高增益雪崩式非晶硒疊層膜光感測器之氧化鋅電洞阻障層研究

Abstract

本研究開發應用於醫療低劑量X光檢測器的高增益雪崩式元件(HARP)中的氧化鋅電洞阻障層。HARP元件是以在高電場條件下會發生雪崩倍增效應之非晶質硒(a-Se)做為光導電材料(photoconductor)。在低曝光劑量的X光顯影應用上，HARP元件除了需要具備高靈敏度的特性之外，也必須有極小的暗電流，以提升影像對比，所以HARP元件在非晶硒層與正極之間具有電洞阻障層來降低元件的暗電流。本研究以反應性濺鍍的方式製備氧化鋅電洞阻障層。本研究有兩個目標：第一個目標，在不影響亮電流大小的情況下，優化氧化鋅電洞阻障層，使HARP元件有最低的暗電流以達成高的明暗電流比。第二個目標，藉由改變氧流量與濺鍍時的基板溫度，探討此兩項製程對於氧化鋅電洞阻障層的影響，並進一步分析其材料微結構和缺陷的特性與HARP元件的暗電流之間的關聯性。根據本研究的實驗結果，我們推論，氧化鋅電洞阻障層內部與氧空缺有關的深層電洞捕獲能階，能夠捕獲從 正極注入的電洞，達成降低HARP元件暗電流的功效。

This research fabricated high-gain avalanche rushing amorphous photoconductors (HARP) for medical low dose X-ray detector applications, using amorphous selenium (a-Se) as the photoconductive layer. The greatest advantage of a-Se is its high photoconversion efficiency result from avalanche multiplication under high electric field. For application of low dose X-ray exposure, HARP devices should have a high photoconversion gain with a very low dark current so that a high image contrast can be obtained. In order to reduce dark current, a hole blocking layer is used between the photoconductive layer and the anode of HARP device. Here are two goals of this research about ZnO hole blocking layer prepared by rf magnetron reactive sputter deposition. First, we optimized the ZnO hole blocking layer. Second, by changing the oxygen flow rate and substrate temperature during deposition, we investigate how these parameter affect the ZnO hole blocking layer and discover the relationship between the microstructure and traps of ZnO hole blocking layer and the dark current of HARP. We concluded that because the deep hole traps related to oxygen vacancy in ZnO hole blocking layer can prevent hole from injecting into the photoconductive layer, the dark current of HARP can be reduce if ZnO hole blocking layer is introduced in HARP.