我們測量不同偏壓下AlGaN/AlN/GaN異質結構的電調制反射光譜研究。AlGaN內部電場(FAlGaN)的大小可以由在AlGaN能帶上方所量測到的Franz-Keldysh oscillation (FKOs) 藉由fitting line-shape of FKOs來計算其大小。FAlGaN和VDC的關係圖存在一些奇特的現象，有別於之前所做的AlGaN/GaN異質結構的研究。
我們利用 Poisson-Schrödinger solver 來模擬實驗結果，顯示了2DEG不只存在於AlN/GaN介面的量子井，還存在於AlGaN/AlN介面的量子井，這也可以由 capacitance-voltage measurement 得到相同的結果。當施加更多的負偏壓VDC時，由之前的實驗結果可以知道，當負偏壓增加的時候，GaN的導電帶將會變得比較平緩，同時會使AlN/GaN介面的2DEG逐漸變少，直到VDC=-2.0V，量子井將會變平，而2DEG將會耗盡。且我們發現當表面的價電帶開始高於AlGaN/AlN 量子井導電帶底部的時候，AlGaN/AlN介面的2DEG開始耗盡。

Electroreflectance spectra of AlGaN/AlN/GaN heterostructures were measured at various biased voltages (Vdc). Strengths of the internal electric field in AlGaN (FAlGaN) were evaluated from periods of Franz-Keldysh oscillations (FKOs), which were observed above band-gap energy of AlGaN. The relation between FAlGaN and Vdc exhibits an anomalous behavior, which is different from the previous results of the AlGaN/GaN heterostructure. It agrees with the theoretical result of a Poisson-Schrödinger calculation, which shows that two dimensional electron gas (2DEG) exists not only in quantum well (QW) at AlN/GaN interface, but also in QW at AlGaN/AlN interface. This is also consistent with electron-density distribution obtained by capacitance-voltage measurements. When Vdc becomes more negative, the previous mechanism of depleting 2DEG is through flatting one side of QW. However, it was found that the depletion of 2DEG can also occur when the top of valence band at surface becoming higher than bottom at QW.

第一章 導論及相關理論
1.1 前言....................................................................................................1
1.2 激子................................................................................................2
1.3 能帶......................................................................................3
第二章 調制光譜
2.1 調制光譜學簡介........................................................................6
2.2調制光譜學的機制.....................................................................8
2.3 反射率、吸收係數與介電函數................................................13
2.4 譜線圖形性質...........................................................................19
2.5 Franz-Keldysh Oscillations 與
asymptotic form........................................................................26
第三章 實驗樣品特性分析
3.1基板….........................................................................................30
3.2應變的產生.................................................................................31
3.3 極化效應…...............................................................................34
3.4 總極化向量...............................................................................38
3.5 表面極化密度….......................................................................38
3.6 exclusion layer............................................................................40
第四章 實驗設計
4.1 實驗樣品...................................................................................41
4.2實驗樣品特性.............................................................................43
4.3 實驗裝置...................................................................................47
第五章 實驗結果與討論
5.1 光譜分析..................................................................................49
5.2實驗結果討論與分析.................................................................52
第六章 結論............................................................................................61
Reference..........................................................................................62
附錄..........................................................................................................64

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