Multiquantum-well Laser Structures Research Articles

Mode pattern dependence on the eccentricity of microstadium resonators

Microdisk and microstadium resonators based on InGaAsP multiquantum-well laser structures were fabricated by focused ion beam employing Ga+ ion milling and polishing followed by selective chemical etching. Stadia with very good morphology and with different eccentricities were fabricated for the study of optical mode selection. Light emission was investigated by infrared microscopy and spectroscopy. The measured emission pattern and the spectra agree well with a simple model based on the summation over periodic orbits or scar modes. The dependence of the scar mode emission with the resonator eccentricity was modeled based on the difference between photon lifetime and orbital round-trip time. The mode selection dependence with the surrounding index of refraction is suggested for chemical sensing applications.

Room-temperature lasing of InGaN multiquantum-well hexagonal microfacet lasers by current injection

InGaN multiquantum-well (MQW) hexagonal microfacet (HMF) lasers have been fabricated by electron cyclotron resonance dry etching of as-grown planar InGaN MQW laser structures followed by metalorganic vapor phase epitaxy regrowth of p-GaN to form mirror facets of the lasers. The mirror facets are smooth and vertical {112̄0} facets of the regrown p-GaN. The HMF lasers lase at 401 nm under pulsed operation at room temperature. There is no significant difference in threshold current density for different cavity lengths of 480 and 770 μm, indicating that the mirror facets act as total reflectors.

Band-structure and optical gain for InAsP/In(GaAs)P MQW laser structures

We present numerical results of the band structure of strain-compensated and strain-uncompensated InAsP/In(GaAs)P multi-quantum well (MQW) structures using the transfer-matrix algorithm based on the Luttinger–Kohn Hamiltonian. For the valence band, the heavy-hole band and the light-hole band are taken into account. The propagation matrices of the order 4×4 were obtained and used to get the solutions of the 4×4 Hamiltonian for the valence band. The valence-band-edge energies as well as the dispersion relations and valence-band mixing are calculated. The envelope wavefunctions of carriers for some QW structures and the optical gain for 1.3 μm InAsP/InGaAsP MQW lasers are calculated and discussed. We found that not only does the strain-compensation improve the quality of the MQW materials, also it modifies the band structure of MQW structures and hence modifies the modes of the optical output. Only TE mode output exists in our strain-compensated InAsP/InGaAsP MQW lasers.

Determination of the band offset and the characteristic interdiffusion length in quantum-well lasers using a capacitance–voltage technique

In this work, a capacitance–voltage (C–V) technique, based on a combination of measured and simulated C–V characteristics, was applied to characterize In0.35Ga0.65As/GaAs multiquantum-well laser structures at room temperature. A theoretical model, including the self-consistent solution of Poisson and Schrödinger equations, was developed to simulate the C–V characteristics and the carrier concentration profiles. Measured C–V carrier concentration profiles were used to obtain the average impurity concentration in active regions. The comparison between experimental and simulated results was used to determine the conduction band offset, yielding ΔEc/ΔEg≈0.8. In the case of samples with postgrowth quantum-well intermixing, this technique was applied to extract the characteristic interdiffusion length.

Time-development of transient-carrier temperature, density, and gain spectrum in ultrashort optical pulse excited InGaAs multiquantum-well laser structure

We present a novel transient gain-spectra measurement method based on the traditional variable pump-stripe technique. Using the pump-stripe technique with ultra-short optical pulse excitation, time-resolved amplified spontaneous emission spectroscopy of an InGaAs-InGaAsP multiquantum-well (MQW) laser structure was measured, and time-development of the transient optical net gain spectra was obtained accordingly. By fitting the measured gain spectra with a model for band-to-band transitions including momentum conservation and an energy- and density-dependent lifetime broadening, dynamics of band filling, carrier density, carrier temperature and bandgap renormalization have been obtained. This opens the possibility to study simultaneously the influence of transient-carrier density and, in particular, transient-carrier temperature on the transient optical gain. Strong gain compression in the whole gain-spectra region due to transient high carrier temperature after ultra-short pulse injection is clearly demonstrated for the first time.

Barrier strain influence on the high-speed properties of compressively strained InGaAsP multiquantum-well laser structures

We report on an extensive experimental study of the barrier strain influence on the high-speed properties of compressively strained quaternary (InGaAsP) multiquantum-well (MQW) lasers emitting at 1.55 /spl mu/m. In the design of strained MQW laser structure emitting at 1.55 /spl mu/m, the main effect of varying the barrier strain amount is to modify the effective well/barrier height for both electrons and holes. In this paper, it is shown experimentally from MQW structures with different barrier strain values, that a strong decrease of the nonlinear gain coefficient can be obtained when the barrier strain is reduced, leading to quantum-well (QW) laser structures with a damping coefficient (called the K-factor) as low as 0.18 ns, i.e., theoretical damping limited bandwidth as high as 50 GHz. This result appears to be qualitatively well explained by a substantial reduction of the carrier capture time to escape time ratio, due to an increase of the well/barrier offset in the conduction and valence bands.

High quality compressively strained InP-based GaInAs(P)/GaInAsP multi-quantum well laser structures grown by metalorganic vapor phase epitaxy

The growth and characterization of strained GaInAs and GaInAsP multiquantum well (MQW) laser structures has been investigated. The use of triple axis x-ray diffraction (XRD), in addition to the conventional high resolution double crystal XRD, yields further information about the structural integrity of these complex structures. Buried heterostructure lasers with eight GaInAsP wells (+1.0% strain, 80A thick) exhibit a record low threshold current of 3.1 mA. By using a constant As/P ratio in the wells and barriers of an MQW laser structure, we have shown that the structure can be annealed at 700°C for 1 h with only a minimal shift (-4 nm) in the photoluminescence emission wavelength. Conventional lattice-matched GaInAs/GaInAsP MQW structures exhibit a shift of-46 nm under the same conditions.

Ray optics determination of the DFB coupling coefficient in separate confinement and multiquantum-well laser structures

A ray optics technique is used to derive a closed-form expression for the first-order backward coupling coefficient /spl kappa/ in a generic five-layer separate confinement distributed feedback laser configuration with sinusoidal, triangular, or rectangular gratings. The expression is applicable to multiquantum-well structures as well as strong coupling configurations, and can be evaluated without using any numerical techniques. For the weak perturbation configurations normally encountered in such devices, the ray optics /spl kappa/ values are in good agreement with those obtained using the standard overlap integral technique.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

MOVPE of In(GaAs)P/InGaAs MQW structures

Abstract We report on MOVPE growth of In(GaAs)P/InGaAs multi-quantum-well (MQW) structures. The growth was carried out at a reactor pressure of 20 hPa in an horizontal lamp heated cold wall reactor with rectangular inner liner tube using as group III elements TMIn and TMGa and as group V elements 100% AsH3 and PH3. Wedge transmission electron microscopy (WTEM), photoluminescence (PL) measurements at 2K and 300 K, and X-ray double crystal diffractometry (DCD) were used for characterization. WTEM technique demonstrates monolayer interfaces and an excellent periodicity of the structures. This is in addition proven by DCD measurements with satellite peaks up to the 8th order. Separate confinement MQW (SCMQW) laser structures with InGaAsP barriers were grown and fabricated to Broad Area (BA) lasers. As a best value we measured threshold current densities of 800 A/cm2. A graded refractive index separate confinement heterostructure (GRINSCH) MQW laser structure with 7 InGaAsP grading layers was also grown and showed very homogeneous laser results with a 20% increased quantum efficiency as compared to SCMQW structures.

Dispersion-induced composite second-order distortion at 1.5 mu m

Experimental and theoretical results have shown that the composite second-order (CSO) nonlinearity of 1.5- mu m AM analog laser links is inadvertently affected by the coupling of laser chirp with fiber dispersion in regular single-mode fiber. To counteract the dispersion effect, it is shown that dispersion-shifted fiber can be employed in place of the regular fiber. Other possible ways to reduce distortion are to use lasers with reduced chirp, presumably with a multiquantum-well laser structure, or lasers with well-controlled spatial hole burning. Short fiber spans (<or=5 km) for applications providing loop distribution in conjunction with fiber amplifiers are feasible without the use of countermeasures.<<ETX>>

Pair-groove-substrate GaAs/AlGaAs multiquantum-well lasers with a self-aligned stripe geometry

GaAs/AlGaAs multiquantum-well (MQW) lasers with a self-aligned structure incorporating a waveguide and current confinement were fabricated on a substrate with a pair of etched grooves using two-step epitaxial growth. First, a current-blocking layer was grown selectively on the substrate by low-pressure organometallic vapour-phase epitaxy (OMVPE), and then the GaAs/AlGaAs MQW laser structure was constructed on the substrate with the OMVPE layer by molecular-beam epitaxy. The mesa-shaped part of the active layer above the current-confinement region provides a lateral refractive-index optical waveguide. The lasers show well controlled transverse-mode oscillations with low threshold currents.