量子點紅外線偵測器之研究

Abstract

本論文分為兩大部分探討量子點紅外線偵測器的傳輸機制。第一部分藉由標準結構之量子點紅外線偵測器進行光響應的研究。焦點放在包括光響應隨偏壓指數增加，高偏壓時之光響應彎曲，以及溫度相依的光響應等三大與量子井紅外線偵測器迥異之處。我們的研究發現量子點紅外線偵測器的光響應強烈受到其光導增益的影響，量子效率則是次要的影響因素。故吾人歸納出電子的傳輸隨著偏壓的增加，而有著三段不同的行為。低偏壓時，增益與等效生命期以及電場成正比。我們根據文獻以及簡潔的曲線擬合，得到非常切合實驗的模擬結果。接著，當量子效率達到最高時，我們又假設此刻電子逃脫量子點束縛的機率為一並且開始發生撞擊游離的效應。這一點透過增益的指數增加行為以及量子效率飽和的假設得以驗證。最後，在高電場的時候各種散射機制的可能性造成增益的彎曲現象；同時這也是造成光響應彎曲的原因。 第二個部分主要探討暗電流的熱活化能部分。透過研究兩個能障寬度不同的試片，我們發現其活化能在以電場為衡量尺度的檢視之下有完全相同的行為。意味著能障加寬並不能阻擋來自熱活化的暗電流，這點就於元件應用十分不利。此外典型量子井紅外線偵測器與量子點元件的活化能顯著地隨偏壓而降低之行為有很大不同。文獻提出此乃共振穿隧之故，本實驗也更近一步確認這個觀點。 總結以上兩部分的基礎研究，我們討論許多改良元件的方式。其中，未來首要努力的方向在於將量子點的第二束縛態調整至距離能障邊緣較近之處以期改善量子效率及熱活化暗電流的效應。

The thesis contains two topics about the transport characteristics of QDIPs. First, an investigation on responsivity was practiced. We have demonstrated that there are three major different features in response behavior between QDIPs and QWIPs, including: electric field dependence, temperature dependence, and bending phenomenon. We have proposed a related simple model to explain the electric field dependence of photo-response behavior. A good simulation was achieved with two reasonable fitting parameters. Generally speaking, gain was the dominant factor which affects responsivity strongly. More precise description must be that the gain and quantum efficiency dominate the responsivity alternately under low-field. As electrons draw sufficient energy from the increasing bias, avalanche mechanism will dominate transport behavior. At very high field, the response will bend down due to some scattering. Second, we focused on the activation energy issue. Our results showed that the activation energy of QDIPs was strongly bias-dependent. It decreased almost linearly with bias whether in thin barrier or in thick barrier QDIPs. Activation energy behaved almost the same when we viewed these two samples under electric field scale. The resonant tunneling is a possible reason for this behavior. We propose some performance improving method to QDIPs based on these two fundamental researches. We will firstly try to tune the bound state out of the quantum dots for better quantum efficiency and lower dark current.