Effects of Ambience on Thermal-Diffusion Type Ga-doping Process for ZnO Nanoparticles

Md Maruful Islam,Toshiyuki Yoshida,Yasuhisa Fujita

doi:10.3390/coatings12010057

Abstract

Various annealing atmospheres were employed during our unique thermal-diffusion type Ga-doping process to investigate the surface, structural, optical, and electrical properties of Ga-doped zinc oxide (ZnO) nanoparticle (NP) layers. ZnO NPs were synthesized using an arc-discharge-mediated gas evaporation method, followed by Ga-doping under open-air, N2, O2, wet, and dry air atmospheric conditions at 800 °C to obtain the low resistive spray-coated NP layers. The I–V results revealed that the Ga-doped ZnO NP layer successfully reduced the sheet resistance in the open air (8.0 × 102 Ω/sq) and wet air atmosphere (8.8 × 102 Ω/sq) compared with un-doped ZnO (4.6 × 106 Ω/sq). Humidity plays a key role in the successful improvement of sheet resistance during Ga-doping. X-ray diffraction patterns demonstrated hexagonal wurtzite structures with increased crystallite sizes of 103 nm and 88 nm after doping in open air and wet air atmospheres, respectively. The red-shift of UV intensity indicates successful Ga-doping, and the atmospheric effects were confirmed through the analysis of the defect spectrum. Improved electrical conductivity was also confirmed using the thin-film-transistor-based structure. The current controllability by applying the gate electric-field was also confirmed, indicating the possibility of transistor channel application using the obtained ZnO NP layers.

Highlights

The use of semiconductor nanoparticles (NPs) and coating techniques for the manufacture of channel layers of thin-film transistors (TFTs) has drawn considerable interest, owing to certain advantages such as a high selectivity of substrate materials, surface morphology, low cost, and large process area [1,2,3]
zinc oxide (ZnO), ZnO:Ga-open air, and ZnO-open air layers, which are shown in Figure 2a–d, respectively
“as-prepared ZnO” indicates ZnO NPs that had not undergone the Ga-doping process, and “ZnO-open air” indicates ZnO-NPs annealed in open air without Ga2 O3 NPs, which is a reference sample for comparing only the effects of heat treatment

Summary

Introduction

The use of semiconductor nanoparticles (NPs) and coating techniques for the manufacture of channel layers of thin-film transistors (TFTs) has drawn considerable interest, owing to certain advantages such as a high selectivity of substrate materials, surface morphology, low cost, and large process area [1,2,3]. ZnO has been extensively studied because of its exceptional properties, such as a high chemical and thermal stability (even when surrounded by hydrogen plasma, as compared with other oxides (such as SnO2 and ITO)), wide band gap [4], large exciton binding energy of 60 meV at room temperature [5], non-toxicity, and low costs These attributes, combined with its applicability in various fields such as electronics, optics, optoelectronics, and conversion photovoltaics [6,7], make it a model material. Significantly reduced resistance behavior when the temperature was 800 C or greater; atmosphere on the thermal-diffusion process and the doping mechanism were not clarihowever, detailed circumstances such as the effect of atmosphere on the thermal-diffusion fied.

Materials

Results and Discussion

Resistivity

Conclusions