半導體量子點雷射之主動層結構研究

Abstract

本篇論文主要在研究不同主動區結構的量子點雷射特性，首先我們將不同結構的量子點雷射做完製程後批裂成不同長度的共振腔，分析討論量子點雷射特性，三層、五層、五層p-doped和七層的飽和增益分別為7.5 cm-1、12.5 cm-1、13.6 cm-1 和 17cm-1。接著對於不同結構的量子點雷射分析10-70 ℃的特徵溫度(T0)，我們觀察到五層p-doped雷射有最高的特徵溫度82K。為了研究不同結構雷射之相對雜訊強度(RIN)，我們將量子點雷射後端鏡面做高反射率(HR)鍍膜，其目的是為了降低起使電流和減低熱效應對雷射的影響。鏡面鍍膜後有較小的鏡面損耗、較高的特增溫度、較高的量子效率和共振腔內較高的光子密度。最後我們仔細討論鏡面鍍膜後的基態相對雜訊強度，從量測到的RIN資料可以分析萃取D參數和K參數，接著從K和D參數可以預期雷射3-dB頻率和微分增益。我們發現當量子點層數增加或p-doped於主動層時，量子點雷射得微分增益、飽和增益和3-dB頻率就會提高。實驗中我們從7層量子點雷射觀察到最高的3-dB頻率為8.1GHz。

This thesis studies the quantum-dots laser diodes (QDLD) with various active layer structures. We first discuss the device characteristics of processed QDLD with cleaved facets and with various cavity lengths. The saturation gain of 3-layers、5-layers、5 p-doped and 7-layers is 7.5 cm-1、12.5 cm-1、13.6 cm-1 and 17cm-1, respectively. The characteristic temperature (T0) of QDLD are also analyzed in the range of 10-70 ℃, a highest T0 of 82 K is obtained with the laser having 5 p-doped QD layers. To study the relative intensity noise, we use high reflectivity (HR) coating on the rear facet of QDLD to reduce their threshold current and thereby to avoid the heating problem. With the HR coating, the lasers have smaller mirror loss, higher T0, higher quantum efficiency and higher photon density in cavity. Finally, we perform detailed RIN measurements on HR-coated QDLD lasing at their ground states. The model simulation gives the K and D factors from the obtained RIN data, which are related to the intrinsic 3-dB frequency and to the differential gain. As a result, we find that, as the number of QD layers increases, the laser has higher differential gain, higher saturation gain, and higher 3-dB frequency. By using p-typed doping around the QDs, the 3-dB frequency of lasers can be enhanced as well. The highest 3-dB frequency of 8.1 GHz is expected from the lasers with 7 QDs layers.