Normally Off GaN Power MOSFET Grown on Sapphire Substrate With Highly Resistive Undoped Buffer Layer

A high-performance normally off GaN-based MOSFET was fabricated. The buffer layer of the MOSFET was grown by varying the growth temperature to control the size of nucleation sites which results in an extremely high buffer resistance
$(> \hbox{10}^{12}\ \Omega/\hbox{sq})$
. The fabricated small-area MOSFET exhibited excellent normally off device characteristics, such as a threshold voltage of 2 V, maximum drain current of 253 mA/mm, on–off current ratio of
$ \hbox{5.5} \times \hbox{10}^{7}$
, destructive breakdown voltage of 830 V, and leakage current of 0.7
$\mu\hbox{A/mm}$
at a
$V_{\rm DS}$
of 600 V. The corresponding values of the large-area MOSFET with a multifinger pattern were 0.6 V, 6 A,
$\hbox{1.3} \times \hbox{10}^{7}$
, 670 V, and 50
$\mu\hbox{A}$
(0.28
$\mu \hbox{A/mm}$
).