Theoretical analysis of the impacts of light illumination on the transient current of sputter-deposited non-doped ZnO films

Yasuhisa Omura,Shingo Sato

doi:10.1063/5.0036882

Abstract

This paper proposes a possible theoretical model to analyze the impacts of light illumination on the post-illumination transient current of sputter-deposited non-doped ZnO films. Although the authors have already demonstrated experimentally the impact of wavelength on the resistance of such films (various light-emitting diodes were used), the influence of ambient gas on their resistance, and the influence of temperature on resistance in detail, no significant theoretical basis was provided. In this paper, the physical images of the phenomena are theoretically reconsidered and a theoretical model is developed based on the experimental results. The mathematical formulation provided involves the time-dependent diffusion current model, and the continuity equation is solved to achieve a plausible solution of the time constant of the transient process. The theoretical solution strongly suggests that oxygen vacancy levels and/or traps around the grain boundaries and inside the grains contribute to the post-illumination transient behavior of dc-biased current. The non-linear effect on the transient process is also discussed for directing future research.

Highlights

Transparent conductive oxides (TCOs) composed of doped metal oxides are frequently used in optoelectronic devices, typically for language processing and debugging (FPD)s and photovoltaic applications because they are transparent at visible wavelengths and have high electrical conductivity.[1]
We consider that the theoretical model successfully explains the substantial non-linearity of the transient process discussed in this paper
This paper proposed a theoretical model to elucidate the transient decay process of post-illumination dark currents observed in the sputter-deposited non-doped ZnO films

Summary

INTRODUCTION

Transparent conductive oxides (TCOs) composed of doped metal oxides are frequently used in optoelectronic devices, typically for language processing and debugging (FPD)s (flat panel displays) and photovoltaic applications because they are transparent at visible wavelengths and have high electrical conductivity.[1]. ZnO (zinc oxide) is a potential alternative It has an electron affinity of 4.35 eV and a direct band gap energy of 3.28 eV and is an n-type semiconductor material with a residual electron concentration of ∼1017 cm−3.6 Prior experiments elucidated the dominant mechanism controlling the electrical property of nondoped ZnO films and impurity-doped ZnO films. The previous paper published by our group revisited the dominant mechanism controlling the electrical property of non-doped ZnO films.[13] It was discovered that films annealed under nitrogen ambient had much lower resistance than those annealed under oxygen ambient and that the out-diffusion of oxygen atoms during. An experiment conducted by our group, showed that the film resistance was sensitive to the wavelength of the illuminating light, which suggests that the optical response is related to the Schottky barrier effect of the top electrode and traps around the grain boundaries. It is expected that the limitation of the simplified conventional theory can be overcome by taking account of the Kohlrausch function,[28] we take a theoretical approach different from it

SAMPLE FABRICATION AND MEASUREMENTS

Review of previous basic results

Impact of temperature on the optical response of current

Basic models for the transient current under the dark condition

Comparison with experimental results and new findings

CONCLUSION