Strained-layer Single Quantum Research Articles

Effects of temperature on transition energies of GaAsSbN/GaAs single quantumwells

The energy transitions of GaAsSbN/GaAs strained-layer single quantum wells (QWs),grown by molecular-beam epitaxy, are studied in detail, using photoluminescence (PL) andphotoreflectance (PR) spectroscopies. The optical transitions energy observed in the PLand PR spectra of GaAsSbN/GaAs QWs show a strong decrease with a small increase inthe N composition. These effects are explained through the interaction between theconduction band and a narrow resonant band formed by nitrogen states in the GaAsSbNalloy. The temperature dependence of ground-state energy of strained-layer QWs isanalyzed using the Bose–Einstein relation in the temperature range from 9 to 295 K. Theparameters that describe the temperature variations of the ground-state energies areevaluated and discussed.

Tomographic Characterization of Dislocations in Failure Regions of Broad Area InGaAs/AlGaAs Strained Layer Single Quantum Well High Power Laser Diodes

Extended abstract of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 – July 30, 2009

Temperature-dependent photoluminescence spectra of GaAsSb/AlGaAs and GaAsSbN/GaAs single quantum wells under different excitation intensities

The mechanism for low-temperature photoluminescence (PL) emissions in GaAsSb/AlGaAs and GaAsSbN/GaAs strained-layer single quantum wells (SQWs), grown by molecular-beam epitaxy, is studied in detail, using PL spectroscopy as a function of temperature and excitation intensity. In all samples, the PL peak energy as well as the full width at half maximum (FWHM), as a function of temperature, present anomalous behaviors, i.e., the PL peak energy shows a successive red/blue/redshift (S-shaped behavior) and the FWHM shows a successive blue/red/blueshift ("inverted S-shaped curve") with increasing temperature. At sufficiently low excitation intensity and in a narrow temperature interval (50 - 80 K), the nitrogen-containing samples present two clear competitive PL peaks. The low-energy PL mechanism (8 - 80 K) is dominated by localized PL transitions, while the high-energy PL mechanism is dominated by the ground state (e1-hh1) PL transition. Additionally, these PL peaks show different temperature dependence with the low-energy PL peak, showing a stronger redshift than the high-energy PL peak. A competition process between localized and delocalized excitons is used to discuss these PL properties.

Effect of temperature on the optical properties of GaAsSbN/GaAs single quantum wells grown by molecular-beam epitaxy

GaAsSbN/GaAs strained-layer single quantum wells grown on a GaAs substrate by molecular-beam epitaxy with different N concentrations were studied using the photoluminescence (PL) technique in the temperature range from 9 to 296 K. A strong redshift in optical transition energies induced by a small increase in N concentration has been observed in the PL spectra. This effect can be explained by the interaction between a narrow resonant band formed by the N-localized states and the conduction band of the host semiconductor. Excitonic transitions in the quantum wells show a successive red/blue/redshift with increasing temperature in the 2–100 K range. The activation energies of nonradiative channels responsible for a strong thermal quenching are deduced from an Arrhenius plot of the integrated PL intensity.

Optical properties of ZnS/ZnMgS strained-layer quantum wells

We report optical properties of ZnS/ZnMgS strained-layer single quantum wells. The main photoluminescence (PL) peak from ZnS is attributed to light-hole (LH) free excitons. The emission due to heavy-hole (HH) excitons was also observed. With decreasing well width, these emission lines shift to higher energy owing to quantum confinement. Time-resolved PL spectra suggest rapid relaxation from HH band to LH band in the ZnS well. Localization of excitons in the ZnMgS barrier, which is due to fluctuation of alloy composition, is also suggested. On the other hand, localization of excitons in the ZnS well, caused by the fluctuation of the well width, was hardly observed for the sample with good quality. The LH exciton emission showed fast initial decay time of 16–36 ps, which seems to also depend on the sample quality.

Photoluminescence study of ZnS/ZnMgS single quantum wells

We report a photoluminescence (PL) study of ZnS/ZnMgS strained-layer single quantum wells. The main PL peak from ZnS is attributed to light-hole free excitons. Quantum confinement causes it to shift from 3.76 eV to higher energy, 3.84 eV, with decreasing well width. Hydrostatic and shear deformation potentials are determined from energies of light- and heavy-hole exciton emission, to be a=−6.4 eV and b=−1.0 eV, respectively.

Localized excitonic emissions of ZnCdSe/ZnSe quantum wells grown on a GaAs(110) cleaved surface

Anomalous optical properties of Zn1−xCdxSe/ZnSe strained-layer single quantum wells (SQWs) fabricated on cleaved GaAs(110) surfaces in ultrahigh vacuum by molecular beam epitaxy have been investigated. From the temperature-dependent photoluminescence measurement, the origins of localized excitonic emissions of two kinds of SQW structures with different Cd compositions are suggested. Localization centers of SQWs with low Cd composition (14%) are mainly originated by the well thickness fluctuation. However, SQWs with high Cd composition (27%) showed localized excitonic emissions at low temperature due to the Cd composition fluctuations rather than the lack of thickness uniformity of the well layer. Estimated averaged depths of localization of excitons by model calculations are 9 and 14 meV for the wells with 14% and 27% Cd compositions, respectively.

ＩｎＧａＡｓ／ＧａＡｓ単一ひずみ量子井戸薄膜の低温成長に関する研究

InGaAs/GaAs strained-layer single quantum well (SSQW) structures have been grown at temperatures from 200 to 540°C by migration enhanced epitaxy (MEE). Fabricated structures were characterized by comparing the measured wavelength of photoluminescence (PL) emission peak with the theoretically calculated one for ideal quantum wells. In the SSQWs made at high temperatures (400 - 540°C), large PL peak shifts to the shorter wavelengths than the calculated ones were observed. This blue shift of the PL peak was attributed to the surface segregation and desorption of In atoms. Lowering the growth temperature of MEE below 300°C, the In segregation was suppressed and the designed PL wavelength from the SSQW was obtained. It was shown that the preparation of GaAs (2 × 4) -As surface without excess Assticking and the long migration time of group III atoms were needed to obtain the high PL intensity from SSQW.

Electroluminescence of GaInSb/GaSb strained single quantum well structures grown by molecular beam epitaxy

GaSb-based heterostructures with strained-layer (x = 0.26 or x = 0.35) single quantum wells and cladding layers were grown by molecular beam epitaxy. The thickness of the GaInSb well was varied from 3.0 to 14.5 nm. Intense room-temperature electroluminescence was observed from mesa diodes with peak emission wavelengths in the spectral range. The dependence of emission energy on well thickness is consistent with the predictions obtained by an effective mass treatment assuming a rectangular type I quantum well and a conduction band offset .

The determination of the band offsets in strained-layer InxGa1-xAs/GaAs quantum wells by low-temperature modulation spectroscopy

We report a determination of the conduction-band offset ratio Oc of the InxGa1-xAs/GaAs strained-layer single quantum wells by low-temperature modulation spectroscopy. Various modulation reflectance measurements include contactless electroreflectance (CER), photoreflectance (PR) and piezoreflectance (PZR) are carried out on four different samples at room temperature and 20 K. The samples have In composition x=0.05 (sample A), 0.11 (sample B), 0.14 (sample C) and 0.21 (sample D) respectively. A number of allowed and forbidden excitonic transitions have been observed. The light-hole transitions were unambiguously identified by comparing the CER spectra with different modulation strengths. The origins of the various spectral features have been assigned by comparison with an envelope-function calculation taking into account the effects of strain. Good agreement between experiments and theory is achieved by taking Qc=0.46+or-0.05, 0.50+or-0.10, 0.54+or-0.07 and 0.63+or-0.05 for samples A, B, C and D respectively. It has been shown that Oc depends linearly with the In composition x between 0.05 and 0.21.

Observation of “parity-forbidden” optical transitions in GaAs/GaAsP strained-layer quantum well

The photoluminescence (PL) of the GaAs/GaAsP strained-layer single quantum well structures have been investigated in detail. It was observed in the PL spectra that besides the normal “parity-allowed” n=1 electron to heavy hole excitonic transition, le-1hh, there are several relatively weak but unambiguous emission peaks which appear at the high energy side of the dominant le-1hh. The good agreement of the experiment with the calculation suggests that the “parity-forbidden” combinations should be responsible for these anomalous optical transitions.

Temperature dependence of photoluminescence linewidth in GaAs/GaAsP strained-layer quantum well structures

The temperature dependence of photoluminescence (PL) spectra for the GaAs/GaAsP strained-layer single quantum well structures has been investigated in detail. For temperatures below 77 K, the PL linewidth was found to first decrease and then to increase slowly as the temperature was enhanced. This phenomenon was clearly seen for the GaAs/GaAsP strained-barrier quantum wells exhibiting higher dislocation densities than the GaAs/GaAsP strained-well quantum wells. This fact strongly suggests that beside the unintentionally introduced impurities, the misfit dislocations may also play an important role in determining the temperature-dependent PL linewidth.

Growth of CdTe/CdZnTe strained-layer single quantum wells by modified hot-wall epitaxy method and their properties

Several CdTe/CdZnTe strained-layer single quantum well (SLSQW) structures, with CdTe well width ranging from 15 to 240 Å, were grown on GaAs(100) substrates, by modified hot-wall epitaxy (HWE) method for the first time. Our HWE system is equiped with a gold tube radiation shield which is more effective in heat confinement and temperature stability than conventional metal tubes. Photoluminescence (PL) measurements of SLSQW showed that the sharp e 1h 1 excitonic transition peaks in the range of 1.597 to 1.624 eV shifted to the higher energy with decreasing well width. From the PL excitation (PLE) measurements of SLSQW, we obtained the n = 1, 2, 3 and n = 1, 2 excitonic transition peaks for the 240 and 120 Å CdTe well width SLSQW structures, respectively. The excitonic transition energies were calculated considering strain effects and this results were agreed well with experimental ones considering the exciton binding energy. Moreover, the FWHMs of excitonic transition peaks obtained from PL and PLE measurements were about 2 meV and Stokes shifts between PL and PLE spectra were about 1 meV. It indicates that the SLSQWs grown by HWE in this study have a high quality comparable to MBE-grown ones.

A corner reflector InGaAs-GaAs strained layer single quantum well coupled laser array

An InGaAs-GaAs-AlGaAs strained layer single quantum laser array with a reactive ion etched corner reflector array as its rear facet has been fabricated. The corner reflectors play a two-fold role as a highly reflective rear mirror and as a phase-locking coupler. Phase locked operation with beam widths as low as 0.64/spl deg/ are obtained at pumping currents up to 4/spl times/I/sub th/ and output powers up to 60 mW. The coupling mechanism and the benefit of the corner reflector to output performance are discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Strained single quantum well InGaAs lasers with a threshold current of 0.25 mA

Strained layer single quantum well InGaAs lasers with a record low threshold current of 1 mA for as-cleaved facets and 0.25 mA with high reflectivity coated facets have been demonstrated. In addition, these lasers display a weak dependence of threshold current, quantum efficiency, and lasing wavelength on cavity length in comparison with those single quantum well lasers previously reported.

Strained layer GaAs1−yPy-AlGaAs and InxGa1−xAs-AlGaAs quantum well diode lasers

Separate confinement strained layer single quantum well diode lasers on GaAs substrates have been fabricated by low-pressure organometallic vapor phase epitaxy. Laser diode structures with a 90 Å quantum well under compressive strain, composed of InxGa1−xAs with x=0.00–0.17, as well as tensile strain, composed of GaAs1−yPy with y=0.00–0.29, have been studied. The emission wavelength ranges from λ=746 nm for y=0.29 up to λ=962 nm for x=0.17. The strain dependence of the threshold current for broad area devices is studied both experimentally and theoretically as a function of temperature. Regions of optimal laser performance, one for compressive and one for tensile strain, are identified.

Very high modulation efficiency of ultftalow threshold current single quantum well InGaAs lasers

A record high current modulation efficiency of 5 GHz/[sqrt](mA) has been demonstrated in an ultralow threshold strained layer single quantum well InGaAs laser.

Strained layer single quantum well double-heterostructure optoelectronic switching laser

The double-heterostructure optoelectronic switch (DOES) has been demonstrated as a strained layer single quantum well laser. Broad area laser devices exhibited the lowest threshold currents (77 A/cm2 for a 2000 μm device length) ever reported for DOES devices. The devices had ideal electrical switching characteristics of 7.2 V and 1.0 mA/cm2 at the switching condition and 1.6 V and 0.4 A/cm2 at the holding condition. The switching and holding currents are also the lowest reported for any DOES device. For the lasers, the loss was measured to be 7.5 cm−1 and an external efficiency as high as 0.6 W/A was measured for a 400 μm device length.

Many Body Effects in Strained Quantum Well Lasers

ABSTRACTUnusually large transverse magnetic component has been observed at energy corresponding to the edge of heavy hole band in the optical emission from unstrained and strained layer single quantum well lasers above threshold condition. The existing model of Fermi sea shake-up is inadequate to explain the enhancement in the TM component beyond lasing threshold. Our results indicate that under lasing conditions the directional properties of the emitting dipole arising from electronic transitions to the heavy hole band is modified such that the dipole moment has equal projections in x, y and z directions.

Metalorganic molecular beam epitaxial growth and characterization of CdSe/ZnSe strained-layer single quantum wells and superlattices on GaAs substrates

Reflection high-energy electron diffraction (RHEED) oscillations that continued up to three cycles were observed during metalorganic molecular-beam epitaxial growth of CdSe on a ZnSe buffer grown on a GaAs substrate, showing two-dimensional layer-by-layer growth despite the large lattice mismatch (6.85%). Based on this result, we could definitely control the growth of CdSe/ZnSe strained-layer single quantum wells with well widths of 1–3 monolayers and of short-period superlattices under in situ RHEED monitoring. Optical properties strongly demonstrated the successful formation of well-defined structures consisting of these highly strained II-VI semiconductor multilayers.