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 $J_{C} = \hbox{4.7}\ \hbox{kA}/\hbox{cm}^{2}$.