GaN/InGaN Heterojunction Bipolar Transistors With $f_{T} > \hbox{5}\ \hbox{GHz}$

We report GaN/InGaN n-p-n double-heterojunction bipolar transistors with the collector current density
$(J_{C}) > \hbox{16}\ \hbox{kA}/\hbox{cm}^{2}$
and the current gain
$(\beta) > \hbox{24}$
grown on a sapphire substrate. The cutoff frequency
$(f_{T})$
of greater than 5 GHz and the maximum oscillation frequency
$(f_{\max})$
of 1.3 GHz are also measured for a GaN/InGaN heterojunction bipolar transistor at
$J_{C} = \hbox{4.7}\ \hbox{kA}/\hbox{cm}^{2}$
.