High performance 110 nm InGaAs/InP DHBTs in dry-etched in-situ refractory emitter contact technology

We report a 110 nm InP/In0.53Ga0.47As/InP double heterojunction bipolar transistor (DHBT) demonstrating a simultaneous ft/fmax of 465/660 GHz and operating at power densities in excess of 50 mW/µm². To our knowledge this is the smallest junction width reported for a III–V DHBT. The narrow 110 nm emitter junction permits the devices to be biased simultaneously at high voltages and high current densities (Je) with peak RF performance at 41 mW/µm² (Je = 23.6 mA/µm², Vce = 1.75 V). Devices incorporate low contact resistance, refractory, in-situ Mo emitter contact to a highly doped, regrown InGaAs cap. A low stress, sputter deposited, refractory, dry-etched W/Ti0.1W0.9 emitter metal process was developed demonstrating both high emitter yield and scalability to sub-100 nm junctions. Previously reported dry etch processes involving Ti/Ti0.1W0.9 metals could not be scaled below 180 nm junction widths due to high metal stress resulting in very low emitter yield [1, 2]. The emitter metal contacts reported here are 100 nm wide and the emitter-base junction width is 110 nm. On-wafer Through-Reflect-Line (TRL) calibration structures were used to measure the RF performance of devices from 140 – 180 GHz.