砷化鎵之微波調制傳輸及砷化銦之傳輸特性研究

Abstract

本人碩士論文主要為研究半導體異質結構中二維電子氣於垂直磁場下之電子傳輸特性，內容包含下列兩個主題： 1. 微波照射下之砷化鎵/砷化鋁鎵異質結構的電子傳輸特性研究： 第一個主題為研究砷化鎵/砷化鋁鎵異質結構在溫度T = 1.4 K於連續微波照射下所展現的傳輸性質。在實驗中我們觀測磁阻於不同功率微波照射下的反應，並和沒有照微波的磁阻做比較，我們發現Shubnikov-de Haas (SdH)振盪之振幅隨微波功率增加而減低而振盪之最小值隨微波功率增加而增大，此可歸因於電子加熱效應。 利用分析SdH振盪之振幅與磁阻最小值，我們可以決定對應的等效電子溫度，由分析的結果我們發現由兩種方式得到的等效電子溫度有相當大的不同(前者恆大於後者)，我們可以藉此分離出半古典傳輸與侷域化的電子並說明兩種電子的共存。 2. 砷化銦二維電子氣之傳輸特性研究： 第二部分則是研究III-V族砷化銦電子氣在溫度0.3 K至80 K間的電性及傳輸性質。藉由磁阻的分析我們可以得到砷化銦樣品的載子濃度及遷移率，把兩塊不同厚度的砷化銦樣品之實驗結果相比較，我們可以發現遷移率較大的樣品，由絕緣態轉到量子霍爾導態的臨界磁場也會越小，其中一塊樣品可用Universal Scaling theory分析此相變發生的臨界指數κ~ 0.21。 接著再由SdH振盪公式的近似式來求電子等效質量m*，可以發現兩塊樣品的電子等效質量分別為0.049 m0與0.042 m0，比砷化鎵的0.067 m0還要更小，其中m0為電子的靜止質量，研究這種小電子等效質量的二維材料之傳輸特性將有助於高速電子元件的發展。

This thesis is focused on the transport properties of two-dimensional electron gas in semiconductor heterojunction under perpendicular magnetic field. It consists of the following two parts: 1. The transport in GaAs/AlGaAs heterojunction under microwave illumination: In the first part, we studied the transport behavior of GaAs/AlGaAs in the temperature T = 1.4 K under exposing of the continuous microwave radiation. We measured the magnetoresistance under different microwave radiation and compared it to those without exposure of microwave radiation. We found that Shubnikov-de Haas (SdH) oscillations amplitudes decreased with increasing the microwave power and the magnetoresistance minimum increased with increasing the microwave power. This can be contributed to the heating effect of electrons. After analyzing of SdH oscillations amplitudes and the magnetoresistance minimum, we can determine the corresponding electron effective temperature. From the result of analysis, we found out that the electron effective temperature determined from these two cases were quite different (the former was always bigger than the latter). By the microwave radiation, we can distinguish the semiclassical transport electrons from the localized electrons and prove the coexistence of them.

2. The transport in InAs 2DEG: The second part is the electric transport behavior of InAs 2DEG in the temperature between 0.3 K and 80 K. From the analysis of magnetoresistance, we can obtain the carrier density and the mobility of our sample. Compared two samples with different thickness, we found that the critical magnetic field of the insulator quantum Hall phase transition was smaller in the higher mobility sample. The critical exponentκ~ 0.21 in one of the two samples from the universal scaling theory. From the analysis of SdH oscillations amplitudes, the obtained electron effective mass was 0.049 m0 and 0.042 m0 in the two samples. It is much smaller than the effective mass 0.067 m0 in GaAs, where m0 is the rest electron effective mass. Studying the transport behavior in these kinds of small electron effective mass materials is beneficial for the development of high speed electronic devices.