量子點紅外線偵測器之研究

Abstract

本論文主要針對由量子點紅外線偵測器(QDIP)量測結果, 利用在量子井紅外線偵測器(QWIP)所發展出來的模型, 將其應用在我們的QDIP元件。首先我們將重點放在電子在QDIP傳輸和頻率的相依性, 因為我們發現了QDIP在光響應大小上會隨著頻率增加而減少, 而同樣的的情況也出現在暗電流的傳輸機制中。根據其他研究團體所提出的解釋, 我們可將光響應電流分成快速傳輸和緩慢傳輸兩種機制。快速傳輸是由從量子井中激發出來的電子所產生。而慢速傳輸是鑿因於量子井中的電子藉由熱或光子的激發離開量子井, 使得量子井帶正電, 造成歐姆接面的電場增強, 誘使更多的載子從歐姆接面流入量子井。我們將此模型應用於QDIP上, 發現雖然和實驗結果有些出入, 但在傳輸的機制上和QWIP相差無幾。 第二部分主要討論QDIP和溫度的相依性, 以及撞擊游離效應在QDIP中造成的影響。我們針對不同的溫度和偏壓下, 引進另外一種模型, 利用量測到的雜訊增益來計算存在於量子點中載子增加的數量, 發現電子數量會隨著偏壓及溫度上升而增加, 並由量子點捕捉電子的能力來討論溫度和電子數量對捕捉機率的影響。為了求出真正的光響應增益和量子效率, 我們假設電子能量在大於活化能時會產生撞擊游離效應。利用量測到的雜訊增益且對計算得到的量子效率做修正, 由此可得到乘積因子。藉由以上的分析, 我們對QDIP的傳輸機制會有更清楚的認識。

In order to explain the phenomenon showed in QDIP, the QWIP model is utilize to explain the behavior in QDIP. From the experiment result, the photo response of QDIP is decrease as the frequency increase. It is interesting that this phenomenon also showed in dark current noise. According to the QWIP model which proposed by other groups, the current contains two component of current, which are fast transient and slow transient. The fast transient comes from the photocarriers generated from the QW. The photocarriers from the QWs induce the local positive charge and thus the slow current component which is injected from the contact to compensate the positive charge in the QWs. Although there still have some inaccuracies to apply this model in QDIP, the trend between them is quite similar. Second, the temperature dependent and impact ionization in QDIP are discussed. We calculated the number of excess carriers in QDs, and observed the number of excess carrier was increase with temperature and bias. In order to have the photocurrent gain and quantum efficiency, the impact ionization is considered. The quantum efficiency could be obtained by calibrating the ratio of the responsivity and noise gain, and then the multiplication factor could be calculated. According to the above analysis, we can realize the mechanism of QDIP more clearly.