3.2 AND 3.8 fum Emission and Lasing in AlGaAsSb/InGaAsSb Double Heterostructures with Asymmetric Band Offset Confinement
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ABSTRACT We report the first observations of electroluminescence (EL) and lasing in laser structures with high Al-content (x=0.64, Eg=1.474 eV) cladding layers and a narrow-gap InGaAsSb active layer (Eg=0.326 eV at T=77K). The structures are LPE-grown lattice-matched to GaSb substrate. Band energy diagrams of the laser structures had strongly asymmetric band offsets. The heterojunction between high Al-content layer and InGaAsSb narrow-gap active layer has a type II broken-gap alignment at 300K. In this laser structure spontaneous emission was obtained at ?X=3.8gtm at T=77K and X=4.25 gim at T=300K. Full width at half maximum (FWHM) of emission band was 34 meV. Emission intensity decreased by a factor of 30 from T=77K to 300K. Lasing with single dominant mode was achieved at X=3.774 jim (T=80K) in pulsed mode. Threshold current as low as 60 mA and characteristic temperature To=26K were obtained at T=80-120K. INTRODUCTION Lately there has been intensive research in mid-infrared III-V (MIR) semiconductor diode lasers emitting from 3 to 5 gim. An important application of these lasers is ecological monitoring and tunable diode laser spectroscopy. Sb-based lasers operating at up to 180-200K in pulsed mode and 110-120K in cw mode were realized [1-4]. Novel type II laser structures using an intersubband transition were demonstrated [3,4]. Main physical processes limiting operation temperature of the longwavelength lasers are non-radiative Auger recombination, intervalence
band absorption, carrier heating, as well as current leakage, due to poor electron and hole confinement. Attempts were made to improve electron and hole confinement by using MBE grown laser structures with high Al-content cladding layers [5]. Further progress in improving MIR laser performances is connected with new physical approaches to laser structure desing optimization. Recently in Ref [6] it was proposed to use high-barrier stopper confined layers for electron and holes in laser structures as a way of reducing thermoionic emission of carriers out of the active layer and decreasing the hole leakage. We try to apply this method to mid-infrared Sbbased laser structures grown by liquid phase epitaxy (LPE). New technical approach was proposed to create narrow-gap laser heterostructures with highly asymmetric band off-set confinements. We report here the first observations of electroluminescence and lasing in MIR laser structures with high Al-content (64%) cladding layers (Eg=1.474 eV) and a narrow-gap In0.94GaAsSb active layer (Eg=0.326 eV at T=77K) grown by LPE and lattice-matched to GaSb substrate. EXPERIMENT Two kinds of double heterostructure (DH) diode lasers were' fabricated on N- and P-GaSb substrates, below we will be referring to them as structure A and structure B respectively (Fig. 1). 101 Mat. Res. Soc. Symp. Proc. Vol. 484 © 1998 Materials Research Society
The N-GaSb substrates were doped by Te to 5*1017cm"3 and the P-GaSb ones were either undoped or Ge doped to 2*10l 9 cm 3 . The laser structures consisted of the following layers: struct
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