GaInAs Quantum Wells Research Articles

Emission Variation of InAs Quantum Dots within (Al)GaInAs Quantum Wells in AlGaAs/GaAs Structures vs Quantum Well Compositions

The parameters of quantum dots (QDs) of InAs inserted in Al0.30Ga0.70As/GaAs hetero structures with additional cap/buffer AlGaInAs quantum wells (QWs) of different compositions have been investigated by photoluminescence, transmission electron microscopy and high-resolution X-ray diffraction methods. QD structures with the buffer layers: In0.15Ga0.85As (#1) or In0.25Ga0.75As (#2) and covering (cap) layers: Al0.10In0.15Ga0.75As (#1) or Al0.40In0.15Ga0.45As (#2), are compared. Structure #1 is characterized by a higher density of QDs, high QD emission intensity and a smaller full width at half maximum of the PL bands, compared to #2. The dependence of the intensity of QD emission against temperatures of 10–500 K has been studied. Significant thermal quenching of the PL intensity was revealed in #1 compared to #2. HR-XRD investigation has confirmed that QD structures are of perfect crystalline quality with sharp QW interfaces and a high number of Pendellösung peaks were detected. To fit the HR-XRD scans, the X′Pert Epitaxy software has been applied. The peculiarities of the QD emission and the parameters of the HR-XRD scans are compared, as well as the advances of the QD structures studied are discussed.

Virtual cavity in distributed Bragg reflectors.

We show theoretically and experimentally that distributed Bragg reflector (DBR) supports a surface electromagnetic wave exhibiting evanescent decay in the air and oscillatory decay in the DBR. The wave exists in TM polarization only. The field extension in the air may reach several wavelengths of light. Once gain medium is introduced into the DBR a novel class of diode lasers, semiconductor optical amplifiers, light-emitting diodes, etc. can be developed allowing a new type of in-plane or near-field light outcoupling. To improve the wavelength stability of the laser diode, a resonant cavity structure can be coupled to the DBR, allowing a coupled state of the cavity mode and the near-field mode. A GaAlAs-based epitaxial structure of a vertical-cavity surface-emitting laser (VCSEL) having an antiwaveguiding cavity and multiple GaInAs quantum wells as an active region was grown and processed as an in-plane Fabry-Pérot resonator with cleaved facets. Windows in the top stripe contact were made to facilitate monitoring of the optical modes. Three types of the optical modes were observed in electroluminescence (EL) studies under high current densities > 1 kA/cm2. Mode A with the longest wavelength is a VCSEL-like mode emitting normal to the surface. Mode B has a shorter wavelength, emitting light at two symmetric lobes tilted with respect to the normal to the surface in the direction parallel to the stripe. Mode C has the shortest wavelength and shifts with a temperature at a rate 0.06 nm/K. Polarization studies reveal predominantly TE emission for modes A and B and purely TM for mode C in agreement with the theory. Spectral position, thermal shift and polarization of mode C confirm it to be a coupled state of the cavity mode and near-field DBR surface-trapped mode.

High-Power 1180-nm GaInNAs DBR Laser Diodes

We report high-power 1180-nm GaInNAs distributed Bragg reflector laser diodes with and without a tapered amplifying section. The untapered and tapered components reached room temperature output powers of 655 mW and 4.04 W, respectively. The diodes exhibited narrow linewidth emission with side-mode suppression ratios in the range of 50 dB for a broad range of operating current, extending up to 2 A for the untapered component and 10 A for the tapered component. The high output power is rendered possible by the use of a high quality GaInNAs-based quantum well gain region, which allows for lower strain and better carrier confinement compared with traditional GaInAs quantum wells. The development opens new opportunities for the power scaling of frequency-doubled lasers with emission at yellow–orange wavelengths.

Effect of Small Microfabrication Damage on Optical Characteristics of Laser Structure with GaInNAs Quantum Well

We investigate the effect of micro-fabrication process damage on the photoluminescence characteristics of laser structures containing a GaInNAs and GaInAs quantum wells. By varying the size of the fabricated island structure, its impact on the photoluminescence intensity is studied. The GaInAs sample shows a strong decrease in its intensity with the reduction of the island size. In contrast, a slight increase is observed from the GaInNAs sample. This indicates the negligible impact of surface recombination on the GaInNAs sample, as well as the optical confinement within the micrometer-size island structure. The results suggest the feasibility of a GaInNAs gain medium for application to microfabricated optical devices.

Atomic-plane-thick reconstruction across the interface during heteroepitaxial bonding of InP-clad quantum wells on silicon

An oxide-free heteroepitaxial bonding of InP-clad GaInAs quantum wells on Si showing an atomic-plane-thick reconstruction across the InP-Si interface and no degradation of the quantum wells luminescence is demonstrated. Several InP surface preparation procedures have been investigated to ensure an oxide-free bonding. Such a bonding procedure without oxide or metal mediation allows embedding very-high-index-contrast nanostructuration within optic and optoelectronic integrated devices, thus enabling tailored designs enhancing dedicated optical functions. Heteroepitaxial bonding is also similarly obtained on nanopatterned Si surface.

Lattice-Matched and Strain-Compensated Materials for Mid-Wave and Long-Wave Infrared Quantum Cascade Lasers

This work reports the growth and characterization of lattice-matched (LM) and strain-compensated (SC) AlInAs/GaInAs/InP heterostructures for quantum cascade lasers (QCLs) emitting in the mid-wave infrared (MWIR) and long-wave infrared (LWIR) wavelength regions. Organometallic vapor phase epitaxy growth conditions such as temperature, growth rate, and V/III ratio were varied to establish a step-flow growth mode. Multiple-quantum-well structures with either (LM) or with SC compressive GaInAs quantum wells and tensile AlInAs barriers were grown to optimize QCL structure growth. Atomic force microscopy and high-resolution x-ray diffraction data indicate excellent structural quality materials for QCLs. LM LWIR QCLs at 9.6 μm have pulsed peak power as high as 2.5 W/facet and pulsed wall-plug efficiency of 5.4%, while SC MWIR QCLs at 4.8 µm have peak power of 1.7 W and 9.7% pulsed wall-plug efficiency. SC MWIR QCLs exhibit very low threshold current density of 0.8 kA/cm2.

The comparison of the band alignment of GaInAsN quantum wells on GaAs and InP substrates for (0 0 1) and (1 1 1) orientations

The aim of this paper is to examine the effect of growth orientation and dilute nitride on the band alignment of GaInAs quantum wells on GaAs and InP substrates by means of model solid theory. The study provides a comparison of the band alignment and the strained band gap of the related GaInAsN QWs in (1 1 1) and (0 0 1) orientation. Our calculated results show that although 111-oriented GaInAsN QWs enables to reach the longer wavelengths, the conduction band offset gets shallow than that of the 001-oriented ones.

Pressure dependence of the electronic structure of a [311] piezoelectricGa0.85In0.15As/AlAssuperlattice

We have studied the electronic subband structure of a piezoelectric [311] ${\text{Ga}}_{0.85}{\text{In}}_{0.15}\text{As}/\text{AlAs}$ superlattice by means of high-hydrostatic pressure and excitation-power-dependent photoluminescence at 78 K. In particular, we unraveled the origin of two optical transitions at around 1.96 and 2 eV at ambient pressure, which were recently found to give rise to an unexpectedly strong resonant enhancement of the acoustic-phonon Raman scattering for such samples with permanent built-in piezoelectric fields [G. Rozas et al., Phys. Rev. B 77, 165314 (2008)]. Here we demonstrate that these transitions are doubly indirect, in real and reciprocal space, corresponding to radiative recombination processes between electrons at the X valleys of the AlAs barriers and heavy holes at the $\ensuremath{\Gamma}$ point of the Brillouin zone but confined to the GaInAs quantum wells. In addition, the partial screening of the piezoelectric field induced by carrier photoexcitation under illumination becomes largely suppressed for pressures above 1.1 GPa due to conduction-band $\ensuremath{\Gamma}\text{-X}$ crossover effects.

Evidence for Fermi level shift in GaInAs/GaAs quantum wells upon nitrogen incorporation

GaInAs/GaAs and GaInNAs/GaAs quantum well (QW) structures grown by metalorganic vapor phase epitaxy have been studied by contactless electroreflectance spectroscopy. In addition to the N-related redshift of QW transitions, an increase in the electric field in the GaAs cap layer has been observed after the incorporation of nitrogen atoms into the GaInAs QW. This observation is associated with the tendency of the Fermi level shift to a given energy in the GaInNAs QW region due to N-related defects.

Development of new-type 1.5 μm light-emitting devices based on Er,O-codoped GaAs

We have fabricated two types of 1.5 μm light-emitting devices based on Er,O-codoped GaAs (GaAs:Er,O) using organometallic vapor phase epitaxy (OMVPE). In a device exhibiting a room-temperature lasing at the GaAs band-edge, the threshold current density increased with Er concentration. The Er intensity rose up steeply and then decreased gradually in the spontaneous emission region. In the stimulated emission region, it remained almost constant, reflecting ultrafast energy transfer to Er ions. In a device exhibiting a room-temperature lasing from strained GaInAs quantum wells (QWs) embedded in GaAs:Er,O, on the other hands, the lasing wavelength was designed to tune to the energy separation between the second excited states 4I11/2 and the ground state 4I15/2 of Er3+ ions. The Er intensity revealed initially steep increase with injected current density in the region for spontaneous emission from the GaInAs QWs. In the stimulated QW emission region, however, the intensity continued to increase with the current density.

Critical layer thickness of GaIn(N)As(Sb) QWs on GaAs and InP substrates for (001) and (111) orientations

The aim of this work is to examine the effect of dilute nitride and/or antimonite on the critical layer thickness of GaInAs quantum wells on GaAs and InP substrates by means of Matthews and Blakeslee force model. The study provides a comparison of the critical layer thickness of the related GaIn(N)As(Sb) QWs in (001) and (111) orientation. Our calculations indicate the importance of antimonite and the proper usage of it with dilute nitrides in order to tailor the active layer thickness and emission wavelength of quantum well laser devices.

Postgrowth annealing of GaInAs∕GaAs and GaInAsN∕GaAs quantum well samples placed in a proximity GaAs box: A simple method to improve the crystalline quality

The effects of thermal annealing on GaInAs∕GaAs and GaInAsN∕GaAs quantum wells, grown by molecular beam epitaxy, were investigated. Optical and structural properties were examined upon annealing when the samples had a 200nm thick SiO2 cap layer, or were placed in a so-called GaAs box or were left uncapped. The GaAs box gave rise to the strongest photoluminescence without significant blueshift or structural changes at moderate annealing temperature. Capping with SiO2 impaired the samples and caused a more pronounced blueshift for the GaInAs quantum wells than for the GaInAsN ones. These results consolidate our understanding of the blueshift mechanisms.

Luminescence Properties in Er,O-codoped GaAs Light-Emitting Devices with Double Excitation Mechanism

AbstractWe fabricated a laser diode (LD) exhibiting a lasing from strained GaInAs quantum wells (QWs) embedded in Er,O-codoped GaAs (GaAs:Er,O) by organometallic vapor phase epitaxy (OMVPE). The lasing wavelength was designed to tune to the energy separation between the second excited states 4I11/2 and the ground state 4I15/2 of Er3+ ions. The threshold current for the lasing at room temperature was six times larger than that of a GaInAs QW-LD without Er doping, reflecting ultrafast carrier capture by an Er-related trap in GaAs:Er,O. The Er intensity revealed initially steep increase with injected current density in the region for spontaneous emission from the GaInAs QWs. In the stimulated QW emission region, the intensity continued to increase with the current density.

MBE grown optically pumped semiconductor disk lasers emitting at 940 nm

We present the optimization and performance of high-power optically pumped semiconductor disk lasers emitting near 940 nm. The emission efficiency at this wavelength is typically low owing to the poor carrier confinement within the shallow GaInAs quantum wells especially at high injection levels. Our work was focused on studying the efficiency of three types of structures with barrier materials made of AlGaAs, GaAs and GaAsP, providing different band offsets. The structures were grown by solid-source molecular beam epitaxy and consisted of a 30.5 pair AlAs/AlGaAs distributed Bragg reflector and an active region comprising 10 groups of triple-quantum-wells. To improve the crystal quality we have applied rapid thermal annealing for each grown wafer. The gain chips were then capillary bonded with water to a type IIa natural diamond heat spreader. The bonded gain elements were tested in a laser cavity with a linear-cavity configuration. Using a 3% output coupler we have obtained a maximum output power of 3 W from the structure with GaInAs/GaAsP composition. The corresponding M 2 value was 1.5 and the optical-to-optical conversion efficiency was 10%.

A high-power 975 nm tilted cavity laser with a 0.13 nm K−1 thermal shift of the lasing wavelength

We address design and performance issues of a 975 nm range tilted cavity laser (TCL) based on GaAs/GaAlAs waveguide and GaInAs quantum wells as an active medium. The all-epitaxial design of a TCL includes a cavity and a multilayer interference reflector (MIR). The cavity and the MIR are constructed as follows. The cavity confines one tilted optical mode, and the wavelength of this mode as a function of the tilt angle follows a first dispersion curve. The reflectivity spectrum of the MIR for tilted incidence of light has a well-pronounced stopband, and the stopband reflectivity maximum follows a second dispersion curve. The two dispersion curves intersect at one optimum tilt angle and one optimum wavelength λ0. At the wavelength λ0 the leakage loss of the optical mode through the MIR to the substrate has a minimum, which favors lasing at this optimum wavelength. The thermal shift of λ0 is governed by the shift of the intersection point. As the photon energy corresponding to the operation wavelength of the laser 975 nm is close to the resonance with the electronic energy gap in GaAs, the refractive index temperature coefficient dn/dT of GaAlAs strongly increases at the GaAs side. This gives a tool to control the thermal shift of λ0 by replacing some layers of the cavity by a superlattice containing narrow insertions of GaAs. Such a superlattice may have the same averaged refractive index at room temperature, but significantly different values of dn/dT, thus affecting the thermal shift of λ0. Within this approach broad-area (100 µm) devices have been fabricated showing a high temperature stability of the lasing wavelength (0.13 nm K−1), low threshold current density (300 A cm−2), a high power operation (>7 W in pulsed mode and >1.5 W in continuous wave mode), a high spectral stability at high output power, and a narrow vertical far-field beam divergence (FWHM ∼ 20°).

Monolithic semiconductor saturable absorber mirror with strain-compensated GaInAs/GaAsP quantum wells

We report a monolithic broadband semiconductor saturable absorber mirror (SESAM) operating for 1025–1100 nm wavelength range with strain-compensated GaInAs/GaAsP quantum wells (QWs). By introducing tensile-strained GaAsP barriers, the compressive strain caused by the GaInAs QWs can be compensated and good quality QWs are obtained. Strain-compensated GaInAs/GaAsP QWs are grown on top of a GaAs/AlAs distributed Bragg reflector (DBR) to form the SESAM structure. The SESAM has a broad high-reflective stopband of about 120 nm and has been successfully used in passively modelocking a Nd:Gd 0.64Y 0.36VO 4 solid-state laser operating at 1064 nm wavelength. Optical pulses as short as 4.5 ps are generated with a peak power of 3.7 kW.

Low threshold GaInAs quantum well lasers grown under low growth rate by solid‐source MBE for 1200 nm wavelength range

Optical property dependence on growth rates of highly-strained GaInAs quantum wells (QWs) on GaAs was studied by solid-source molecular beam epitaxy (MBE). Noticeable improvement of the photoluminescence (PL) was observed by lowering the growth rate of highly-strained GaInAs. A sample grown at a growth rate of 0.05 µm/h under a low growth temperature and high As pressure showed a high PL intensity and a flat surface in atomic force microscope (AFM) measurements. The lowest threshold current density of 117 A/cm2/well is achieved for GaInAs/GaAs double QW lasers at 1190 nm wavelength. A low growth rate is found to be effective to grow highly-strained GaInAs QWs. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Temperature dependence of the ambipolar carrier migration in a structure with InAs quantum dots grown in a strained GaInAs quantum well

The lateral carrier migration in a structure with InAs quantum dots (QDs) imbedded in a Ga0.85In0.15As quantum well grown on a GaAs substrate is investigated by confocal microscopy in a temperature range from 80 to 300K. Carrier spreading is measured by recording the ground and the first excited QD state emission. Carrier migration seems to be dominated by the diffusion in the GaAs barrier. The characteristic length of this transport phenomenon is 1.5μm at 80K. The characteristic migration length shows a linear increase with temperature up to a value of 1.7μm at 150K and then it remains constant up to 300K. The excited-state emission is spread in a spot with a smaller radius (1.0–1.2μm) and it has the same temperature dependence of the spreading distance as the characteristic migration length of carriers that recombine in the ground state.

Sb surfactant effect on highly strained GaInAs/GaAs quantum well grown by molecular beam epitaxy

Sb-introduced highly strained GaInAs/GaAs quantum wells (QWs) were grown by solid-source molecular beam epitaxy. The Sb introduction procedure and growth temperature dependence of photoluminescence (PL) property were investigated. Sb introduction into the upper part of the QW showed poor PL property and this result indicates that the three-dimensionally grown GaInAs is not recovered by the surfactant effect of Sb. For the case of the Sb introduction into the lower part of the QW, as the Sb introduction into the whole QW the PL peak intensity and linewidth improved as well. A noticeable PL improvement was also observed with increase in the growth temperature only for the case of Sb introduction. Sb introduction widened the growth temperature window for highly strained GaInAs QWs.

Growth of GaNxAs1−x atomic monolayers and their insertion in the vicinity of GaInAs quantum wells

The deposition of N-rich GaNAs atomic monolayers was investigated. Such layers were successfully grown while exposing a GaAs surface to a nitrogen plasma source during a growth interruption at 400 °C in a molecular beam epitaxy reactor. N accumulation was confirmed and evaluated by secondary ion mass spectroscopy. This process is compatible with regrowth, as in situ monitored by reflection high-energy electron diffraction. The crystal shows good structural quality, as displayed by transmission electron microscopy, that reveals that the accumulation occurred within 1 nm. In a series of samples, two of these ultrathin GaNAs layers were inserted in GaAs barriers, on each side of a GaInAs quantum well (QW). A drastic effect of the N-rich layers on the QW photoluminescence (PL) intensity was observed, as well as on the carrier recombination dynamics, with a strong influence of the spacer thickness between the QW and the N-rich layers. A time-resolved PL analysis of these samples evidenced nonradiative relaxation times in the range of a few ps. This very short carrier lifetime is attributed to the presence of nonradiative centres related to the N-rich layers close to the QW, and can be used to design ultrafast optical devices.