Strained-layer Quantum Research Articles

Temperature Dependent Quenching Mechanisms of the Luminescence of InGaAs/GaAs Strained Quantum Wells

ABSTRACTIn this work we report on detailed temperature dependent photoluminescence measures on InGaAs/GaAs strained layer quantum well structures. Excitation energies above and below the GaAs band gap have been used in order to separate the contributions of the carrier trapping to the generation-recombination processes from the recombination mechanisms proper of the quantum wells. The results show that a decrease of the trapping efficiency contributes to the photoluminescence quenching, and suggest that the strong photoluminescence quenching observed in these structures should be mainly attributed to defects present in the quantum wells. A clear dependence of the luminescence quenching on the excitation intensity has also been found.

Optical characterization of band-edge lineups in GaAs/GaAs1− xP x strained-layer quantum wells

GaAs/GaAs 1− x P x single quantum well (QW) structures which involve strained-barrier or strained-barrier or strained-well layers, have successfully grown by low pressure metal-organic vapor phase epitaxy (MOVPE) on GaAs or GaAs t− y P y substrates. Owing to the extremely strong and highly resolved excitonic transitions of electron to heavy hole and electron to light hole, which are observed in photoluminescence and reflectance spectra, the conduction- and the strain-split valence-band-edge lineups have been determined. Furthermore, we demonstrate for the first time that the band-edge lineups are strongly dependent not only on the configuration of the elastic strain in the quantum well structure but also on the value of the elastic strain or the phosphorus composition.

InGaAs/InGaAsp/InP strained-layer quantum well lasers at ~2 μm

The first successful operation of InGaAs strained layer quantum well (Sl-QW) injection lasers at about 2 microns is reported. The threshold current density and the external differential quantum efficiency of 5 microns wide and 800 microns long ridge waveguide lasers were 2.5 kA/sq cm and 6 percent, respectively. The devices had a reverse leakage current of less than 20 micro-A at -1 V indicating epitaxial layers with low defect density.

Evaluation of nucleation and defects in MBE-grown strained InAs/GaAs quantum structures on variously oriented substrates

We have grown InAs/GaAs strained-layer quantum structures (SLQSs) on variously oriented GaAs substrates by molecular beam epitaxy to examine the possibility of devices with self-constructed microstructures. Three-dimensional nucleation and defects originated from large lattice mismatch in InAs/GaAs SLQSs have been evaluated by various measurements, such as X-ray diffraction, photoluminescence and photoconductivity. The critical points as functions of growth temperature and substrate orientation for the generation of 3D nuclei, misfit dislocations and defects are discussed.

Effects of growth direction on lasing performance in GaAsAl xGa 1−xAs quantum wells

The properties of GaAsAlGaAs quantum well lasers are studied theoretically as a function of the crystallographic growth direction. The growth directions considered are [001] [111], [110], [310], [311] and [211]. The electronic dispersion is obtained using an 8×8 k·p Hamiltonian which couples the electron, heavy-hole, light-hole and spin-orbit split-off bands. We calculate the threshold current for single quantum well lasers and determine the lowest threshold current for the growth directions considered. It is seen that for some growth directions the threshold current can be less than that previously calculated for a strained-layer quantum well laser. The results also differ from a previous model which completely decoupled the valence and conduction bands.

Phase-locked ridge waveguide InGaAs-GaAs-AlGaAs strained-layer quantum well heterostructure laser arrays

We report the characteristics of separate confinement heterostructure InGaAs/GaAs/AlGaAs strained-layer quantum well heterostructure (λ≳1 μm) ridge waveguide laser arrays grown by metalorganic chemical vapor deposition, and etched by reactive ion etching. The ten element arrays have ridge widths of 4 μm on 8 μm centers. Several etch depths are examined, covering the range from gain-guided to strongly index-guided elements. For these structures, values of effective index step, Δneff, below ∼6×10−3 are necessary to achieve interelement coupling. For Δneff=1.3×10−3, the devices lase in the highest array mode up to ∼1.5 times threshold with a nearly diffraction-limited double-lobed far-field pattern. For higher currents, additional structure in the far-field pattern is observed, and is accompanied by splitting of the longitudinal modes due to operation in additional array modes.

Photoluminescence characterization of pseudomorphic modulation-doped quantum wells at high carrier sheet densities

A systematic study has been made of the photoluminescence spectra of modulation-doped strained-layer quantum wells at high electron sheet densities. Peaks associated with both the n=1 and n=2 electron subbands are observed, and the relative intensities are shown to be a result of the symmetry properties of the quantum wells. It is demonstrated that only the full width half maximum of the n=2 subband peak is useful for characterizing high carrier densities.

Many-body effects in the gain spectra of strained quantum wells

A many-body theory for the optical susceptibility in highly excited strained-layer quantum wells is presented. Gain spectra are computed for the example of InxGa1−xAs/InP and different In concentrations, yielding zero, tensile, and compressive strain.

Very low threshold current density 1.5 μm GaInAs/AlGaInAs graded-index separate-confinement-heterostructure strained quantum well laser diodes grown by organometallic chemical vapor deposition

Very low threshold current densities of 200 and 400 A/cm2 were obtained in 1.5 μm GaInAs/AlGaInAs tensile and compressive strained-layer quantum well laser diodes (SL-QW LDs), grown by organometallic chemical vapor deposition, with continuously graded-index separate-confinement-heterostructure. The differential quantum efficiency of SL-QW LDs showed less sensitive to temperature in contrast to that of a lattice matched QW LD. This is attributed to the decrease of intervalence band absorption due to the strain-induced reduction in the valence band density of state. The polarization of output power for a tensile SL-QW LD showed transverse magnetic (TM) mode, while that for a lattice matched and a compressive SL-QW LDs showed transverse electric (TE) mode.

Molecular beam epitaxial growth and optical properties of strained rectangular and asymmetric triangular InGaAs quantum well structures

We present the growth and optical properties of rectangular and asymmetric triangular strained layer quantum well (QW) structures involving In x Ga 1- x As. The growth, as monitored by reflection high energy electron diffraction (RHEED), indicated some form of surface disorder and a two-dimensional growth mode throughout. In addition, the surface morphologies suggest no lattice relaxation and hence no strain-relieving defects in the layers. The low temperature photoluminescence (PL) spectra for the various QW structures were dominated by a single feature attributed to the n = 1 electron to heavy hole excitonic recombination. The linewidth for a single 50 Å In 0.13Ga 0.87As/GaAs QW was measured to be 1.8 meV, indicative of high quality InGaAs material as well as smooth heterointerfaces. Also observed are higher PL intensities for the asymmetric triangular MQWs as compared to the rectangular well case.

Strained layer quantum well semiconductor optical amplifiers: Polarization insensitive amplification

Abstract : Optical amplifiers are important devices for future optical fiber transmission and other photonic technologies. Semiconductor laser amplifiers are attractive candidates for these applications because of theirs high gain, compactness, possibility of integration with light source and so on. In comparison with fiber amplifiers such as Er+-doped fibers, the semiconductor laser amplifiers have a disadvantage which is large difference between TE and TM gain. Therefore, to control the TE/TM mode gain is a key item in the development of semiconductor amplifiers. For polarization insensitive amplification in the semiconductor laser amplifier, several approaches have been proposed by geometric designing of active layers. 1-3 In this paper, we describe an approach to the polarization insensitive optical amplifier in which active layer consisted of GaInAsP multiple quantum well structures with biaxially tensile strains within well layers. A group has reported a strained layer quantum well amplifier with tensed barriers. 4 In this work, we investigated the effects of biaxially tensile strain on amplification in the quaternary strained quantum well amplifiers. The polarization insensitive amplification was successfully demonstrated.

Comparison of the theoretical and experimental differential gain in strained layer InGaAs/GaAs quantum well lasers

A theoretical model that uses simple, analytic valence band equations to calculate the differential gain in strained layer InGaAs/GaAs quantum wells shows good agreement with experimental differential gain values obtained from multiple quantum well strained layer lasers. The differential gain in these devices is 7 times greater than in bulk, p-type doped InGaAsP lasers. Calculations including nonlinear damping effects indicate that modulation bandwidths exceeding 60 GHz should be achievable in strained layer quantum well lasers.

Metal-semiconductor-metal demultiplexing waveguide photodetectors in InGaAs/GaAs quantum well structures by selective bandgap tuning

A two-wavelength demultiplexing metal-semiconductor-metal (MSM) waveguide photodetector has been fabricated using impurity-free vacancy diffusion and partial intermixing of an InGaAs/GaAs strained layer quantum well structure. The importance of growth and process parameters, such as aluminium composition in the cladding layer and the oxygen plasma treatment of the sample during processing, on the related device performance is discussed. This photodetector is a potential candidate for monolithic integration with other optoelectronic devices.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Tellurium-based II-VI compound semiconductors and heterostructures under strain

Reviews work on some of the electronic and structural properties of CdTe-(CdZn)Te and CdTe-(CdMn)Te strained-layer quantum wells and superlattices under high pressure. The hydrostatic pressure dependence of the band gap of CdTe is deduced to be Eg=Ego+76P (meV GPa-1)-4P2(meV GPa-2) consistent with all the available data, and for ZnTe is Eg=Ego+105P-2P2. Results obtained by piezomodulation of the subband structure of such systems are also presented. The authors determine the values of the CdTe shear deformation potentials: b=-1.17 eV and d=-3.20 eV.

Characteristics of coherent two-dimensional grating surface emitting diode laser arrays during CW operation

Recent progress in the development of monolithic two-dimensional coherent grating surface emitting (GSE) laser arrays is presented. Such GSE arrays have operated continuously to more than 3 W/surface and pulsed to more than 30 W/surface. They have achieved continuous wave (CW) threshold current densities of under 140 A/cm/sup 2/ with CW differential quantum efficiencies of 20-46% per surface. Linewidths in the 40-100 MHz range were obtained with output powers of 100-300 mW per surface. The arrays typically consist of 10-30 mutually injection coupled gain sections with 10 laterally coupled ridge-guided lasers in each gain section. A single GaInAs strained-layer quantum well with a graded-index separate confinement heterostructure (GRINSCH) geometry allows junction down mounting with light emission through the transparent GaAs substrate. A surface relief grating is used for feedback and outcoupling.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Wavelength switching in narrow oxide stripe InGaAs-GaAs-AlGaAs strained-layer quantum well heterostructure lasers

We have observed current-controlled wavelength switching in narrow oxide stripe In0.17Ga0.83As-GaAs-Al0.20Ga0.80As strained-layer single quantum well heterostructure lasers. Laser emission switches from the lowest (n=1) quantized state transition in the quantum well at low currents to the first excited state transition (n=2) at higher currents, with an energy difference of ≊50 meV. For currents near the switching point, we have also observed time-dependent lasing behavior, with a switch in the laser emission from the n=1 to the n=2 transition. The order of this temporal switching (from n=1 to n=2) is opposite that observed in narrow stripe gain-guided GaAs-AlGaAs quantum well lasers, due to strong antiguiding in InGaAs lasers, which negates the effect of a thermal guide.

Index-guided operation in narrow stripe InGaAs-GaAs strained-layer quantum well heterostructure lasers by MeV oxygen implantation

Stable index-guided operation of variable stripe strained-layer InGaAs-GaAs-AlGaAs lasers achieved by MeV oxygen implantation-induced disorder of the active region is demonstrated. Well-behaved near- and far-field patterns for lasers implanted with 5×1016 cm−2 and 1×1017 cm−2 oxygen are observed to be stable with increasing drive current. Comparison with unimplanted, oxide-defined stripe lasers fabricated from the same wafer indicates a dramatic improvement in emission characteristics as a result of the presence of a lateral real-index waveguide in the oxygen-disordered regions which is stronger than the carrier-induced antiguide present in unimplanted InGaAs-GaAs strained-layer lasers.

High temperature operation of λ = 1.5 μm tensile strained multiple quantum well sipbh lasers

The high temperature operation of 1.5 μm wavelength, strained-layer multiple quantum well, semi-insulating planar buried heterostructure lasers is reported. The lasers, which are grown by low-pressure organometallic vapour phase epitaxy and which have four 1.6% tensile strained In0.3Ga0.7As wells (thickness 8 nm), operate in CW mode up to heatsink temperatures of 140°C. The CW output power at 100°C is 26 mW per facet. These results are a marked improvement when compared to data reported thus far for 1.5 μm wavelength lasers.

Metalorganic chemical vapor deposition of InGaAs-GaAs-AlGaAs strained-layer quantum well lasers

Data are presented here on various aspects of the growth and materials-related performance of InGaAs-GaAs-AlGaAs strained-layer quantum well lasers. Certain problematic traits unique to the indium alkyls have motivated the use of the relatively new precursor ethyldimethylindium. The stability of the source vapor pressure and the quality of the source are evidenced here in the growth of strained-layer lasers. Thermal considerations involving the active region growth temperature and annealing of laser structures are addressed. Growth of the strained active region at 575°C led to an emission wavelength of 1.11 μm. Short anneals of laser structures, on the other hand, brought about a slight reduction in the laser emission wavelength due to interdiffusion of indium and gallium in the quantum well to a lower average composition. Quantum wells near and well above the Matthews-Blakeslee predicted critical layer thickness have been evaluated in terms of threshold current density and device reliability. Laser with strained quantum wells substantially thicker than the predicted critical layer thickness have excellent time zero threshold current densities but exhibit inferior lifetime performance.

Oscillatory photoluminescence excitation in InGaAs/GaAs strained-layer quantum well structures

Photoluminescence and photoluminescence excitation spectra of strained-layer InGaAs/GaAs single quantum wells have been studied at 2 K. Photogeneration of carriers in the well is found to be negligible compared with that in the barriers. Efficient transfer of photogenerated carriers from the barrier into the well is found to occur within a few picoseconds for the 26 AA quantum well. Oscillations due to the emission of GaAs LO phonons by the electrons photoexcited high into the conduction band of the GaAs barrier have been observed in the excitation spectra of quantum well luminescence. The dependence of electron diffusivity on the electron temperature is proposed as the main cause of the observed oscillations.