InGaP/GaAs Sub-Square-Micron Emitter HBT with fmax > 100 GHz

Abstract

InGaP/GaAs heterojunction bipolar transistors (HBTs) with a sub-square-micron emitter have been fabricated using a novel self-aligned emitter etching process with low damage and good lateral and vertical controllability. HBTs with an emitter size of 0.4×1.7 µ m fabricated using this process exhibited a current gain of 44 which is comparable to that of AlGaAs/GaAs HBTs. Furthermore, the HBTs exhibited excellent microwave performance. For an HBT with an emitter size of 0.4×2.2 µ m, a cutoff frequency (f T) of 55 GHz and a maximum oscillation frequency (f max) of 100 GHz were reached at a collector current (I C) as low as 1.0 mA, and a peak f T of 62 GHz and a peak f max of 105 GHz were obtained at I C=2.3 mA. As far as we know, this f max is the highest reported for GaAs-based HBTs with an emitter area of less than 1 µ m2. This process is thus promising for fabrication of high-speed HBT ICs with low power consumption.