梁啟德臺灣大學：物理研究所林明谷Lin, Ming-GuMing-GuLin2007-11-262018-06-282007-11-262018-06-282004http://ntur.lib.ntu.edu.tw//handle/246246/54466本論文研究砷化鎵之自旋極化與氮化鎵之微波調制傳輸。內容包括以下二部分： 1.在外加平行磁場下稀薄的砷化鎵電子系統之遷移率與載子濃度相關性： 第一部分的結果是有關高品質具閘極二維電子氣的低溫磁阻測量。在稀薄電子濃度極限下，我們發現在平行磁場下自旋極化明顯。使用簡單的模型，我們估計此稀薄二維電子氣的藍道g係數大概是3.32。這個藍道g係數比一般砷化鎵二維電子系統(0.44)還大的原因是認為在極低電子濃度之電子與電子的交互作用效應所造成的，而且在整個測量範圍內庫侖位能與動能比值rs並沒有值得注意地變化。此外我們還研究在不同平行磁場下稀薄電子氣的遷移率μ與電子濃度n之相關性。我們發現在 關係下指數項This dissertation describes the measurements on the spin polarization in GaAs and microwave-modulated transport in GaN electron systems. This dissertation consists of the following two parts. 1.Mobility dependence on carrier density in a dilute GaAs electron gas in an in-plane magnetic field I report low-temperature magnetoresistivity measurements of a high-quality gated two-dimensional electron gas (2DEG). In the dilute electron density limit, we show evidence for spin polarization in an in-plane magnetic field. Using a simple model, we estimate the Landé g-factor in this dilute 2DEG to be about 3.32. This enhanced Landé g-factor compared with that of a bulk GaAs 2D electron system (0.44) is ascribed to electron-electron interaction effects at ultra-low electron densities and the fact that over the whole measurement range rs does not vary significantly. Moreover, we report the mobility μ dependence on electron density n of a dilute electron gas at different in-plane magnetic fields. It is found that exponentChapter 1 Introduction......................................1 1.1 GaAs two-dimensional electron gas ......................1 1.1.1 Properties of GaAs devices ...........................1 1.1.2 The modulation doped GaAs/AlGaAs heterostructure......2 1.2 Density of states.......................................7 1.3 AlGaN/GaN electron system...............................9 Chapter 2 Theoretical background............................12 2.1 Classical Hall effect...................................12 2.2 Hall bar mesa patterned in a heterostructure wafer......14 2.3 Quantum Hall effect.....................................15 2.3.1 Landau levels and Shubnikov-de Haas oscillations......16 2.3.2 Quantum Hall effect...................................20 Chapter 3 Sample fabrication and measurement techniques.....24 3.1 Sample fabrication......................................24 3.1.1 Sample structure......................................24 3.1.2 Optical lithography...................................25 3.2 Cryogenic system: Sorption pumping 3He cryostat.........27 3.2.1 Condensation of He....................................28 3.2.2 Controlling the temperature...........................29 3.3 Measurement set-up and four-terminal resistance.........29 Chapter 4 Mobility dependence on carrier density in a dilute GaAs electron gas in an in-plane magnetic field.............33 4.1 Introduction............................................33 4.2 Spin polarization.......................................34 4.3 Density of state varies by applying an in-plane magnetic field.......................................................38 4.4 Changing the carrier densities..........................40 4.5 The ratio of Coulomb energy to kinetic energy...........42 4.6 Results and discussions.................................43 4.6.1 Measurements of the diagonal resistivity in an in-plane magnetic field..............................................43 4.6.2 Estimating the g-factor in an in-plane magnetic field model.......................................................47 4.6.3 Mobility dependence on electron density of a dilute electron gas at different in-plane magnetic fields..........49 4.7 Summary.................................................50 Chapter 5 Microwave-modulated Shubnikov-de Haas-like oscillations in an Al0.4Ga0.6N/GaN electron system......................................................53 5.1 Introduction............................................53 5.2 Experiment..............................................54 5.3 Results and discussions.................................56 5.3.1 Microwave-modulated SdH oscillations..................56 5.3.2 Microwave-modulated SdH oscillations dependence on microwave power.............................................58 5.4 Summary.................................................61 Chapter 6 Conclusions.......................................641077830 bytesapplication/pdfen-US砷化鎵微波調制氮化鎵自旋極化GaAsspin polarizationmicrowave-modulatedGaNthesishttp://ntur.lib.ntu.edu.tw/bitstream/246246/54466/1/ntu-93-R91222027-1.pdf