Effect of heat treatment of sputter deposited ZnO films co-doped with H and Al

Abstract

ZnO films co-doped with H and Al (HAZO) were prepared by sputtering ZnO targets containing Al 2 O 3 dcontent of 1 (HA 1 ZO series) and 2 wt.% (HA 2 ZO series) on Corning glass (Eagle 2000) at substrate temperature of 150°C with Ar and H 2 /Ar gas mixtures. The effects of hydrogen addition to Al-doped ZnO (AZO) films with different Al contents on the electrical, optical and structural properties of the as-grown films as well as the vacuum-and air-annealed films were examined. For the as-deposited films, the free carrier number in both series of HAZO films increased with increasing H 2 content in sputter gas. HA 2 ZO film series prepared from target containing 2 wt.% Al 2 O 3 showed better crystallinity and higher carrier concentration than HA 1 ZO film series deposited using target containing 1 wt.% Al 2 O 3 . The crystallinity and the Hall mobility of HA 2 ZO film series decreased with increasing H 2 content in sputter gas, while those of HA 1 ZO film series showed a reversed behavior. Although HA 2 ZO film series yielded lower resistivity than HA 1 ZO film series due to higher carrier concentrations, the higher figure of merit (expressed as 1/ρα, where ρ and α represents the resistivity and absorption coefficient, respectively) was observed for HA 1 ZO film series because of substantially low absorption loss in these films. When annealed in air ambient, HA 1 ZO film series showed much stronger stability than HA 2 ZO film series. Vacuum-annealing resulted in drop of the carrier concentrations as well as large shrinkage in lattice constant, which indicated that the hydrogen dopants are in relatively volatile state and can be removed easily from the films upon annealing.

Structural, Optical, and Electrical Properties of Hafnium–Aluminum–Zinc-Oxide Films Grown by Atomic Layer Deposition for TCO Applications

“…The above-mentioned quaternary materials can be grown by a vast variety of techniques, including sol–gel, CVD, sputtering, or atomic layer deposition (ALD). The samples with the lowest resistivities, reaching as low as ∼2 to 4 × 10 –4 Ω cm, are usually obtained with RF sputtering and in a H 2 -rich atmosphere enhancing free carrier formation due to hydrogen-related defects. − Although promising for enhancing electrical properties, H shallow donors are reported to be unstable and thus prone to diffusing out even in moderate temperatures, leading to long-term electrical instability of the material. − Another well-adopted deposition technique for ZnO thin films is ALD. It offers precise control of the film thickness due to the self-limiting character of the reactions during every half-cycle.…”

“… 51 − 53 Although promising for enhancing electrical properties, H shallow donors are reported to be unstable and thus prone to diffusing out even in moderate temperatures, leading to long-term electrical instability of the material. 53 − 55 Another well-adopted deposition technique for ZnO thin films is ALD. It offers precise control of the film thickness due to the self-limiting character of the reactions during every half-cycle.…”

Fabrication of chemically stable hydrogen- and niobium-codoped ZnO transparent conductive films

“…[27][28][29] Triggered by this nding, many experimental studies conrmed that the hydrogen doping of pure ZnO and metal-doped ZnO lms can improve their electrical properties and stability in air. [30][31][32][33][34][35][36][37][38][39][40][41] Therefore, it is expected that codoping allows ZnO lms to benet from combined effects of H and Nb dopants, which has not been experimentally demonstrated yet. Here we report on the fabrication of H-and-Nb-codoped ZnO (HNZO) lms in an atmosphere of Ar and H 2 with different hydrogen ow rates which allow for investigating the effect of hydrogen ux on structural, electrical, and optical properties of Nb-doped ZnO (NZO) lms.…”

Improved conductivity of indium-tin-oxide film through the introduction of intermediate layer

“…A simpler path is through thermal annealing of the as-deposited films at different temperatures 100e600 C [11,12]. Alternatively, substrate temperature ranging 100e450 C have been applied during the sputtering process to replace the post deposition calcination [13]. Although these attempts have enhanced the conductivity, further improvement is desirable for advanced applications.…”