Characterization of a 2D Electron Gas at the Interface of Atomic‐Layer Deposited Al 2 O 3 /ZnO Thin Films for a Field‐Effect Transistor

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.