臺灣博碩士論文加值系統

我們透過Shubnikov-de Haas(SdH)量測研究AlxGa1-xN/GaN異質結構的電子性質。在sample x=0.35及0.31發現由於電子佔據兩個最低的次能帶而產生兩個SdH振盪，能量差分別為128及109 meV。在sample x=0.25，發現兩個SdH振盪產生拍頻效應，很可能是由自旋裂距造成的。自旋裂距的能量為9.0 meV。我們也發現這些sample在經過藍色LED照光後有正持續光導效應。實驗部份，我們在低溫高磁場系統中新加裝“微調閥”，以精確控制樣品之溫度從0.3K至10K。便於SdH變溫實驗測量。

We have studied the electronic properties of AlxGa1-xN/GaN heterostructures by using Shubnikov–de Haas(SdH) measurement. Two SdH oscillations were detected on the samples of x=0.35 and 0.31, due to the population of the first two subbands with the energy separations of 128 and 109 meV, respectively. For the sample of x=0.25, two SdH oscillations beat each other, probably due to a finite zero-field spin splitting. The spin-splitting energy is equal to 9.0 meV. The samples also showed a persistent photoconductivity effect after illuminating by blue light-emitting diode. For the part of experiment , we installed a "Regulator" on low temperature and high magnetic field system, in order to control the temperature of sample from 0.3K to 10K accurately. For the convenience of
SdH measurements at different tempertures.

第一章 簡介
1-1 前言…………………………………………………………… 1
1-2 實驗基本設備………………………………………………… 3
1-3 量子井二維電子氣的電子特性……………………………… 4

第二章 理論部分
2-1 Shubnikov-de Haas效應……………………………………… 6
2-2 量子霍爾效應(Quantum Hall Effect；QHE)………………… 8
2-3 正持續光導效應(PPC)及負持續光導效應(NPPC)…………… 9
2-4 Landau Level和Spin Splitting Landau Level…………… 11

第三章 數據的讀取
3-1 硬體部份……………………………………………………… 12
3-2 軟體部份……………………………………………………… 17

第四章 實驗儀器
4-1 杜瓦瓶的主要構造及功能…………………………………… 18
4-2 Helium 4 Insert……………………………………………… 22
4-3 Helium 3 Insert……………………………………………… 23
4-4 實驗室管路配置……………………………………………… 26

第五章 實驗步驟及儀器操作原理
5-1 準備工作……………………………………………………… 30
5-1-1 檢查各儀器線路………………………………………… 30
5-1-2 抽真空夾層……………………………………………… 31
5-1-3 抽transfer tube………………………………………… 33
5-1-4 Sample處理……………………………………………… 34
5-1-5 Insert處理……………………………………………… 35
5-2 預冷(precooling)…………………………………………… 40
5-2-1 Purge Needle Valve………………………………………40
5-2-2 傳內層(液氦層)………………………………………… 40
5-2-3 傳外層(液氮層)………………………………………… 42
5-3 Transfer 液氦……………………………………………… 45
5-3-1 清空液氦層……………………………………………… 45
5-3-2 檢查needle valve………………………………………… 46
5-3-3 Transfer 液氦…………………………………………… 47
5-4 降溫及變溫…………………………………………………… 51
5-4-1 降溫……………………………………………………… 51
5-4-2 變溫……………………………………………………… 54
5-5 程式及儀器接線……………………………………………… 56
5-5-1 SdH量測…………………………………………………… 56
5-5-2 QHE量測…………………………………………………… 57
5-5-3 Rxx及RH量測……………………………………………… 58
5-6 更換sample…………………………………………………… 66
5-6-1 更換sample……………………………………………… 66
5-6-2 結束實驗………………………………………………… 69

第六章 實驗結果與討論
6-1 實驗樣品……………………………………………………… 72
6-2 結果與討論…………………………………………………… 75
6-1-1 各別討論………………………………………………… 75
6-2-2 綜合討論………………………………………………… 76
6-3 未來的計劃…………………………………………………… 97

References…………………………………………………………… 98

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