Conference Paper

# Novel temperature characteristics of gain behaviors in quantum-dot lasers

Graduate Inst. of Electro-Opt. Eng., Nat. Taiwan Univ., Taipei, Taiwan

DOI: 10.1109/NUSOD.2005.1518151 Conference: Numerical Simulation of Optoelectronic Devices, 2005. NUSOD '05. Proceedings of the 5th International Conference on Source: IEEE Xplore

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**ABSTRACT:**We have performed pump-probe differential transmission spectroscopy (DTS) measurements on In<sub>0.4</sub>Ga<sub>0.6</sub>As-GaAs-AlGaAs heterostructures, which show that at room temperature, injected electrons preferentially occupy the excited states in the dots and states in the barriers layers. The relaxation time of these carriers to the dot ground state is >100 ps. This leads to large gain compression in quantum-dot (QD) lasers and limits the attainable small-signal modulation bandwidth to ∼ 5-7 GHz. The problem can be alleviated by tunneling "cold" electrons into the lasing states of the dots from an adjoining injector layer. The design, growth, and steady-state and small-signal modulation characteristics of tunnel injection In<sub>0.4</sub>Ga<sub>0.6</sub>As-GaAs QD lasers are described and discussed. The tunneling times, directly measured by three-pulse DTS measurements, are ∼ 1.7 ps and independent of temperature. The measured small-signal modulation bandwidth for I/I<sub>th</sub> ∼ 7 is f<sub>-3 dB</sub> = 23 GHz and the gain compression factor for this frequency response is ε = 8.2 × 10<sup>-16</sup> cm<sup>3</sup>. The differential gain obtained from the modulation data is dg/dn ≅ 2.7 × 10<sup>-14</sup> cm<sup>2</sup> at room temperature. The value of the K-factor is 0.205 ns and the maximum intrinsic modulation bandwidth is 43.3 GHz. Analysis of the transient characteristics with appropriate carrier and photon rate equations yield modulation response characteristics identical to the measured ones. The Auger coefficients are in the range ∼ 3.3 × 10<sup>-29</sup> cm<sup>6</sup>/s to 3.8 × 10<sup>-29</sup> cm<sup>6</sup>/s in the temperature range 15°C<T<85°C, determined from large-signal modulation measurements, and these values are smaller than those measured in separate confinement heterostructure QD lasers. The measured high-speed data are comparable to, or better than, equivalent quantum-well lasers for the first time.IEEE Journal of Quantum Electronics 09/2003; · 2.11 Impact Factor

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