Edge-emitting Laser Structure Research Articles

Optically Pumped Edge-Emitting GaAs-Based Laser With Direct Orange Emission

Room temperature lasing operation at 599 nm for a AlGaInP/AlInP/GaAs edge-emitting laser structure is reported. The structure was grown on GaAs substrate and pumped optically with a 532 nm Q-switched laser. The lasing threshold for a 2 mm long and 25 μm wide ridge waveguide structure was 30 mW of average pump power. The orange output beam had an optical spectral width of 1.7 nm.

Cavity mode gain alignment in GaAsSb-based near-infrared vertical cavity lasers studied by spectroscopy and device measurements

We present a combination of spectroscopy and device measurements on GaAsSb/GaAs vertical-cavity surface-emitting laser (VCSEL) structures to determine the temperature at which the wavelength of the VCSEL cavity mode (CM) aligns with that of the quantum well (QW) ground-state transition (GST), and therefore the gain peak. We find that, despite the achievement of room temperature (RT) continuous wave lasing in VCSEL devices, the QW transition and the CM are actually slightly misaligned at this temperature; room temperature electroluminescence measurements from a cleaved edge of the VCSEL wafer indicate that the 300 K QW GST energy is at 0.975 ± 0.005 eV, while the CM measured in the VCSEL surface reflectivity spectra is at 0.9805 ± 0.0002 eV. When the wafer sample is cooled, the CM and QW GST can be brought into alignment at 270 ± 10 K, as confirmed by temperature-dependent electro-modulated reflectance (ER) and edge-electroluminescence spectroscopic studies. This alignment temperature is further confirmed by comparing the temperature dependence of the emission energy of a fabricated VCSEL device with that of an edge-emitting laser structure with a nominally identical active region. The study suggests that for further device improvement, the room temperature CM and QW GST energies should be more closely matched and both designed to a smaller energy of about 0.95 eV, somewhat closer to the 1.31 μm target. The study amply demonstrates the usefulness of non-destructive ER characterisation techniques in VCSEL manufacturing with GaAsSb-based QWs.

Toward 1550-nm GaAs-Based Lasers Using InAs/GaAs Quantum Dot Bilayers

By choice of appropriate growth conditions and optimization of the strain interactions between two closely stacked InAs/GaAs quantum dot (QD) layers, the emission wavelength of the QDs can be significantly extended, giving room-temperature emission from highly uniform QD ensembles in excess of 1500 nm. These QD bilayers are incorporated into edge-emitting laser structures and room-temperature ground-state lasing at 1420 nm and electroluminescence at 1515 nm are observed. Under high-bias conditions, asymmetric broadening of peaks in the laser gain spectra are observed, extending positive net modal gain from the devices to beyond 1500 nm, and the origin of this broadening is discussed.

Effects of non-uniform size distribution on the spectral optical gain properties of InGaAs/InGaAsP quantum dots

We present a theoretical study of the optical gain, emission wavelength, and threshold current density for edge emitting laser structures with an active region based on InGaAs/InGaAsP quantum dots. The analysis of the effects of the size distribution of the dots is also presented. Spectral gain curves are generated for InGaAs/InGaAsP dots where high optical gain and high independence of spectral characteristics are obtained for a uniform distribution of dots. With typical non-uniform distribution, we show a reduction in gain by a factor of 6. Also, we predict the onset of new transition peaks and a red shift in the most probable operating lasing wavelength. Finally, we demonstrate that there is a large range of full width at half maximum (FWHM) of the dots size distribution where variations in the maximum gain and associated wavelength, as well as threshold current density, are minimum.

GaN Surface-Emitting Laser With Monolithic Cavity-Folding Mirrors

We report on the demonstration of a GaN-based surface-emitting laser (SEL) in a folded-cavity (FC) scheme. Two 45deg-angled sidewall deflectors were monolithically integrated at both the edges of an otherwise conventional InGaN multiple-quantum-well edge-emitting laser structure. Despite a low effective mirror reflectivity of R(<1%), the optically pumped broad-area laser structure produced laser oscillation in the vertical direction with a low threshold pump intensity of ~350kW/cm2. Computer simulations on the FC, which was based on the finite-difference time-domain method, not only quantified the cavity quality of our FC-SEL device but also suggested methods to lower the laser threshold

Fabrication and molecular beam epitaxy regrowth of first-order, high contrast AlGaAs∕GaAs gratings

We present a fabrication technique and molecular beam epitaxy (MBE) regrowth of first-order, high contrast AlGaAs∕GaAs diffraction gratings for laser emitting at 980nm. An immersion holography technique is used to uniformly pattern first-order gratings with a pitch of 155nm. MBE is used to overgrow Al0.75Ga0.25As on etched GaAs gratings. It is found that slow growth rates with optimum arsenic overpressure are necessary to overgrow gratings with low pitting defect densities. These first-order, high contrast gratings are integrated as distributed Bragg reflectors in an edge-emitting laser structure. Single-mode emission at 1μm with a side mode suppression ratio greater than 30dB is demonstrated.

Optically pumped lead–chalcogenide midinfrared lasers on Si substrates

Double heterostructure (DH) and quantum well (QW) EuSe/PbSe/Pb1−xEuxSe edge-emitting laser structures on Si substrates are grown by molecular-beam epitaxy. They operate up to 250 K when pumped with 870 nm low-cost laser diodes with peak powers of ∼7 W, and emit up to 200 mW peak output power at ∼5 μm wavelength. Differential quantum efficiencies are up to 20%. The threshold powers are limited by Shockley–Read recombination due to the high dislocation densities (108 cm−2) in the active layers. Nearly similar maximum operation temperatures were observed when employing (111)—instead of (100)—oriented layers, as well when using QW rather than DH structures. Reduction of dislocation densities to 107 cm−2 is feasible and will lead to nearly an order of magnitude lower threshold powers.

Correlation between lasing properties and band alignment of edge emitting lasers with (Ga,In)(N,As)/Ga(N,As) active regions

AbstractWe have investigated the optical properties of edge‐emitting laser structures containing three Ga0.7In0.3N0.005As0.995 quantum wells embedded in GaNxAs1–x barriers grown by metal‐organic vapour‐phase epitaxy. In a series of three samples the nitrogen content x of the barrier was varied from 0% to 3%. We studied the optical transitionsand the threshold of these laser structures by using pressure‐dependent photomodulated reflectance (PR) up to 20 kbar at room temperature. Additionally we measured the pressure dependence of the lasing energy and the threshold current of the corresponding laser structures as function of hydrostatic pressure. Due to the large red‐shift of the Ga(N,As) band gap with increasing N of about 150 meV per percent N, the variation of x leads to a considerable change of the carrier confinementof holes and, in particularly, of electrons. The strong increase of the threshold current of the laser device with pressure suggests a swiftly increasing threshold carrier density due to the increasing effective mass and non‐parabolicity.an enlarged carrier density at threshold Comparing the pressure dependence of the lasing energy and the conduction band edge furthersupports this conclusion.

Progress in GaN-based quantum dots for optoelectronics applications

Our recent progress in GaN-based quantum dots (QDs) for optoelectronics application is discussed. First, we discussed an impact of the use of GaN-based QDs on semiconductor lasers, showing theoretically that reduction of threshold current by using the QDs in GaN-based lasers is much more effective compared to those in GaAs-based or InP-based lasers. Then discussed are our growth technology including self-assembling growth of InGaN QDs on sapphire substrates by atmospheric-pressure metalorganic chemical vapor deposition. Using the self-assembling growth technique, we have succeeded in obtaining lasing action in an edge-emitting laser structure with the InGaN QDs embedded in the active layer under optical excitation with the emission wavelength of 410 nm. Toward UV light wavelength emission, we have recently established self-assembled GaN QDs of high quality and high density under very low V-III ratio. We clearly observed two photoluminescence peaks from both the QDs and the wetting layer at room temperature, which clearly shows the nanostructures are formed with the Stranski-Krastanow growth mode.