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研究生：	陳勁宇 Chen, Chin-Yu
論文名稱：	三五族垂直式共振腔面射型雷射之研製 Investigation and Fabrication of III-V Vertical Cavity Surface Emitting Lasers (VCSELs)
指導教授：	蘇炎坤 Su, Yan-Kuin
學位類別：	碩士 Master
系所名稱：	電機資訊學院 - 微電子工程研究所 Institute of Microelectronics
論文出版年：	2014
畢業學年度：	102
語文別：	英文
論文頁數：	96
中文關鍵詞：	氮化鎵、砷化鎵、垂直式共振腔面射型雷射
外文關鍵詞：	GaN, GaAs, VCSEL
相關次數：	點閱：100 下載：0
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本論文之主要研究目的在於探討氮化鎵以及砷化鎵兩種材料為主的面射型雷射。文中利用模擬軟體來做元件設計並加以改善後，藉以分別製作出光激發藍綠光氮化鎵垂直式共振腔面射型雷射及電激發砷化鎵氧化侷限面射型雷射。
在氮化鎵雷射部分，首先針對主動層的設計作模擬，探討不同銦含量對主動層發光波長的影響，同時比較不同量子井寬度、量子障壁寬度與材料增益之間的差異。在元件反射鏡方面，設計分為兩種結構。其一是上下皆採用由二氧化鈦及二氧化矽所組成的介電質布拉格反射鏡，並在不同對數下作反射率的比較。另一則是採用金屬銀和鋁作為上反射鏡，而下反射面則採用介電質布拉格反射鏡。整體元件直徑大小設計為10微米，其共振腔長度、各層材料厚度及摻雜濃度透過模擬軟體微調後完成並使元件達到雷射狀態。在設計中使元件主動層位於模擬光場之波腹處，藉以增加光子及載子複合。而氧化銦錫由於吸收較高，將其設計於駐波節點以減少光學吸收。上述分別由兩種不同反射鏡所組成之氮化鎵雷射電壓、電流、光強度、發光頻譜等模擬結果也在文中作討論比較。
於實作方面，則採用上述之混合式金屬─布拉格反射鏡共振腔結構。首先探討金屬銀、鋁反射鏡於不同鍍率下其反射率及表面粗糙度間的差異。在分析金屬共振腔光譜的研究中，我們也發現此種結構能有效的提供光學侷限環境。此外，元件尺寸減小則有益於提升光學特性，且對旁模抑制有顯著的效果，但尺寸縮減也意味著製程困難度的增加。而在製作完整元件後，我們進行布拉格反射鏡之反射頻譜分析，並透過微光激發光譜儀在低溫77 K的量測，發現在輸入功率密度為20.8 kW/cm2時，元件可能已達到雷射狀態，發出的兩雷射波長位於531.2及532.2奈米處。
而在砷化鎵雷射部分，其模擬設計概念與前述氮化鎵之模擬相同。在製作元件前，實驗先針對砷化鎵側壁蝕刻參數作最佳化，我們發現氯氣對於蝕刻垂直度扮演重要的角色。而不同溫度下之蝕刻、負載效應也在本文中作探討。最後，電激發砷化鎵雷射元件成功製作完成。藉由電激發光量測系統在室溫下量測，發現元件於輸入電流約1.4毫安培時已達到雷射狀態，雷射波長為847.06奈米。然而隨著電流增加，旁模亦隨之出現。此外，在實驗中也觀察到紅移效應產生，雷射基模隨著電流加大而向長波長移動，這是由於元件的熱能造成能帶變小，使發光波長變長所致。

The main purpose of this thesis is to investigate the GaN-based and GaAs-based surface emitting laser. We make use of the simulation tool to design the whole device and improve its performance, with a view to developing the optically pumped blue-green GaN-based vertical cavity surface emitting lasers (VCSELs) and electrically pumped GaAs-based oxide confined surface emitting lasers.
As for GaN-based laser, first we do the simulation and design the active region to investigate how the amount of indium influences the emitting wavelength. In addition, we make a comparison between the different width of quantum well, barrier and material gain. In respect of reflection mirror, there are two designs. For the first design, titanium oxide (TiO2) and silicon oxide (SiO2) are employed to produce both top and bottom distributed Bragg reflectors (DBRs). We also discuss the reflectivity variation with different pairs of DBRs. For the other devisal, metal film of silver as well as aluminum, and TiO2/SiO2 DBRs are utilized to form the top and bottom mirrors, respectively. The diameter of the device is designed to be 10 μm, and the cavity length, the thickness as well as the doping level of each layer are optimized and simulated to make lasing achieved. A general idea of the design is to make multiple quantum wells (MQWs) located at an antinode of light field for enhancing the coupling of photon and carriers, and have indium tin oxide (ITO) situated at a node of the optical standing wave for minimization of absorption loss. The GaN-based lasers composed of two different mirrors mentioned above are characterized in the simulation results, inclusive of turn on voltage, threshold current, light intensity and emitting wavelength.
On the processing part, we apply the hybrid metal-DBR mirror mentioned above to form the cavity. To begin with, we make a survey on the relationship between the reflectivity and surface roughness of silver/aluminum film under different deposition rate. In respect of research on the metal cavity under optical pumping at 77 K, we find that the structure can provide a good optical confinement. Besides, shrinking the device size can not only enhances the optical performance but also helps in the suppression of satellite modes. After the fabrication process, we analyze the reflectivity spectrum of DBRs. The demonstration of the optically pumped VCSEL suggests that lasing is likely to be achieved at an input power density of 20.8 kW/cm2 by micro-photoluminescence spectrometer under 77 K with two lasing peaks located at 531.2 and 532.2 nm.
As for GaAs-based laser, the simulation design concept is similar to that mentioned above. Before the device fabrication, an experiment is conducted to optimize the etching parameters for GaAs-based VCSEL so as to attain a better vertical confinement. It is observed that chlorine (Cl2) plays an important role in the GaAs etching process for vertical confinement. Furthermore, the influence of temperature on GaAs etching and loading effect are also considered in the article. At last, room temperature current injected GaAs-based oxide confined VCSEL is successfully fabricated. By electroluminescence measurement, we find that lasing is achieved at the threshold current of 1.4 mA, beyond which a lasing peak emerges at 847.06 nm with a gradual red-shift, and satellite modes appears as the driving current increases. Red-shift can be attributed to the raised temperature which brings about the shrinkage in semiconductor band gap.

Contents

Abstract (in Chinese)	I
Abstract (in English)	III
Acknowledgement	V
Contents	VI 
Table Captions	VIII 
Figure Captions	IX

Chapter 1 Introduction	1
1-1 A Brief History of Vertical Cavity Surface Emitting Lasers (VCSELs)	1
1-1-1 GaN-based VCSELs	1
1-1-2 GaAs-based VCSELs	4
1-2 Motivation	6
1-3 Organization of This Thesis	7

Chapter 2 Basic Theory and Characteristics of Semiconductor Lasers	11
2-1 Device Structure	12
2-1-1 Edge Emitting Lasers (EELs)	12
2-1-2 Vertical Cavity Surface Emitting Lasers (VCSELs)	13
2-1-3 Distributed Bragg Reflectors (DBRs)	13
2-2 Characteristics of VCSELs	15
2-2-1 Resonance Condition	15
2-2-2 Effect of Temperature	18
2-2-3 Effect of Micro-cavity	20

Chapter 3 GaN-based Vertical Cavity Surface Emitting Laser	26
3-1 Simulation and Design of Current Injected Blue-green GaN-based VCSEL Employing TiO2/SiO2 Dielectric DBRs	27
3-1-1 Multiple Quantum Wells (MQWs) Design	27
3-1-2 Reflectors Design	28
3-1-3 Cavity Length Design and Resonance Condition	29
3-1-4 L-I-V Characteristics and Emission Spectrum	30
3-1-5 Summary	31
3-2 Simulation and Design of Current Injected Blue-green GaN-based VCSEL Employing Hybrid Metal-DBR Mirrors	31
3-2-1 Multiple Quantum Wells (MQWs) Design	31
3-2-2 Reflectors Design	32
3-2-3 Cavity Length Design and Resonance Condition	32
3-2-4 L-I-V Characteristics and Emission Spectrum	34
3-2-5 Summary	34
3-3 Material Gain Spectrum and Fabrication of Metal Cavity	35
3-3-1 Experiment Details	35
3-3-2 Ag/Al Mirror Reflectivity and Surface Roughness	36
3-3-3 Device SEM Images and Material Gain Spectrum at 77K	37
3-3-4 Summary	38
3-4 Optically Pumped GaN-based VCSEL with Hybrid Metal-DBR Mirrors at 77K	38
3-4-1 Experiment Details	38
3-4-2 TiO2/SiO2 DBR Reflectivity	39
3-4-3 Micro-photoluminescence Measurement at 77K	40
3-4-4 Summary	40

Chapter 4 GaAs-based Vertical Cavity Surface Emitting Laser	65
4-1 Simulation and Design of GaAs-based Oxide Confined VCSEL	65
4-1-1 Reflectors Design	65
4-1-2 Cavity Length Design and Resonance Condition	66
4-1-3 L-I-V Characteristics and Emission Spectrum	67
4-1-4 Summary	67
4-2 Optimization of Etching Parameters for GaAs-based VCSEL	68
4-2-1 SiO2 Etching mask by ICP and BOE	68
4-2-2 Parameters of AlGaAs Etching	68
4-2-3 Influence of Temperature on AlGaAs Etching	69
4-2-4 Summary	70
4-3 Fabrication of current injected GaAs-based oxide confined VCSEL	70
4-3-1 Experiment Details	70
4-3-2 L-I-V Characteristics and Emission Spectrum	71
4-3-3 Red-shift	72
4-3-4 Summary	72

Chapter 5 Conclusions and Prospects	86
5-1 Conclusions	86
5-2 Prospects	88

Reference	91


                                    

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