Design and Engineering of High Aspect Ratio Beta-Ga2O3 FinFETs using MOCVD Based In situ Ga Etching

Switched-mode power converters are critical components in modern electrical circuits, enabling the efficient conversion and management of electrical energy for applications such as electric vehicles, power supply for consumer electronics, power grid, locomotive traction and industrial motor drives. Projections indicate that by the year 2030, approximately 80% of electric power will pass through some form of power electronics.

The primary components of a power converter are power switches such as field effect transistors and the efficiency of the converter is largely dependent on the power losses occurring within these devices. Although silicon represents the most prevalent commercial technology for power semiconductor devices, the limited breakdown field of silicon (0.3 MV/cm) results in substantial power losses, thereby restricting the efficiency and operation frequency of silicon-based power electronics.

Ultra-wide bandgap semiconductors (UWBG) such as β-Ga2O3 are seen as promising platforms for developing next generation of power devices owing to the much higher breakdown field strength. With a large critical breakdown field strength of 8 MV/cm and the availability of cost-effective bulk substrates, β-Ga2O3 devices can significantly outperform Silicon and wide-band gap SiC and GaN, while maintaining low cost.

Significant improvements in the performance of β-Ga2O3 devices have been achieved in the past few years particularly for two terminal devices such as diodes, with reports approaching the theoretical material limits of β-Ga2O3. However, the performance of field effect transistors (power switches), which are vital components in power converters, are still far away from the theoretical material limits.

The proposed work aims to advance the field of β-Ga2O3 field effect transistors by engineering high aspect ratio β-Ga2O3 FinFETs capable of achieving high breakdown voltage and low-on resistance, surpassing state-of-the-art performance of SiC and GaN. This advancement will facilitate the scalability and widespread adoption of β-Ga2O3 transistors in the medium-voltage and high-voltage power device market.

The proposed work aims to design and fabricate β-Ga2O3 high aspect ratio (ASR) FinFET devices, capable of achieving improved device performance by decoupling the relation between breakdown voltage and charge density. The fabrication of tall high aspect ratio fins is made possible by the newly developed ‘in-situ Ga etching’ technique which can be carried out within an MOCVD reactor.

This new etching technique simultaneously enables high etch rates, damage free etched surfaces and vertical 90o sidewalls in β-Ga2O3 surpassing the limitation of standard dry and wet etching techniques. The key areas of focus in this proposed work include 1) investigation of anisotropic properties of in-situ Ga etching, 2) development of in-situ etch-followed-by-regrowth approach for engineering high quality ohmic contacts and dielectric interfaces 3) field management for achieving multi-kilo volt class breakdown voltage in lateral high ASR FinFETs using high permittivity dielectrics such as BaTiO3 and 4) investigation of normally off operation.

The successful outcome of this proposal will enable demonstration of β-Ga2O3 three terminal devices that surpass the current state of the art wide band gap devices.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.