−400 mA mm<sup>−1</sup>Drain Current Density Normally-Off Polycrystalline Diamond MOSFETs
Xiaohua Zhu, Siwu Shao, Yu Hao Chang, Runming Zhang, Sylvia Yuk Yee Chung, Yu Fu, Te Bi, Yabo Huang, Kang An, Jinlong Liu, Chengming Li, Hiroshi Kawarada
Abstract
This letter reports a high drain current density and normally-off operation metal-oxide-semiconductor field-effect transistors (MOSFETs) with a gate insulator of 100 nm-Al<sub>2</sub>O<sub>3</sub>. A heavily boron-doped layer as the source/drain region was deposited on a (110) polycrystalline diamond substrate to achieve a low ohmic contact resistance. The MOSFETs demonstrate a maximum current density of −400 mA mm<inline-formula> <tex-math notation="LaTeX">$^{-{1}}$ </tex-math></inline-formula> normalized by gate width and a maximum current density of <inline-formula> <tex-math notation="LaTeX">$- 2000\,\,\mu \text{m}$ </tex-math></inline-formula> mA mm<sup>−1</sup> normalized by gate length and gate width, which are the highest values for normally-off diamond FETs. The Grain boundaries (GBs) and the nitrogen impurities (<inline-formula> <tex-math notation="LaTeX">$\sim {3}\,\,\times \,\,{10}^{{17}}$ </tex-math></inline-formula> cm<inline-formula> <tex-math notation="LaTeX">$^{-{3}}$ </tex-math></inline-formula>) as ionized donors in the channel region caused the threshold voltage (<inline-formula> <tex-math notation="LaTeX">${V}_{\text {th}}$ </tex-math></inline-formula>) to shift in the negative direction, exhibiting normally-off characteristics. This technique provides a promising method to achieve high-performance diamond devices, and help improve safety and save energy in switching systems.