Carrier Dynamics in Self-Assembled InAs QD Laser Structures and Broad-Area InAs QD Lasers Grown by Molecular Beam Epitax
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Carrier Dynamics in Self-Assembled InAs QD Laser Structures and Broad-Area InAs QD Lasers Grown by Molecular Beam Epitaxy Yongkun Sin, Stephen LaLumondiere, William Lotshaw, and Steven C. Moss Electronics and Photonics Laboratory, The Aerospace Corporation El Segundo, CA 90245-4691 ABSTRACT We investigated carrier dynamics in both proton-irradiated InAs-GaAs quantum dot laser structures and in high power broad-area InAs-GaAs quantum dot lasers with windowed ncontacts using time-resolved PL (TR-PL) techniques. INTRODUCTION Near-IR quantum dot (QD) lasers are attractive sources as pump lasers and transmitters for satellite communications systems due to three-dimensional localization of carriers that makes them more suitable for radiation hardening than lattice-matched or strained quantum well (QW) lasers. A few research groups have reported encouraging results of QD lasers showing enhanced resistance to radiation damage [1-3], but complete understanding of physical mechanisms leading to this enhancement is still lacking. Also, it is well known that point defects induced by proton irradiation behave as nonradiative recombination centers (NRCs), but the role that NRCs play in reliability and degradation mechanisms in QD lasers is not well understood. In the present study, we investigated carrier dynamics in proton-irradiated InAs-GaAs QD laser structures as well as in high power broad-area InAs-GaAs QD lasers. Also, comparison was made between carrier lifetimes measured from InAs-GaAs QD lasers and those measured from strained-layer InGaAs-AlGaAs single QW lasers. EXPERIMENTAL METHODS We studied carrier dynamics in InAs-GaAs quantum dot laser structures (unprocessed lasers) before and after they were irradiated with protons. The structures were grown using MBE and quantum dots were self-assembled by the Stranski–Krastanov (SK) process. The samples had PL peaks at ~ 1 μm at RT. QD layers, grown under slightly different conditions, were clad by 100 nm thick GaAs waveguide layers and then AlGaAs cladding layers. Proton energies of 10, 30, and 50 MeV were used for this experiment and the fluence was 1 – 3×1012/cm2. We also studied pre-proton irradiation carrier dynamics in high power broad-area InAs-GaAs QD lasers at ~1150 nm. The lasers were grown by MBE and quantum dots were also formed by the SK process. ARHR coated broad-area lasers with 200 μm wide waveguides and ~3.6 mm long cavities were mounted in p-side down configuration. The lasers showed threshold currents of ~ 900 mA and slope efficiencies of ~ 0.6W/A under CW operation. We used the angle polishing technique to introduce window regions to these lasers by forming openings in the backside n-contacts to perform time-resolved electroluminescence (TR-EL) and time-resolved photoluminescence (TRPL). TR-EL allows us to directly observe spontaneous emission from the entire active layer
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through the window while lasers are under test. We used this technique to capture EL images in real time from the window region during entire accelerated lifetests until device degr
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