A new approach in the design of (Al)InGaAsSbGaSb quantum-well separate confinement heterostructure (QW-SCH) diode lasers has led to continuous-wave (CW) room-temperature lasing up to 2.7 m. This has been achieved by using quasiternary heavily strained InGaSb(As) QW's inside a broad-waveguide SCH laser structure. The QW compositions are chosen in the region outside the miscibility gap and, as a consequence, do not suffer from clustering and composition inhomogeneity normally found with quaternary InGaAsSb compounds of 2.3-2.7-m spectral range. Very low threshold current density (300 A/cm 2 ) and high CW output powers (>100 mW) were obtained from devices operating in the 2.3-2.6-m wavelength range.Index Terms-Broad-waveguide separate confinement quantum-well laser structure, continuous-wave operation, heavily strained quantum well, mid-infrared AlGaAsSb-InGaAsSb diode lasers.

This report was prepared as an account of work sponsored by the United States Government. AbstractThe hotside operating temperatures for many projected thennophotovoltaic (TPV) conversion system applications are approximately 10oO 'C, which sets an upper limit on the TPV diode bandgap of 0.6 eV from efficiency and power density considerations. This bandgap requirement has necessitated the development of new diode material systems, never previously considered for energy generation. To date, InGaAsSb quaternary diodes grown lattice-matched on GaSb substrates have achieved the highest performance. This report relates observed diode performance to electrooptic properties such as minority carrier lifetime, diffusion length and mobility and provides initial links to microstructural properties. This analysis has bounded potential diode performance improvements. For the 0.52 eV InGaAsSb diodes used in this analysis the measured dark current is 2 x Ncm2 (no photon recycling), and an absolute thermodynamic limit of 1.4 x A/cm2. These dark currents are equivalent to open circuit voltage gains of 20 mV (7%), 60 mV (20%) and 140 mV (45%), respectively.

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By incorporating a broad transverse waveguide ͑1.3 m͒ in 0.97-m-emitting InGaAs͑P͒/InGaP/ GaAs separate-confinement-heterostructure quantum-well diode-laser structures we obtain record-high continuous-wave ͑cw͒ output powers for any type of InGaAs-active diode lasers: 10.6-11.0 W from 100-m-wide-aperture devices at 10°C heatsink temperature, mounted on either diamond or Cu heatsinks. Built-in discrimination against the second-order transverse mode allows pure fundamental-transverse-mode operation ( Ќ ϭ36°) to at least 20-W-peak pulsed power, at 68ϫthreshold. The internal optical power density at catastrophic optical mirror damage ͑COMD͒ P COMD is found to be 18-18.5 MW/cm 2 for these conventionally facet-passivated diodes. The lasers are 2-mm-long with 5%/95% reflectivity for front/back facet coating. A low internal loss coefficient (␣ i ϭ1 cm Ϫ1 ) allows for high external differential quantum efficiency d ͑85%͒. The characteristic temperatures for the threshold current T 0 and the differential quantum efficiency T 1 are 210 and 1800 K, respectively. Low differential series resistance R s : 26 m⍀; leads to electrical-to-optical power conversion efficiencies in excess of 40% from 1 W up to 10.6 W cw output power, and as much as 50% higher than those of 0.97-m-emitting Al-containing devices. © 1998 American Institute of Physics. ͓S0003-6951͑98͒03335-X͔ Broad-stripe, InGaAs-active diode lasers ͑ ϭ0.89-1.06 m͒ are routinely used for pumping solid-state fiber lasers, frequency doubling, and for numerous medical applications. Al-free devices ͑i.e., InGaAs/InGaP/GaAs structures͒ have superior ''wallplug'' efficiency compared with conventional Al-containing devices 1 due to their low differential series resistance. 1,2 Furthermore, the low oxidation rate of InGaP permits high-quality epitaxial regrowths over gratings for longitudinal-mode control ͑i.e., distributed-feedback lasers͒ 3,4 or over etched structures for lateral-mode control. 5-9 Thus, the Al-free material system is highly desirable for both broad-stripe spatially incoherent devices as well as for temporally and/or spatially coherent index-guided diode lasers.Recently, we have reported 10 continuous-wave ͑cw͒ output powers of 8 W from 0.98-m-emitting InGaAs/InGaP/ GaP lasers of a 100-m-wide stripe, 4-mm-long cavity, 1-m-thick transverse waveguide, and mounted on Cu heatsinks. Such broad-waveguide ͑BW͒ devices also demonstrated fundamental-transverse-mode operation to high drive levels, 11 as expected since the cutoff thickness for the second-order transverse mode is 1.05 m. BW devices with a waveguide thickness of 1.3 m exhibited lasing in both the fundamental and the second-order transverse modes. 12 We report here maximum cw output powers of 10.6-11 W, record-high values for any type of InGaAs-active-region diode lasers. The devices show pure fundamental-transversemode operation to at least 20 W peak pulsed power. We achieve these results using a 1.3-m-waveguide structure, designed to suppress oscillation of the second-order transverse mode.The InGaAs͑P͒/In...

We have characterized 2.5-m-wavelength InGaAsSb/AlGaAsSb/GaSb two-quantum-well diode lasers that emit 1 W continuous waves from a 100-m-wide aperture at a temperature of 12°C. The threshold current density is 250 A/cm 2 , and the external quantum efficiency near threshold is 0.36. The wall-plug efficiency reaches a maximum of 12% at a current of 2 A. Operating in the pulsed-current mode, the devices output nearly 5 W at 20°C. These lasers exhibit internal losses of about 4 cm Ϫ1 and differential series resistances of about 0.1 ⍀. A broad-waveguide design lowers internal losses, and highly doped transition regions between the cladding layers and the GaSb reduces series resistance.