Kelson D. Chabak

Bio: Kelson D. Chabak is an academic researcher from Air Force Research Laboratory. The author has contributed to research in topics: Gallium nitride & High-electron-mobility transistor. The author has an hindex of 24, co-authored 72 publications receiving 2489 citations. Previous affiliations of Kelson D. Chabak include United States Department of Defense & University of Illinois at Urbana–Champaign.

3.8-MV/cm Breakdown Strength of MOVPE-Grown Sn-Doped $\beta $ -Ga 2 O 3 MOSFETs

Abstract: A Sn-doped (100) $\beta $ -Ga2O3 epitaxial layer was grown via metal–organic vapor phase epitaxy onto a single-crystal, Mg-doped semi-insulating (100) $\beta $ -Ga2O3 substrate. Ga2O3-based metal–oxide–semiconductor field-effect transistors with a 2- $\mu \text{m}$ gate length ( $L_{G})$ , 3.4- $\mu \text{m}$ source–drain spacing ( $L_{\textrm {SD}})$ , and 0.6- $\mu \text{m}$ gate–drain spacing ( $L_{\textrm {GD}})$ were fabricated and characterized. Devices were observed to hold a gate-to-drain voltage of 230 V in the OFF-state. The gate-to-drain electric field corresponds to 3.8 MV/cm, which is the highest reported for any transistor and surpassing bulk GaN and SiC theoretical limits. Further performance projections are made based on layout, process, and material optimizations to be considered in future iterations.

Enhancement-mode Ga2O3 wrap-gate fin field-effect transistors on native (100) β-Ga2O3 substrate with high breakdown voltage

Abstract: Sn-doped gallium oxide (Ga2O3) wrap-gate fin-array field-effect transistors (finFETs) were formed by top-down BCl3 plasma etching on a native semi-insulating Mg-doped (100) β-Ga2O3 substrate. The fin channels have a triangular cross-section and are approximately 300 nm wide and 200 nm tall. FinFETs, with 20 nm Al2O3 gate dielectric and ∼2 μm wrap-gate, demonstrate normally-off operation with a threshold voltage between 0 and +1 V during high-voltage operation. The ION/IOFF ratio is greater than 105 and is mainly limited by high on-resistance that can be significantly improved. At VG = 0, a finFET with 21 μm gate-drain spacing achieved a three-terminal breakdown voltage exceeding 600 V without a field-plate.

Demonstration of high mobility and quantum transport in modulation-doped β-(AlxGa1-x)2O3/Ga2O3 heterostructures

Abstract: In this work, we demonstrate a high mobility two-dimensional electron gas (2DEG) formed at the β-(AlxGa1-x)2O3/Ga2O3 interface through modulation doping. Shubnikov-de Haas (SdH) oscillations were observed in the modulation-doped β-(AlxGa1-x)2O3/Ga2O3 structure, indicating a high-quality electron channel formed at the heterojunction interface. The formation of the 2DEG channel was further confirmed by the weak temperature dependence of the carrier density, and the peak low temperature mobility was found to be 2790 cm2/Vs, which is significantly higher than that achieved in bulk-doped Beta-phase Gallium Oxide (β-Ga2O3). The observed SdH oscillations allowed for the extraction of the electron effective mass in the (010) plane to be 0.313 ± 0.015 m0 and the quantum scattering time to be 0.33 ps at 3.5 K. The demonstrated modulation-doped β-(AlxGa1-x)2O3/Ga2O3 structure lays the foundation for future exploration of quantum physical phenomena and semiconductor device technologies based on the β-Ga2O3 material system.

$\beta$ -Ga2O3 MOSFETs for Radio Frequency Operation

Abstract: We demonstrate a $\beta $ -Ga2O3 MOSFET with record-high transconductance ( ${g}_{m}$ ) of 21 mS/mm and extrinsic cutoff frequency ( ${f}_{T}$ ) and maximum oscillating frequency ( ${f}_{\max }$ ) of 3.3 and 12.9 GHz, respectively, enabled by implementing a new highly doped ohmic cap layer with a sub-micron gate recess process. RF performance was further verified by CW Class-A power measurements with passive source and load tuning at 800 MHz, resulting in ${P}_{{OUT}}$ , power gain, and power-added efficiency of 0.23 W/mm, 5.1 dB, and 6.3%, respectively. These preliminary results indicate potential for monolithic or heterogeneous integration of power switch and RF devices using $\beta $ -Ga2O3.

Donors and deep acceptors in β-Ga2O3

Abstract: We have studied the properties of Si, Ge shallow donors and Fe, Mg deep acceptors in β-Ga2O3 through temperature dependent van der Pauw and Hall effect measurements of samples grown by a variety of methods, including edge-defined film-fed, Czochralski, molecular beam epitaxy, and low pressure chemical vapor deposition. Through simultaneous, self-consistent fitting of the temperature dependent carrier density and mobility, we are able to accurately estimate the donor energy of Si and Ge to be 30 meV in β-Ga2O3. Additionally, we show that our measured Hall effect data are consistent with Si and Ge acting as typical shallow donors, rather than shallow DX centers. The high temperature Hall effect measurement of Fe doped β-Ga2O3 indicates that the material remains weakly n-type even with the Fe doping, with an acceptor energy of 860 meV relative to the conduction band for the Fe deep acceptor. Van der Pauw measurements of Mg doped Ga2O3 indicate an activation energy of 1.1 eV, as determined from the temperature dependent conductivity.

A review of Ga2O3 materials, processing, and devices

Abstract: Gallium oxide (Ga2O3) is emerging as a viable candidate for certain classes of power electronics, solar blind UV photodetectors, solar cells, and sensors with capabilities beyond existing technologies due to its large bandgap. It is usually reported that there are five different polymorphs of Ga2O3, namely, the monoclinic (β-Ga2O3), rhombohedral (α), defective spinel (γ), cubic (δ), or orthorhombic (e) structures. Of these, the β-polymorph is the stable form under normal conditions and has been the most widely studied and utilized. Since melt growth techniques can be used to grow bulk crystals of β-GaO3, the cost of producing larger area, uniform substrates is potentially lower compared to the vapor growth techniques used to manufacture bulk crystals of GaN and SiC. The performance of technologically important high voltage rectifiers and enhancement-mode Metal-Oxide Field Effect Transistors benefit from the larger critical electric field of β-Ga2O3 relative to either SiC or GaN. However, the absence of clear demonstrations of p-type doping in Ga2O3, which may be a fundamental issue resulting from the band structure, makes it very difficult to simultaneously achieve low turn-on voltages and ultra-high breakdown. The purpose of this review is to summarize recent advances in the growth, processing, and device performance of the most widely studied polymorph, β-Ga2O3. The role of defects and impurities on the transport and optical properties of bulk, epitaxial, and nanostructures material, the difficulty in p-type doping, and the development of processing techniques like etching, contact formation, dielectrics for gate formation, and passivation are discussed. Areas where continued development is needed to fully exploit the properties of Ga2O3 are identified.

Ultrawide-Bandgap Semiconductors: Research Opportunities and Challenges

Abstract: J. Y. Tsao,* S. Chowdhury, M. A. Hollis,* D. Jena, N. M. Johnson, K. A. Jones, R. J. Kaplar,* S. Rajan, C. G. Van de Walle, E. Bellotti, C. L. Chua, R. Collazo, M. E. Coltrin, J. A. Cooper, K. R. Evans, S. Graham, T. A. Grotjohn, E. R. Heller, M. Higashiwaki, M. S. Islam, P. W. Juodawlkis, M. A. Khan, A. D. Koehler, J. H. Leach, U. K. Mishra, R. J. Nemanich, R. C. N. Pilawa-Podgurski, J. B. Shealy, Z. Sitar, M. J. Tadjer, A. F. Witulski, M. Wraback, and J. A. Simmons

1-kV vertical Ga2O3 field-plated Schottky barrier diodes

Abstract: Ga2O3 field-plated Schottky barrier diodes (FP-SBDs) were fabricated on a Si-doped n−-Ga2O3 drift layer grown by halide vapor phase epitaxy on a Sn-doped n+-Ga2O3 (001) substrate. The specific on-resistance of the Ga2O3 FP-SBD was estimated to be 5.1 mΩ·cm2. Successful field-plate engineering resulted in a high breakdown voltage of 1076 V. A larger-than-expected effective barrier height of 1.46 eV, which was extracted from the temperature-dependent current–voltage characteristics, could be caused by the effect of fluorine atoms delivered in a hydrofluoric acid solution process.

Perspective: Ga2O3 for ultra-high power rectifiers and MOSFETS

Abstract: Gallium oxide (Ga2O3) is emerging as a viable candidate for certain classes of power electronics with capabilities beyond existing technologies due to its large bandgap, controllable doping, and the availability of large diameter, relatively inexpensive substrates. These applications include power conditioning systems, including pulsed power for avionics and electric ships, solid-state drivers for heavy electric motors, and advanced power management and control electronics. Wide bandgap (WBG) power devices offer potential savings in both energy and cost. However, converters powered by WBG devices require innovation at all levels, entailing changes to system design, circuit architecture, qualification metrics, and even market models. The performance of high voltage rectifiers and enhancement-mode metal-oxide field effect transistors benefits from the larger critical electric field of β-Ga2O3 relative to either SiC or GaN. Reverse breakdown voltages of over 2 kV for β-Ga2O3 have been reported, either with or without edge termination and over 3 kV for a lateral field-plated Ga2O3 Schottky diode on sapphire. The metal-oxide-semiconductor field-effect transistors fabricated on Ga2O3 to date have predominantly been depletion (d-mode) devices, with a few demonstrations of enhancement (e-mode) operation. While these results are promising, what are the limitations of this technology and what needs to occur for it to play a role alongside the more mature SiC and GaN power device technologies? The low thermal conductivity might be mitigated by transferring devices to another substrate or thinning down the substrate and using a heatsink as well as top-side heat extraction. We give a perspective on the materials’ properties and physics of transport, thermal conduction, doping capabilities, and device design that summarizes the current limitations and future areas of development. A key requirement is continued interest from military electronics development agencies. The history of the power electronics device field has shown that new technologies appear roughly every 10-12 years, with a cycle of performance evolution and optimization. The older technologies, however, survive long into the marketplace, for various reasons. Ga2O3 may supplement SiC and GaN, but is not expected to replace them.