GaInAs Quantum Wells Research Articles

Improvement in Photoluminescence Efficiency of GaInNAs/GaAs Quantum Wells Grown by Metalorganic Chemical Vapor Deposition for Low-Threshold 1.3 µm Range Lasers

A quality improvement of the III–V dilute nitride semiconductor alloy, GaInNAs, grown by metalorganic chemical vapor deposition (MOCVD) on a GaAs substrate is reported for 1.3 µm-wavelength lasers. GaInNAs wafers were grown at various growth temperatures, V/III ratios, and growth rates. The photoluminescence (PL) efficiency of GaInNAs/GaAs quantum wells (QWs) was increased by lowering the growth temperature and increasing the V/III ratio in the growth conditions conventionally used for nitrogen (N)-free GaInAs/GaAs QW growth. These conditions are important for realizing high PL efficiency because they prevent the inhomogeneity of the immiscible alloy of GaInNAs. It was also observed that the optimal window for the growth temperature, V/III ratio, and growth rate for the GaInNAs is narrower than that of N-free GaInAs QWs. After careful optimization of the growth conditions, GaInNAs/GaAs QW lasers with various emission wavelengths were fabricated. Low-threshold current densities of 0.17 kA/cm2/well, 0.18 kA/cm2/well, and 0.44 kA/cm2/well are obtained for emission wavelengths of 1.25 µm, 1.30 µm, and 1.34 µm, respectively. The results obtained for growth conditions and lasing characteristics are useful in further improving 1.3 µm or longer wavelength GaInNAs lasers grown by MOCVD.

Sb surfactant effect on GaInAs/GaAs highly strained quantum well lasers emitting at 1200 nm range grown by molecular beam epitaxy

A surfactant effect of antimony (Sb) on highly strained GaInAs quantum wells (QWs) was studied by molecular beam epitaxy. Noticeable improvement of the photoluminescence (PL) was observed by adding the dilute Sb. The QWs showed an increased PL intensity and narrow linewidth of 23 meV for the wavelength range up to 1180 nm. An atomic force microscope study showed a flattened surface morphology by the introduction of the Sb. Broad-area lasers with a GaInAsSb/GaAs double-QW active layer emitting at 1170 nm showed a low threshold current density of 125 A/cm2 per well for an infinite cavity length.

Characterization by X-ray diffraction and electron microscopy of GaInAs and GaAsN single layers and quantum wells grown on GaAs

Abstract Experiments were performed on thick GaInAs and GaAsN layers and on GaInAs quantum wells grown on (1 1 1) B and (0 0 1) GaAs substrates. The aim of this work is to develop an experimental procedure in order to evaluate the chemical compositions and relaxation state of the samples at global as well as nanometre scale. Chemical analyses (EDS, RBS, etc.), X-ray diffraction (reciprocal space map, sin2ψ, etc.) and XTEM were carried out. The validity of the sin2ψ method on the above mentioned thin layers has been tested. Good accuracy is obtained for In and N composition but more work has to be done in order to optimize the determination of the relaxation state. Coupling TEM observations to these calculations gives valuable information on the relaxation mechanisms (misfit dislocations, stacking faults, microtwins, etc.).

GaInAs/GaAs quantum-well growth assisted by Sb surfactant: Toward 1.3 μm emission

The growth of highly strained GaInAs quantum wells on GaAs is investigated in the presence of Sb. Sb appears as an adequate isoelectronic surfactant: the lateral relaxation of strain is shown to be significantly delayed in comparison with a Sb-free growth. This effect is used to extend the emission wavelength of GaInAs quantum wells. We obtained a 9-nm-thick Ga0.59In0.41As0.986Sb0.008 quantum wells with smooth interfaces, emitting at 1.27 μm at room temperature.

In-plane photovoltage and photoluminescence studies in sequentially grown GaInNAs and GaInAs quantum wells

We have investigated in-plane photovoltage (IPV) and photoluminescence (PL) in sequentially grown Ga0.8In0.2As/GaAs and Ga0.8In0.2N0.015As0.985/GaAs quantum wells. Temperature, excitation intensity, spectral and time dependent study of the IPV, arising from Fermi level fluctuations along the layers of the double quantum well structure, gives valuable information about the nonradiative centers and hence about the optical quality of the GaInNAs quantum well. It also provides information about the radiative transition energies in all the layers. In order to obtain either the trap activation energies and the detrapping rates of photogenerated carriers in the GaInNAs the IPV results are analyzed in terms of a theoretical model based on random doping fluctuations in nominally undoped multilayer structures. The PL results are analyzed in terms of the band anticrossing model to obtain the electron effective mass from the coupling parameter CNM.

Analysis of Photoluminescence Efficiency of Annealed GaInNAs Quantum Well Grown by Solid Source Molecular Beam Epitaxy

ABSTRACTThe carrier dynamics of a 7.5 nm GaInNAs quantum well (QW) are studied by photoluminescence (PL) at a low temperature regime of 4 K to 150 K. The PL emission efficiency of the QW is initially evaluated to examine the recombination mechanisms in the QW. A dual-activation-energy model is later found to fit the integrated PL intensity vs. temperature curve better than a single-activation-energy model. The two states that correspond to the above activation energies could have resulted in a much faster PL intensity quenching in the GaInNAs QW as compared to that of a reference GaInAs QW. One of the states is identified as a localized state that traps carriers at a low temperature range of less than ∼100 K. The other state has a larger quenching effect at temperatures higher than 100 K and this state is not studied in this paper. By fitting the original PL spectra with two Gaussian functions, the temperature dependent PL integrated intensity of both Gaussian functions was also studied to further characterize the GaInNAs QW. The analysis gives evidence of the localization behaviour in this QW.

Growth and characterization of Ga0.8In0.2(N)As quantum wells with GaNxAs1−x(x⩽0.05) barriers by plasma-assisted molecular beam epitaxy

GaInNAs has received significant attention due to the ability to achieve 1300 nm wavelengths on GaAs substrates. In most cases, nitrogen is added directly into the GaInAs quantum wells, which degrades their optical properties. In this work, we investigate how the placement of nitrogen in Ga0.8In0.2As/GaAs heterostructures affects their optical characteristics. The location of nitrogen was studied in three different structures: nitrogen in barriers alone, nitrogen in wells alone, and nitrogen in the wells and barriers. Our results show that placing nitrogen in the barriers instead of wells provides better luminescence properties. We also observed that the addition of a GaAs spacer at the barrier-well interfaces further improves the luminescence properties of the structure.

Ferromagnetism in a quantum Hall system due to exchange enhancement in a GaInAs quantum well

We have investigated Ga 0.47In 0.53As/Al 0.48In 0.52As quantum well structures at magnetic fields close to the filling factor 1. At the critical current, a bistable and abrupt switching (transition width less than 4 ppm with respect to the filling factor) between quantum Hall conduction and dissipative conduction was observed at filling factors 1< ν<1.5. As confirmed by Hartree–Fock calculations, we attribute this switching to a feedback effect between the current-dependent population of different spin levels and the exchange-enhanced spin gap. The effect is accompanied by a ferromagnetic memory of the spin polarization when changing the external magnetic field.

Bandgap modification in GaInAs/InP quantum well structures using switched ion channelling lithography

A novel technique has been developed tolithographically modify GaInAs/InP quantum well (QW)structures. 10 MeV 69Ga3+ ions are implanted into a40 nm InP/ 9 nm GaInAs/InP (100) substrate along the [100] direction. A 50 nm thick Au mask switches a fraction of thealigned ions into dechannelling trajectories. The dechannelledions enhance the ion beam induced intermixing of the GaInAs QWwith the surrounding InP cladding layers. Low-temperaturephotoluminescence (PL) was used to study bandgap modificationof the GaInAs QW after implantation for a fluence range of 4×1011-4×1013 69Ga3+ ions cm-2. Alarger bandgap energy shift was observed with PL under the Aumask (28 meV) compared to areas not covered with the Au mask(12 meV). Furthermore, the integrated PL intensity was found tobe lower in the masked areas, which is consistent with agreater defect concentration in the regions under the Au mask.

High-temperature operating 1.3-μm quantum-dot lasers for telecommunication applications

High-performance 1.3-μm-emitting quantum-dot lasers were fabricated by self-organized growth of InAs dots embedded in GaInAs quantum wells. The influence of the number of quantum-dot layers on the device performance was investigated. Best device results were achieved with six-dot layers. From the length dependence; a maximum ground state gain of 17 cm/sup -1/ for six dot layers could be determined. Ridge waveguide lasers with a cavity length of 400 μm and high-reflection coatings show threshold currents of 6 mA and output powers of more than 5 mV. Unmounted devices can be operated in continuous wave mode up to 85/spl deg/C. A maximum operating temperature of 160/spl deg/C was achieved in pulsed operation for an uncoated 2.5-mm-long ridge waveguide laser.

Effect of Surface Quality on Overgrowth of Highly Strained GaInAs/GaAs Quantum Wells and Improvement by a Strained Buffer Layer

The introduction of a thin strained GaInAs buffer layer is proposed in the metalorganic chemical vapor phase deposition of GaInAs/GaAs quantum wells for ≥1.2 µm wavelength emission. This buffer layer is found to be very effective in improving the surface quality on which highly mismatched GaInAs quantum wells with an indium content around 40% are grown. Atomic force microscopy measurements demonstrate that the insertion of this strained GaInAs buffer layer can reduce the density of three dimensional islands in a highly strained GaInAs layer by one order of magnitude. We show that highly strained GaInAs/GaAs quantum wells with an indium content around 40% are more sensitive to surface quality than in the case of a lower indium content. This technique has enabled us to achieve a high-quality GaInAs/GaAs quantum well laser emitting at a wavelength near 1.2 µm.

Indium surface segregation in strained GaInAs quantum wells grown on (1̄ 1̄ 1̄) GaAs substrates by MBE

Surface segregation of indium during molecular beam epitaxy of Ga 0.85In 0.15As/GaAs ( 1 ̄ 1 ̄ 1 ̄ ) quantum wells is studied by means of in situ X-ray photoelectron spectroscopy measurements. The intensity ratio of In-4d/Ga-3d core-level spectra is used to precisely determine the amount of segregated Indium at the surface during the growth of GaInAs on GaAs substrates. GaAs ( 1 ̄ 1 ̄ 1 ̄ ) substrates exactly oriented and tilted 2° toward [ 2 1 ̄ 1 ̄ ] or [ 2 ̄ 1 1 ] have been investigated. The results are compared to those obtained on (1 0 0) GaAs substrates. We show that the amplitude of the In segregation phenomenon is larger for the GaAs ( 1 ̄ 1 ̄ 1 ̄ ) substrate tilted 2° toward [ 2 1 ̄ 1 ̄ ] than for the other substrates investigated for growth temperatures ranging from 380°C to 540°C. Having determined by atomic force microscopy the dependence of the terrace step structure of the GaAs ( 1 ̄ 1 ̄ 1 ̄ ) surface with the direction of the substrate tilt, we propose a kinetic explanation of our results. We show that an increase of the In segregation phenomenon is related to an increase of the adatom diffusion length obtained by an increase of the growth temperature and/or a modification of the terrace step structure.

Light-hole resonant tunnelling through tensile-strained GaInAs quantum wells

We have experimentally investigated the light- and heavy-hole states in tensile-strained GaInAs quantum wells using photoluminescence and photocurrent spectroscopies. Under special conditions, the strain resulting from the lattice mismatch is large enough to reverse the order of the light- and heavy-hole levels (the first light-hole level becomes the ground state). We obtained an experimental light-to-heavy-hole splitting of 50 meV in agreement with calculations. To take advantage of this situation, we realized and characterized the first p-i-p resonant tunnelling diode on an InP substrate. Resonances are clearly visible in the conductance-voltage characteristics but the first resonance is not yet enhanced as expected in this structure. We discuss the reasons that prevent the observation of the first light-hole resonance.

Faceted GaInAs/InP nanostructures grown by selective area chemical beam epitaxy

InP was grown by chemical beam epitaxy in narrow windows of widths varying between 20 and 2 μm, oriented along the [011] or [01̄1] directions opened in a SiO2 mask on an (001) InP substrate. Several facets appear along the sidewalls and on the edge of the mesas owing to different growth rates on different crystallographic planes. These can be understood as consequences of the migration of group III species from one crystallographic plane to another. We have studied the formation of such facets and their effects on the growth of GaInAs/InP structures of various thicknesses. The samples were studied using a field emission scanning electron microscope (SEM) and low temperature photoluminescence (PL). SEM micrographs show that for lines oriented along the [011] direction the dominant InP sidewall facets are (111)B planes on which GaInAs does not grow as long as Ga and In species can migrate towards (001). For the orthogonal direction, however, the lateral growth rate of the InP sidewalls is large and the faceting of the mesas is more complicated. The PL spectra of GaInAs quantum wells grown on such mesas exhibit several peaks whose energy depends on the initial width of the mask. They can be interpreted in terms of crystallographic plane dependent migration and desorption rates of Ga and In species. The (111)B facets of [011] directed mesas were used to produce inverted V-shaped mesa wire structures.

High-Power Infrared (8-Micrometer Wavelength) Superlattice Lasers

A quantum-cascade long-wavelength infrared laser based on superlattice active regions has been demonstrated. In this source, electrons injected by tunneling emit photons corresponding to the energy gap (minigap) between two superlattice conduction bands (minibands). A distinctive design feature is the high oscillator strength of the optical transition. Pulsed operation at a wavelength of about 8 micrometers with peak powers ranging from approximately 0.80 watt at 80 kelvin to 0.2 watt at 200 kelvin has been demonstrated in a superlattice with 1-nanometer-thick AlInAs barriers and 4.3-nanometer-thick GaInAs quantum wells grown by molecular beam epitaxy. These results demonstrate the potential of strongly coupled superlattices as infrared laser materials for high-power sources in which the wavelength can be tailored by design.

Weak antilocalization and spin precession in quantum wells.

The results of magnetoconductivity measurements in GaInAs quantum wells are presented. The observed magnetoconductivity appears due to the quantum interference, which lead to the weak localization effect. It is established that the details of the weak localization are controlled by the spin splitting of electron spectra. A theory is developed which takes into account both linear and cubic in electron wave vector terms in spin splitting, which arise due to the lack of inversion center in the crystal, as well as the linear terms which appear when the well itself is asymmetric. It is established that, unlike spin relaxation rate, contributions of different terms into magnetoconductivity are not additive. It is demonstrated that in the interval of electron densities under investigation (0.98-1.85)*10^(12) 1/cm^2 all three contribution are comparable and have to be taken into account to achieve a good agreement between the theory and experiment. The results obtained from comparison of the experiment and the theory have allowed us to determine what mechanisms dominate the spin relaxation in quantum wells and to improve the accuracy of determination of spin splitting parameters in A3B5 crystals and 2D structures.

Universal Behaviour of Magnetoconductance due to Weak Localization in Two-Dimensional Systems - Example of GaInAs Quantum Wells

Weak localization corrections to conductivity of a two-dimensional electroii gas are studied by measurements of the magnetic field dependence of the conductivity in GalnAs quantum wells. We observe that, when presented as a function of the normalized magnetic field (x = B/Btr , where B is the magnetic field, B« = h/4eτD, D is the dichusion constant and τ is momentum relaxation time), dicherent samples show very similar high field behaviour. A theoretical description is developed that allows one to describe in a consistent way high and low field behaviour. The theory predicts universal (B -1 /2 ) behaviour of the conductivity correction for all 2D systems in the high field limit (r > 1). Low field behaviour depends strongly on spin and phase relaxation mechanisms. Comparison of the theory with experiment confirms the universal behaviour in the high fleld limit and allows one to estimate the spin and phase relaxatioii times for dicherent GalnAs quantum wells.

Dry-etched wire distributed feedback laser

We report on the realization and the properties of dry-etched wire and wire-DFB lasers and compare them with two-dimensional (2-D) reference lasers. The starting vertical structure, which was optimized for low threshold, consists of four GaInAs quantum wells embedded in a GaInAsP waveguide. Even for very small longitudinal confinement factors of the order 0.23, the dry-etched wire lasers show laser operation up to 60/spl deg/C and a threshold current density at room temperature of 5 kA/cm/sup 2/ for simple oxide stripe lasers. For the wire lasers, an increase of the differential material gain of more than one order of magnitude (about a factor of 20) was measured, compared to conventional 2-D lasers. The wires were also arranged periodically with different grating constants to allow gain-coupled DFB laser operation. Clear single-mode emission has been found, as expected, from the gain-coupling mechanism. >

Strong Stark effect of the intersubband transitions in the three coupled quantum wells: Application to voltage-tunable midinfrared photodetectors

The quantum-confined Stark effect in the AlInAs/GaInAs three-coupled-quantum-well (TCQW) structures is studied theoretically. The basic AlInAs/GaInAs TCQW structures are composed of three GaInAs quantum wells separated by two narrow AlInAs barriers. Results indicated that the three-depth TCQW structure exhibits a very large and near-linear voltage-control Stark shift for the energy of the 1→4 intersubband transition (ΔE41). The amount of the Stark shift of calculated intersubband energy separation ΔE41 is about 175 meV as the applied electric field varied from −90 to 90 kV/cm. This large Stark shift can be exploited for fabricating a voltage-tunable midinfrared photodetector operating in λ=3–5 μm atmospheric window region. By employing the enhanced Stark shift of the 1→4 intersubband transition in the three-depth TCQW structure, a highly sensitive voltage-tunable midinfrared photodetector is proposed. The operation of this device is based on the infrared absorption by electrons in the ground-state subband E1 transited to the third-excited-state subband E4 of the TCQW. Since the infrared radiation is absorbed via the intersubband resonance absorption (ℏω=E4−E1), the detected infrared wavelength can be tuned by the ΔE41 which can be adjusted by an applied electric field. The tunability of this three-depth TCQW structure has been studied theoretically. Based on the theoretical calculations, a tuning range from 3 to 5 μm is predicted for the three-depth TCQW structure by varying the applied electric field in the 90 to −80 kV/cm range.

AlGaInAs/InP 1.5 µm MQW DFB laser diodesexceeding 20 GHz bandwidth

Buried mushroom multiquantum well DFB laser diodes with compressively strained GaInAs quantum wells and asymmetric confinement layer design are fabricated with a combined MBE/MOCVD technology. Packaged devices exhibit high –3 dB IM bandwidths for very low bias levels and a record bandwidth for this material system of 21 GHz.