臺灣博碩士論文加值系統

氮化鎵材料系統由於發光波長涵蓋整個可見光光譜、以及直接能隙的特性，未來有許多有潛力的產品應用。而垂直共振腔面射型雷射由於其低能耗、圓形光斑、高頻寬、及低發散角的特性，相較於邊射型雷射以及發光二極體有更大的優勢。隨著無線通訊的需求增加，傳統的wi-fi 已即將不敷使用，而使用氮化鎵材料為發光元件的可見光通訊系統在無線電波段之外開闢了另一個通訊波段，並擁有無電磁波干擾、保密性好等特性，可補足目前無線電波段之無線通訊所無法滿足應用的場合。因此在未來氮化鎵垂直共振腔面射型雷射的發展更是令人期待。

於本論文中，我們藉由模擬軟體Photonic Integrated Circuit Simulator in 3D (PICS3D)進行理論計算，探討多層量子井的層數、分佈式布拉格反射鏡的層數、以及透明電流傳輸層的厚度，對於氮化鎵垂直共振腔雷射所造成的閾值電流以及輸出光強度的影響，並且改善傳統結構、取得最佳輸出特性的元件結構，使得氮化鎵垂直共振腔面射型雷射，擁有低閾值電流、高輸出效率的特性。

The GaN-based material system features high emission efficiency with the characteristic of direct-bandgap, whose emission wavelength can cover overall visible light spectrum by tuning alloy composition. The advantages enable these materials have many potential applications. On the other hand, compared to edge-emitting laser and light-emitting diode, vertical-cavity surface-emitting lasers have the superiority of low power consumption, circular beam shape, high modulation response, and low divergence angle. Recently, the wireless communication is in high demand, but the use of radio frequency spectrum is getting saturation. Accordingly, visible light communication (VLC) system, where the visible light wavelength region is still not fully used for communication, ease the situation. Accordingly, the development of GaN-based VCSEL is expected.

In this thesis, the theoretical simulation (Photonic Integrated Circuit Simulator in 3D (PICS3D)) is conducted to optimize the performance of GaN-based VCSELs. We are going to discuss about the effects caused from the well number of multi-quantum well, the pair number of the distributed Bragg reflector, and the thickness of the transparent current spreading layer, including threshold current and output power. After improving the traditional device structure, the optimized GaN-based VCSEL device is achieved, which features low threshold current and high slope efficiency.

摘要 i
Abstract ii
致謝 iii
Content iv
List of Tables vi
List of Figures vii
Chapter 1 Introduction 2
1.1 Free-space optical communication 2
1.2 GaN-based vertical cavity surface emitting lasers 2
1.3 The state-of-the-art of electrical pumped GaN-based VCSELs 5
1.4 Organization of the thesis 6
Chapter 2. GaN-based VCSEL theoretical backgrounds 7
2.1 Basic principle of lasers 7
2.1.1 The three basic of lasers 7
2.1.2 Process of light emission 8
2.1.3 Population inversion and light amplification 9
2.1.4 Standing wave of resonance cavity 10
2.2 Basic VCSEL structure and properties 11
2.2.1 Distributed Bragg reflector (DBR) 13
2.2.2 Radiative recombination and non-radiative recombination 15
2.2.3 Multi-quantum well (MQW) structure 17
2.2.4 Optical confinement factor 18
2.2.5 Threshold condition 20
2.2.6 Basic output power versus current characteristics 22
2.2.7 Current crowding effect and transparent current spreading layer 24
Chapter 3. Experiment setup 25
3.1 Numerical simulation 25
3.2 Power-current measurement 28
Chapter 4. Structure optimization and top DBR design 29
4.1 GaN-based VCSEL structure design 29
4.2 Design of the well number of multi-quantum well 31
4.3 Reflectivity of different DBR pair number 33
4.4 Design of the number of top DBR pairs for lower threshold current and higher slope efficiency 35
4.5 Design of indium-tin-oxide layer thickness 38
Chapter 5. Conclusion and future work 43
Reference 47

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