Influence of Carrier Distribution on Temperature-Dependent Characteristics in Quantum-Dot Lasers
Date Issued
2008
Date
2008
Author(s)
Lin, Yen-Chih
Abstract
In this thesis, we investigate the influence of carrier distribution on temperature-dependent characteristics in quantum-dot lasers. From the measurement of laser light output versus injected current at temperatures of 78 K to 340 K, it shows that the behavior of threshold current of a quantum-dot laser has the S-shaped temperature dependence. We also find that the threshold currents of the ground states and the excited states versus temperature at two-state lasing condition have the complementary characteristics. This process corresponds to the transition from nonthermal to thermal coupling of carrier distribution in a quantum-dot system with increasing temperature. In the measurement of spectrally-resolved dynamic properties, we get different results at cryogenic and room temperatures. At cryogenic temperature, carriers in a quantum-dot system are in a nonthermal coupling state, and thus lasing groups lase independently and have the same relaxation oscillation behaviors. However, the carriers have reached thermal coupling at room temperature, leading to the complementary relaxation oscillation characteristics. In addition, we fabricated a windowed-stripe laser structure to study the dynamic behaviors of a quantum-dot laser under current injection and femtosecond optical pulse excitation simultaneously. We carried out measurements at different temperatures and found that quantum-dot lasers stopped lasing temporarily at room temperature while they did not have such a phenomenon at cryogenic temperature. This is because carriers are confined by the potential energy and do not have enough energy to redistribute among the quantum dots ensemble at cryogenic temperature. From the temperature-varying experiments above, we find that the transition from nonthermal to thermal coupling of carrier distribution in a quantum-dot system with increasing temperature will affect both the static and dynamic properties of a quantum-dot laser profoundly.
Subjects
quantum-dot laser
characteristic temperature
thermal coupling
Type
thesis
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