三五族面射型雷射之設計及優化

Abstract

近年來，三五族光電材料引起廣泛的研究。三五族材料中，砷化鎵以及氮化鎵材料由於其所能涵蓋的發光波長可從近紫外到近紅外，以及直接能隙的特性，作為光電元件可發揮極大的潛力。面射型雷射由於其低功耗、圓形光斑以、高頻寬及較低發散角等特性，相比於邊射型雷射也可以有一定的發揮。砷化鎵面射型雷射目前已廣泛應用於短距離光纖通訊中，且已被制定為下一世代高速網路短距傳輸的標準光源，然而其頻寬仍受限於主動區的設計，以及寄生效應的影響。氮化鎵面射型雷射，在2007年交通大學首度達成電流操作後，許多團隊持續投入氮化鎵面射型雷射的開發，大部分皆著重在磊晶的品質提升，以及布拉格反射鏡與雷射的結合。然而在氮化鎵光電元件中，不均勻的電子電洞移動率、歐傑非輻射複合等特性造成載子注入效率不佳。雖然在氮化鎵發光二極體中，有相當多利用電子阻擋層提升注入效率的研究，然而相關的研究在氮化鎵面射型雷射中仍沒有太多的斬獲。 在本篇論文中，對於砷化鎵面射型雷射的頻寬提升，利用模擬分析的方式設計高應力量子井發光區，以達到高微分增益提升頻寬。同樣的，利用模擬分析的方式，設計多層低介電係數氧化層，以及對於布拉格反射鏡的摻雜優化以減低寄生的電阻、電容。對於熱效應的影響，新型的布拉格反射鏡利用砷化鎵/砷化鋁的搭配，降低底層反射鏡的熱阻，提升元件的操作效率。對於氮化鎵面射型雷射，本論文同樣利用模擬分析，設計出超晶格電子阻擋層，此結構可減緩磊晶層間應力導致的能帶歪曲，並提供一個虛擬的高能障，阻擋電子的溢流。

Recently, GaAs- and GaN-based materials had shown its superior potential for Opto-Electronic device applications, which is due to its emission wavelength can cover from near ultra violet to near infrared wavelength by tuning the alloy composition. And the high emission efficiency due to its direct band gap character. On the other hand, compared to edge-emitting lasers (EELs), vertical-cavity surface-emitting lasers (VCSELs) have low power consumption, circular beam shape, high bandwidth and low divergence angle. The well-established GaAs-based VCSELs are widely used for the fiber communications. However, in order to meet the requirement of the next generation high speed Ethernet standard. The bandwidth of GaAs-based VCSELs still have room for improvement. For the GaN-based VCSELs, since the first electrically pumped GaN VCSEL was demonstrated at 2007 by National Chiao Tung University. Researchers devoted hugh efforts on the further improvement of GaN VCSEL by increasing the epitaxy quality and optimizing the fabrication process. However, the unbalance of electron/hole mobility and Auger recombination lead to a low injection efficiency in GaN VCSEL. And there has no much efforts on this issue. In this thesis, the theoretical simulation is conducted to optimize the performance of GaAs and GaN VCSELs. For the GaAs VCSEL, the intrinsic and extrinsic limitation are released via the use of highly strained MQW, multiple oxide layers and modulation doping in DBR. Furthermore, AlAs/GaAs bottom DBR is designed for high thermal conductivity character. For the GaN VCSEL, superlattice electron blocking layer (EBL) is designed to compare with the bulk EBL. Compared to the bulk EBL, superlattice EBL can release the QCSE effect, and furthermore, it provides a virtual energy potential to block the electrons from escaping the MQW.