探討室溫下InAs量子點在GaAs蕭特基二極體中的特性並利用電路學上波德圖的方式來做分析

Abstract

本論文先從電性量測中發現在3.3 ML樣品室溫下量子點中填滿了載子，可以將量子點視為電容開路，因此建構了3.3 ML樣品在室溫下可以等效成3個由RC元件組成的電路。接著探討室溫下InAs量子點(quantum dots, QDs)在GaAs蕭特基二極體(Schottky diode)中的特性，將探討QDs樣品應用於低通濾波器(low-pass filter)的可能性，並利用電路學上的波德圖方式來做分析，而QDs成長厚度為3.3 ML。因此，藉由波德圖可以將量子點樣品之參數R_S 、R_QD 、C_S給求出。此時分析在不同外加偏壓之下的輸出訊號增益值。我們發現了此低通濾波器的輸出增益與QDs的物理特性有極大的關係，隨著偏壓的變化可以調變R_S 、R_QD 、C_S的大小，進而可以透過偏壓來控制高低頻增益大小以及極點與零點位置，而達到藉由偏壓來控制低通濾波器輸出的頻率與增益。最後，我們透過光激發下的波德圖，來觀察樣品在照光下量子點的物理特性。經過與光激發下的電性量測比較後，發現R_QD與載子的熱放射速率有相似的趨勢，可驗證量子點內載子的活化能大小可用來調控低通濾波之輸出頻率與增益。

We used three parameters, RS, RQD, and CS, to describe the characteristics of GaAs Schottky diode with 3.3 ML InAs quantum dots (QDs) at room temperature. And then, the QDs sample is applied on a low-pass filter, and the properties of sample can be probed using the method of Bode plot. We found that the frequency and gain of out-put signals for low-pass filter can be modulated by the three parameters: RS, RQD, and CS. The high-frequency gain is controlled by RS, and the low-frequency gain is controlled by RQD, and the pole and zero positions are controlled by CS. Besides, These parameters can be accurately determined using the analysis of Bode Plot under various applied bias. Furthermore, the properties of QDs under illumination can be also probed using the illuminated Bode Plot. According to the admittance-spectrum under illumination, the activation energy of QDs is reduced by light. Therefore, we found that the out-put gain and frequency are related to the activation energy of QDs.