Crystallization of ZnO thin films via thermal dissipation annealing method for high-performance UV photodetector with ultrahigh response speed

Dongwan Kim,Jae-Young Leem

doi:10.1038/s41598-020-79849-z

Abstract

ZnO-based ultraviolet (UV) photodetector can be easily fabricated by using sol–gel spin-coating method, however, the crystallization of amorphous state ZnO thin films is necessary to fabricate high performance UV photodetector. Thus, we devised a thermal dissipation annealing (TDA) method in which the heat transfer to the ZnO thin films can be synchronized with the heat release from the substrate. It was found that sol–gel spin-coated ZnO thin films can be crystallized through the mobility difference of ZnO molecules placed at the surface of ZnO thin films. Also, UV photodetector based on ZnO thin films annealed with the TDA method exhibited faster rise and decay time constant (τr = 35 ms and τd = 73 ms, respectively), a higher on/off current ratio, and reproducible photocurrent characteristics compared to that of the ZnO thin films annealed by using furnace and IR lamp. Therefore, these results indicated that the TDA method is a feasible alternative route for the fabrication of ZnO based high performance optoelectronic devices.

Highlights

Ultraviolet (UV) photodetectors have attracted considerable research interest in the last few years because of their great potential and commercial impact in a wide variety of fields, such as secure space-tospace communications, pollution monitoring, water sterilization, flame sensors, and missile plume detection applications[1,2]
We developed a novel annealing method, the thermal dissipation annealing (TDA) method, that eliminates the thermal energy from substrates through a thermal dissipation annealing system combined with an IR lamp and cold plate to restrict the defect formation in the ZnO lattice through mobility difference of ZnO molecules
In other words, when the ZnO thin films are annealed by using the TDA method without a separate space, a temperature below the dew point on the ZnO thin films surface for a cooling time of 30 s allows moisture to form and the generated moisture decreases the annealing efficiency and heat transfer rate of the TDA method

Summary

Introduction

Ultraviolet (UV) photodetectors have attracted considerable research interest in the last few years because of their great potential and commercial impact in a wide variety of fields, such as secure space-tospace communications, pollution monitoring, water sterilization, flame sensors, and missile plume detection applications[1,2]. In other words, when the ZnO thin films were annealed without a cold plate, the nanoparticle size of ZnO thin films increased because of Ostwald ripening, and the cracks between the wrinkled network structures decreased; there was no change in the morphology because the mobility of the ZnO molecules at the surface and bottom of wrinkled network structures did not differ.

Results

Conclusion