陳永芳臺灣大學：物理研究所邱奕行Chiu, Yi-HsingYi-HsingChiu2007-11-262018-06-282007-11-262018-06-282004http://ntur.lib.ntu.edu.tw//handle/246246/54578在本論文，我將描述在高遷移率砷化鎵二維電子氣之傳輸特性。內容包括以下二部分： 1. 砷化鎵二維電子氣之自旋分裂 我們在低溫下量測砷化鎵/砷化鋁鎵異質結構的電子傳輸特性。在我們的系統中，觀察到在藍道能階填充係數為1，3，5和7時，經由活化能實驗量測到g係數的提升為9.28。我們也觀察到自旋分裂的消失出現在一個臨界的磁場值1.48 T，因此自旋能階差趨近為零。藉由此臨界磁場值，我們可以估計由無序膨脹所造成的能階寬度為0.79 meV，這個值符合我們經由不確定原理所估計出來的結果。 2. 在高遷移率砷化鎵二維電子氣之半古典巨大正磁阻 我將描述在高遷移率砷化鎵二維電子氣所觀察到的巨大正磁阻。巨大正磁阻一直到80 K都出現，顯示出其來源為類似古典的效應。我們由磁阻率與磁場的關係可以知道，在量測的溫度範圍下，隨著溫度的增加，磁場的次方項愈來愈小，顯示電子—聲子散射愈來愈強。由最近Polyakov與其共同研究者所提出的理論，可以解釋我們的實驗結果。此理論強調：在垂直磁場下，經由雜質造成的短範圍電位伴隨著長範圍電位的相互作用影響，會產生不飽和的正磁阻。In the thesis, I shall report the transport properties in a high-mobility GaAs two-dimensional electron gas (2DEG). I will introduce them in the following two parts. 1. Spin-splitting in a GaAs two-dimensional electron gas We have measured the low-temperature electron transport properties in a GaAs/AlGaAs heterostructure. In our system, the enhanced effective g-factor of 9.28 is measured from activation experiments at Landau-level filling factors 1, 3, 5 and 7. We also observe collapse of spin-splitting in which the spin gap approaches 0 at a critical magnetic field of 1.48 T. According to the critical magnetic field , we can expect that the energy caused by the disorder broadening is of 0.79 meV. It is consistent with what we expect from the uncertainty principle. 2. Huge quasi-classical positive magnetoresistance in a high-mobility GaAs two-dimensional electron gas I shall report observation of huge positive magnetoresistance (PMR) in a high-mobility GaAs 2DEG. The PMR persists up to 80K, demonstrating its quasi-classical origin. We find that whereChapter 1 Introduction 1 1-1 GaAs two-dimensional electron gas ………………….………………… ............1 1-1-1 The modulation doped GaAs/AlGaAs heterostructure ...……………………………1 1-1-2 Varying the carrier density…………………………………………………………2 1-2 Density of states …………………………………………………………………......4 1-2-1 Density of states for a 3-D system………………………………...…………………4 1-2-2 Density of states for lower-dimensional systems……………………………………6 1-3 Activation energy……………………………………………………………………....8 Chapter 2 Theoretical Background 10 2-1 Classical Hall effect …………………………………………………………..…….10 2-2 Quantum Hall effect …………………………………………………………..…….12 2-2-1 Landau levels and Shubnikov-de Haas oscillations ………………………….....…13 2-2-2 Edge states …………………………………………………………………….…...15 2-2-3 Quantum Hall effect..................................................................................................17 2-3 The classical Drude theory……………………………………………………….....19 Chapter 3 Sample fabrication and experimental techniques 22 3-1 Sample fabrication…………………………………… ………………….……….…22 3-1-1 Sample structure…………………………………………………………………..22 3-1-2 Sample features…………………………………………………………………...23 3-1-2-1 Hall bar…………………………………………………………………………….23 3-1-2-2 Ohmic contacts…………………………………………………………………….24 3-1-2-3 Front gate…………………………………………………………………………..25 3-1-3 Sample packaging and handing…………………………………………………...26 3-2 Cryogenic system: Sorption pumped 3He cryostat……………………………..27 3-2-1 3He condensing…………………………………………………………………....28 3-2-2 Controlling the temperature……………………………………………………….28 3-3 Four-terminal resistance measurements………………………………………….29 Chapter 4 Spin-splitting in a GaAs two-dimensional electron gas 30 4-1 Introduction……………………………………………………………………………30 4-2 Integer quantum Hall effect (IQHE)………………………………………………30 4-3 Filling factor、Carrier concentration and Mobility...............................................31 4-4 The spin splitting phenomenon…………………………………….…..33 4-5 Spin gaps at odd-number filling factors………………………………………..36 4-6 Measurement of the exchange-enhanced |g|-factor at odd-number filling factors..............................................................................................................................39 4-7 Disorder broadening……………………………………………………………….41 4-8 Summery………………………………………………………………………………43 Chapter 5 Huge quasi-classical positive magnetoresistance in a high-mobility GaAs two-dimensional electron gas 45 5-1 Introduction ………………………………………………………………………....45 5-2 Theoretical background……………………………………………………………..46 5-2-1 The Boltzmann-Drude theory……………………………………………………..46 5-2-2 Quantum and classical corrections to the conductivity…………………………...47 5-3 Experiments…………………………………………………………………………...48 5-4 Results and discussion………………………………………………………………49 5-4-1 Results…………………………………………………………………………….49 5-4-2 Discussion……………………………………………………………………...…55 5-5 Summary………………………………………………………………………………59 Chapter 6 Conclusions 621518485 bytesapplication/pdfen-US二維電子氣砷化鎵巨大正磁阻高遷移率自旋分裂two-dimensional electron gashigh-mobilityGaAsSpin-splittinghuge positive magnetoresistancethesishttp://ntur.lib.ntu.edu.tw/bitstream/246246/54578/1/ntu-93-R91222049-1.pdf