Transparent Conductive Indium Zinc Oxide Films: Temperature and Oxygen Dependences of the Electrical and Optical Properties

Abstract

Achieving high-efficiency optoelectronic devices often requires the development of high transparency in the extended range and high-conductivity materials, which can be ensured by the high mobility of charge carriers being used as the electrode. Among the candidate materials, transparent conductive indium zinc oxide (IZO) has attracted significant interest because of its superior electron mobility (5−60 cm2/V·s) and the thermal stability of its structure. In this study, the IZO films were deposited by the radio frequency magnetron sputtering of the IZO ceramic target (containing 10 wt.% ZnO) by varying the two variables of the substrate temperature and the oxygen content in the working gas. Here, the importance of the deposition of the IZO films at a low substrate temperature, not exceeding 100 °C, in order to get the minimum values of the film resistivity is revealed. At a substrate temperature of 100 °C, the film deposited in pure argon demonstrated a minimum resistance of 3.4×10−4 Ω·cm. Despite the fact that, with the addition of O2 in the working gas, an increase in resistivity was observed, the IZO film that deposited under 0.4% O2 content demonstrated the highest mobility (μ = 35 cm2/V·s at ρ = 6.0 × 10−4 Ω·cm) and enhanced transparency in the visible (VIS, 400−800 nm) and near-infrared (NIR, 800−1250 nm) ranges (TVIS ≥ 77% and TNIR ≥ 76%). At an oxygen content above 0.4%, a significant deterioration in electrical properties and a decrease in optical characteristics were observed. SEM and XRD studies of the microstructure of the IZO films allowed the clarification of the effect of both the substrate temperature and the oxygen content on the functional characteristics of the transparent conducting IZO films.

Transparent Conducting Amorphous IZO Thin Films: An Approach to Improve the Transparent Electrode Quality

“…Our earlier studies of the influence of technological conditions of RF sputtering deposition on the functional properties of IZO films showed that the optimal substrate temperature for the deposition of amorphous IZO films is 100 °C [ 29 ]. Upon sputtering in a pure argon medium, the transport of carriers in the IZO film is characterized by high free electron concentration n > 7 × 10 20 cm –3 and low resistivity ρ of 3.35 × 10 −4 Ω·cm, while when using a Ar/O 2 (0.4%) gas mixture as a working gas, the carrier concentration decreased down to 2.7 × 10 20 cm −3 , but the Hall mobility µ increased by 50% to a value of 39.2 cm 2 /V·s, which in combination resulted in a not so dramatic increase in resistivity ρ up to 5.5 × 10 −4 Ω·cm (see the Supplementary Materials (SM), Figure S1 ).…”

“…A home-made RF magnetron sputtering setup was used to deposit the N × [ n -ZnO/µ-ZnO] multilayers (MLs) at working gas pressure of 0.5 Pa from 2-inch IZO disk targets with In 2 O 3 /ZnO weight ratio of 9:1 onto glass substrates heated to 100 °C. A detailed description of the experimental setup is given in [ 29 , 32 ]. Switching between the n -IZO and µ-IZO deposition modes was carried out by controlled periodic change in the composition of the working gas from pure Ar to an Ar/O 2 (0.4%) gas mixture.…”

“…Currently, among numerous well-studied TCO materials an amorphous indium zinc oxide (IZO) system is one of the more promising materials for the TE application due to its high transmittance, good electrical properties, thermal stability, ultrasmooth surface and easy etchability by organic acids [ 11 , 25 , 26 , 27 , 28 ]. In addition, it can be deposited at low substrate temperature using an industry-friendly technique such as magnetron sputtering [ 25 , 29 ].…”

“…However, the oxygen vacancies’ high concentration adversely affects the electron mobility and transparency of IZO films. At the same time, in low-temperature amorphous IZO films deposited in a reactive medium (Ar/O 2 gas mix as the working gas), quite high values of Hall mobility are achievable, which are even higher than in polycrystalline ITO films deposited at high substrate temperature [ 26 , 29 ]. As a result, these IZO films exhibit fairly good conductivity (despite a reduced concentration of donor oxygen vacancies), as well as high transparency in the visible- and near-IR ranges.…”

Al-Doped ZnO Thin Films with 80% Average Transmittance and 32 Ohms per Square Sheet Resistance: A Genuine Alternative to Commercial High-Performance Indium Tin Oxide

“…During the last decades, transparent conducting oxides (TCOs) have been considered attractive materials in different areas due to their high electrical conductivity and large transparency in the visible and near-infrared regions of the electromagnetic spectrum [1][2][3][4]. TCOs are used in a wide variety of devices, e.g., in solar cells, light-emitting diodes (LEDs), organic light-emitting diodes (OLEDs), liquid crystal displays, touch screens, photothermal conversion systems, and intelligent windows [5][6][7][8][9][10][11]. The sheet resistance required for a thin transparent electrode strictly depends on the type of application where it is implemented.…”