Strained GaInAs Quantum Research Articles

Diode lasers emitting at 1220 nm with a highly strained GaInAs quantum well and GaAsP compensating layers MOCVD-grown on a GaAs substrate

Heterostructures with an active region containing a Ga0.59In0.41As quantum well located between GaAs1 − y P y compensating layers were studied using photoluminescence spectroscopy. It was shown that an increase in the phosphorus content in compensating layers makes it possible to obtain unrelaxed heterostructures with wider Ga0.59In0.41As quantum wells. On the basis of photoluminescence studies, the parameters of such a composite active region were chosen with a view to attaining the longest lasing wavelength possible. Laser heterostructures with a composite active region consisting of a highly strained Ga0.59In0.41As quantum well located between GaAs0.85P0.15 compensating layers were grown on GaAs substrates by metalloorganic chemical vapor deposition. Stripe mesa-structure laser diodes of 100-μm aperture emitting at 1220 nm were fabricated. The highest emission power of these laser diodes in the continuous-wave regime amounted to 2 W per output mirror.

Diode lasers emitting at 1190 nm with a highly strained GaInAs quantum well and GaAsP compensating layers MOCVD-grown on a GaAs substrate

Laser heterostructures with an active region consisting of a highly strained GaInAs quantum well located between GaAsP compensating layers were grown by metal-organic chemical vapor deposition on GaAs substrates. Stripe mesa-structure laser diodes of 100 μm aperture emitting at 1190 nm were fabricated. The highest emission power of these diodes in the CW mode amounted to 4.5 W per output mirror. Due to the presence of compensating GaAsP barriers, the GaInAs quantum well remains unrelaxed, which eliminates the spread in the maximum emission power of laser diodes produced from the same heterostructure.

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.

Investigation on the emission wavelength of GaInNAs/GaAs strained compressive quantum wells on GaAs substrates

In this paper, we study the effect of the incorporation of nitrogen in strained GaInAs quantum well structures. We evaluate the influence of nitrogen on the conduction band energy by using the band anticrossing model. The incorporation of nitrogen appears to decrease the bandgap energy and increase the emission wavelength. The reduction of energy is due to the interaction of the energy of the conduction band with the level of nitrogen and more the concentration of nitrogen increases, more the energy of the band gap decreases. On the other hand, the emission wavelength increases, the advantage of the incorporation of nitrogen in such structures is to vary the wavelength between 0.980 and 1.3μm while exploiting of course the composition of gallium, composition of nitrogen and the thickness of the quantum well. Less temperature insensitive devices are so intended to be fabricated.

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.

Optical characteristics of lowly strained GaInAs quantum dots

AbstractWe have investigated the optical properties of lowly strained GaInAs quantum dots (QDs). The structures were grown for a constant nominal GaInAs layer thickness but varying content (strain) from below to far above the critical thickness conditions. In order to investigate the properties of such an uncommon QD system, photoreflectance (PR) and photoluminescence, combined with scanning electron microscopy, have been used. Optical transitions connected with the ternary layer have been observed and followed from the lowest content quantum well case through the transformation into 3D islands on the wetting layer (WL) and a coexistence of the QD‐related and WL‐related transitions. Due to the observation of both heavy hole and light hole related transitions in PR spectra, the thickness of the wetting layer versus changed indium content could be determined by comparing the experimental data with the results of the effective mass envelope function calculations. (© 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 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.

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.

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.

Strained GaInAs quantum well mid-IR emitters

Strained GaInAs grown on InP offers an alternative to antimonide-based technology for mid-IR light emitting diodes and lasers operating at wavelengths up to approximately 2.4 microns. Such devices consist of compressively strained GaInAs carrier quantum well, with either lattice-matched or tensile-strained GaInAs carrier confinement barriers, and lattice-matched AlInAs optical confinement layers. The paper explores the wavelength limits which are dictated by the requirements for pseudomorphic growth and adequate carrier confinement. The electrical and optical results obtained from structures emitting at 2.1 and 1.8 microns at room temperature are reported and the data compared with the results of the Van de Walle model solid theory.

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.

Indirect-band-gap transition in strained GaInAs/InP quantum-well structures

Using photoluminescence (PL) and time-resolved measurements, the valence-band structure of tensile strained GaInAs quantum wells has been evaluated. From temperature-dependent PL, LO-phonon-assisted transitions at energies of about 32 meV below the band gap transition were observed. In addition, a hundredfold increase in the carrier lifetime of tensile strained quantum wells compared to unstrained layers was measured. Both findings are strong indications that the maximum of the valence band in k space is shifted away from the center of the Brillouin zone in tensile strained quantum wells near a critical composition, where the lowest heavy-hole and light-hole levels cross each other, thus giving rise for indirect optical transitions as predicted by theory.

Influence of Rapid Thermal Annealing on the Properties of Strained GaInAs Quantum Well Lasers

The influence of rapid thermal annealing on the properties of GaInAs strained quantum well lasers is studied. Photoluminescence performed at 300 and 77 K shows that an optimum is found for annealing at 800°C-10 s. The threshold current density of the laser decreases by a factor of 2 to 3 while its internal quantum efficiency increases from 30% up to 60%. The origin of the non radiative traps involved in the process is discussed.

Indium surface segregation in strained GaInAs quantum wells grown on GaAs by MBE

Surface segregation of indium in strained Ga 0.8In 0.2As/GaAs quantum wells is studied by means of sequential MBE depositions controlled by reflection high energy electron diffraction (RHEED) observations, each followed by in-situ ultraviolet photoelectron spectroscopy (UPS) measurements. The amount of segregated In at the surface and the composition profiles at the interfaces are precisely determined and are found to be quantitatively described by a simple model of local equilibrium between the surface and subsurface layers. The measured profiles differ strongly from the intended square profiles and must be taken into account to correctly predict the position of the energy levels in such quantum wells. This is confirmed by photoluminescence (PL) measurements that show the expected energy shifts. We also demonstrate the possibility to improve the abruptness of the GaAs on GaInAs interface using short annealing steps to reevaporate the segregated In.