在GaN的wurtzite結構中，有Ga-或N-polarity二種極性存在，不同的極性有著不同方向的極化電場。本文使用N-polarity、n-type 而磊晶層厚度分別是1.1μm及70nm之GaN，藉由PR (Photoreflect- ance)及CER(Contactless Electroreflectance)的實驗技術，發現厚(thick)的樣品可由摻雜形態(n- or p-type)來決定其表面能帶的彎曲現象，而薄(thin)的樣品可由其極性(polarity)來決定。此結果與理論上的帕松-薛汀格(Poisson-Schrödinger)方程式之解吻合。因此，當樣品夠薄的話，其極化電場將主導樣品的表面電場時，CER的實驗技術將可決定其GaN的極性。

The wurtzite GaN has either Ga or N polarity. The direction of polarization, hence it’s associated polarization-induced electric fields (Fp), is determined by the polarity of the sample. In the present work, we prepared both N-face polarity and n-type doping of GaN with thicknesses are 1.1μm and 70nm. Photoreflectacne (PR) and contactless electroreflectance (CER) were used in combination to study the nature of the surface band bending which was found to be determined by the type of doping for the thick sample and by the polarity for the polarity for the thin sample. This is in agreement with a theoretical calculation by Poisson-Schrödinger solver. Hence, CER can determine the polarity of GaN film as long as the sample is thin enough of the Fp to become dominant in the surface region.

致謝..................................................................................................Ⅰ
摘要..................................................................................................Ⅱ
Abstract..........................................................................................Ⅲ
第一章 導論及相關理論
1.1 前言............................................................................................1
1.2 能帶............................................................................................2
1.3 蝕刻..........................................................................................5
第二章 調制光譜
2.1 調制光譜學簡介........................................................................7
2.2 調制光譜學的機制....................................................................9
2.3 電子躍遷理論..........................................................................10
2.4 介電函數和反射率的關係......................................................13
2.5 低電場調制..............................................................................16
第三章 樣品結構特性分析
3.1 GaN能帶圖.................................................................................19
3.2 GaN結構分析.............................................................................21
3.3 空乏區電場(Fd)的產生機制..................................................24
3.4 極化效應與極化電場..............................................................27
3.5 GaN的蝕刻.................................................................................35
3.6 GaN理論能帶計算.....................................................................39
第四章 實驗設計
4.1 實驗樣品介紹..........................................................................42
4.2 實驗架構與調制原理..............................................................43
4.3 實驗相位分析..........................................................................48

第五章 實驗結果與討論
5.1 實驗圖形分析..........................................................................53
5.2 實驗數據分析..........................................................................55
5.3 薄的樣品的總極化向量的計算..............................................63
5.4 實驗結果討論..........................................................................66
第六章 結論............................................................................................68
Reference................................................................................................69


表格目錄
表3-1 Wurtzite結構的InN、GaN及AlN之自發極化向量、彈性常數與壓電常數..............................................................................................30
表5-1 厚的樣品其PR fitting(n=2)結果............................................56
表5-2 厚的樣品其CER fitting(n=2)結果..........................................56
表5-3 薄的樣品其PR fitting(n=2.5)結果........................................58
表5-4 薄的樣品其CER fitting(n=2.5)結果......................................59
表5-5 薄的樣品其PR fitting(n=2)結果............................................61
表5-6 薄的樣品其CER fitting(n=2)結果..........................................61
表5-7 薄的樣品擬合曲線與實驗數據差值的標準差..........................63

圖表目錄
圖1.1 絕緣體、半導體、導體的能帶示意圖............................................3
圖1.2 半導體的直接與間接電子躍遷....................................................4
圖3.1 GaN能帶結構示意圖....................................................................19
圖3.2 六方晶格中的布里淵區示意圖..................................................20
圖3.3 GaN的Γ點受擾動時產生的能階分裂示意圖............................20
圖3.4 GaN結構示意圖............................................................................21
圖3.5 c/a=1.633時之GaN結構示意圖.................................................22
圖3.6 c/a=1.6259時之GaN結構示意圖...............................................22
圖3.7 GaN立體結構示意圖....................................................................24
圖3.8 p型n型半導體接面能帶示意圖.................................................25
圖3.9 Wurtzite結構示意圖..................................................................30
圖3.10 Ga-及N-face其Psp、Ppe的方向示意圖.......................................31
圖3.11 Ga-及N-face其Psp、Ppe及 的方向示意圖...............................33
圖3.12 厚跟薄的樣品其 及 的方向示意圖...................................34
圖3.13 GaN在NaOH溶液中化學反應示意圖.........................................36
圖3.14 以SEM量測Ga-及N-polarity的GaN蝕刻前後範品結果......37
圖3.15 以SEM量測薄的樣品蝕刻前後結果.........................................38
圖3.16 以AFM量測薄的樣品蝕刻前後結果.........................................39
圖3.17 厚的樣品其能帶圖....................................................................40
圖3.18 薄的樣品其能帶圖....................................................................40
圖4.1 樣品結構圖..................................................................................42
圖4.2 PR實驗裝置圖..............................................................................46
圖4.3 CER實驗裝置圖............................................................................47
圖4.4 厚的樣品外加電壓之電場示意圖..............................................48
圖4.5 薄的樣品外加電壓之電場示意圖..............................................49
圖4.6 厚的樣品照光前及照光後對能帶的影響圖..............................50
圖4.7 薄的樣品照光前及照光後對能帶的影響圖..............................50
圖4.8 相位比較圖..................................................................................52
圖5.1 厚的樣品其PR及CER光譜圖比較..............................................53
圖5.2 薄的樣品其PR及CER光譜圖比較..............................................54
圖5.3 厚的樣品其PR實驗值與擬合(n=2)曲線...................................57
圖5.4 厚的樣品其CER實驗值與擬合(n=2)曲線.................................57
圖5.5 薄的樣品其PR實驗值與擬合(n=2.5)曲線...............................60
圖5.6 薄的樣品其CER實驗值與擬合(n=2.5)曲線.............................60
圖5.7 薄的樣品其PR實驗值與擬合(n=2)曲線...................................62
圖5.8 薄的樣品其CER實驗值與擬合(n=2)曲線.................................62
圖5.9 薄的樣品其Psp及Ppe方向示意圖................................................64

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