摘要

本文是將s-i-n+ type GaAs 在不同雷射光強度之下作PR實驗，得出的光譜出現許多FKO(Franz-Keldysh oscillation)，可由FFT(fast Fourier transform)求得電場F。由PR實驗量出的電場F會受到光電效應的影響，很難去估計調制場強度( )的大小。
我們利用鎖相放大器量測pump beam在s-i-n+ type GaAs上的光電壓Vs，再由F-Vbias圖估計空乏區寬度d，將Vs除以空乏區寬度d，可以求得調制場強度 ，本文將討論F和 的關係。

Abstracts
Photoreflectance(PR) of surface-intrinsic n+ type doped GaAs has been measured for various power densities of pumping laser.The spectra exhibited many Franz-Keldysh oscillations,where by the electric field(F) can be determined from the technique of the fast fourier transform.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 in the PR measurements.Hence we have investigated the relation between F and modulating field by using electroreflectance to simulate PR.In this work,the relation will be confirmed by using solely PR.Here a method was devised to obtain the strength of modulating field in the PR measurements.The photo-voltage(Vs)of the pump beam can be measured directly with a lock-in amplifier by making electrical contacts on the front and rear sides of the sample.The strengh of modulation field is equal to Vs/d due to a uniform F in the undoped layer,where d is the thickness of the undoped layer.

目錄

第一章 簡介 1
第二章 調制光譜 3
2.1 介電函數和反射率的關係 3
2.2 介電函數 7
2.3 低電場調制 11
2.4 中電場調制 13
2.5 數據分析 19
2.6 砷化鎵的能帶結構 23
第三章 調制反射光譜實驗細節與分析 3.1 實驗樣本 25
3.2 實驗儀器與測量方法簡介 27
3.3 調制原理 31
3.4 實驗原理 35
第四章 結果與討論 37
4.1 F-Vbias的關係 37
4.2 實驗結果與討論 39
第五章 結論 44

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