量子點紅外線偵測器之研究

Abstract

本論文主要比較10層與30層量子點紅外線偵測器的元件特性。首先比較在相同電場下兩元件暗電流的表現。根據我們實驗結果分析得知，30層元件相較於10層元件，因有較高的活化能而導致較低的暗電流。更進一步地探討暗電流差異，實際上30層元件具有較低的摻雜濃度，額外減低其暗電流，而加大兩元件暗電流差距。比較兩因素造成的個別效應，發現活化能的差異是造就暗電流差異的主因。由於30層元件具有低暗電流特性，使其較利於高溫操作。在光響應的表現上，30層元件卻劣於10層元件。此乃因30層元件本身多層數導致較低的光導增益，加上較低的摻雜濃度，使其量子效率反而較低所致。即使如此，在整體偵測度的比較上，30層元件在高溫高電場的表現明顯優於10層元件。30層元件最高的操作溫度為150K，比10層元件高了20度。在120K高溫下，30層元件的偵測度高於1×108cmHz1/2/W且增大偏壓仍能維持穩定而不劣化。對於30層元件在高溫高電場的優異表現主要來自於此操作條件下的低暗電流特性。隨著溫度上升或加大偏壓，30層元件的暗電流增加較緩，雜訊電流因而低於10層元件，此說明了30層元件為何具有優異的溫度表現與較廣的工作偏壓範圍。 最後我們提出一套理論解釋較厚的主動層具有較低的暗電流，並利用程式來模擬實驗結果。到目前為止我們仍無法模擬主動層為量子點時元件活化能隨偏壓的相依關係，故利用量子井模擬來作近似分析。在活化能方面，雖然模擬結果與實驗值有所出入，但趨勢是吻合的。較厚的主動層相較於傳統10層量子點紅外線偵測器在高溫高偏壓下的確會有較高的活化能，進而擁有較佳的表現。

Comparisons of the device characteristics between 10-period and 30-period quantum dot infrared photodetectors are presented in this thesis. At first, we compared the dark current of the two devices at the same electric field. According to the analysis of our experimental result, the 30-period device had higher activation energy which resulted in lower dark current than 10-period one. To further discuss the dark current difference, the 30-period device actually had lower doping concentration, which was another factor that decreased dark current. But, to compare the individual effect of the two factors, the activation energy dominated the dark current difference. The 30-period device is good for operating at high temperature due to the low dark current characteristics. On the performance of their responsivity, the 30-period device is poorer than the 10-period one. It’s because that the 30-period device had more layers to decrease the photoconductive gain and had lower doping concentration that results in the lower quantum efficiency. Even though, to compare the whole detectivity, the performance of the 30-period device at high temperature and high electric field is better than the 10-period one. The highest operation temperature of the 30-period device is about 150K which is about 20K higher than that of the 10-period device. At 120K the detectivity for the 30-period sample is higher than 1×108cmHz1/2/W and stays almost constant for a wide voltage range. The excellent performance for the 30-period device at high temperature and high electric field is attributed to the low dark current on this operational situation. The dark current of the 30-period device increases slowly with increasing temperature and bias, so that it has the lower noise current than the 10-period device. It also accounts for why the 30-period has excellent temperature performance and the wide voltage range. Finally, we advanced an assumption to explain that thick active region had lower dark current and used the program to simulate the experiment result. So far we couldn’t still utilize the quantum dots to simulate the activation energy on bias, so we tried to use quantum wells to simulate the activation energy of the two devices at the same electric field. Although, the simulation result is different from the experiment one, but we believe that quantum dots have the same trend. Accordingly, the thick active region indeed has higher activation energy to perform the better performance than common 10-period quantum dot infrared photodetectors at high temperature and bias.