The Remarkable Thermal Stability of Amorphous In‐Zn‐O Transparent Conductors

Abstract

Transparent conducting oxides (TCOs) are increasingly critical components in photovoltaic cells, low‐e windows, flat panel displays, electrochromic devices, and flexible electronics. The conventional TCOs, such as Sn‐doped In2O3, are crystalline single phase materials. Here, we report on In‐Zn‐O (IZO), a compositionally tunable amorphous TCO with some significantly improved properties. Compositionally graded thin film samples were deposited by co‐sputtering from separate In2O3 and ZnO targets onto glass substrates at 100 °C. For the metals composition range of 55–84 cation% indium, the as‐deposited IZO thin films are amorphous, smooth (RRMS < 0.4 nm), conductive (σ ∼ 3000 Ω−1 · cm−1), and transparent in the visible (TVis > 90%). Furthermore, the amorphous IZO thin films demonstrate remarkable functional and structural stability with respect to heating up to 600 °C in either air or argon. Hence, though not completely understood at present, these amorphous materials constitute a new class of fundamentally interesting and technologically important high performance transparent conductors.

Transparent Electrodes for Efficient Optoelectronics

“…Even with an amorphous structure (different from polycrystalline IO:H and ICO:H), IZO can have electron mobilities up to 60 cm 2 V −1 s −1 for free carrier densities between 1-3 × 10 20 cm −3 . [111,125,126] An attractive feature of these TCOs is that they already have excellent optoelectronic properties in their as-deposited state; these properties are not much affected by post-deposition annealing and offer opportunities for temperature-sensitive applications. A possible drawback is their relatively high absorption in the UV-vis range due to optical band gap narrowing.…”

“…TCOs with good temperature stability are mainly multicompound amorphous materials, such as IZO and ZTO. [125,186] In nanowire networks, clustering of the network due to a temperature step would increase the roughness of the electrode and induce the formation of shorts in e.g. organic devices.…”

Recent Advances in Understanding the Structure and Properties of Amorphous Oxide Semiconductors

“…Unlike Si-based semiconductors, AOSs were shown to exhibit optical, electrical, thermal, and mechanical properties that are comparable or even superior to those possessed by their crystalline counterparts. [48][49][50][51][52][53][54][55][56][57][58] Table 1 summarizes the key physical properties of best-performing crystalline TCOs and AOSs; the differences (or the lack thereof) between the two will be discussed in detail in the respective sections below. …”

“…[9,[13][14][15][16][17][18][19]24] As the billion-dollar display industry moves forward, the amorphous phase of the complex oxides is favored both for flexible and high-resolution display applications. [13][14][15][16][48][49][50][51][52][53][54][55][56][57][58][59] The unique properties of AOSs were first demonstrated in 1990, [60] and the research area has been growing exponentially since then. Unlike Si-based semiconductors, AOSs were shown to exhibit optical, electrical, thermal, and mechanical properties that are comparable or even superior to those possessed by their crystalline counterparts.…”

Low temperature high-mobility InZnO thin-film transistors fabricated by excimer laser annealing

“…In this study, we focused on an IZO TFT with a higher field-effect mobility than an a-IGZO TFT. We assumed that an ELA process crystallizes IZO with nanograins easily since this material has a lower crystallization temperature than a-IGZO 12,13 and that an IZO film composed of nanograins has better characteristics than a noncrystallized IZO TFT since carrier scattering is suppressed in the disordered film. We considered it is necessary to use a laser with a wavelength shorter than 400 nm, for the laser to be absorbed by the IZO film since IZO has a wide band gap (higher than 3 eV).…”