| Summary: | 碩士 === 國立臺灣大學 === 光電工程學研究所 === 94 === With the improvement of quantum dot growth technology, we investigate the characteristics of quantum dot lasers to fully utilize the available bandwidth of optical fiber communication systems. In this dissertation, we focus on the designed quantum dot structures to achieve less temperature dependence, lower threshold current density and higher tuning bandwidth of semiconductor laser diodes and semiconductor optical amplifiers.
We propose a new simple method to measure the broadband gain spectrum with a two-section device. Without any other external tunable lasers and complicated setup, broadband gain spectrum is obtained immediately and precisely for each current density and temperature. Broadband gain spectrum comprises two compositions, one is homogeneous broadening arising from carrier lifetime, the other is inhomogeneous broadening which represents the size uniformity of quantum dots. Besides, the proportion of degeneracy in first, second and third quantized state is 2 to 4 to 6 which decide the amplitude of these states. Broadband gain spectrum red shifts when current density increase and temperature increase, and also influenced by electron occupation probability with its fermi-level increasing with increasing current density and decreasing with increasing temperature.
The temperature dependence of threshold current is not described by a single exponential term with a characteristic temperature. Characteristic temperature of quantum dots varies with temperature. We also find negative temperature effect of characteristic temperature, which arises from red shift of gain curve. when temperature increases, the bandgap energy can be further decreased to achieve a longer emission wavelength.
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