砷化鎵與砷化鎵銦二維電子系統之磁阻震盪研究

Abstract

介觀系統，是指尺度介於微觀與巨觀尺度間的系統，可以看作是尺度縮小的巨觀物體。隨著資訊技術的發展，半導體元件大小也逐漸逼近物理極限，而為了維持或達到更好的效能，許多量子現象也必須加以考慮。因此，本篇論文利用二維電子系統，探討系統中載子的有效質量。樣品選擇了 GaAs/AlGaAs 與 InGaAs/InAlAs 這兩個異質結構所產生的二維電子系統，量測在不同溫度與磁場下的電阻率，並藉由在進入絕緣-量子霍爾態轉變前的 Shubnikov-de Haas (SdH) 震盪求得 載子的有效質量。特別是前者樣品，加入了 InAs 量子點並視為雜質再施以不同的偏壓，產生不同的載子濃度後，進一步的改變載子屏蔽雜質的程度，達到在同一樣品上卻有不同雜質數的目的，更容易探討在此介觀系統中雜質對載子有效質量的影響。我們的實驗結果顯示隨著增加雜質的程度，載子的有效質量也一同增加，且更進一步地提高電子-電子的交互作用。也顯示出在研究絕緣-量子霍爾態轉變時，交互作用為一項需要考慮的因素。

Mesoscopic system, a system with scale between the size of a quantity of atoms and of materials measuring micrometers and can be treated as a tiny macroscopic object. With the development of information technology, the size of semiconductor device starts to approach the boundary of classical physics and into the region ruled by quantum mechanics. In order to maintain or reach higher performance of semiconductor device, a lot of quantum phenomenon need to be considered. Therefore, in this thesis we use two two-dimensional electron systems to probe the effective mass of carrier. One sample is GaAs/AlGaAs and the other is InGaAs/InAlAs heterostructure. By measuring the longitudinal resistivity at difference temperatures and magnetic fields and before the system enters insulator-quantum Hall (I-QH) transition, we use Shubnikov-de Haas oscillations to determine the effective mass of carriers. Especially the former one, it contains InAs self-assembled quantum dots to further manipulate the effective disorder by means of varying the gate voltage which will change the ability of carrier to screen out the disorder potential. We find that the measured effective mass increases with increasing effective disorder. Such results indicate increasing strength of electron-electron interactions with increasing effective disorder. Therefore, our experimental results suggest that interaction effects need to be considered in the I-QH transition.