Characterization of a 2D Electron Gas at the Interface of Atomic‐Layer Deposited Al<sub>2</sub>O<sub>3</sub>/ZnO Thin Films for a Field‐Effect Transistor
Hyun Jae Lee, Taehwan Moon, Seung Dam Hyun, Sukin Kang, Cheol Seong Hwang
Abstract
Abstract The 2D electron gas (2DEG) phenomenon that occurs at the amorphous thin film hetero‐oxide interface attracts great attention since it can avoid the use of a single‐crystal oxide substrate. In this study, the analysis of 2DEG at the interface of amorphous‐Al 2 O 3 ( a ‐AO)/ZnO is conducted using ZnO as the bottom substrate, where both the oxide films are grown by atomic layer deposition. Having used Al(CH 3 ) 3 as the Al‐precursor for the a ‐AO film growth on the previously grown ZnO film, its strong reducing power induces the 2DEG formation at the interface. As a result of the Hall measurement, the 2DEG at the a ‐AO/ZnO interface shows sheet resistance of 2.7 × 10 4 Ω ▫ −1 and Hall mobility of 8.4 cm 2 V −1 s −1 . Using angle‐resolved X‐ray photoelectron spectroscopy, the thickness of the 2DEG layer is calculated as 0.62 nm, which is ≈120% of the c‐axis of the wurtzite ZnO unit cell. The field‐effect transistor fabricated exhibits a threshold voltage of −2.4 V, sub‐threshold swing of 0.33 V dec −1 , and on/off ratio of 9.4 × 10 6 , which significantly outperforms similar devices from previous works. The outstanding operation of 2DEG at the interface of AO/ZnO as a channel presents a possibility for application to a 2D‐based integrated circuit.