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We report on GaSb-based 2.X µm diode lasers with an improved waveguide design, leading to a reduced beam divergence in the fast axis of 44° full width at half maximum (FWHM), compared to 67° FWHM of a conventional broadened waveguide design. 2.3 µm ridge-waveguide lasers with the improved epitaxial design showed, besides the narrow beam profile in the fast axis, an excellent slow axis beam quality [M(exp 2)

High-power high-brightness 1.93-µm wavelength (AlGaIn)(AsSb) tapered diode lasers with a narrow vertical waveguide design are reported for the first time. A nearly diffraction-limited continuous-wave output power of 1.5 W together with a remarkable low fast axis divergence of 43° full-width at half-maximum have been demonstrated. The maximum brightness amounts to 32 MW/cm2 sr.

We have fabricated and characterized high-power 2.0 µm-wavelength (AlGaIn)(AsSb) quantum-well diode lasers emitting a power of 1.7 W in continuous-wave operation and over 9 W in pulsed operation at 300 K heat sink temperature. For potential further improvement of laser performance, the different contribution to the internal losses alpha(ind i) has been analyzed in detail for the present laser structure. Consistent results have been obtained for a series of samples, for which different design parameters were varied systematically: As expected, the losses in the cladding layers are dominated by fee carrier absorption in the p-doped cladding. The cross section for free-hole absorption in Al(0.84)Ga(0.16)As(0.06)Sb(0.94) is determined to Sigma(ind P)= 4.6x10(exp -17) cm2, which is comparable to values reported in the literature for (AlGaIn)(AsP)-based lasers emitting at 1.5 µm. The losses in the active region were found to increase linearly with increasing number of quantum wells at a rate of 1.5 cm-1 per quantum well, whereas the losses in the separate confinement layers are negligible.

Strained triple-quantum-well, large-optical-cavity GaInSb/AlGaAsSb/GaSb diode lasers emitting at 1.98 mum at 300 K are investigated with regard to their high-power capability. As the heating of the active region is a limiting factor for these devices, a quantitative model is derived to simulate the performance of these lasers including thermal effects. The standard laser parameters, deduced from measurements on ridge waveguide lasers, and the measured thermal resistance of the mounted devices were then taken as input parameters. The output power and power efficiency of the lasers calculated using the presented model. Good agreement was found between calculated data and the measurements for different heatsink temperatures as well as for different laser geometries and mounting techniques. The maximum output power achieved for p-side down mounted 1000 X 150 mum2 broad-area laser was 1.7 W at 300 K in cw operation.

Strained single- and triple-quantum-well (SQW and TQW), large optical cavity GaInAsSb/ AlGaAsSb/GaSb laser diodes emitting at 2.26 mu m are investigated. Internal loss coefficients as low as 5 and 7.7 cm(exp -1) for the SQW and TQW, respectively, and relatively high internal quantum efficiencies of 65% (SQW) and 69% (TQW) were obtained. Extrapolated threshold current densities for infinite cavity lengths of 55 and 150 A/cm2 have been deduced for the SQW and TQW, respectively. These values scale very well with the number of QWs and are among the lowest reported for diode lasers in this wavelength range. A differential quantum efficiency as high as 50% and a total power efficiency of 23% were achieved at 280 K. The temperature dependence of the threshold current density revealed a high characteristic temperature of 110 K. Single-ended output powers of 240 mW in continuous-wave mode and exceeding 0.5 W in pulsed operation were obtained for a TQW laser with high-reflection/antireflection coated facets at 280 K, mounted substrate-side down.

The influence of strain in Ga(0.7)In(0.3)As(y)Sb(1-y) quantum wells (QWs) embedded in Al(0.24)Ga(0.76)As(y)Sb(1-Y) barriers on the photoluminescence (PL) emission wavelength and intensity has been investigated. The strain was adjusted by varying the As content in the QW and barrier layers. For As mole fractions in the (GaIn)(AsSb) QW layers between y = 0.25 and 0.05, the average strain perpendicular to the growth plane changes from (delta a/a) = 2.0 x 10(exp -3) to 10.4 x 10(exp -3) for lattice matched (AlGa)(AsSb) barriers. At room temperature, highest PL intensities are obtained for QW structures with a net compressive strain of (delta a/a) = 8.7 x 10(exp -3). In order to compensate the compressive strain in the QWs, strain-balanced laser core structures with barriers under tensile strain have been investigated. This was found to allow a reduction of the average strain in the laser core without shifting its emission wavelength. Ridge waveguide large optical cavity (LOC) laser diodes containing three compressively strained (Galn)(AsSb) QWs embedded between lattice matched (AlGa)(AsSb) barriers show room temperature cw laser emission at a wavelength of 2.26 mu m. For 64 mu m wide and 600 mu m long devices, a differential quantum efficiency of 43% and a threshold current density of 395 A/cm2 with a characteristic temperature of T(0) = 110 K are obtained.

The incorporation of As and In during MBE growth in (AlGaIn)/(AsSb) layers used for the fabrication of diode lasers in the 2.0-2.5 mu m wavelength range has been investigated. The As content was found to depend linearly on the beam equivalent pressure for As mole fractions between y = 0.05 and y = 0.20. Broad area A1GaAsSb/GaInAsSb singlequantum well laser diodes with quasi-cw output at room temperature at an emission wavelength of 2.03 mu m and a threshold current density of 515 A/cm2 for 1370 mu m long and 70 mu m wide devices have been fabricated. In order to shift the emission wavelength of the laser structures to longer wavelengths, the growth of lattice matched AlGaAsSb/ GaInAsSb laser core structures with different In and As mole fractions in the quantum wells has been investigated.