在PR實驗中，應用FFT得到的內建電場(Fbi)會受pump
beam的光電效應影響，使得計算結果(Fbi-δF )較實際值
為小，因此為了逼近實際的Fbi，調制場強度(δF)的估計
對PR實驗而言非常重要。Aperovich, et.al1 在1997年
敘述了一種估算ER實驗δF的方法：利用FFT轉換之圖形
虛部的正、負極值位置所計算之電場，分別對應(Fbi-δF/2),(Fbi+δF/2)
將兩個電場相減就可以得到δF。我們把這個方法應用在
PR實驗上，希望能夠估算出在PR實驗中pump beam在樣品
上形成的調制場強度。我們利用鎖相放大器直接量測
pump beam在樣品上形成的光電壓Vs ，將Vs 除以空乏區
寬度d，同樣可以得到調制場強度δF=Vs /d。本文將利用
這兩種方法得到的結果(δF)作詳細的討論。

The photoreflectance(PR) and Electroreflectance(ER)
of surface-intrinsic-n+ type doped GaAs exhibit
many Franz-Keldysh oscillations (FKOs), which
enable the electric field (F) to be determined
from the technique of the fast Fourier transform
(FFT). It is known that F's determined from PR are
subjected to photovoltaic effect, but it is
difficult to estimate the strength of modulating
field (dF) of the pump beam in the PR measurements
. Alperovich et. al. have used imaginary part of
FFT to determine the strengths of dF's in the ER
measurements [V. L. Alperovich, et. al. Appl. Phys
. Lett. 71, 2788 (1997)]. Here, we will apply this
method to the PR measurements. The dF's thus
obtained will be compared with those deduced from
photo-voltage measurements. The result shows that
the method of Alperovich's can be used to
determine the strength of dF in the PR measurements.

第一章 簡介……………………………………..1
第二章 半導體光學特性………………………..4
介電函數………………………………..4
電子躍遷………………………………..8
吸收係數α……………………………10
第三章 譜線形狀分析…………………………12
WKB理論……………………………..14
Franz-Keldysh 振盪…………………...17
FKO 漸近式………………………….22
第四章 GaAs材料特性………………………...24
能帶結構…………………………...…..24
S-i-n+結構………..………………….…27
第五章 實驗設計……………………………….30
實驗樣本……………………………….30
實驗儀器與測量方法………………….31
數據分析方法………………………….36

第六章 實驗結果與討論………………………39
調制場的決定…………………………39
第七章 結論……………………………………49
參考文獻………………………………………..50

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