寬頻半導體雷射的載子動力學

Abstract

我們在這個論文裡進一步研究量子點雷射的行為，包括量子點元件裡的兩種反競爭效應，以及量子點外共振腔雷射的穩定性。 在我們所觀察到的第一種反競爭效應裡，在激發態波長的雷射光，會幫助在基態波長的雷射光得到更多載子。實驗裡所使用的激發態雷射光其波長是1170nm，基態雷射光的波長則是在1240nm到1265nm之間。反競爭效應最明顯的時候，是基態雷射光在1245nm到1250nm之間以及在1260nm時。量子點元件裡測量到的反競爭效應其強度主要受量子點對激發態雷射光的吸收效率影響，因此當基態波長雷射共振腔的損耗減少，使得量子點內的載子數目減少而更容易吸收激發態的雷射光時，反競爭效應就會增強。 在第二種反競爭效應的實驗裡，使用的雷射二極體會自己在1250 nm產生雷射共振。反競爭效應發生在當外加的共振腔激發起另一道在基態波長的雷射光時，位於1170 nm的激發態發光因此增強10dB以上。這個效應在外部共振腔的雷射共振波長與元件本身的雷射波長(1250 nm)相差15nm時最為明顯。 我們的第二個研究主題是量子點外共振腔雷射的穩定性，量子點外共振腔雷射能穩定工作的電流範圍比量子井外共振腔雷射能穩定工作的電流範圍小。從實驗的數據可以了解，當共振腔的長度增加或是當共振腔的回饋減少時，量子點外共振腔雷射的行為會更傾向於不穩定。從理論模擬可以證明這種不穩定行為與量子點的兩個特質有關，第一個是載子在激發態以及基態間躍遷速率的限制(phonon bottle neck effect) ，第二個是激發態載子對基態雷射Fabry-Perot模態波長的影響。

In this dissertation, we further study the behaviors of quantum dot lasers. The topics include two types of anti-competition behaviors and the stability of quantum dot external cavity lasers. In the first type anti-competition behavior, the laser corresponding to the excited-state emission wavelength assists the laser corresponding to the ground-state emission wavelength to gain more carriers. In our experiment, the excited-state laser emission is at 1170 nm. The ground-state laser emission is between 1240 nm to 1265 nm. This anti-competition behavior is most obvious when the ground-state laser emission is between 1245 nm to 1250 nm or is at 1260 nm. In the experimental setup for the second type anti-competition behavior, the laser diode can oscillate by it self at 1250 nm. The second type anti-competition behavior occurs when the external cavity induces another laser oscillation at the ground-state wavelength. The emission of the excited-states at 1170 nm wavelength increases by more than 10dB. This effect is most obvious when the wavelength of the laser induced by the external cavity differs from 1250 nm by 15 nm. The second topic in this dissertation is the stability of the quantum dot external cavity laser. The current range in which the quantum dot external cavity laser can operate stably is smaller than that of the quantum well external cavity laser. The experiment indicates that the quantum dot external cavity laser tends to be more unstable when the cavity length increases, and when the feedback efficiency decreases. The unstable behavior is theoretically confirmed to be relating to the characteristics of the quantum dot materials. The first is the finite carrier transition time between the ground state and the excited state inside a quantum dot. The second is the shift of the Fabry-Perot mode wavelength versus the excited-state carrier population.