High-Performance Ultra-Wide Bandgap Semiconductor AlGaN and Ga2O3 Devices

In this presentation, we will discuss some of our recent activities on building the next generation of high-performance wide bandgap and ultra-wide bandgap semiconductor technologies. Ultra-wide bandgap semiconductor materials such as Aluminium (Gallium) Nitride (AlGaN) and Gallium Oxide are promising for next-generation high-frequency, power, and extreme-environment electronics. The high breakdown field strength, favorable doping and transport properties, and the availability of heterostructure engineering give them great potential for future high-frequency and power electronics. In this presentation, we discuss the opportunities, challenges, and recent highlights of our work in the area.

We will begin by discussing some recent highlights from our work on high Al-content AlGaN transistors for high-frequency applications. Contact resistance was a key limiting factor for AlGaN devices in the last two decades. We will discuss recent innovations in heterostructure engineering, including using graded compositional profiles [1,2], and engineered channel/contact interfaces that enabled record resistance as low as 1e-6 Ohm-cm2 to >80% AlGaN channels. To overcome the thermal conductivity limits inherent to AlGaN channels, it is critical to have ultra-thin buffers integrated epitaxially with the substrate.We will discuss the heterostructure engineering approaches that enables integration of ultra-thin (< 100 nm) AlGaN epitaxial layers directly onto high thermal conductivity heat spreading buffers such as AlN. Finally, we will discuss results of high frequency device performance from highly scaled (sub 100-nm) gate length transistors using scaled polarization-graded field effect transistors (PolFETs) as well as abrupt heterostructure field effect transistors, achieving state-of-art cutoff frequency up to 40 GHz [3].

We will then discuss our recent efforts toward developing Gallium Oxide power devices for high voltage applications, including the materials and device processing technologies needed for vertical Gallium Oxide transistors. We will discuss advanced etching methods to realize high aspect-ratio structures and novel (high-permittivity) deielectrics [4] that can enable device structures to support the extreme fields enabled by these ultra-wide bandgap materials. This presentation will discuss recent work that have enabled us to design and demonstrate devices that support extreme electric fields - lateral transistors with > 5.5 MV/cm average electric field strength [5], and vertical Schottky diodes with > 5 MV/cm average electric field strength [6].

We acknowledge funding from Army Research Office (ARO UWBG Center, Award No. W911NF2220163), AFOSR (GAME MURI, Award No. FA9550-18-1- 0479), ONR Grant No. N00014-22-1-2260, NSF DMR-2329108, and ECCS-2235373.

[1] Bajaj, Sanyam et al "AlGaN channel field effect transistors with graded heterostructure ohmic contacts." Applied Physics Letters 109, no. 13 (2016)
[2] Razzak, Towhidur et al "Design of compositionally graded contact layers for MOCVD grown high Al-content AlGaN transistors." Applied Physics Letters 115, no. 4 (2019)]
[3] Xue, Hao et al. "Al0. 75Ga0. 25N/Al0. 6Ga0. 4N heterojunction field effect transistor with fT of 40 GHz." Applied Physics Express 12, no. 6 (2019): 066502
[4] Xia, Zhanbo et al. "Metal/BaTiO3/β-Ga2O3 dielectric heterojunction diode with 5.7 MV/cm breakdown field." Applied Physics Letters 115, no. 25 (2019).
[5] Kalarickal, Nidhin Kurian, et al "β-(Al 0.18 Ga 0.82) 2 O 3/Ga 2 O 3 double heterojunction transistor with average field of 5.5 MV/cm." IEEE Electron Device Letters 42, no. 6 (2021): 899-902.
[6] Dhara, Sushovan et al . "β-Ga2O3 trench Schottky diodes by low-damage Ga-atomic beam etching." Applied Physics Letters 123, no. 2 (2023).