Enhancing ON- and OFF-State Performance of Quasi-Vertical GaN Trench MOSFETs on Sapphire With Reduced Interface Charges and a Thick Bottom Dielectric
Renqiang Zhu, Huaxing Jiang, Chak Wah Tang, Kei May Lau
Abstract
In this letter, we report the enhancement of ON- and OFF-state performance in vertical GaN trench MOSFETs through fabrication process optimization. The ON-state device performance was effectively improved by reducing MOS channel interface charges with a piranha cleaning process prior to the gate dielectric deposition. For the OFF-state, the breakdown voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text{BR}}$ </tex-math></inline-formula> ) of the device was greatly enhanced via suppressing the electric field in the gate dielectric near the bottom of the gate trench with a thick bottom dielectric process. As a result, high-performance quasi-vertical GaN trench MOSFETs grown on sapphire substrates with a 4- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> -thick drift layer are demonstrated, exhibiting a low specific ON-resistance of 0.95 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}\Omega \cdot \text{cm}^{2}$ </tex-math></inline-formula> , a high maximum drain current of 3.4 kA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , a large threshold voltage of 6.1 V (defined at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}_{\text{D}}$ </tex-math></inline-formula> of 1 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ), and a high <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text{BR}}$ </tex-math></inline-formula> of 485 V.