二維電子氣系統在強磁場下電性非平衡現象之研究

Electric instability in a two-dimensional electron gas system under high magnetic fields

李清平(Ching-Ping Lee)

指導教授 ： 陳正中

國立清華大學/理學院/物理學系/博士(2015年)

摘要

此份論文研究砷化鎵/砷化鎵鋁異質結構二維電子氣在強磁場下的電性不穩定行為。當外加直流電流超過臨界電流後，二維電子氣的縱向電位會突然下降、擾動，表現出電性不穩定的行為。此現象只出現在蘭道能級是完全分開的情況下、其填充系數小於2，且晶格溫度相對高溫的環境下。我們發現臨界電流會隨著磁場增加而增加，也會隨著晶格溫度增加而增加。然而，相對的，電性不穩定的行為是隨著磁場增加而增加，卻隨著溫度增加而減小。
電性不穩定的發生可以由兩個現象學理論來解釋，其一是Andreev等人[25]所發表的理論，其二是Kurosawa等人[1]所發表的理論。數據分析的結果顯示縱向電阻會隨著外加電流增加而下降，且當加外電流增加至臨界電流時，會有負微分電阻的產生，負微分電阻被認為是電性不穩定的前兆。電性不穩定是由於負微分電阻的存在，造成材料內部有電荷域的生成。縱向電阻率隨著外加電流的下降可以被歸因於電子能量分部的改變以及電子在蘭道能級之間的跳躍。

關鍵字

二維電子氣 ； 電性不穩性 ； 負微分電阻

並列摘要

We present a study of electric instability in GaAs/AlGaAs hetero-structure two-dimensional electron gas system under high magnetic fields. As the applied dc current exceeds a threshold value Ith, the longitudinal voltage Vxx drops, fluctuates and exhibits electric instability. The observed instability occurs only in well-separated low-lying Landau levels with a filling factor ν ≦ 2 at relatively high lattice temperatures. We find that Ith increases with increasing magnetic field B and the lattice temperature TL. In contrast, electric instability becomes more pronounced at higher B, but gradually diminishes with increasing TL.
The onset of electric instability has been predicted by two phenomenological theories, one is the theory of Andreev et al. [25], and the other is the theory of Kurosawa et al. [ 1]. Data analysis suggests that longitudinal resistance Rxx is suppressed by increasing I and exhibits negative differential resistivity (NDR) when I = Ith, where NDR is viewed as a precursor signal of electric instability. The electric instability is caused by domain growth. The electric instability is actuated by the suppression of Rxx with increasing I, which can be understood in terms of the capability of the spectral diffusion of electrons and electron transfer to higher levels via inelastic inter-Landau levels scattering within the limit of one-occupied Landau level.

並列關鍵字

two-dimensional electron gas ； electric instability ； negative differential resistance

參考文獻

[1] Tatsumi KUROSAWA, Hajime MAEDA and Hidehiko SUGIMOTO, “Hot Carrier

[32] A. Kunold and M. Torres, “Nonlinear transport theory for negative-differential

[45] K. P. Martin, R. J. Higgins, J. J. L. Rascol, HyungMo Yoo and John R. Arthur,

[46] Scott Dietrich, Sergey Vitkalov, D. V. Dmitriev and A. A. Bykov, “Quantum

[56] M. Heiblum, M. I. Nathan and C. A. Chang, “CHARACTERISTICS OF AuGeNi