二維硒化銦電子系統的量子干涉現象

Abstract

近年來，愈來愈多研究者關注二維材料的新穎量子特性。在眾多二維材料中，III–VI 族半導體—γ相硒化銦具有高電子遷移率且缺乏反演對稱性，因而成為一種值得研究的材料。由於缺乏反演對稱性，硒化銦中出現了很強的自旋—軌道耦合效應，從而導致磁阻行為的改變。本論文研究了硒化銦/二氧化矽和硒化銦/六方氮化硼系統中的弱反定域效應。我們製作出多電極硒化銦場效電晶體元件，其具有幾乎歐姆接觸，製程中也無須光阻。我們在硒化銦/六方氮化硼系統上研發出一種特別的「互補性接觸」解決其接觸問題，使其同時具有高遷移率場效通道與低電阻接觸，並以優化的交流-直流小訊號鎖相放大技術在五十到二克爾文的溫度範圍內進行四點量測與霍爾量測，從中計算載子遷移率和密度。而在量子擴散體系中，硒化銦也是探索量子干涉現象的良好二維電子系統。我們用Hikami-Larkin-Nagaoka方程擬合硒化銦磁阻，分析不同的量子散射途徑，包括自旋軌道耦合、非彈性散射和彈性散射。探討相位同調性與自旋弛緩現象對溫度、基板效應、水平電場和垂直電場的關聯性。硒化銦磁阻現象提供了有關二維電子系統中散射過程的基本資訊。我們量測到的自旋—軌道耦合效應實驗結果符合先前的理論與實驗研究。

Two-dimensional materials draw great attention because of their novel quantum electronic properties. Among them, γ-indium selenide (γ-InSe), which belongs to the III–VI semiconductor group, is an intriguing material because of its high electron mobility and lack of inversion symmetry. Because of the lack of inversion symmetry, strong spin-orbit coupling in InSe arises, leading to modified magnetoresistance behavior that is the focus of this study. In this thesis, the weak antilocalization effect in γ-InSe/silicon dioxide (SiO2) and γ-InSe/hexagonal-boron nitride (h-BN) systems are studied. A resist-free fabrication process is developed to realize multi-probe InSe field-effect transistor devices with near-ohmic contacts. A special “complementary contact method” is developed with high-mobility channel and low-resistance contact, solving the contact issue on γ-InSe/h-BN. We perform the electronic transport and Hall effect measurement with a greatly improved standard AC+DC lock-in technique for temperatures ranging from 50 K to 2 K, from which the mobility and carrier density are evaluated. In the quantum diffusive regime, the InSe devices are a good platform for exploring quantum interference in two-dimensional electronic systems. The magnetoresistance of the InSe devices is fitted by the Hikami-Larkin-Nagaoka equation, yielding different quantum scattering paths, including spin-orbit coupling, inelastic scattering, and elastic scattering. The dependence of the phase coherency and spin relaxation on temperature, substrates, in-plane electric, and the out-of-plane electric field is extensively discussed. The magnetoresistance behavior of the InSe devices offers original information about the scattering process in two-dimensional electronic systems. Our spin-orbit coupling result consistently matches previous theoretical and experimental research.