Characterization of rf-sputtered HfMgZnO thin films
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Characterization of rf-sputtered HfMgZnO thin films Hantsun Chung1, Jian-Zhang Chen1,*, I-Chun Cheng2 Graduate Institute of Applied Mechanics, National Taiwan University, Taipei 10617, Taiwan 2 Graduate Institute of Photonics and Optoelectronics & Department of Electrical Engineering, National Taiwan University, Taipei 10617, Taiwan *Email: [email protected] 1
ABSTRACT MgZnO becomes amorphous or short-range-ordered with the addition of hafnium oxide. The films are rf-sputter deposited onto glass substrates (Eagle 2000, Corning Inc.) from Mg0.05HfxZn0.95-xO targets (x=0, 0.025, 0.05, 0.075, 0.1) in pure Ar ambient at room temperature. The sputtered Mg0.05Zn0.95O exhibits strong (002) preferred orientation with XRD peak located at 2θ=34.16o. The XRD peak intensity is also greatly reduced, indicating the material amorphorization proceeds with the addition of Hf. The grain size, estimated from the full-widthat-half-maximum (FWHM) of the (002) XRD peak, decreases from 24.1 to 3.3 nm as the Hf content x increases from 0 to 0.025 in Mg0.05HfxZn0.95-xO. No sharp XRD peaks are detected in the as-sputtered films when more than 5.0 at.% Hf are added into the materials. The films remain in amorphous or short-range-ordered states after annealing at 600 oC for 30 mins. All Mg0.05HfxZn0.95-xO films (100 nm in thickness) are highly transparent (> 80 %) in the visible region from 400 to 800 nm and have sharp absorption edges in the UV region. The tauc bandgap ΔE (eV), as a function of hafnium composition x, is fitted as ΔE=3.336+6.08x for room temperature as-deposited films, and ΔE=3.302+2.60x for films after 30 min 600 oC annealing. The annealing process decreases the bandgap shift caused by the incorporation of Hf in the materials. INTRODUCTION ZnO based oxide electronics has drawn much attention recently due to its high electron mobility and large-area deposition capability [1-4]. By alloying MgO into ZnO, the bandgap is enlarged and the intrinsic carrier density is reduced [5-9]. Due to that Mg-O bonds are more ionic character than Zn-O ones, it is expected that MgZnO has less oxygen vacancies and more stable crystal structure than ZnO [10, 11]. It has been shown that the ZnO-based TFTs with MgO alloyed in the active layers exhibit better bias temperature stability [5, 6, 12]. In addition to MgZnO single active layer TFTs [5, 6, 8, 9, 12-14], two dimensional electron gases may form in MgZnO/ZnO heterojunctions, which also attract a lot of research interests [15-21]. To further improve the uniformity for large-area deposited films, amorphous or shortrange ordered phase is desirable [1]. In this study, we demonstrate the Mg0.05Zn0.95O become amorphous or short-range-ordered with the addition of hafnium oxide. We also characterize the properties of films rf-sputtered from HfxMg0.05Zn0.95-xO targets. The effect of post-annealing on the film is also experimented. EXPERIMENT
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The films are rf-sputter deposited onto glass substrates (Eagle 2000, Corning Inc.) from HfxMg0.05Zn0.95-xO targets without intentional heating. The deposi
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