GaAsSb Quantum Wells Research Articles

Dual-frequency GaAs/InGaP laser diode with a GaAsSb quantum well

The results of investigation of a metal-organic-vapor-phase-epitaxy-grown GaAsSb/GaAs/InGaP laser structure are presented. Steady two-band generation caused by spatially direct and indirect optical transitions is obtained. Observation of the sum frequency shows the effective intracavity mixing of modes in semiconductor lasers of such a type.

Study of GaAsSb/GaAs type-II quantum well with top InAs quantum dot layer using complementary spectroscopy techniques

The optical characterization of GaAsSb/GaAs type-II quantum wells (QWs) with top InAs quantum dot (QD) layer composite structures was carried out using the complementary surface photovoltage (SPV) and photoluminescence (PL) spectroscopies. The obtained SPV and PL spectra revealed that the features originated from InAs QDs, modulated potential wells in GaAsSb QWs, the wetting layer (WL) as well as the GaAs cap layer/barrier at room temperature. The optical transition from the modulated potential wells in GaAsSb QWs in the composite structures showed a redshift when the spacer layer was narrowed from 10 to 5 nm. This is attributed to the lower modulated potential minimum in GaAsSb QWs caused by the strain exerted by InAs QDs in the composite structures with the narrower spacer layer. The power-dependent PL measurement showed that the luminescences from the GaAsSb/GaAs heterostructure blue-shifted with increasing excitation power owing to the type-II band alignment. These results demonstrated that SPV and PL are useful techniques for the nondestructive optical characterization of GaAsSb QWs with top InAs QD composite structures.

Structural and optical properties of GaAsSb QW heterostructures grown by laser deposition

The possibility of using the laser deposition method to grow crystalline light-emitting structures with GaAsSb/GaAs quantum wells (QWs) is experimentally demonstrated for the first time. The growth temperature of the GaAs1 − xSbx layers is varied within the range 450–550°C; according to X-ray diffraction analyses, the content of antimony reaches xSb ≈ 0.37 at a growth temperature of 450°C. Low-temperature (4 K) photoluminescence spectroscopy demonstrates the presence of a peak associated with the GaAsSb/GaAs QW at around 1.3 μm at the minimum laser-light pumping level. The optimal growth temperature Tg = 500°C and arsine flow rate PA = 2.2 × 10−8 mol/s at which the best emission properties of QWs with xSb ∼ 0.17–0.25 are observed at temperatures of 77 and 300 K are determined. It is shown that GaAsSb/GaAs QWs with similar parameters (width and composition) grown by laser deposition at 500°C and metal-organic vapor-phase epitaxy at 580°C have comparable optical quality.

InAs/GaAsSb quantum dot solar cells.

The hybrid structure of GaAs/GaAsSb quantum well (QW)/InAs quantum dots solar cells (QDSCs) is analyzed using power-dependent and temperature-dependent photoluminescence. We demonstrate that placing the GaAsSb QW beneath the QDs forms type-II characteristics that initiate at 12% Sb composition. Current density-voltage measurements demonstrate a decrease in power efficiency with increasing Sb composition. This could be attributed to increased valence band potential in the GaAsSb QW that subsequently limits hole transportation in the QD region. To reduce the confinement energy barrier, a 2 nm GaAs wall is inserted between GaAsSb QW and InAs QDs, leading to a 23% improvement in power efficiency for QDSCs.

Waveguide effect of GaAsSb quantum wells in a laser structure based on GaAs

The waveguide effect of GaAsSb quantum wells in a semiconductor-laser structure based on GaAs is studied theoretically and experimentally. It is shown that quantum wells themselves can be used as waveguide layers in the laser structure. As the excitation-power density attains a value of 2 kW/cm2 at liquid-nitrogen temperature, superluminescence at the wavelength corresponding to the optical transition in bulk GaAs (at 835 nm) is observed.

The influence of growth conditions on carrier recombination mechanisms in 1.3 μm GaAsSb/GaAs quantum well lasers

We investigate the temperature and pressure dependence of the threshold current density of edge-emitting GaAsSb/GaAs quantum well (QW) lasers with different device characteristics. Thermally activated carrier leakage via defects is found to be very sensitive to the growth conditions of GaAsSb QWs. An optimization of the growth conditions reduces the nonradiative recombination mechanisms from 93% to 76% at room temperature. This improvement in carrier recombination mechanisms leads to a large improvement in the threshold current density from 533 Acm−2/QW to 138 Acm−2/QW and the characteristic temperature, T0 (T1), from 51 ± 5 K (104 ± 16 K) to 62 ± 2 K (138 ± 7 K) near room temperature.

Fabrication and properties of GaAsSb/GaAs heterostructures doped with a magnetic impurity

Structures made up of a GaAsSb/GaAs quantum well (QW) and δ-layers of manganese and carbon in the GaAs cap layer have been grown and studied for the first time. The resulting heteronanostructures have good crystal perfection, which is confirmed by X-ray diffraction analysis and photoluminescence studies. It was found that, at temperatures below 20–25 K, the heteronanostructures have ferromagnetic properties as they exhibit nonlinear magnetic-field dependences of the Hall resistance and a negative magnetoresistance. Profiling of the elemental composition by secondary ion mass spectrometry revealed the opposite effect of δ doping the GaAs cap layer with carbon and manganese on the profile of the GaAsSb QW: the introduction of carbon makes the GaAsSb/GaAs heterointerface less abrupt due to the segregation of antimony, whereas doping with manganese hardly affects the antimony distribution profile in the QW.

Photoluminescence and Band Alignment of Strained GaAsSb/GaAs QW Structures Grown by MBE on GaAs

An in-depth optimization of growth conditions and investigation of optical properties including discussions on band alignment of GaAsSb/GaAs quantum well (QW) on GaAs by molecular beam epitaxy (MBE) are reported. Optimal MBE growth temperature of GaAsSb QW is found to be 470 ± 10 °C. GaAsSb/GaAs QW with Sb content ~0.36 has a weak type-II band alignment with valence band offset ratio QV ~1.06. A full width at half maximum (FWHM) of ~60 meV in room temperature (RT) photoluminescence (PL) indicates fluctuation in electrostatic potential to be less than 20 meV. Samples grown under optimal conditions do not exhibit any blue shift of peak in RT PL spectra under varying excitation.

Strained GaAsSb/GaAs QW structures grown by MBE on GaAs (1 0 0) for applications near 1.3 micron

An in-depth optimization of growth conditions and investigation of optical properties of GaAsSb quantum well (QW) on GaAs—through different designs of barrier and cladding layers grown by molecular beam epitaxy (MBE)—are reported. Optimal MBE growth temperature of GaAsSb QW is found to be 470±10 °C. GaAsSb/GaAs QW with ∼0.36 Sb mole fraction has a weak type-II band alignment with a valence band offset ratio, Q V around 1.06. A full-width at half-maximum (FWHM) of ∼60 meV in room temperature (RT) photoluminescence (PL) spectrum indicates less than 20 meV fluctuation in electrostatic potential. Samples grown under optimal conditions do not exhibit any blueshift of peak in RT–PL spectra under varying excitation intensities.

A study of the low‐energy interference oscillations in photoreflectance of GaAsSb/GaAs quantum well structures

AbstractWe present a room temperature photoreflectance (PR) investigation of GaAsSb/GaAs/AlGaAs quantum well (QW) structures grown on GaAs substrates by molecular beam epitaxy. We encounter strong low energy interference oscillations (LEIO), which tend to obscure any PR signals arising from the QW. By varying the angle of incidence, we exploit the LEIO to estimate the refractive index of the layer responsible and thus identify it. Furthermore, we demonstrate the ability to model the lineshapes of the observed LEIO accurately, through calculations of the Seraphin coefficients. This then allows us to deduce the actual thickness of the layer responsible, which is found to be close to the nominal value. These calculations in turn suggest a way to avoid the LEIO – by shortening the laser excitation wavelength. This successfully reveals good PR signals from the QW region, yielding several transition wavelengths, which we then compare with a theoretical model, assuming a small type II offset between GaAsSb QW and GaAs spacer layers. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Growth of strained GaAsSb layers on GaAs (0 0 1) by MOVPE

We investigated the growth of GaAsSb layers and quantum wells (QW) on GaAs (0 0 1) by MOVPE. Sb concentrations up to 12% were achieved at low arsine partial pressure and low growth temperature. Varying the tri-methyl antimony pressure primarily changed the growth rate but not the Sb incorporation. The in situ reflectance anisotropy spectrum during growth resembles that of a GaSb surface. Sb has a strong tendency towards segregation and is only incorporated after reaching a certain critical surface coverage. These findings can be explained by a very mobile and highly Sb enriched surface layer which forms by surface melting due to strain.

Enhanced photoluminescence from GaAsSb quantum wells

We describe promising semiconductor materials for optoelectronics. GaAsSb/AlSb quantum wells on GaSb substrates show photoluminescence near 1.54 μm (0.8 eV) that increases with increasing arsenic fraction. The materials can be monolithically integrated with AlGaSb/AlSb or AlGaAsSb/AlAsSb Bragg mirrors.

Long-wavelength strain-compensated GaAsSb quantum-well heterostructures laser grown by metalorganic chemical vapor deposition

We report data on strain-compensated GaAsSb double-quantum-well lasers having a type-I band alignment and grown by metalorganic chemical vapor deposition on GaAs substrates. In order to compensate for strain effects and to establish a type-I band alignment, tensile-strained higher-band-gap GaAsP quantum-well barriers have been employed. A lasing wavelength of λ∼1.200 μm from a 500 μm long device at 1.15Ith has been achieved at room temperature in pulsed-mode operation. The maximum output power was 20 mW for the same device. A low threshold current density of 608.0 A/cm2 was obtained for 1370 μm long and 60 μm stripe lasers. The calculated internal quantum efficiency and internal loss were 33.8% and 8.4 cm−1, respectively. We also calculated an infinite cavity length threshold current density of 265 A/cm2. From these data, a gain constant G0∼1728 cm−1 and transparency current density of 135 A/cm2 were calculated. The result showed that the strain-compensated GaAsSb quantum wells are promising active materials for 1.3 μm vertical-cavity surface-emitting lasers.

Low Temperature Photoluminescence Studies of Narrow Bandgap Gaassbn Quantum Wells on GaAs

We present low-temperature (T = 4K) photoluminescence studies of the effect of adding nitrogen to 6-nm-wide single-strained GaAsSb quantum wells on GaAs. The samples were grown by both MBE and MOCVD tech-niques. The nominal Sb concentration is about 30%. Adding about 1 to 2% N drastically reduced the bandgap energies from 1 to 0.75 eV, or 1.20 to 1.64 μm. Upon performing ex situ rapid thermal anneals, 825°C for 10s, the band gap energies as well as the photoluminescence intensities increased. The intensities increased by an order of magnitude for the annealed samples and the band gap energies increased by about 50 - 100 meV, depending on growth temperatures. The photoluminescence linewidths tended to decrease upon annealing. Preliminary results of a first-principles band structure calculation for the GaAsSbN system are also presented.

Properties of GaAsSb QW Heterostructures Having Various Barrier Materials Grown by Metalorganic Chemical Vapor Deposition

ABSTRACTPseudomorphic GaAs1-xSbx quantum-well (QW) structures grown on GaAs substrates by metalorganic chemical vapor deposition (MOCVD) have been studied with various barrier materials to investigate the energy band lineup. To determine the band lineup of these structures, we have performed low-temperature current-dependent cathodoluminescence (LT-CL) measurements at 10K. For the structure with GaAs barriers, the data show strong evidence of Type-II staggered band lineup, which means that holes are confined in the valence band heavy-hole level of the GaAs1-xSbx quantum well and electrons are confined in the conduction band of the GaAs barrier.For the InGaP barriers, however, we observed only one peak that is related to transitions of a Type-I band lineup. From the LT-CL results, we find that the valence-band discontinuity ratio (Qv) between the GaAs0.73Sb0.27 double quantum wells (DQWs) and the GaAs barriers is ∼1.20. Furthermore, to improve the carrier confinement, we propose that InGaP barriers provide a Type-I band lineup with the GaAsSb QW.

Growth and optical properties of GaAsSb quantum wells for 1.3 μm VCSELs

We report compositional dependencies of the 2d–3d growth mode transition for GaAsSb on GaAs. In addition, Sb incorporation, desorption, and segregation versus growth temperature and V/III ratio are measured by secondary-ion-mass spectroscopy. Photoluminescence investigations of Sb compositional dependence of GaAsSb quantum wells and confinement in heterojunctions are reported.

Continuous-wave operation of 1.30 µm GaAsSb/GaAsVCSELs

1.30 /spl mu/m VCSELs using GaAsSb quantum wells, which operate continuous-wave at and above room temperature (RT), are reported. A threshold current as low as 1.2 mA at RT and a maximum CW operating temperature of 70/spl deg/C are demonstrated.

Low-threshold operation of 1.3-/spl mu/m GaAsSb quantum-well lasers directly grown on GaAs substrates

GaAsSb quantum-well (QW) edge-emitting lasers grown on GaAs substrates were demonstrated. The optical quality of the QW was improved by optimizing the growth conditions and introducing a multi-QW to increase the gain. As a result, 1.27-μm lasing of a GaAs/sub 0.66/Sb/sub 0.34/-GaAs double-QW laser was obtained with a low-threshold current density of 440 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , which is comparable to that in conventional InP-based long-wavelength lasers. 1.30 μm lasing with a threshold current density of 770 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> was also obtained by increasing the antimony content to 0.36. GaAsSb QW was found to be a suitable material for use in the active layer of a 1.3-μm vertical-cavity surface-emitting lasers.

Room temperature low-threshold CW operationof 1.23 µm GaAsSb VCSELs on GaAs substrates

Room temperature (RT) continuous-wave (CW) operation of vertical-cavity surface-emitting lasers (VCSELs) with GaAsSb quantum wells on GaAs substrates has been demonstrated. A 6 × 6 µm2 oxide-confined device exhibited RT-CW lasing with a threshold current of 0.7 mA at 1.23 µm, which is the longest reported wavelength of GaAs-based VCSELs yet reported.

GaAsSb: A novel material for 1.3 µm VCSELs

GaAsSb quantum wells (QWs) on GaAs substrate are proposed for the active layer of 1.3 /spl mu/m VCSELs. High-quality GaAsSb QWs showed intense 1.32 /spl mu/m photoluminescence at room temperature. Room-temperature pulsed operation of GaAsSb/GaAs broad stripe laser diodes at a wavelength of 1.22 /spl mu/m was demonstrated for the first time.