suitable for long wavelength electroluminescence due to higher electron confinement potential allowing suppression of thermal carrier escape from quantum dots.     

The growth of infrared antimonide-based semiconductor lasers by metal-organic chemical vapor deposition

We describe the metal-organic chemical vapor deposition (MOCVD) growth of InAsSb/InAs and GaAsSb/GaAs(P) multiple quantum well (MQW) and InAsSb/InAsP and InAsSb/InPSb strained-layer superlattice (SLS) active regions for use in mid-infrared emitters. We also describe the growth and initial characterization of GaAsSbN/GaAs MQW structures. By changing the layer thickness and composition of the InAsSb SLSs and MQWs, we have prepared structures with low temperature (<20 K) photoluminescence wavelengths ranging from 3.2 to 6.0 m. We have made gain-guided, injection lasers using undoped, p-type AlAs_0.16Sb_0.84 for optical confinement and both strained InAsSb/InAs MQW and InAsSb/InAsP and InPSb SLS active regions. The lasers and LEDs utilize the semi-metal properties of a p-GaAsSb/n-InAs heterojunction as a source for electrons injected into the active regions. Cascaded, semi-metal, mid-infrared, injection lasers with pseudomorphic InAsSb multiple quantum well active region lasers and LEDs are reported. We also report on GaAsSb/GaAs(P) lasers and LEDs emitting at 1.1 to 1.2 m grown on GaAs substrates and using AlGaAs layers for confinement.     

Molecular beam epitaxy growth methods of wavelength control for InAs/(In)GaAsN/GaAs heterostructures

We discuss the molecular beam epitaxy (MBE) growth methods of emission wavelength control and property investigations for different types of InAs/(In)GaAsN/GaAs heterostructures containing InGaAsN quantum-size layers: (1) InGaAsN quantum wells deposited by the conventional mode in a GaAs matrix, (2) InAs quantum dots deposited in a GaAsN matrix or covered by an InGaAs(N) layer, and (3) InAs/InGaAsN/GaAsN strain-compensated superlattices with quantum wells and quantum dots. The structures under investigation have demonstrated photoluminescence emission in a wavelength range of ～1.3-1.8?μm at room temperature without essential deterioration of the radiative properties.     

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.     

Longwave generation in laser structures based on InGaAs(N) quantum wells on GaAs substrates

The MBE growth regime has been optimized for the obtaining of laser structures based on InGaAs(N)/GaAs quantum wells (QWs) with high indium content. Structures containing InGaAs and InGaAsN isolated QWs exhibit low-threshold longwave emission at room temperature. Lasers based on QWs of the In_0.35GaAs and In_0.35GaAsN_0.023 types are characterized by the radiation wavelengths λ=1.085 and 1.295 μm at a threshold current density of 60 and 350 A/cm², respectively.     

Optical nutation in GaAs/GaxA11−xAs quantum well structures

Abstract

The possibility of occurrence of the coherent optical transient effect known as optical nutation has been analytically established in the semiconductor quantum well (QW) structure, namely GaAs/Ga_xA1_1?xAs most extensively used in optical electronics. Ultra-short-pulse low-intensity band-to-band excitation of electrons to the 1s Wannier-Mott exciton state of the crystal has been considered to play an important role in the coherent radiation—QW interaction. Numerical estimations of the complex optical susceptibility and the transmitted intensity under the transient regime reveal ringing behaviour confirming the occurrence of optical nutation in III-V semiconducting QW structures.     

Reliability and degradation of 980 NM InGaAs/GaAs strained quantum well lasers

Degradation behaviours of 980 nm InGaAs/GaAs strained quantum well (QW) lasers are clarified and compared with normal AlGaAdGaAs, InGaAsP/InP and GaAs/GaAs QW lasers. Through various ageing tests, it is confirmed that 980 nm InGaAs/GaAs strained QW lasers are applicable to optical fibre transmission systems where the components are required to be highly reliable.     

Interdiffusion effect on GaAsSbN/GaAs quantum well structure studied by 10-band k•p model

The effect of annealing on the photoluminescence (PL) in GaAsSbN/GaAs quantum well (QW) grown by solid-source molecular-beam epitaxy (SS-MBE) has been investigated. Low-temperature (4 K) PL peaks shift to higher energy sides with the increase of annealing temperature. An As-Sb atomic interdiffusion at the heterointerface is proposed to model this effect. The compositional profile of the QW after interdiffusion is modeled by an error function distribution and calculated with the 10-band k•p method. When the diffusion length equals to 1.4 nm, a corresponding transition energy blueshift of 36 meV is derived. This agrees with the experimental result under the optimum condition (750 °C at 5 min).     

Photoreflectance study of strained GaAsN/GaAs T-junction quantum wires grown by metal-organic vapor phase epitaxy

Strained GaAsN T-junction quantum wires (T-QWRs) with different N contents grown on GaAs by two steps metal-organic vapor phase epitaxy in [001] and [110] directions, namely QW1 and QW2 respectively, have been investigated by photoreflectance (PR) spectroscopy. Two GaAsN T-QWRs with different N contents were formed by T-intersection of (i) a 6.4-nm-thick GaAs0.89N0.011 QW1 and a 5.2-nm-thick GaAs0.968N0.032 QW2 and (ii) a 5.0-nm-thick GaAs0.985N0.015 QW1 and a 5.2-nm-thick GaAs0.968N0.032 QW2. An evidence of a one-dimensional structure at T-intersection of the two QWs on the (001) and (110) surfaces was established by PR resonances associated with extended states in all the QW and T-QWR samples. It is found that larger lateral confinement energy than 100 meV in both of [001] and [110] directions were achieved for GaAsN T-QWRs. With increasing temperature, the transition energy of GaAsN T-QWRs decreases with a faster shrinking rate compared to that of bulk GaAs. Optical quality of GaAsN T-QWRs is found to be affected by the N-induced band edge fluctuation, which is the unique characteristic of dilute III-V-nitrides.     

Temperature dependence of optical transitions in AlxGa1–xAs/GaAs quantum well structures grown by molecular beam epitaxy

Quantum well (QW) structures of Al_xGa_1–xAs/GaAs were characterized by photoluminescence technique as a function of the temperature between 10 and 300 K. The structures were grown on a 500 nm thick GaAs buffer layer with Molecular Beam Epitaxy technique. We have studied the properties of in-situ Cl₂-etched GaAs surfaces and overgrown QW structures as a function of the etching temperature (70 and 200 °C). Several models were used to fit the experimental points. Best fit to experimental points was obtained with the Pässler model.     

Ultrafast carrier dynamics in p-doped inAs/GaAs quantum-dot amplifiers

Using a differential transmission pump-probe experiment in heterodyne detection, the ultrafast gain and refractive-index dynamics of the ground-state transition in InAs/GaAs quantum- dot amplifiers emitting near 1.3 mum at working condition, that is at room temperature and under electrical injection were measured. An ultrafast gain recovery on a subpicosecond time scale is observed at high electrical injection indicating fast carrier relaxation into the dot ground state, which is appealing for high-speed applications with these devices. Comparing p-doped and undoped devices of otherwise identical structure and operating at the same gain, a faster absorption recovery but a slower gain dynamics in p-doped amplifiers was observed. This finding should help in elucidating the role of p-doping in the design of QD-based devices with high-speed performances.     

Effects of non-uniform size distribution on the spectral optical gain properties of InGaAs/InGaAsP quantum dots

We present a theoretical study of the optical gain, emission wavelength, and threshold current density for edge emitting laser structures with an active region based on InGaAs/InGaAsP quantum dots. The analysis of the effects of the size distribution of the dots is also presented. Spectral gain curves are generated for InGaAs/InGaAsP dots where high optical gain and high independence of spectral characteristics are obtained for a uniform distribution of dots. With typical non-uniform distribution, we show a reduction in gain by a factor of 6. Also, we predict the onset of new transition peaks and a red shift in the most probable operating lasing wavelength. Finally, we demonstrate that there is a large range of full width at half maximum (FWHM) of the dots size distribution where variations in the maximum gain and associated wavelength, as well as threshold current density, are minimum.     

Self-consistent optical gain and threshold current calculations for near infrared intersubband semiconductor lasers

Abstract

A theoretical investigation of the optical gain of electrically pumped intersubband lasers is presented. Using a prototype four-level near-infrared (1.55 μm) triple quantum well structure, self-consistent numerical simulations of the rate equations, energy density equations, optical gain and spontaneous emisson spectra of triple quantum well structures have been implemented at temperatures of 100 K and 300 K. It is predicted that the threshold currents of such lasers are significantly smaller than those for mid-infrared quantum cascade lasers.     

Alternation of band gap and localization of excitons in InGaNAs nanostructures with low nitrogen content

Continuous wave photoluminescence (cw PL) spectroscopy has been used to study the optical properties of a set of InGaNAs epilayers and single quantum wells with nitrogen concentration less than a few per cent at different temperatures and different excitation powers. We found that nitrogen has a critical role on the emission light of InGaNAs nanostructures and the recombination mechanism. The incorporation of a few per cent of nitrogen leads to shrinkage of the InGaNAs band gap. The physical origin of such band gap reduction has been investigated both experimentally and theoretically by using a band anticrossing model. We have found that localization of excitons that have been caused by incorporation of a few per cent of nitrogen in these structures is the main explanation of such anomalous behavior observed in the low-temperature photoluminescence spectra of these nanostructures. The localization energies of carriers have been evaluated by studying the variation of the quantum well (QW) emission versus temperature, and it was found that the localization energy increases with increasing nitrogen composition. Our data also show that, with increasing excitation intensity, the PL peak position moves to higher energies (blue shift) due to the filling of localized states and capture centers for excitons by photo-generated carriers.     

Zinc blende GaAsSb nanowires grown by molecular beam epitaxy

We report the growth of GaAsSb nanowires (NWs) on GaAs(111)B substrates by Au-assisted molecular beam epitaxy. The structural characteristics of the GaAsSb NWs have been investigated in detail. Their Sb mole fraction was found to be about?25%. Their crystal structure was found to be pure zinc blende (ZB), in contrast to the wurtzite structure observed in GaAs NWs grown under similar conditions. The ZB GaAsSb NWs exhibit rotational twins around their [111]B growth axis, with twin-free segments as long as 500?nm. The total volumes of GaAsSb segments with twinned and un-twinned orientations, respectively, were found to be equal by x-ray diffraction analysis of NW ensembles.