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7 February 2006 Tunnel quantum well-on-dots InGaAs-InAs high-gain medium for laser diodes
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Structures of tunnel coupled pairs consisting of InGaAs quantum wells grown on top of self-assembled InAs quantum dots (QW-on-QDs) were employed to improve the gain medium in laser diodes. Photoluminescence, transmission electron microscopy and electroluminescence were used to study the properties of multiple-layer QW-on-QDs active medium. QW-on-QDs tunnel structures with 4.5 nm tunnel barrier thickness and with different ground state (GS) relative separations were grown by variation of InGaAs QW while the QD growth process was kept constant. We have developed a tunnel QW-on-QDs structure with a resonance transition which is red-shifted ~35 meV relative to QW GS. This transition with narrow linewidth, 21.6 meV at T=77K, likely indicates an efficient LO-phonon assisted tunneling of carriers from QW into QD ensemble states. The highest gain was achieved with a QW-on-QDs active medium with GS relative separation of close to 35-40 meV. Optimized triple-pair tunnel QW-on-QDs laser diodes with cleaved mirrors emitting at 1145 nm (corresponding to QD GS) exhibited a saturated modal gain exceeding 80 cm-1 with minimum cavity length of 0.14 mm. Small signal modulation characteristics of these lasers were measured. From the damping factor and resonance frequency dependence on driving current, the damping-limited cut-off frequency for this QW-on-QDs medium can be estimated as exceeding 30 GHz. All-epitaxial vertical cavity surface emitting lasers with triple-pair tunnel QW-on-QDs as active medium demonstrated continuous wave mode lasing with 5.7 mA minimum threshold current at QD GS emission wavelength, 1131 nm.
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V. Tokranov, M. Yakimov, J. van Eisden, and S. Oktyabrsky "Tunnel quantum well-on-dots InGaAs-InAs high-gain medium for laser diodes", Proc. SPIE 6129, Quantum Dots, Particles, and Nanoclusters III, 612908 (7 February 2006);


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