The unique material properties of Gallium Oxide make it promising for a range of future applications, but innovative materials and device engineering are needed to translate these ultimate material limits to real technology. This presentation will discuss our recent work on epitaxy, heterostructure design, and electrostatics to achieve high-performance β-Ga2O3 lateral and vertical electronic devices. We will discuss some advances in materials growth and device design for lateral structures which enabled key transistor demonstrations including the first β-(Al,Ga)2O3/β-Ga2O3 modulation-doped structures with excellent transport properties, double-heterostructure modulation-doped structures, scaled delta-doped transistors with cutoff frequency of 27 GHz, and self-aligned lateral field effect transistors with > 900 mA/mm current density. We will discuss the use of a new damage-free epitaxial etching technique using Ga atomic flux that enables highly precise fabrication of 3-dimensional structures. We will also show some applications of atomic Ga-flux etching to realize excellent field termination in vertical diodes, and lateral FINFETs with enhanced performance. Finally, we will discuss promising results using high-permittivity dielectrics integrated with semiconductors that have enabled lateral transistors with > 5.5 MV/cm breakdown field, the highest for a field effect transistor in any material system. We acknowledge funding from DOE/NNSA under Award Number(s) DE-NA000392, AFOSR GAME MURI (Award No. FA9550-18-1-0479, project manager Dr. Ali Sayir), and NSF ECCS-1809682.
Ultra-wide bandgap (~ 4.8 eV) beta phase gallium oxide (β-Ga2O3) grown by metal organic chemical vapor deposition (MOCVD) has demonstrated promising electronic transport properties with room temperature electron mobilities reaching 194 cm2/V-s and background doping as low as 9×1014 cm-3 [Zeng et al, Appl. Phys. Lett. 114, 250601 (2019)]. Commensurate with these values is a total trap concentration that is ~10x lower, with a different distribution of states throughout the bandgap than what has been observed for β-Ga2O3 grown by other methods [Zhang et al., Appl. Phys. Lett. 108, 052105 (2016), Farzana et al, Appl. Phys. Lett. 123, 161410 (2018)]. Given the promise of MOCVD-grown β-Ga2O3, a deeper understanding of the nature of defects in this material is of interest. This work provides a comprehensive picture of the current state of knowledge regarding deep levels in MOCVD-grown β-Ga2O3, including trapping properties, energy and concentration distributions in the bandgap, potential physical sources, and comparisons with other growth methods. By applying a suite of complementary defect spectroscopy methods-deep level optical spectroscopy, deep level transient spectroscopy, and admittance spectroscopy, quantitative characterization of defect states within the ~ 4.8 eV bandgap is possible. We find that, through systematically varying growth conditions, differing trends in concentrations for individual states are observed, implying that growth optimization is possible. Combined with observations made after high energy particle irradiation, we can differentiate between states of intrinsic and extrinsic origin.
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