Surface Leakage in GaN/InGaN Double Heterojunction Bipolar Transistors

We report a study on the surface-leakage current in GaN/InGaN double heterojunction bipolar transistors (DHBTs) that are grown on a sapphire substrate. Surface-leakage-current densities on an unpassivated DHBT are $\hbox{9.6} \times \hbox{10}^{-5}$– $\hbox{5.8} \times\break \hbox{10}^{-4}\ \hbox{A/cm}$ for $J_{C} = \hbox{0.5}{-}\hbox{50}\ \hbox{A}/\hbox{cm}^{2}$. A fabricated n-p-n GaN/InGaN DHBT shows the common–emitter dc current gain of 42, the collector-current density of 5.2 $\hbox{kA}/\hbox{cm}^{2}$, and the common–emitter breakdown voltage $(BV_{\rm CEO})$ of 75 V.