We report on the tradeoff between current gain β and the base sheet resistance RSH in metalorganic chemical vapor deposition-grown NpN InP∕GaAs1−xSbx∕InP double-heterojunction bipolar transistors (DHBTs) with heavy base carbon-doping levels resulting in hole concentrations NB ranging from 4×1019 to 12×1019∕cm3. In contrast to Ga0.47In0.53As and GaAs–based transistors, which both display gain variations proportional to 1∕(NB×WB)2 due to Auger recombination at high doping levels, neutral base recombination in InP∕GaAsSb∕InP DHBTs is not limited by Auger processes, and the measured current gain is proportional to 1∕(NB×WB). We show that GaAs1−xSbx base layers offer a growing lifetime advantage over Ga0.47In0.53As with increasing doping levels. Potential explanations for the observed suppression of Auger recombination in the InP–GaAsSb system are proposed.

Two-dimensional (2D) numerical simulations of self-aligned sub-micron InP/GaAsSb double heterojunction bipolar transistors (DHBTs) were performed to investigate the effects of base band gap narrowing and surface recombination. Base energy band gaps of 0.72 eV and 0.67 eV for GaAs 0.51 Sb 0.49 bases with doping levels of 5×1018 and 5×10 19 cm -3 were extracted from the comparison between the measurement data and simulation results. We took into account the surface Fermi level pinning and introduced a surface state model for the emitter side wall and extrinsic base surface. To the best of our knowledge, a good match between measured and simulated InP/GaAsSb DHBTs characteristics, from low to high current densities has not been achieved prior to the present work.

The overall microwave performance of heterostructure bipolar transistors (HBTs) depends on transistor feature sizes, and in particular on the collector to emitter area ratio. Whereas several properties associated with the InP/GaAsSb material system would suggest that NpN InP/GaAsSb/InP DHBTs should scale very well, initial results in aggressively scaled devices defined by electron beam lithography led to depressed maximum oscillation frequencies such that f MAX << f T . In the present work we report the first results achieved at SFU for devices patterned by electron beam lithography: our DHBTs are based on standard uniform layers (i.e. structures do not incorporate any performance-enhancing schemes such as compositional or impurity gradients) so as to establish performance benchmarks in the development of a new generation of epitaxial layers for aggressively scaled InP/GaAsSb DHBTs. We show that attractive performance levels are attainable in well-scaled devices based on nonetheless simple epitaxial structures.