标题: | 改善非晶硒光感测器暗电流与热稳定性之研究 Dark current suppression and thermal stability improvement for amorphous selenium based photosensors |
作者: | 余东原 Yu, Tung-Yuan 潘扶民 Pan, Fu-Ming 材料科学与工程学系所 |
关键字: | 非晶硒;电洞阻障层;多层膜结构;光感测元件;Amorphous Se (a-Se);hole blocking layer (HBL);multilayer structure;photosensor |
公开日期: | 2015 |
摘要: | 非晶硒光感测器是以非晶硒(a-Se)做为光导电材料(photoconductor)。非晶硒在光感测器应用上,因需具备高的光转换效能,必须要有极小的暗电流与高的热稳定性,以提升影像对比。本实验研究利用一个新的电洞阻障层材料应用在单层与多层结构的非晶硒光感测器上来降低元件暗电流与热稳定性,在非晶硒层与正电极之间利用反应性溅镀的方式制备氧化锌(ZnO)电洞阻障层来降低元件的暗电流。利用蒸镀机并使载台旋转的方式沉积非晶硒和砷化硒 (a-Se/AsxSe1-x)多层膜结构,并应用在非晶硒光感测元件来提升元件的热稳定性。 实验方法是沉积ZnO电洞阻障层时,藉由改变氧流量的不同,利用XPS, Raman 和PL观察氧空缺在氧化锌薄膜中的变化,并由DLTS分析得知ZnO有两个深层电洞缺陷分别在价带上方0.94和0.24 eV。电性结果发现氧空缺的多寡对于a-Se光感测元件有很大的影响,当a-Se光感测元件中的电洞阻障层ZnO氧空缺越多有较低的暗电流与较高的崩坏电场。 在多层膜方面,利用双舟蒸镀机并使载台旋转的方式沉积a-Se/AsxSe1-x多层膜结构作为a-Se光感测元件,用来改善元件热稳定性,在AsxSe1-x层中的As原子浓度和各层间的厚度与蒸发舟温度有关。由XRD、RAMAN与 SIMS分析发现,在沉积过程中,As会扩散进入a-Se层中并改善多层膜之热稳定性。尽管As的加入会让a-Se中的载子缺陷增加,降低了蓝光的转换效率,但它有效的降低暗电流,比单层a-Se低了两个数量级。此外a-Se/AsxSe1-x 光感测元件因为有高的热稳定性,所以有较高的崩坏电场。这低的暗电流以及高的崩坏电场让a-Se/AsxSe1-x多层膜元件有高的影像对比,并适合应用在光感测元件上。 This research fabricated amorphous photosensors using amorphous selenium (a-Se) as the photoconductive layer. For photosensor application, a-Se should have a high photoconversion gain with a very low dark current and high thermal stability so that a high image contrast can be obtained. We have proposed a new hole blocking layer for dark current reduction in single and multilayer structure a-Se based photoconductor for photosensor applications. ZnO thin films as a hole blocking layer (HBL) between a-Se and anode electrode were deposited by applying a reactive sputter deposition technique to suppress the dark current in the a-Se photosensor. And then the multilayer structure a-Se based film was fabricated using an alternating multilayer structure of a-Se and AsxSe1-x by applying a rotational thermal evaporation deposition technique to enhance the thermal stability in the a-Se photosensor. The ZnO HBL layers prepared at various oxygen flow rates were characterized using X-ray photoelectron spectroscopy, Raman scattering analysis, and photoluminescence spectroscopy. The results indicated that the oxygen flow rate considerably influenced the density of oxygen vacancies in the ZnO thin films. Deep-level transient spectroscopy measurement was conducted, reveals two hole trap levels in the ZnO thin films deposited using a reactive sputter deposition process; one of the levels was located at 0.94 eV and the other was located at 0.24 eV, above the valence band edge. The number of oxygen vacancies in the ZnO thin film considerably influenced the electrical performance of the a-Se photosensor. The a-Se photosensor containing the ZnO HBL that comprised the most oxygen vacancies exhibited the lowest dark current and highest breakdown field. The multilayer a-Se based photosensors with an alternating multilayer structure comprising a-Se and AsxSe1-x were fabricated using a rotational thermal evaporation deposition process. The atomic concentration of As in the amorphous AsxSe1-x layer and the thickness of each a-Se and AsxSe1-x layer depended on the evaporation temperature. The thermal stability of the multilayer thin film was examined through X-ray diffractometry, Raman spectroscopy analyses, and time-of-flight secondary ion mass spectrometry. During the deposition of the amorphous AsxSe1-x layers, As diffused into the underlying a-Se layers, improving the thermal stability of the multilayer photosensor. Although the As doping introduced carrier traps in the a-Se layers, the multilayer photosensors demonstrated an effective quantum efficiency comparable to that of the single layered a-Se sensor under blue light illumination but with a lower dark current density by two orders of magnitude. Moreover, the a-Se/AsxSe1-x sensor was robust to a higher breakdown field because of its high thermal stability. The improved thermal stability and low dark current density enabled using the a-Se/AsxSe1-x multilayer structure as a sensitive photosensor with a high image contrast. |
URI: | http://140.113.39.130/cdrfb3/record/nctu/#GT079818831 http://hdl.handle.net/11536/126936 |
显示于类别: | Thesis |