臺灣博碩士論文加值系統

本論文主要是探討矽摻雜的多層結構，是否可以有效改善隨後成長的氮化鎵磊晶薄膜的品質。由於已有文獻指出，矽的輕摻雜，可以有效改善氮化鎵薄膜的電性，亦即可以提昇電子的遷移率，並降低背景電子濃度。但矽摻雜卻會增強代表深階缺陷的黃光帶的強度，所以可行的方法是先成長一層矽的輕摻雜氮化鎵，再成長未摻雜的氮化鎵，如此就可以同時獲得良好的電特性及光特性。
在我們使用的多層結構中，每一層都包含兩個副層，分別是先成長100Ǻ的未摻雜氮化鎵，再成長100Ǻ的矽摻雜氮化鎵，所以在我們的多層結構中，兩個副層形成厚度200Ǻ的基本週期。在這樣的結構設計中，如同以多重緩衝層的方法可以連續地改善磊晶薄膜的特性，而我們每一個矽的輕摻雜層，都會改善隨後成長的氮化鎵薄膜，因此，最上層的未摻雜氮化鎵將可獲得最佳的薄膜品質。
在實驗上，則以有機金屬化學氣相沉積法成長一系列具不同層數 ( 1, 7, 10, 20, 30, 40 ) 的試片。我們發現，在C-V量測中，施體濃度從2.82 x 1016 cm-3下降到3.8 x 1015 cm-3。在原子力顯微鏡 ( AFM ) 的觀測中，發現代表差排缺陷的暗點密度，從1.26 x 109 cm2下降到2.5 x 108 cm2。在光激螢光譜中，近能帶隙的光激螢光對黃色螢光的強度比 ( INBE / IYL )，從20上升到120，進一步對近能帶隙的波長做光激螢光的暫態量測，可以發現生命期由42ps提高到55ps。
這些結果證明了矽摻雜的氮化鎵多層結構，可有效降低差排及其它缺陷的密度，明顯地改善最上層未摻雜氮化鎵磊晶薄膜的電特性與光特性。

This study aims essentially at recognizing whether the Si-doped multi-layers can improve the quality of GaN epitaxial films effectively. It is widely reported that slight Si-doping improves the electrical quality of GaN films effectively; i.e., it enhances the mobility and reduces the background electron concentration. However, Si-doping will enhance the yellow band intensity, which represents deep level defects. To obtain high-quality epitaxial layer simultaneously with good electrical and optical quality, a practical solution is to grow slightly Si-doped GaN layer first and then to grow an undoped GaN layer.
Each layer of our multi-layer structure involves two sub-layers. First, a 100Ǻ undoped GaN sub-layer is grown. Then a 100Ǻ Si-doped GaN layer is grown as another sub-layer. These two sub-layers form fundamental period with the thickness of 200Ǻ for our multi-layer structure. The use of the multi-layer structure given above is possible to have the same effect as a multi-buffer-layer structure, which can continuously improve the quality of GaN film. Each slightly Si-doped sub-layer plays the role of a buffer, which can improve the quality of the overgrowth GaN sub-layer. This defect reduction process occurs repeatedly through the whole multi-layer structure. Consequently, the final top layer of undoped GaN will exhibit the best film quality.
During our experiments, we have grown by MOCVD, a series of samples with the multi-layer structure of different numbers of period ( the numbers used are 1, 7, 10, 20, 30, 40 ). In the C-V measurement, we have found that donor concentration decreases from 2.82 x 1016 cm-3 to 3.8 x 1015 cm-3. Through the Atomic Force Microscopy (AFM) observations, we have found that the density of dark spots, which are corresponding to dislocations, decreases from 1.26 x 109 cm2 to 2.5 x 108 cm2. In the photoluminescence spectra, the intensity ratio ( INBE / IYL ) of near band-edge emission to yellow luminescence raises from 20 to 120. Further from PL transient measurement performed at the wavelength of near band-edge emission, we found that the lifetime raises from 42ps to 55ps.
All the results demonstrated that Si-doped GaN multi-layer structure can be used to reduce the densities of dislocations and other defects effectively, and obviously improve the electrical and optical qualities of the top undoped GaN epitaxial films.

Contents
Abstract ( in Chinese )…………………………………………………1
Abstract ( in English )…………………………………………………..2
Acknowledgement…………………………………………………...…4
Contents…………………………………………………………………5
Figure Captions…………………………………………………………6
Chapter 1. Introduction…...……………………………………………8
Chapter 2. Growth and Measurement Technique
2-1. Principles of CVD………...………………………...13
2-2. MOCVD Growth of GaN on Sapphire……………15
2-3. Measurement Technique
2-3.1 Hall Measurement (van der Pauw type)
2-3.2 Capacitance-Voltage Measurement
2-3.3 Atomic Force Microscopy
2-3.4 Luminescence Properties and
Photoluminescence Measurement
Chapter 3. Experimental Procedure
3-1. Growth of the Si-doped GaN Multi-layer………..28
3-2. Characterization Measurement…………………..30
Chapter 4. Results and Discussion
4-1. Electrical Characterization………………………...31
4-2. Dislocation Mediated Surface Morphology………35
4-3. Optical Characterization…………………………...39
Chapter 5. Conclusions………………………………………………42
References ...………………………………………………………….44

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[4] J. Jayapalan, B. J. Skromme, et al., Appl. Phys. Lett. 73, 31, (1998) 1188.