梁啟德臺灣大學：物理研究所薛文章Hsueh, Wen-ChangWen-ChangHsueh2007-11-262018-06-282007-11-262018-06-282007http://ntur.lib.ntu.edu.tw//handle/246246/54619本篇論文主要描述加在二維氮化鎵和砷化鎵電子系統下的加熱電子。本論文包含下列二個主題: 1. 在二維氮化鎵下加熱電子和電流尺度的關係 我們量測無磁場下在二維氮化鎵異質結構電子傳輸特性，以從0.27 K 到 60 K 量測到的縱向電阻率當成溫度計，在低溫可看到像絕緣體的行為。我們固定晶格溫度在 0.27 K 後改變電流從 10^-7 A 到 10^-4 A 量測縱向電阻率，可得到電流尺度關系式 Te ~ I^a 和 電子能量損耗率P ~ Te^n -TL^n。 最後我們選擇高功率區修正有效電子溫度對改變電流和能量損耗的函數。 2. 在二維砷化鎵下加熱電子和態密度的關系 我們分別完成在砷化鎵二維電子氣不同溫度以及不同電流下傳輸特性的量測，得到在填充係數等於3, 5, 7, 9 附近以及在填充係數等於2上的電流尺度a 的值 。我們觀察到在自旋向上的區域中電阻率有強大地不對稱行為，這現象可以在高遷移率的樣品中看到。我們分析活化能得到自旋能隙、增強的g-系數和臨界磁場Bc，我們也量測低場量子霍爾效應和發現藍道能階間隔比感應侷域化遷移率能隙大了許多。The thesis describes the electron heating in two-dimensional GaAs and GaN electron systems. This dissertation consists of the following two topics. 1. The relation between electron heating and current scaling in GaN/AlGaN two-dimensional electron system We have measured the electron transport properties in a AlGaN/GaN heterostructure without magnetic field. We measured the longitudinal form 0.27 K to 60K as a self-thermometer. An insulator-like behavior is seen at low temperature. We also measured the longitudinal as a function varying with currents from 10^-7 A to 10^-4 A at a fixed lattice temperature 0.27 K. We obtained a current scaling relation, Te ~ I^a , and the electron energy loss rate, P ~ Te^n -TL^n. Finally, we picked the high-power regime to modify the effective carrier temperature as a function of current and energy loss rate. 2. The relation between electron heating and density of state in GaAs/AlGaAs two-dimensional electron system We performed transport measurements on a GaAs/AlGaAs 2DEG as a function of magnetic fields at different temperatures and currents, respectively. We got the value a of the current scaling in the vicinity of filling factors v = 3, 5, 7, and 9 and at the filling factor v = 11. We observed that the longitudinal resistivity has a strongly asymmetric behavior in the spin-up regions. This phenomenon can be seen in a high mobility sample. We analyzed the activation energy to obtain the spin gap, the enhanced g-factor, and the critical field Bc. We also probed the low-field QHE and found the Landau-level spacing is much larger than the localization-induced mobility gap.Chapter 1 Introduction to two-dimensional electron systems 1 1.1 Two-dimensional electron systems.....1 1.2 GaAs/AlGaAs two-dimensional electron system.....2 1.2.1 The diamond and zinc-blende structures.....2 1.2.2 The modulation doped GaAs/AlGaAs heterostructure.....3 1.3 GaN/AlGaN two-dimensional electron systems.....4 1.4 Varying carrier concentration in a 2DES.....6 1.5 References.....8 Chapter 2 Theoretical Background 9 2.1 Density of states.....9 2.1.1 Density of states for a three-dimensional system.....9 2.1.2 Density of states for a lower-dimensional systems......11 2.2 The classical Drude theory.....13 2.3 Classical Hall Effect....15 2.4 Landau quantization.....17 2.4.1 Landau levels.....17 2.4.2 Shubnikov-de Hass oscillations.....18 2.4.3 Integer quantum Hall effect.....20 2.4.4 Edge states.....21 2.5 References.....24 Chapter 3 Sample fabrication and experimental techniques 25 3.1 Sample fabrication.....25 3.1.1 Hall bar.....25 3.1.2 Ohmic contacts.....27 3.1.3 Sample packaging and handing.....27 3.2 Cryogenic system.....28 3.2.1 Preparation.....25 3.2.2 He3 condensing.....29 3.2.3 Controlling the temperature.....29 3.3 Four-terminal resistance measurements.....30 3.4 References.....31 Chapter 4 The relation between electron heating and current scaling in a GaN/AlGaN two-dimensional electron system 32 4.1 Introduction.....32 4.2 Theoretical background and previous work.....34 4.2.1 Current scaling.....34 4.2.2 Electron-phonon scattering.....38 4.2.3 Two bath model.....41 4.3 Sample structure and experiments.....42 4.3.1 Sample structure.....42 4.3.2 Experiments.....43 4.4 Results and discussions.....43 4.5 Conclusion.....49 4.6 References.....50 Chapter 5 The relation between electron heating and density of state in a GaAs/AlGaAs two-dimensional electron system 53 5.1 Introduction.....53 5.2 Theoretical background and previous work.....54 5.2.1 The Arrhenius equation and activation energy.....54 5.2.2 The spin splitting.....56 5.2.3 Density of state and electron heating.....57 5.3 Sample structure and experiments.....59 5.4 Results and discussions.....60 5.5 Conclusion.....70 5.6 References.....71 Chapter 6 Conclusions 72en-US砷化鎵砷化氮量子霍爾效應電子加熱two-dimensional electron systemGaNGaAselecton heatingspin splittingthesis