Development of GaN Vertical Trench-MOSFET With MBE Regrown Channel

GaN vertical trench-MOSFETs incorporating molecular beam epitaxy (MBE) regrown channel are developed and investigated. The channel regrowth by MBE prevents repassivation of the p-type GaN body while promising higher channel mobility. Two different designs of the lateral portion of the regrown channel are compared: without or with an n<sup>+</sup>-GaN buried layer. Without an n<sup>+</sup> buried layer, a respectable 600-V breakdown voltage (BV) is measured in the absence of edge termination, indicating a decent critical field strength (>1.6 MV/cm) of the regrown channel. However, the ON-resistance is limited by the highly resistive lateral channel due to Mg incorporation. With an n<sup>+</sup> buried layer, the limitation is removed. Excellent ON-current of 130 mA/mm and ON-resistivity of <inline-formula> <tex-math notation="LaTeX">$6.4 ~\rm {m\Omega \cdot cm^{2}}$ </tex-math></inline-formula> are demonstrated. The BV is limited by high source–drain leakage current from the channel due to drain-induced barrier lowering (DIBL) effect. Device analysis together with TCAD simulations points out the major cause for the DIBL effect: the presence of interface charge beyond a critical value (<inline-formula> <tex-math notation="LaTeX">$\sim 6\times 10^{12}\,\,\rm {cm^{-2}}$ </tex-math></inline-formula>) at the regrowth interface on etched sidewalls. This paper provides valuable insights into the design of GaN vertical trench-MOSFET with a regrown channel, where simultaneous achievement of low ON-resistivity and high BV is expected in devices with reduced interface charge density and improved channel design to eliminate DIBL.

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