The demonstration of the first single-crystal Ga2O3 transistor by the Jpaanese National Institute of Information and Communications Technology (NICT) in 2011 started the development of transistors with a lateral geometry. However, lateral devices are not amenable to the high currents and high voltages required for many applications owing to large device areas and reliability issues arising from self-heating and surface instabilities.
Vertical devices carry higher current drives without having to enlarge the chip size, simplified thermal management, and far superior field termination. A group at NICT led by Masataka Higashiwaki has used silicon as an n-type dopant in Ga2O3 devices, but the community has long struggled to identify a suitable p-type dopant. Earlier this year, the same group published on the feasibility of nitrogen (N) as a p-type dopant. The latest work with the Tokyo University of Agriculture and Technology (TUAT) integrates Si and N doping using ion implantation for the first time to produce a Ga2O3 vertical MOSFET.
"Our success is a breakthrough development that promises a transformational impact on Ga2O3 power device technology," said Higashiwaki, Director of the Green ICT Device Advanced Development Center at NICT. "Ion implantation is a versatile fabrication technique widely adopted in the mass production of commercial semiconductor devices such as Si and silicon carbide (SiC) MOSFETs. The demonstration of an all-ion-implanted vertical Ga2O3 transistor greatly enhances the prospects for Ga2O3-based power electronics."
"We initially investigated magnesium for p-type doping, but this dopant failed to deliver its expected performance since it diffuses significantly at high process temperatures," said Man Hoi Wong, a researcher of the Green ICT Device Advanced Development Centre. "Nitrogen, on the other hand, is much more thermally stable, thereby creating unique opportunities for designing and engineering a variety of high-voltage Ga2O3 devices."