Reducing the Persistent Photoconductivity Effect in Zinc Oxide by Sequential Surface Ultraviolet Ozone and Annealing Treatments

Abstract

We developed a method to reduce the persistent photoconductivity (PPC) effect of zinc oxide (ZnO) thin film transistors (TFTs) by sequential surface treatment, which includes preannealing/ultraviolet ozone/postannealing (PUP) treatments. Preannealing treatment improves the surface uniformity of the film and eliminates the residual solvent and contaminant molecules without affecting the zinc–oxygen bonds. The ultraviolet ozone (UVO) treatment reduces the oxygen vacancy and increases the amount of metal hydroxide groups on the surface of ZnO by converting adsorbed O2 – on the ZnO and atmospheric oxygen to highly chemisorbed OH–. Postannealing treatment improves the film quality by making the film densely and inducing zinc–oxygen bonding in the ZnO film. Therefore, the negative threshold voltage shift decreased upon visible light irradiation of the PUP ZnO TFT. The treatment also improved the photoresponsivity upon the irradiation with ultraviolet (UV) light. Moreover, the photoelectric recovery time after the irradiation of the UV light was shortened, which means that the PPC effect on the PUP ZnO TFT decreased. The decrease in the PPC effect originated from the reduced oxygen vacancies and the increased surface metal hydroxide groups upon PUP treatment. Our experiment results suggest a method to reduce the PPC effect on ZnO TFTs via PUP treatment, which is useful for developing high-performance UV phototransistors that are based on ZnO.

A Review of Phototransistors Using Metal Oxide Semiconductors: Research Progress and Future Directions

“…demonstrated a method to reduce the PPC issue by sequential surface treatment, which includes pre‐annealing, UV–ozone treatment, and post‐annealing treatment as shown in Figure a. [ 72 ] In each step, the ZnO film was affected in three effects by the treatment: 1) pre‐annealing treatment improved the surface uniformity of the ZnO film and reduced the residual solvent, 2) UV–ozone treatment decreased the oxygen vacancy, and 3) post‐annealing treatment refined the ZnO film density and induced zinc–oxygen bonding. Owing to the improved film quality, the photoelectric recovery time after the irradiation of the UV light was shortened, indicating that the PPC effect on the ZnO phototransistor is decreased as shown in Figure 7b.…”

“…The inset shows the graph on a log scale for the initial 4 s. a,b) Reproduced with permission. [ 72 ] Copyright 2019, American Chemical Society. c) Schematic diagram of IGZO film with hydrogen rich Al 2 O 3 dielectric structure.…”

Facile Polydimethylsiloxane Treatment of Indium Gallium Zinc Oxide Phototransistor for Visible Light‐Based Multilevel Photomemory

“…We compared the optoelectronic characteristics of previous research related to oxide phototransistors without an absorption layer to confirm the performance of our devices, as shown in Table S1 (Supporting Information). [ 39–52 ] PDMS treatment significantly enhanced the detection ability of IGZO phototransistors in the visible region.…”

Reduction of Persistent Photoconduction with IGZO/ZnON-Tandem-Structure Visible–Near-Infrared Phototransistors

“…Various methods have been proposed to overcome this issue from a material, structural, and circuit point of view. Many studies have aimed to reduce the oxygen vacancies in the semiconductor by annealing in oxidizing conditions such as high-pressure oxygen or ultraviolet ozone gas, doping of similar size anion elements such as nitrogen and sulfur, and controlling the metal–cation ratio of the multicomponent oxide semiconductor . Several studies have reported a reduction of the PPC while reacting with the visible or near-infrared light of organic/inorganic or low-dimensional material/inorganic hybrid structure devices. , With regard to material or structural approaches, some studies considered the applied gate bias pulse sequence, which can rapidly recombine generated electron–hole pairs or trapped carriers upon light exposure. , However, these methods come with their own challenges, including difficulty controlling the process conditions, the unintended interface with the ex situ process, and the need for an additional circuit and metal line for the gate pulse bias.…”

“…Various methods have been proposed to overcome this issue from a material, structural, and circuit point of view. Many studies have aimed to reduce the oxygen vacancies in the semiconductor by annealing in oxidizing conditions such as high-pressure oxygen 7 or ultraviolet ozone gas, 8 doping of similar size anion elements such as nitrogen and sulfur, 9 and controlling the metal−cation ratio of the multicomponent oxide semiconductor. 10 Several studies have reported a reduction of the PPC while reacting with the visible or nearinfrared light of organic/inorganic or low-dimensional material/inorganic hybrid structure devices.…”