title: Study on the photoresponse of amorphous In-Ga-Zn-O and zinc oxynitride semiconductor devices by the extraction of sub-gap-state distribution and device simulation.
abstract: Persistent photoconduction (PPC) is a phenomenon that limits the application of oxide semiconductor thin-film transistors (TFTs) in optical sensor-embedded displays. In the present work, a study on zinc oxynitride (ZnON) semiconductor TFTs based on the combination of experimental results and device simulation is presented. Devices incorporating ZnON semiconductors exhibit negligible PPC effects compared with amorphous In-Ga-Zn-O (a-IGZO) TFTs, and the difference between the two types of materials are examined by monochromatic photonic C-V spectroscopy (MPCVS). The latter method allows the estimation of the density of subgap states in the semiconductor, which may account for the different behavior of ZnON and IGZO materials with respect to illumination and the associated PPC. In the case of a-IGZO TFTs, the oxygen flow rate during the sputter deposition of a-IGZO is found to influence the amount of PPC. Small oxygen flow rates result in pronounced PPC, and large densities of valence band tail (VBT) states are observed in the corresponding devices. This implies a dependence of PPC on the amount of oxygen vacancies (VO). On the other hand, ZnON has a smaller bandgap than a-IGZO and contains a smaller density of VBT states over the entire range of its bandgap energy. Here, the concept of activation energy window (AEW) is introduced to explain the occurrence of PPC effects by photoinduced electron doping, which is likely to be associated with the formation of peroxides in the semiconductor. The analytical methodology presented in this report accounts well for the reduction of PPC in ZnON TFTs, and provides a quantitative tool for the systematic development of phototransistors for optical sensor-embedded interactive displays.
authors.affiliation: †School of Electrical Engineering, Kookmin University, Seoul 136-702, Republic of Korea.
authors.forename: Jun Tae
authors.initials: JT
authors.lastname: Jang
authors.affiliation: ‡Department of Materials Science and Engineering, KAIST, Daejeon 305-338, Republic of Korea.
authors.forename: Jozeph
authors.initials: J
authors.lastname: Park
authors.affiliation: §School of Electrical and Electronic Engineering, Yonsei University, Seoul 120-749, Republic of Korea.
authors.forename: Byung Du
authors.initials: BD
authors.lastname: Ahn
authors.affiliation: †School of Electrical Engineering, Kookmin University, Seoul 136-702, Republic of Korea.
authors.forename: Dong Myong
authors.initials: DM
authors.lastname: Kim
authors.affiliation: †School of Electrical Engineering, Kookmin University, Seoul 136-702, Republic of Korea.
authors.forename: Sung-Jin
authors.initials: SJ
authors.lastname: Choi
authors.affiliation: #Department of Materials Science and Engineering, Chungnam National University, Daejeon 305-764, Republic of Korea.
authors.forename: Hyun-Suk
authors.initials: HS
authors.lastname: Kim
authors.affiliation: †School of Electrical Engineering, Kookmin University, Seoul 136-702, Republic of Korea.
authors.forename: Dae Hwan
authors.initials: DH
authors.lastname: Kim
keywords: In−Ga−Zn-O; density-of-states; oxide semiconductor; persistent photoconductivity; phototransistors; sensor-embedded interactive display; thin-film transistors; zinc oxynitride