Novel temperature characteristics of gain behaviors in quantum-dot lasers
ABSTRACT In quantum dots, the increment of temperature results in red shift of gain spectrum. Thermal state-filling and electron-phonon scattering lead to extremely large and even negative T0. Theoretical prediction is confirmed experimentally.
[Show abstract] [Hide abstract]
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; DOI:10.1109/JQE.2003.814374 · 2.11 Impact Factor
[Show abstract] [Hide abstract]
ABSTRACT: Self-assembled quantum dot structures used for lasers have shown significant variation in the dot size distribution. In this article, we address the issues related to carrier occupation of these dots as a function of temperature in the absence and presence of lasing. The carrier distributions among different dots are derived in this paper through detailed balance. It is found that at low temperatures the carrier occupation is highly nonequilibrium but with increased temperature it tends towards an equilibrium distribution. Based on this distribution, the threshold current density versus temperature has been calculated. Multimode operation of lasers at different injection levels and temperatures is also examined. The theoretical results are compared with published experimental results. © 1999 American Institute of Physics. Peer Reviewed http://deepblue.lib.umich.edu/bitstream/2027.42/69377/2/JAPIAU-85-10-7438-1.pdfJournal of Applied Physics 05/1999; 85(10). DOI:10.1063/1.369375 · 2.19 Impact Factor
Temperature dependence of the photoluminescence emission from InAs quantum dots in a strained Ga0.85In0.15As quantum well. 2004. Semicond. Sci. Technol 19 33-38..