光激發砷化鎵銦量子點微碟雷射之動態特性研究

Abstract

微碟雷射具有高品質係數與低模態體積，因此有良好的侷限性能將共振模態侷限在腔體中，並且能使得微碟雷射有非常低的臨界激發功率以及較大的自發輻射因子，因此微碟雷射具有在光積體電路上被應用的潛力。微碟雷射較大的Purcell factor使得自發輻射被增強而有較短的載子生命期(carrier lifetime)，使的微碟雷射具有能快速調變的特性。 在本文中我們成功的製作幾種尺寸的砷化銦量子點微碟雷射，其中最小的尺寸為直徑1.55 μm。在80 K下以脈衝光源激發其臨界激發功率約為10 μW。我們從80 K到200 K量測其模態的紅移。從動態量測結果可以看到微碟雷射具有相當短的啟動時間，約為200 ps，並且沒有鬆弛震盪的現象。以兩個指數函數擬合(fitting)時間解析光子衰減曲線，可以得到4 μm的微碟雷射跟其他尺寸的微碟雷射相比具有最大的自發輻射(spontaneous emission)增益，約為六倍左右。

Microdisk lasers have attracted much attention due to their high quality factors and small mode volumes. Therefore, optical modes can be highly confined in the microdisk cavities. These two factors result in ultralow lasing threshold and large spontaneous emission factor, which provides potential applications for microdisk lasers in photonic integrated circuits. Large Purcell factors of microdisk lasers induce strong enhancement of spontaneous emission and small carrier lifetime, which causes fast modulation speed of microdisk lasers. In this thesis, we fabricated InGaAs quantum-dot microdisk lasers in several sizes with the smallest disk size down to 1.55 μm in diameter. The lasing threshold reduces down to 10 μW under pulse excitation at 80 K. The mode shifts were measured from 80 K to 200 K and their values are about 0.5Å/K. The transient behaviors of microdisk lasers show fast turn-on time of 200 ps without occurrence of relaxation oscillations. From the double-exponential function fitting of time-resolved photoluminescence decay curves, the enhancement of the spontaneous emission factor is about 6 for a 4-μm-diameter microdisk laser.