Electrical Properties of MOCVD-Grown AlSiO Gate Dielectric on (001) β-Ga2O3

Abstract

Abstract Body: β-Ga2O3 has become a promising semiconductor for high power applications. High-quality dielectrics are crucial for enabling high performance β-Ga2O3 field-effect transistors (FETs) especially because achieving p-type doping does not seem feasible for this material system. The material properties of high-quality gate dielectric include high dielectric constant, negligible gate leakage, low density of interface and bulk traps, and large breakdown field. Recently, aluminum silicon oxide (AlSiO) has been proposed as a high-performance and reliable gate dielectric for GaN-based devices [1], [2]. Previous studies showed that the alloying of Al2O3 with silicon to form AlSiO has the potential to combine the merits of both SiO2 and Al2O3 thus realizing low density of interface traps (Dit), high conduction/valence band offset and high breakdown strength [3], [4]. The promising results of AlSiO as a dielectric for GaN-based devices motivated us to expand its applications to Ga2O3. In this work, the interface and bulk properties of aluminum-silicon-oxide (AlSiO) dielectric grown by metal-organic chemical vapor deposition (MOCVD) on (001) β-Ga2O3 were investigated systematically using a deep UV-assisted capacitance-voltage methodology. The AlSiO dielectric, with a silicon composition of 40%, was grown by metal organic chemical vapor deposition (MOCVD) in a close coupled showerhead chamber. The AlSiO deposition temperature was 700 °C, and the TMAl, Si2H6, and O2 flows were 3.2 μmol/min, 3.2 μmol/min, and 4.4 mmol/min, respectively. AlSiO with various thicknesses (10 nm, 20 nm, and 30 nm) were deposited on three different Ga2O3 samples treated by UV-ozone followed by an HF dip. This improved surface preparation with a combination of UV-ozone and wet chemical treatment reduced near-interface traps resulting in a negligible hysteresis. The fast trap density was extracted to be 2.18×1011 cm-2, and the slow trap density excluding the contribution from fast traps was calculated to be 2.73×1011 cm-2. A net positive interface fixed charge of 1.56×1012 cm-2 was measured. The Dit was extracted accurately by accounting for dielectric bulk traps employing deep UV-assisted C-V method and physical models. An average interface state density of 6.63 ×1011 cm-2 eV-1 and AlSiO bulk trap density of 4.65×1017 cm-3 eV-1 were quantified, which is half of that for Al2O3 deposited by atomic layer deposition (ALD). In addition, a high dielectric breakdown field of ~7.8 MV/cm and more effective suppression of gate leakage were achieved on these devices compared with ALD-Al2O3 on similar metal-oxide-semiconductor (MOS) structures. The negligible hysteresis, lower interfacial trap density, low leakage current and high breakdown electric field achieved on AlSiO/Ga2O3 MOSCAPs reveals MOCVD AlSiO as a promising gate dielectric for high-performance Ga2O3 devices. [1] S. H. Chan et al., Jpn. J. Appl. Phys., vol. 55, no. 2, p. 021501, Feb. 2016. [2] D. Kikuta et al., J. Vac. Sci. Technol., vol. 35, no. 1, p. 01B122, Jan. 2017. [3] C. Gupta, et al., IEEE Electron Device Lett., vol. 38, no. 11, pp. 1575–1578, Nov. 2017. [4] I. Sayed et al., Appl. Phys. Lett., vol. 115, no. 17, p. 172104, Oct. 2019.