Characterization of a 2D Electron Gas at the Interface of Atomic-Layer Deposited Al2O3/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-Al2O3 (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(CH3)(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 x 10(4) omega (-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 approximate to 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 x 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.