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.

Comparative studies on the physical and electronic properties of reactively sputtered ZnO and ZnON semiconductors

“…Studies on In and Zn-based multi-component metal oxides such as InGaZnO [2], InZnO [3], HfInZnO [4] and InZnSnO [5] have been constantly reported, focusing mainly on high field effect mobility and high stability with respect to bias, temperature and illumination stress. Since Ye et al reported on zinc oxynitride (ZnON) semiconductors in 2009 [6], semiconductors based on this compound have drawn attention due to several advantages such as high field effect mobility ($ 100 cm 2 /Vs) and device stability with respect to illumination [7][8][9][10]. Recently, studies on nitrogendoped ZnO have gained attention for various applications such as photo-electrochemical devices and photo-sensors involving the design of the material's optical band structure [10][11][12][13].…”

“…Since Ye et al reported on zinc oxynitride (ZnON) semiconductors in 2009 [6], semiconductors based on this compound have drawn attention due to several advantages such as high field effect mobility ($ 100 cm 2 /Vs) and device stability with respect to illumination [7][8][9][10]. Recently, studies on nitrogendoped ZnO have gained attention for various applications such as photo-electrochemical devices and photo-sensors involving the design of the material's optical band structure [10][11][12][13]. Especially, nitrogen plays important roles when zinc oxynitride is formed.…”

Effect of top gate bias on photocurrent and negative bias illumination stress instability in dual gate amorphous indium-gallium-zinc oxide thin-film transistor

“…22,23,28 Such photogenerated carriers are the source of photocurrent. 15,22,23,28 Using such photocurrents in metal oxide based TFTs (singe gate), the optical sensor-embedded interactive displays are demonstrated by several groups. 15,23 It has been reported that photosensing capability increases with the increasing subgap states (V O ).…”

“…15,22,23,28 Using such photocurrents in metal oxide based TFTs (singe gate), the optical sensor-embedded interactive displays are demonstrated by several groups. 15,23 It has been reported that photosensing capability increases with the increasing subgap states (V O ). 23 The addition of oxygen during deposition passivates such subgap states existing near the valance band.…”

“…15,23 It has been reported that photosensing capability increases with the increasing subgap states (V O ). 23 The addition of oxygen during deposition passivates such subgap states existing near the valance band. 24 It modifies the Fermi position and also the band gap.…”