DC and RF performance of InAs-based bipolar transistors at very low bias

We fabricated metamorphic InAs bipolar junction transistors (BJTs) with a narrow bandgap in the base to reduce operating voltages, and we report RF results that we believe to be the first published for InAs-based bipolar transistors. InAs BJTs were grown by molecular beam epitaxy on InP substrates using strain-relief graded InAlAs buffer layers and optimized graded emitter-base and collector-base junctions. Large area devices (75×75 μm² emitter) exhibit DC current gain β of 85. Higher β exceeding 100 was observed from tunneling-emitter bipolar transistors with various InAlAs barrier designs, indicating lower holes injection from the base to the emitter. Small-area devices have been fabricated using the standard front-side process from our InP HBT line. Microwave properties measured from devices with emitter size of 1.5×10 μm² were very promising, showing a cutoff frequency over 50 GHz in devices with thick base and collector layers. An extremely low base-emitter voltage of 0.3 V was measured at peak frequency. These InAs-based bipolar transistors on InP substrates with good DC and RF performance demonstrate the viability of future narrow bandgap heterojunction bipolar transistors with state-of-the-art speed performance at low operating voltage.