High-Performance Indium-Based Oxide Transistors with Multiple Channels Through Nanolaminate Structure Fabricated by Plasma-Enhanced Atomic Layer Deposition

Abstract

An atomic-layer-deposited oxide nanolaminate (NL) structure with 3 dyads where a single dyad consists of a 2-nm-thick confinement layer (CL) (In_0.84Ga_0.16O or In_0.75Zn_0.25O), and a barrier layer (BL) (Ga₂O₃) was designed to obtain superior electrical performance in thin-film transistors (TFTs). Within the oxide NL structure, multiple-channel formation was demonstrated by a pile-up of free charge carriers near CL/BL heterointerfaces in the form of the so-called quasi-two-dimensional electron gas (q2DEG), which leads to an outstanding carrier mobility (μ_FE) with band-like transport, steep gate swing (<i>SS</i>), and positive threshold voltage (<i>V</i>_TH) behavior. Furthermore, reduced trap densities in oxide NL compared to those of conventional oxide single-layer TFTs ensures excellent stabilities. The optimized device with the In_0.75Zn_0.25O/Ga₂O₃ NL TFT showed remarkable electrical performance: μ_FE of 77.1 ± 0.67 cm²/(V s), <i>V</i>_TH of 0.70 ± 0.25 V, <i>SS</i> of 100 ± 10 mV/dec, and <i>I</i>_ON/OFF of 8.9 × 10⁹ with a low operation voltage range of ≤2 V and excellent stabilities (Δ<i>V</i>_TH of +0.27, -0.55, and +0.04 V for PBTS, NBIS, and CCS, respectively). Based on in-depth analyses, the enhanced electrical performance is attributed to the presence of q2DEG formed at carefully engineered CL/BL heterointerfaces. Technological computer-aided design (TCAD) simulation was performed theoretically to confirm the formation of multiple channels in an oxide NL structure where the formation of a q2DEG was verified in the vicinity of CL/BL heterointerfaces. These results clearly demonstrate that introducing a heterojunction or NL structure concept into this atomic layer deposition (ALD)-derived oxide semiconductor system is a very effective strategy to boost the carrier-transporting properties and improve the photobias stability in the resulting TFTs.