使用光調制反射光譜(PR)觀測半導體各能隙，激發光源之光子能量須大於樣品上之待測能隙，以使樣品表面產生電子－電洞對，在原內建電場(Fbi)驅使下，電子-電洞對會分離使得Fbi強度變小，對進行PR量測。本實驗使用光子能量高於砷化鎵E_1 及E_1+∆E_1 能階之汞燈，與光子能量介於砷化鎵能階E_0能隙與E_1+∆E_1能階隙間之紫光(405nm)、綠光(532nm)、紅光(670nm)雷射作為激發光源，藉此用來觀測砷化鎵E_1 及E_1+∆E_1能隙，並比較討論PR光譜的振幅與樣品內建電場變化量之關係。

Semiconductor band-gap energy can be measured by using photoreflectance (PR) spectroscopy. It used a pump-beam and a probe-beam and measure modulated reflectance (DR) of the probe-beam by chopping on and off the pump-beam. The photon-energy of the pump-beam has to be greater than the band-gap energy of the sample so that electron-hole pair can be produced in the sample. The electron-hole pairs are separated by built-in electric field (Fbi) of the sample and thus reduce strength of Fbi. In this work the Hg lamp was used for the pump beam to observe E_1 and E_1+∆E_1 transitions of GaAs, and its photon energy is greater than E_1 and E_1+∆E_1 bandgaps. We also used the purple, green and red laser to observe GaAs, and their photon energy are greater than E_0 but smaller than E_1gaps. Finally, we will compare the amplitude of the PR spectra with the strength of the Fbi reduced by the pump-beam.

第一章 序論 1
第二章 半導體能帶理論 2
2.1能帶理論 2
2.2直接能隙與間接能隙 3
2.3激子[5] 4
2.4空乏電場[4][6] 4
第三章 調制光譜學 7
3.1調制光譜學簡介 7
3.2調制光譜學與介電函數關係 8
3.3電子躍遷理論 9
3.4利用電子躍遷性質導出介電函數 11
3-5調制光譜學-低電場調製 15
3-6調制光譜學-中電場調製(FKOs效應) 17
第四章 樣品特性 20
4.1垂直梯度冷卻法簡介 20
4.2砷化鎵(GaAs)樣品簡介 21
4.3砷化鎵(GaAs)能帶結構 21
第五章 實驗設置 23
5.1 PR實驗 23
5.2電子運動模型 25
5.3 光感應電流理論 25
第六章 實驗結果 28
6.1汞燈(235nm)與紫光雷射(405nm)在GaAs E1及E1+∆E1能階PR圖形比較 28
6.2紫光、紅光、汞燈激發光源在GaAs E1及E1+∆E1比較 29
6.3 紫光、綠光雷射激發光源在GaAs E1及E1+∆E1比較 35
6.4 結論 38
參考資料 39

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