Sub-300 nm InGaAs/InP Type-I DHBTs with a 150 nm collector, 30 nm base demonstrating 755 GHz fmax and 416 GHz fT
We report InP/InGaAs/InP double heterojunction bipolar transistors (DHBT) fabricated using a simple mesa structure. The devices employ a 30 nm highly doped InGaAs base and a 150 nm InP collector containing an InGaAs/InAlAs superlattice grade. These devices exhibit a maximum f<sub>max</sub> = 755 GHz with a 416 GHz /f<sub>T</sub>. This is the highest f<sub>max</sub> reported for a mesa HBT. Through the use of i-line lithography, the emitter junctions have been scaled from 500-600 nm down to 250-300 nm -all while maintaining similar collector to emitter area ratios. Because of the subsequent reduction to the base spreading resistance underneath the emitter R<sub>b,spread</sub> and increased radial heat flow from the narrower junction, significant increases to f<sub>max</sub> and reductions in device thermal resistance θ<sub>JA</sub> are expected and observed. The HBT current gain β ≈ 24-35, BV<sub>ceo</sub> = 4.60 V, BV<sub>cbo</sub> = 5.34 V, and the devices operate up to 20 mW / μm<sup>2</sup> before self-heating is observed to affect the DC characteristics.