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

An atomic-layer-deposited oxide nanolaminate (NL) structure with 3 dyads where a single dyad consists of a 2-nm-thick confinement layer (CL) (In0.84Ga0.16O or In0.75Zn0.25O), 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 (μFE) with band-like transport, steep gate swing (SS), and positive threshold voltage (VTH) 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 In0.75Zn0.25O/Ga2O3NL TFT showed remarkable electrical performance: μFEof 77.1 ± 0.67 cm2/(V s), VTHof 0.70 ± 0.25 V, SSof 100 ± 10 mV/dec, and ION/OFFof 8.9 × 109with a low operation voltage range of ≤2 V and excellent stabilities (ΔVTHof +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.