【Member Papers】High-Performance ZrO₂/β-Ga₂O₃ (001) Metal–Insulator–Semiconductor Capacitors

      Researchers from the Hunan University have published a dissertation titled "High-Performance ZrO₂/β-Ga₂O₃ (001) Metal–Insulator–Semiconductor Capacitors" in IEEE Transactions on Electron Devices.

Project support

      This work was supported in part by the Natural Science Foundation of Hunan Province under Grant 2023JJ30146 and in part by the Jie Bang Headed Project of Changsha, Hunan, China, under Grant kq2301006.

Background

      For the past few years, the wide bandgap semiconductor materials, such as silicon carbide (SiC), gallium nitride (GaN), zinc oxide (ZnO), diamond, and beta-gallium oxide (β-Ga₂O₃), have garnered considerable attention due to their great potential in power and optoelectronic systems. β-Ga₂O₃ has emerged as a subject of substantial interest owing to its appealing characteristics. With a wide bandgap of approximately 4.6 eV and a high breakdown strength of around 8 MV/cm, it exhibits a superior Baliga figure of merit (BFOM) of approximately 3214, surpassing that of SiC and GaN. This elevated BFOM positions β-Ga₂O₃ as a more promising candidate for high-power applications compared to other materials. Furthermore, its commercially available large-area, high-quality substrate, coupled with precise control over doping concentration in the epitaxial layer, further bolsters its attraction. These outstanding properties mentioned above have spurred significant research into high-performance β-Ga₂O₃-based Schottky diodes, solar-blind ultraviolet photodetectors, and metal–insulator–semiconductor field-effect transistors (MISFETs).

Abstract

      In this study, we have fabricated high-performance metal-insulator-semiconductor (MIS) capacitor using atomic layer-deposited ZrO₂/beta-gallium oxide (β-Ga₂O₃) (001) heterojunction. The energy band alignment for the ZrO₂/β-Ga₂O₃ heterojunction and electrical properties for the ZrO₂/β-Ga₂O₃ MIS capacitor are investigated. Valence band offset (ΔE_V) and conduction band offset (ΔE_C) for the ZrO₂/β-Ga₂O₃ heterojunction, determined by X-ray photoelectron spectroscopy (XPS) technique, are −0.42 and 1.42 eV, respectively. Its band alignment configuration exhibits a type II (staggered gap) structure. Gate leakage current and frequency-dependent capacitance-voltage (C–V) characteristics for the ZrO₂/β-Ga₂O₃ MIS capacitor are investigated. The ZrO₂/β-Ga₂O₃ MIS capacitor demonstrates a low gate leakage current. The Poole-Frenkel (PF) conduction model is employed to elucidate the gate leakage current mechanism. No significant frequency dispersion is observed based on the frequency-dependent C–V characteristics. The fixed charge and trapped charge densities in the ZrO₂ film are calculated to be 7.9×10¹² and 1.27×10¹² cm⁻², respectively. The minimum interface trapped charged density is extracted to be 4.1×10¹⁰ cm⁻²⋅eV⁻¹ at an energy of 0.6 eV below the conduction band of β-Ga₂O₃, representing the lowest reported value for the dielectric/β-Ga₂O₃ (001) interface. These results indicate the formation of high-quality ZrO₂ film on the β-Ga₂O₃, making it a potential candidate as gate dielectrics in β-Ga₂O₃ power devices.

Conclusion

      In conclusion, we have fabricated high-performance ZrO₂/β-Ga₂O₃ (001) MIS capacitors. The energy band alignment between ZrO₂ and β-Ga₂O₃ (001) was determined by the XPS measurements. E_V and E_C of ZrO₂/β-Ga₂O₃ (001) heterojunction were determined to be −0.42 and 1.40 eV, respectively. Band alignment configuration for the ZrO₂/β-Ga₂O₃ (001) heterojunction exhibits a type II (staggered gap) structure. Although a minor difference in E_V between ZrO₂ and β-Ga₂O₃, E_C exceeding 1 eV provides a large barrier for electrons transport from β-Ga₂O₃ into ZrO₂. The ZrO₂/β-Ga₂O₃ MIS capacitor exhibited low J. To further investigate the leakage current mechanism of the MIS capacitor, the PF model was taken into account after excluding other models. ε_r of ZrO₂ was determined to be 20.0, aligning well with previously reported values. The analysis of the C–V curves of the electrical properties of ZrO₂/β-Ga₂O₃ (001) MIS capacitors yielded the extracted values of Q_f and N_bt at 7.9 × 10¹² and 1.27 × 10¹² cm⁻², respectively. The minimum D_it value was extracted to be 4.1 × 10¹⁰ cm⁻² ·eV⁻¹ at an energy of 0.6 eV below E_C of β-Ga₂O₃ (001) for ZrO₂/β-Ga₂O₃ MIS capacitor, to the best of our knowledge, which is the lowest reported value for the dielectric/β-Ga₂O₃ (001) interface. These findings indicate the potential of ALD-deposited high-k ZrO₂ as a promising gate dielectric for the fabrication of high-performance β-Ga₂O₃ (001) MISFETs.