摘要
本文係利用電調制反射光譜(Electroreflectance spectrum)來量測及分析氮化鋁鎵/氮化鎵(AlGaN/GaN)之異值結構在不同偏壓(Vdc)下光譜的變化，我們發現當光能量(Photon energy)大於AlGaN能隙(energy gap)時會有Franz-Keldysh oscillations（FKOs）訊號的產生，因此我們可以藉由FKOs的振盪週期來計算AlGaN的電場強度。又因為晶體晶格非中心對稱、陰電性的不同以及晶格的不匹配，使AlGaN/GaN在其介面由於極化不連續而產生正極化電荷(σp)，因此會有電子被吸引到此介面而形成二維電子氣（two-dimensional electron gas, 2DEG）。
實驗中藉由Vdc的改變，其中Vdc為外加在樣品上的直流偏壓，我們發現當負偏壓越來越大時，AlGaN的導電帶會越來越陡，但是GaN的導電帶則越趨平坦，並且超過在某一負電壓時會造成GaN相位的反相，由此可知GaN的電場方向被改變了，因此在某一負偏壓下時，GaN的電場會變為零，此時在介面上的2DEG也已經消失，而剩下AlGaN的電場可以用來計算極化電荷。我們的實驗值和理論值相當接近，是判斷σp相當精確的方法。

Electroreflectance spectra of AlGaN/GaN heteostructure were measured for various biased voltage (Vbias). There are Franz-Keldysh oscillations (FKOs) exhibiting above band gap of AlGaN, and strength of electric field of AlGaN (FAlGaN) can be evaluated from periods of the FKOs. A positive polarization charge

目錄
第一章
前言......................................................1
第二章 調制光譜
2.1 調制光譜學簡介........................................4
2.2調制光譜學的機制.......................................6
2.3 反射率、吸收係數與介電函數...........................11
2.4 譜線圖形分析.........................................17
2.5 Franz-Keldysh Oscillations 與 asymptotic form........23
第三章 樣品之特性
3.1 應變的產生...........................................27
3.2 極化效應.............................................32
3.3 Total Polarization...................................39
3.4 極化片電荷密度.......................................39
3.5 二維電子氣的特性.....................................40
第四章 實驗設計
4.1 實驗樣品.............................................42
4.2實驗樣品特性..........................................44
4.3 實驗裝置.............................................49
第五章 實驗結果與討論....................................51
第六章 結論..............................................63



圖表目錄
圖2.1在空氣與材料介面處入射波、透射波及反射波的示意圖....12
圖2.2(a)能量不變的情形...................................21
圖2.2(b)吸收光子的情形...................................22
圖2.2(c)吸收光子的情形...................................22
圖2.3 利用Airy function 繪製Franz-Keldysh 線形函數圖形...26
圖3.1應變的產生(a)ae<as壓縮應變..........................28
(b)ae>as伸張應變.........................................28
圖3.2差排錯位的產生(te>tc)...............................29
圖3.3為 異質結構成長示意圖(a)應變前......................31
(b)應變後......................31
圖3.4 AlGaN/GaN極化向量示意圖............................33
圖3.5　c/a=1.633時之GaN結構示意圖........................34
圖3.6　c/a＝1.6259時之GaN結構示意圖......................35
圖3.7 AlGaN/GaN極化方向與dipole影響示意圖................36
圖3.8 AlGaN/GaN能帶圖....................................41
圖4.1(a)原始樣品.........................................42
圖4.1(b)樣品加工後.......................................43
圖4.2(a) 蕭基接觸V-I曲線圖...............................44
圖4.2(b) 歐姆接觸V-I曲線圖...............................45
圖4.3蕭基二極體的結構....................................46
圖4.4(a) 電中性..........................................46
圖4.4(b) 平衡狀態........................................47
圖4.5(a) 順向偏壓........................................47
圖4.5(b) 逆向偏壓........................................48
圖4.6 電調制反射光譜實驗儀器裝置圖.......................50
圖5.1 AlGaN/GaN的電調制電場光譜對應不同Vdc...............51
圖5.2 FAlGaN對應Vdc的關係................................53
圖5.3 (a)Vdc＝0V，(b)-3V < Vdc < 0V(c) Vdc = 3V(d) Vdc < -3V.......................................................55
圖5.4 EF對應Vdc的關係圖 (a)實驗值(Eg(GaN)=3.42eV) (b)理論值.......................................................57
圖5.5 GaN A-exciton Amplitude在不同偏壓(Vdc)下的關圖.....60
圖5.6 GaN A-exciton phase(徑度)對應Vdc的關係圖...........60

References
1. S. Rajan, H. Xing, S. DenBaars, U. K. Mishra, and D. Jena, Appl. Phys.Lett. 84, 1591 (2004).
2. O. Ambacher, J. Majewski, C. Miskys, A. Link, M. Hermann, M. Eickhoff, M. Stutzmann, F. Bernardini, V. Fiorentini, V. Tilak, B. Schaff, and L. F. Eastman, J. Phys.: Condens. Matter 14, 3399 (2002).
3. F. Bernardini, V. Fiorentini, and D. Vanderbilt, Phys. Rev. B 56, 10024 (1997).
4. K. Shimada, T. Sota, K. Suzuki, and H. Okumura, Jpn. J. Appl. Phys., Part 2, 37, L1421 (1998).
5. E. J. Miller, E. T. Yu, C. Poblenz, C. Elsass, and J. C. Speck, Appl. Phys. Lett. 80, 3551 (2002).
6. J. A. Garrido, J. L. S&aacute;nchez-Rojas, A. Jim&eacute;nez, E. Mu&ntilde;oz, F. Omnes, and P. Gibart, Appl. Phys. Lett. 75, 2407 (1999).
7. L. Jia, E. T. Yu, D. Keogh, P. M. Asbeck, P. Miraglia, A. Roskowski, and R. F. Davis, Appl. Phys. Lett. 79, 2916 (2001).
8. D. E. Aspnes, Phys. Rev. B 10, 4228 (1974)
9. S. R. Kurtz, A. A. Allerman, D. D. Koleske, A. G. Baca, and R. D. Briggs, J. Appl. Phys. 95, 1888 (2004).
10. A. Drabi&#324;ska, K. P. Korona, R. Bo&#380;ek, J. M. Baranowski, K. Pakula, T. Tomaszewicz, and J. Gronkowski, Phys. Status Solidi C 0, 329 (2002).
11. A. T. Winzer, R. Goldhahn, G. Gobsch, A. Link, M. Eickhoff, U. Rossow, and A. Hangleiter, Appl. Phys. Lett. 86, 181912 (2005).
12. O. Ambacher, J. Smart, J.R. Shealy, N.G. Weimann, K. Chu, M.Murphy, W.J. Schaff and L.F. Eastman, Jorunal of Applied Physics,Vol 85, 3222, (1999).
13. O. Ambacher, B. Foutz, J. Smart, J.R. Shealy, N.G. Weimann, K.Chu, M. Murphy, A.J. Sierakowski, W.J. Schaff and L.F. Eastman,Jorunal of Applied Physics, Vol 87, 334, (2000).
14. M. Cardona, in Modulation Spectroscopy (Academic, New York,1969).
15. D. E. Aspnes, in Handbook on Semiconductors, edited by M.Balkanski (North-Holland, New York, 1980), Vol.2, p. 109.
16.F.H.Pollak,in Hand book on Semiconductors, edited by M. Balkanski(North-Holland, New York, 1994).
17. H. Shen and M. Dutta, J. Appl. Phys. 78, 2151 (1995).
18. See, for example, R. N. Bhattacharya, H. Shen, P. Parayanthal, and F.H. Pollak, Phys. Rev. B 37, 4004 (1988).
19. B. O. Seraphin and N. Bottka, Phys. Rev, 145, 628 (1966)
20. D. E. Aspnes, Surf. Sci. 37, 418 (1973).
21. P.Y. Yu and M. Cardona, Fundamentals of Semiconductors：Physics and Materials Properties(New York,1996,springer)
22. D. E. Aspnes and A. A. Studna, Phys. Rev, B 7, 4605 (1973)
23. S. C. Jain, M. Willander, J. Narayan, and R. Van Overstraeten, J.Appl. Phys. Lett. 87, 965 (2000)
24. W. Shan, R. J. Hauenstein, A. J. Fischer, and J. J. Song, W. G. Perry, M. D. Bremser, and R. F. Davis, B. Goldenberg, Phys. Rev. B 54, 13460 (1996)
25. D. Brunner, H. Angerer, E. Bustarret, R. H&ouml;pler, R. Dimitrov, O. Ambacher, and M. Stutzmann, J. Appl. Phys. 82, 5090 (1997).
26. S. R. Kurtz, A. A. Allerman, D. D. Koleske, and G. M. Peake, Appl. Phys. Lett. 80, 4549 (2002).
27. X. Yin, X Guo, F. H. Pollak, G. D. Pettit, J. M. Woodall, T. P. Chin, and C. W. Tu, Appl. Phys. Lett. 60, 1336 (1992).
28. C. H. Chang, D. P. Wang, C. C. Wu, C. L. Hsiao, and L. W. Tu, Appl. Phys. Lett. 87, 202103 (2005).
29.H.Shen and F.H.Pollak,Phys.Rev.B42,7097(1990)
30. Charles Kittel, Introduction to Solid State Physics,(7th edition)