半導體量子結構雷射元件之研究

Abstract

本篇論文目的在針對光纖通訊應用之半導體量子井及量子點雷射做探討。這裡針對三個主要的研究課題來進行研究：（一）1300 nm 發光波段量子井雷射之理論比較，（二）設計及研製具有窄垂直發散角之 980 nm 砷化銦鎵量子井雷射，以及（三）長波長砷化銦量子點與量子點雷射之研製。 在比較四元半導體複合材料的量子井雷射研究中，我們考慮了鎵銦砷磷、鎵鋁銦砷與鎵銦氮砷等材料系統，各材料系統之成分經過適當選擇使得壓力應變量子井雷射的發光波段設計在 1300 nm 的波段。我們以理論模擬來比較這三種材料系統所構成之四種不同異質介面的能帶結構及材料增益。模擬結果顯示雖然不同材料系統的能帶結構相當不同，但是材料增益的參數卻幾乎相近。儘管如此，鎵銦氮砷/砷化鎵異質介面仍然是較佳的選擇，此乃因該材料系統具有最大的傳導帶能差，能夠有效降低載子的洩漏及降低對溫度效應的敏感度。 在窄垂直發散角砷化鎵量子井雷射的研究中，我們在傳統的雷射結構中插入兩層低折射率的磊晶層，首先針對此一特殊設計的結構沿磊晶方向作一維的光場模擬，最佳的波導層含鋁成分及低折射率層的厚度並實際應用於雷射的研製，實驗結果獲致相當小的垂直發散角13.5度，而其臨限電流 36 mA 及發光效率 0.95 W/A 皆符合實際應用可接受的範圍。最後我們並對此結構作二維的光場模擬，我們選擇離散頻譜折射率的方法作分析，模擬分析結果與實驗數據相當的吻合。該系統式的研究對於窄發散角雷射提供了設計對稱光束半導體雷射的準則。 在長波段量子點及量子點雷射方面，我們先對於量子點的成長及驗證做仔細的探討，最佳成長條件並應用於成長量子點雷射上。我們選擇砷化鎵基板上成長砷化銦覆蓋砷化鎵銦的量子點材料系統，實驗成果包括獲致室溫下光激光發光波段為 1300 nm 的量子點以及基態雷射發光波段接近1170 nm 的量子點雷射。同時我們也對量子點雷射的重要特性作量測，我們觀測到在低溫操作下量子點雷射的特徵溫度超過 580 K且為負值，而在常溫操作下特徵溫度只有接近 70 K。同時為了整篇論文的完整性，我們也對量子井雷射做了對等的量測，並對這些結果作討論及比較。

Semiconductor quantum well (QW) and quantum dot (QD) lasers for the fiber-optic communication are investigated in this dissertation. Three topics are covered: (1) theoretical comparison of QW lasers emitting in 1300-nm band, (2) design and demonstration of 980-nm InGaAs QW lasers with narrow vertical beam divergence, (3) long-wavelength InAs QDs and QD lasers. As regard to comparing QW lasers composed of GaInAsP, AlGaInAs and GaInNAs material systems, the quaternary compositions are carefully chosen for compressively strained QW active layers emitting in the 1300-nm band. Four heterostructure combinations out of three material systems are compared theoretically both in band structure and material gain. Despite the differences in the band structure, the material gain is around the same for all these systems. However, the GaInNAs/GaAs system should be a better choice because its large conduction band offset would decrease the carrier leakage over the barrier and reduce the device’s temperature sensitivity. In the study of InGaAs QW lasers with narrow beam divergence, one-dimensional cavity design is first conducted to the specially designed structure with two inserted low-index layers. The optimum composition of waveguide cladding layers and thickness of low-index layers are applied in the laser structure growth. The vertical beam divergence as small as 13.5 degree is then demonstrated experimentally. The threshold current of 36 mA and the slope efficiency of 0.95 W/A are in the acceptable range. Finally, two-dimensional mode analysis is carried out by the discrete spectral index method. The modal analysis agrees with the experimental results. The systematic studies on QW lasers with narrow beam divergence design provide the guidelines for designing semiconductor lasers with near symmetric beam aspect ratio. For long-wavelength QDs and QD lasers, the growth and characterization are carefully performed on the nano-structures first and then applied in the laser design. InAs/InGaAs/GaAs QDs emission as long as 1300 nm and QD lasers with ground-state lasing emission around 1170 nm are demonstrated experimentally. The important characteristics of QD lasers are measured. Negative characteristic temperature above 580 K is observed at cryogenic temperature range while only 70 K around room temperature. The physics behind experimental observations and the discrepancy with theoretical prediction are also discussed. For the sake of completeness, those characteristics for QW lasers are measured and compared.