No abstract

The cascade pumping scheme reduced the threshold current density of high power type-I quantum well GaSb-based λ ∼ 3 μm diode lasers down to ∼100 A/cm2 at room temperature. Laser heterostructures had single GaInAsSb quantum well gain stages connected in series by means of GaSb/AlSb/InAs tunnel junctions followed by InAs/AlSb electron injectors. Devices with densely stacked two and three gain stages and 100-μm-wide aperture demonstrated peak power conversion efficiency of 16% and continuous wave output power of 960 mW. Corresponding narrow ridge lasers demonstrated above 100 mW of output power. The experiment showed that the bandwidth of the gain and its rate of increase with current depended strongly on the thickness of AlSb layer separating electron injectors from quantum wells. The possible impact of electron injector interfaces and ionized impurities on the carrier scattering and recombination in the active quantum well is discussed.

A mid-IR ͑3.3-3.5 m͒ type-II interband cascade laser has been demonstrated at temperatures up to 300 K in pulsed mode and 150 K in cw mode. Threshold current densities as low as 13.2 A/cm 2 and power efficiencies as large as 17% have been achieved under cw conditions at 80 K.

We discuss an ultrawide, voltage-tunable type-II mid-IR interband cascade laser. Its design has a charge accumulation layers outside of the optically active quantum wells that unclamps the electron-hole concentrations and facilitates above-threshold Stark shifts. Our results demonstrate laser tuning of 120 nm ͑120 cm −1 ͒.

We show that the large features often found below the band gap in modulated spectra of GaAs samples are linked not only to impurities but also to back-surface reflection effects. Their proximity to the band edge depends on the geometry of the cavity in which the multiple reflections occur, the impurity species, and the temperature. Impurity contributions to the energy-dependent absorption coefficient become manifest in a multiple-reflection-enhanced reflectance edge. Externally applied perturbations modulate this reflectance edge, thereby producing first-derivative-like spectral features. At 5 K the extrema of the impurity-related features roughly correspond to the energies associated with donor and acceptor states. However, at room temperature they disagree significantly and therefore do not specify an impurity species with certainty.