Strain-compensated InGaAs Research Articles

Low-threshold strain-compensated InGaAs/(In,Al)GaAs multi-quantum well nanowire lasers emitting near 1.3 μm at room temperature

Realizing telecom-band lasing in GaAs-based nanowires (NW) with low bandgap gain media has proven to be notoriously difficult due to the high compressive strain built up in the active regions. Here, we demonstrate an advanced coaxial GaAs-InGaAs multi-quantum well (MQW) nanowire laser that solves previous limitations by the introduction of a strain compensating InAlGaAs buffer layer between the GaAs core and the MQW active region. Using a buffer layer thickness comparable to the core diameter applies a significant tensile strain to the GaAs core which efficiently minimizes the compressive strain in the InGaAs MQW and enables large In-content without plastic relaxation. Experimental verification is shown for NW-lasers with an In-content of up to 40% in the MQW, evidencing a clear strain-relieved redshift of the lasing emission and a strong reduction of the lasing threshold compared to highly strained MQWs in state-of-the-art GaAs NW-lasers. This way we achieve optically pumped room temperature lasing operation with a threshold below 50 μJ cm−2 in the telecom O-band close to 1.3 μm.

Scattering-rate approach for efficient prediction of temperature-dependent characteristics of mid-infrared quantum cascade lasers

A computationally efficient temperature-dependent model for scattering processes in mid-infrared quantum cascade lasers is developed. In this approach, the total intersubband scattering rate is described as the product of the overlap integral for the squared moduli of the envelope functions and a form factor that depends on transition energy, temperature, and material. Both inelastic and elastic scattering processes are included in the treatment. The model is used to calculate the temperature-dependent threshold current density $ {J_{{\rm th}}}(T) $Jth(T) in a 10-period strain-compensated InGaAs–InAlAs mid-infrared quantum cascade laser structure and determine the characteristic temperature $ {T_0} $T0 in $ {J_{{\rm th}}}(T) = {J_0}\exp {(T/{T_0})} $Jth(T)=J0exp⁡(T/T0). The effect of doping is also modeled.

Sub-300-femtosecond operation from a MIXSEL.

Peak power scaling of semiconductor disk lasers is important for many applications, but their complex pulse formation mechanism requires a rigorous pulse characterization to confirm stable fundamental modelocking. Here we fully confirm sub-300-fs operation of Modelocked Integrated eXternal-cavity Surface Emitting Lasers (MIXSELs) with record high peak power at gigahertz pulse repetition rates. A strain-compensated InGaAs quantum well gain section enables an emission wavelength in the range of Yb-doped amplifiers at ≈1030 nm. We demonstrate the shortest pulses from a MIXSEL with a duration of 253 fs with 240 W of peak power, the highest peak power generated from any MIXSEL to date. This peak power performance is comparable to conventional SESAM-modelocked VECSELs for the first time. At a 10-GHz pulse repetition rate we still obtained 279-fs pulses with 310 mW of average output power, which is currently the highest output power of any femtosecond MIXSEL. Continuous tuning of the pulse repetition rate has been demonstrated with sub-400-fs pulse durations and >225 mW of average output power between 2.9 and 3.4 GHz. The strain-compensated MIXSEL chip allowed for more detailed parameter studies with regards to different heat sink temperatures, pump power, and epitaxial homogeneity of the MIXSEL chip for the first time. We discuss in detail, how the critical temperature balance between quantum well gain and quantum well absorber, the partially saturated absorber and a limited epitaxial growth quality influence the overall device efficiency.

Native-oxide-confined high-index-contrast λ=1.15 μm strain-compensated InGaAs single quantum well ridge waveguide lasers

High performance native-oxide-confined high-index-contrast (HIC) ridge waveguide (RWG) diode lasers are fabricated in a strain-compensated In0.4Ga0.6As single quantum well structure by employing a deep dry etch plus nonselective O2-enhanced wet thermal oxidation process. The thermal native oxide grown on the etch-exposed RWG sidewalls of the Al0.74Ga0.26As waveguide cladding layers and GaAs core with GaAsP–InGaAs quantum well provides both strong optical and electrical confinements for the active region. Due to a smoothing of sidewall roughness by the O2-enhanced oxidation, the lasers exhibit a low internal loss in αi=7.2 cm−1 for a w=7.2 μm narrow stripe HIC RWG structure, only 53% larger than that of w=87.2 μm broad-area devices, enabling their room temperature operation at a low 300 A/cm2 threshold current density.

Wavelength dependent phase locking in quantum cascade laser Y-junctions

Midinfrared quantum cascade lasers with monolithically integrated Y-junctions are investigated. Two different emission wavelengths of 10.5 and 4.2μm were realized in two different material systems, lattice-matched GaAs∕AlGaAs on GaAs and strain-compensated InGaAs∕InAlAs∕AlAs on InP. With identical Y-junction dimensions, phase locking is observed in both structures. In GaAs based devices, fundamental lateral modes are present in the coupled waveguides, which are coherently synchronized at the Y-junction. In InP based devices, modes of higher order are excited, which originate from coupling. The generation of multiple modes yields an out-of-phase fraction which reduces the level of coherence.

InP-based lattice-matched InGaAsP and strain-compensated InGaAs∕InGaAs quantum well cells for thermophotovoltaic applications

Quantum well cells (QWCs) for thermophotovoltaic (TPV) applications are demonstrated in the InGaAsP material system lattice matched to the InP substrate and strain-compensated InGaAs∕InGaAs QWCs also on InP substrates. We show that lattice-matched InGaAsP QWCs are very well suited for TPV applications such as with erbia selective emitters. QWCs with the same effective band gap as a bulk control cell show a better voltage performance in both wide and erbialike emission. We demonstrate a QWC with enhanced efficiency in a narrow-band spectrum compared to a bulk heterostructure control cell with the same absorption edge. A major advantage of QWCs is that the band gap can be engineered by changing the well thickness and varying the composition to the illuminating spectrum. This is relatively straightforward in the lattice-matched InGaAsP system. This approach can be extended to longer wavelengths by using strain-compensation techniques, achieving band gaps as low as 0.62eV that cannot be achieved with lattice-matched bulk material. We show that strain-compensated QWCs have voltage performances that are at least as good as, if not better than, expected from bulk control cells.

1.02-μm vertical-cavity surface-emitting lasers with strain-compensated InGaAs quantum wells

We demonstrate strain-compensated InGaAs/GaAsP/GaAs 1.02-μm vertical-cavity surface-emitting lasers (VCSELs) grown monolithically on a GaAs substrate using molecular beam epitaxy. VCSELs at this wavelength are optimal light sources for recently developed graded-index perfluorinated plastic optical fibers. Preliminary results show that the VCSELs oscillate in continuous-wave mode at temperatures up to 80 °C.

Low-threshold strain-compensated InGaAs(N) (/spl lambda/ = 1.19-1.31 μm) quantum-well lasers

Highly strained (/spl Delta/a/a /spl sim/ 2.5%) In/sub 0.4/Ga/sub 0.6/As and In/sub 0.4/Ga/sub 0.6/As/sub 0.995/N/sub 0.005/-quantum-well (QW) active lasers utilizing strain-compensating InGaP-GaAsP buffer layers and GaAs/sub 0.85/P/sub 0.15/ barrier layers, grown by metal-organic chemical vapor deposition (MOCVD), are demonstrated with lasing emission wavelength of 1.185 and 1.307 μm, respectively. Threshold and transparency current density for the strain compensated InGaAsN QW lasers, with emission wavelength of 1.295 μm, are measured to be as low as 290 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (L = 1500 μm) and 110 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , respectively, with characteristic temperature of T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> and T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> of 130 K and 400 K.

High-performance strain-compensated InGaAs-GaAsP-GaAs (/spl lambda/=1.17 μm) quantum well diode lasers

This letter reports studies on highly strained and strain-compensated InGaAs quantum-well (QW) active diode lasers on GaAs substrates, fabricated by low-temperature (550/spl deg/C) metal-organic chemical vapor deposition (MOCVD) growth. Strain compensation of the (compressively strained) InGaAs QW is investigated by using either InGaP (tensile-strained) cladding layer or GaAsP (tensile-strained) barrier layers. High-performance /spl lambda/=1.165 μm laser emission is achieved from InGaAs-GaAsP strain-compensated QW laser structures, with threshold current densities of 65 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> for 1500-μm-cavity devices and transparency current densities of 50 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The use of GaAsP-barrier layers are also shown to significantly improve the internal quantum efficiency of the highly strained InGaAs-active laser structure. As a result, external differential quantum efficiencies of 56% are achieved for 500-μm-cavity length diode lasers.

Investigation of strain-compensated lnGaAs(P)/lnGaAs(P)/lnP multiple quantum well structures grown by LP-MOVPE

A controversy exists regarding the effectiveness, in the high strain case, of the strain-compensated InGaAs(P)/InGaAs(P)/InP multiple quantum well (MQW) structures. In this paper, the mechanism of the crystal quality degradation in the high strain case is analyzed. Based on our experiments and analysis, we suggest that the crystal quality degradation is predominately affected by the growth temperature and V/III ratios in the gas phase. We demonstrate that, in the case of high strain in the wells, high quality and stable strain-compensated MQW structures can be grown at relatively low growth temperature and relatively high V/III ratios in the gas phase through decreasing the strain in barriers and increasing the thicknesses of barriers simultaneously to achieve zero net strain.

Highly reliable operation of strain-compensated0.98 µmInGaAs/InGaP/GaAs lasers with InGaAsP strained barriers for EDFAs

Highly reliable operation of 0.98 mu m strain-compensated InGaAs/ InGaAsP lasers is demonstrated for the first time with an estimated lifetime of 170 kh at 25 degrees C. Moreover, we reveal that the degradation rates at 90 degrees C and 80 mW output power are four times smaller than those of identical lasers with GaAs barriers.