Abstract
ON-state conductance properties of vertical GaN <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> -channel trench MISFETs manufactured on different GaN substrates and having different gate trench orientations are studied up to 200 °C ambient temperature. The best performing devices, with a maximum output current above 4 kA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and an area specific ON-state resistance of 1.1 mΩ·cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , are manufactured on ammonothermal GaN substrate with the gate channel parallel to the a-plane of the GaN crystal. The scalability of the devices up to 40 mm gate periphery is investigated and demonstrated. It is found that, in addition to oxide interface traps, the semiconductor border traps in the p-GaN layer limit the available mobile channel electrons and that the channel surface roughness scattering limits the channel mobility. Both strongly depend on the gate trench orientation and on the GaN substrate defect density.
Highlights
Vertical GaN-based MISFETs for high voltage power switching applications have the potential to outperform Si and SiC based competitors in terms of power density and switching speed [1], [2], [3], [4], [5]
Unlike Si- or SiC- based MOSFETs, GaN does not have a native oxide that can serve as gate insulator
A large conductance difference is observed between the two hydride vapor phase epitaxy (HVPE) substrates as well
Summary
Vertical GaN-based MISFETs for high voltage power switching applications have the potential to outperform Si and SiC based competitors in terms of power density and switching speed [1], [2], [3], [4], [5]. Several prominent concepts for vertical GaN transistors are considered worldwide: Current Aperture Vertical Electron Transistors (CAVETs) [4], regrown semi-polar channel and p-type gate structure [2], vertical junction field-effect transistor (VJFET) [5], trench gate MISFET [1] and vertical FinFETs [7], [9]. The GaN-based Trench-MISFET owns the advantage of one epitaxial growth step, intrinsic normally-off nature and low gate currents. A foreign insulating layer must be deposited between the gate metal and the channel for field effect modulation. A gate oxide deposited on such “etch-damaged” surfaces can lead to distortion of the space charge region preventing channel inversion
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