臺灣博碩士論文加值系統

本論文探討生長於氧化鋁或矽基板之III-族氮化物薄膜或元件的特性。其中，以原子層磊晶法在矽基板上生長氮化鎵及氮化鋁鎵薄膜，主要探討中溫(800ºC)氮化鋁鎵緩衝層對後續生長之氮化鎵薄膜結晶及發光品質之影響。實驗結果顯示當氮化鋁鎵緩衝層鋁含量為58％、厚度為180nm時後，後續生長之氮化鎵薄膜品質最佳且無裂紋產生。此外，分別在(001)和(111)矽基板上生長高鋁含量之氮化鋁鎵薄膜，透過Ｘ光繞射及穿透式電子顯微分析，發現在(111)矽基板上生長氮化鋁鎵為單晶結構而在(001)矽基板上生長之氮化鋁鎵為多晶柱狀結構。利用二次離子質譜分析後，發現鋁原子在(001)矽基板和氮化鋁鎵薄膜間的擴散問題較為嚴重。此外，在氮化鋁鎵薄膜成長於具溝渠圖案之氮化鎵的研究主題中，本研究將2um厚、無裂紋之氮化鋁鎵薄膜成功地生長在圖樣化氮化鎵薄膜上。研究發現置入溝渠於氮化鎵有助於提升後續生長之氮化鋁鎵薄膜之光激發光強度。透過試片表面和横截面之電子顯微鏡影像觀察，發現生長於圖樣化氮化鎵上之氮化鋁鎵內差排密度明顯降低。在氮化鎵發光二極體元件中插入氮化鎵/氮化鋁鎵超晶格結構之研究主題中，氮化鎵/氮化鋁鎵超晶格結構可以有效抵擋來自底層氮化鎵薄膜的貫穿式差排延伸至多層量子井，進而降低元件漏電流及提高其電致發光的強度。

In this dissertation, the characteristics of III-nitride films (or light–emitting diodes) grown on Si (or sapphire substrates) were investigated. For the III-nitride film growth, atomic layer deposition (ALD) was employed to grow GaN and AlGaN films on Si substrates. AlxGa1-xN films having various Al-contents were grown on (111) Si substrates over a temperature range of 800~1000°C. It was found that crack free AlxGa1-xN films were achieved when the films were grown at 800 ºC. The best HT-GaN film was achieved on (111) Si substrate by process optimization using an 800°C grown 180nm-thick Al0.58Ga0.42N buffer layer. In addition, investigation of the differences of the AlGaN films grown on (111) Si substrates and those grown on (001) Si substrates was also conducted to explore the influence of substrate orientation on the characteristics of AlGaN films. Experimental results show that AlxGa1-xN films grown on (111) Si substrates exhibit better crystalline quality than the films deposited on (001) Si substrates. Cracks were found in the high Al-content AlxGa1-xN/(111) Si samples but they were not observed in the AlxGa1-xN films grown on (001) Si substrates having the same film thicknesses and Al compositions. Based upon the results of x-ray diffraction measurements and transmission electron microscopic observations, it appears that mono-crystalline AlxGa1-xN films were achieved on (111) Si substrates while columnar structure was observed in the AlxGa1-xN/(001) Si samples. Enhanced Al inter-diffusion in the AlxGa1-xN /(001) Si samples was identified by secondary ion mass spectroscopic analyses. AlGaN films were also grown on stripe-grooved GaN templates having various trench depths. 2um-thick crack free AlGaN films were achieved when the films were grown on GaN templates having 1.0mm-deep trenches. The improved PL intensities of AlGaN films grown on the grooved GaN templates are attributed to the reduction of the threading dislocation densities in the films. The interactions and the origin of dislocations in the AlGaN/grooved GaN templates were also revealed by TEM observations. In addition, the influence of short-period superlattice (SPSL)-inserted structures in the underlying undoped GaN on the characteristics of GaN-based light emitting diodes (LEDs) were also studied. It was found that the investigation of pseudomorphic Al0.3Ga0.7N(2nm)/GaN(2nm) SPSL- inserted structures is helpful to improve current-voltage (I-V) characteristics of GaN-based LEDs with the best LED being inserted with 2 sets of 5-pair Al0.3Ga0.7N(2nm)/GaN (2nm) SPSL structure. Based upon the results of etch pit counts, double-crystal X-ray diffraction measurements and transmission electron microscopic observations of the GaN-based LEDs, it was found that the Al0.3Ga0.7N(2nm)/GaN(2nm) SPSL-inserted structures tended to serve as threading dislocation filters in the LEDs so that the improved I-V characteristics were achieved.

Acknowledge (in Chinese)...............................i
Abstract (in Chinese)..................................ii
Abstract...............................................iii
Table of Contents........................................v
List of Figures.......................................viii

Chapter 1 Background......................................1
1.1 Evolution of GaN materials and devices ..................................................3
1.2 Challenges in GaN-based light emitting devices...................................................4
1.3 Overview of this dissertation....................6
References................................................9
Chapter 2 Literature review..............................12
2.1 Approaches employed for the improvement of GaN films on
Si substrates.........................................13
2.1.1 GaN films on (111) Si substrates using AlN buffer layers...................................................14
2.1.2 GaN films on (111) Si substrates using III-Nitride multi-buffer layers......................................15
2.2 Approaches employed for the quality improvement of AlGaN films on sapphire substrates.......................16
2.3 Approaches employed to improve the characteristics of a GaN-based LED.........................................17
2.3.1 Epitaxial lateral overgrowth (ELOG technique)......18
2.3.2 Patterned substrate technique .....................19
References...............................................26
Chapter 3 Process techniques.............................29
3.1 Setup of the home-made ALD system....................29
3.2 Fundamental aspects of ALD...........................30
3.3 Characterization methods.............................35
3.3.1 X-ray diffraction..............................................35
3.3.2 Photoluminescence spectroscopy.............................................36
3.3.3 Secondary ion mass spectrometry ….......................................................38
3.3.4 Transmission electron microscopy...................39
3.3.5 Scanning electron microscopy...............................................40References...............................................48
Chapter 4 On the characteristics of AlGaN films grown on (111) and (001) Si substrates............................49
4.1 Introduction.............................................49
4.2 Experimental procedures............................. 50
4.3 Results and discussion...............................................52
4.4 Summary..................................................55
References...............................................62

Chapter 5 Deposition of AlGaN films on (111) Si substrates and optimization of GaN growth on Si using intermediate- temperature AlGaN buffer layers.........................64
5.1 Introduction..................................... ..64
5.2 Experimental procedures.............................65
5.3 Results and discussion... ..........................67
5.3.1 Deposition of AlGaN films on (111) Si substrates at
intermediate temperatures...............................67
5.3.2 HT GaN films deposited on (111) Si substrates using
Al0.58Ga0.42N buffer layers grown at 800°C.............68
5.4 Summary. ...........................................70
References..............................................78

Chapter 6 Influence of the trench depths of grooved GaN templates on the characteristics of overgrown AlGaN films...................................................80
6.1 Introduction........................................80
6.2 Experimental procedures..............................................81
6.3 Results and discussion..............................................82
6.4 Summary.............................................87
References..............................................98

Chapter 7 Improvement in the characteristics of GaN-based light emitting diodes by inserting AlGaN/GaN short-period superlattices in GaN underlayers........................99
7.1 Introduction........................................99
7.2 Experimental procedures..............................................100
7.3 Results and discussion..............................................101
7.4 Summary.............................................107
References..............................................116
Chapter 8 Conclusions...................................118
Chapter 9 Future work...................................120
About the author........................................121

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chapter 6
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