AlGaN/GaN Heterojunction Bipolar Transistors With High Current Gain and Low Specific <sc>on</sc>-Resistance

N-p-n AlGaN/GaN heterojunction bipolar transistors (HBTs) on sapphire substrates with high current gain <inline-formula> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula> of 129, low specific ON-resistance (<inline-formula> <tex-math notation="LaTeX">${R}_{ \mathrm{\scriptscriptstyle ON},\text {sp}}{)}$ </tex-math></inline-formula> of 0.28 <inline-formula> <tex-math notation="LaTeX">$\text{m}\sf \Omega \cdot $ </tex-math></inline-formula>cm2 and high current density <inline-formula> <tex-math notation="LaTeX">${J}_{C}$ </tex-math></inline-formula> of ~15 kA/cm2 (if normalized to emitter area, <inline-formula> <tex-math notation="LaTeX">${R}_{ \mathrm{\scriptscriptstyle ON},\text {sp}} \sim 0.15 \text{m}\sf \Omega \cdot \text{m}^{{2}}$ </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">${J}_{C} \sim 28.4$ </tex-math></inline-formula> kA/cm2) have been demonstrated. The analysis of component of <inline-formula> <tex-math notation="LaTeX">${R}_{ \mathrm{\scriptscriptstyle ON},\text {sp}}$ </tex-math></inline-formula> yields the collector resistance is ~5.2% of the total <inline-formula> <tex-math notation="LaTeX">${R}_{ \mathrm{\scriptscriptstyle ON},\text {sp}}$ </tex-math></inline-formula>, showing the low ON-resistance advantage of GaN HBTs. The open-base avalanche breakdown voltage (BVCEO) is ~160 V. High-temperature performance of GaN HBT is also evaluated. The <inline-formula> <tex-math notation="LaTeX">${R}_{ \mathrm{\scriptscriptstyle ON},\text {sp}}$ </tex-math></inline-formula> is reduced as temperature increasing in the range of 25 °C–100 °C due to enhanced hole concentration in the base layer. The cutoff frequency (<inline-formula> <tex-math notation="LaTeX">${f}_{T}{)}$ </tex-math></inline-formula> of greater than 4 GHz is determined at <inline-formula> <tex-math notation="LaTeX">${V}_{\text {CE}} =$ </tex-math></inline-formula> 9 V. These results dominate that GaN HBTs have been anticipated to become a new technology for next-generation power switches and RF power amplifier circuit.