結晶硒應用於可見光感測器之研究

Abstract

本研究主要開發以結晶硒為新型可見光感光材料，並將其運用於未來8K超高畫質攝影元件上，比起傳統使用於感光元件的矽材料，結晶硒具有更高的吸收係數，能夠大大增加元件對於可見光的吸收度與靈敏度，在縮小感光元件上的像素時，可因為吸收較多的可見光而保持較高的靈敏度，未來可開發出同時具備高靈敏度與高解析度的影像感測器。 本研究製作結晶硒光感測器的方式首先是以反應性濺鍍的方式，在銦錫氧化物(ITO)透明基材上沉積氧化鋅(ZnO)電洞阻障層與碲(Te)附著層，並以熱蒸鍍法沉積單層非晶硒(a-Se)，最後以大氣退火方式使非晶硒相轉化為結晶硒，觀察非晶硒與結晶硒兩種感光層在465 nm藍光與620 nm紅光兩者不同波長的光源下明暗電流的差異。為了更瞭解結晶硒感光層對於元件的亮暗電流影響，本實驗以不同退火條件，觀察結晶硒晶粒大小的差異，並與光電性量測配合，探討晶粒尺寸對於結晶硒光感測器之影響。根據研究結果顯示，在感光層厚度相同的500 nm下，結晶硒感光層相較於吸收度較小的非晶硒感光層，在紅光波長下具有非常優異的亮電流表現，且亮電流隨結晶硒晶粒尺寸越大，也明顯呈現出提升的趨勢，因此推測亮電流載子的複合現象與結晶硒的晶界有關，在暗電流方面，晶粒大小對於暗電流則無明顯影響。

This research developed crystalline selenium(c-Se) as a new photosensitive layer at visible wavelength and used it in the future 8K ultra-high definition image sensor. Because c-Se had a higher absorption coefficient than Si, which was used in traditional photosensitive layer, it could enhance the image sensor sensitivity. A higher absorption coefficient of photosensitive layer would keep higher sensitivity when reduced the pixel size. By this material we could develop a high sensitivity and high definition image sensor.

To fabricate c-Se photodetector, the ZnO hole blocking layer and Te adhesion layer were prepared by reactive sputter deposition on ITO substrate. The a-Se was deposited by thermal evaporation. The a-Se could be transformed into c-Se by annealing under atmosphere. In order to understand c-Se photodetector sensing ability between different wavelength of light, we used a 465 nm blue light and a 620 nm red light as light sources and compared c-Se with a-Se photosensitive layer. We also researched the effects of c-Se crystal size on dark and photo current by electrical measurement. According to our research, the thickness of 500 nm c-Se had a higher photocurrent compared with 500 nm a-Se owing to its high absorption coefficient. The photocurrent of c-Se photodetector increased gradually with crystal size and related to combination phenomenon in grain boundary. There was no significant different in dark current of c-Se photodetector between different c-Se crystal size.