In this study, an atomic layer deposited (ALD) Al2O3 with a thickness of 40 nm was used as a dielectric layer for gallium oxide (Ga2O3) metal-oxide-semiconductor (MOS) capacitors. Interface state (Dit) of 1.6×1012 cm-2/eV was extracted at 0.7 eV from conduction band (EC).
Introduction
β-Ga2O3 is a promising candidate for power device applications due to its wide bandgap of 4.7–4.9 eV with a breakdown electric field 8 MV/cm, which is about three times larger than those of SiC and GaN power device materials. Along with the reports on high voltage Schottky diodes, MOS transistors have now been reported. In this research, ALD-Al2O3 with a thickness of 40 nm has been used as a gate dielectric and its interface properties are investigated.
Experiment
A 40-nm-thick-Al2O3 gate dielectric film was deposited by ALD on the surface of a Ga2O3 substrate with n-type epitaxial layer. The doping density (Nd) of the epitaxial layer was 2.3×1016 cm-3. The samples were transferred to a sputter chamber and 50-nm-thick W film followed by 50-nm-thick TiN was deposited by RF magnetron sputtering as a gate electrode. The capacitor was patterned by reactive ion etching (RIE) to form gate electrodes. Finally, a 10-nm-thick Ti followed by a 50-nm-thick TiN was deposited on the backside of the substrate as an Ohmic contact. Figure 1 shows the schematic illustration of the fabricated MOS capacitor.
Results
Capacitance-voltage (C-V) curves measured from 1 kHz to 100 kHz are shows in fig.2. The equivalent oxide thickness (EOT) of the dielectric layer was 18.3 nm. The Dit of the capacitor was evaluated by conductance method. Figure 3 shows the extracted Dit distribution in the bandgap of Ga2O3, where a 1.6×1012 cm-2/eV was obtained at 0.7 eV from EC.
Conclusion
Interface property of Al2O3/β-Ga2O3 was evaluated by conductance method. A 1.6×1012 cm-2/eV was obtained at 0.7 eV from EC.
References
[1] M. Higashiwaki et al., Appl. Phys. Lett, 103, 123511 (2013)
[2] K. Zeng, Y. Jia, and U. Singisetti, IEEE Electron Device Lett. 37, 906 (2016)