4.4 kV $β$-Ga$_2$O$_3$ Power MESFETs with Lateral Figure of Merit exceeding 100 MW/cm$^2$

Abstract: Field-plated (FP) depletion-mode MOVPE-grown $\beta$-Ga$2$O$_3$ lateral MESFETs are realized with superior reverse breakdown voltages and ON currents. A sandwiched SiN$_x$ dielectric field plate design was utilized that prevents etching-related damage in the active region and a deep mesa-etching was used to reduce reverse leakage. The device with L${GD}$ = 34.5 $\mu$m exhibits an ON current (I${DMAX}$) of 56 mA/mm, a high I${ON}$/I${OFF}$ ratio $>$ 10$^8$ and a very low reverse leakage until catastrophic breakdown at $\sim$ 4.4kV. The highest measurable V${BR}$ recorded was 4.57 kV (L${GD}$ = 44.5 $\mu$m). An LFOM of 132 MW/cm$^2$ was calculated for a V${BR}$ of $\sim$ 4.4 kV. The reported results are the first $>$ 4kV-class Ga$2$O$_3$ transistors to surpass the theoretical FOM of Silicon. These are also the highest I${DMAX}$ and lowest R${ON}$ values achieved simultaneously for any $\beta$-Ga$_2$O$_3$ device with V${BR}$ $>$ 4kV to date. This work highlights that high breakdown voltages (V$_{BR}$), high lateral figure of merit (LFOM) and high ON currents can be achieved simultaneously in $\beta$-Ga$_2$O$_3$ lateral transistors.