建立電路模型探討InAs量子點累積過量電子對蕭基二極體電性之影響

Abstract

本論文主要探討在低溫成長InAs/InGaAs量子點的過程中造成的EL2缺陷，會讓過量激發的電子累積於量子點中造成壓降，類似量子點具有電容器的特性，進而去影響Capping Layer砷化鎵的空乏區變化。首先，利用光激發螢光頻譜(PL)對樣品的基本光性做探討，得到量子點群的發光訊號能量，再將樣品做深層能階暫態頻譜(DLTS)的量測，觀察各樣品間缺陷存在的與否。我們發現照光可以去影響具有EL2缺陷的量子點樣品的電容電壓(C-V)量測結果，令我們深感興趣。因此我們試著將樣品假設為兩個區塊討論，令Capping Layer砷化鎵蕭基二極體為並聯的電阻為RS以及電容為CS，再串聯具有電容器特性量子點之電容值為CQD，建立簡單的RC等效電路模型。在掃動偏壓的條件下推導RC等效電路的電流電壓(I-V)關係式，發現電流值正比於偏壓掃動的速率；進一步探討外接電容器對單純砷化鎵蕭基二極體的C-V量測的影響，引入RC等效電路的I-V關係式去修正一般已知的Poisson’s equation，推導不同掃動速率對於C-V的關係，發現掃動速率較緩慢會造成較高的電容值。實際將具有EL2缺陷的量子點樣品在照光下進行不同掃動速率的量測，發現上述I-V、C-V之公式推導結果皆與樣品實際量測結果的趨勢相符，確立上述量子點具有電容器特性的假設。基本量測顯示電容值對於照光的反應與EL2缺陷存在與否有很大的相關性，因此最後討論當量子點周遭具有施體型缺陷的情況下，會造成能帶圖如何變化，使其誘發具有電容器特性的機制。

In the study, the InAs/InGaAs quantum dots (QDs) growth under low temperature produces the EL2 defect. We discuss excess electrons accumulated in quantum dots (QDs) generate the potential drop, and the ability of electron confinement is enhanced by EL2 defect. Initially, the optical properties are studied by photoluminescence (PL), and the information of defect is found by deep level transient spectroscopy (DLTS). We observe the QDs with EL2 defect, the Capacitance-Voltage (C-V) performance were influenced obviously under illumination. Therefore, we assume the sample is the GaAs Schottky diode series connect with the QDs of capacitor property. We establish the equivalent RC circuit model, using the RS parallel connect with the Cs represent the GaAs Schottky diode, and the CQD represent the QDs. Under sweeping bias, we inference the Current-Voltage (I-V) relationship, that current and sweep rate are in direct proportion. Furthermore, we correct the Possion’s equation when the GaAs Schottky series connect with a capacitor. The capacitance is dependent on the RC time constant due to the applied bias contribute different ratio to two devices. The InAs QDs with EL2 defect sample were studied by C-V and I-V measurement under illumination, then the result is similar to the assumption of RC equivalent circuit. The response of capacitance and current are dependent on EL2 defect and light energy. Finally, we discuss the band bending around the QDs, and the EL2 defect induce the QDs with the property of capacitor.