Novel HBT structure for high f/sub t/ at low current density

Abstract

Through modifications of the epitaxial structure of a GaAs/AlGaAs HBT, the junction capacitance (C/sub be/) and recombination rate in the base-emitter junction region have been substantially reduced. The modified structure leads to both higher f/sub t/ and higher /spl beta/ at low current densities (10/sup 2spl les/J/sub cspl les/10/sup 4/ A/cm/sup 2/). The modifications include a lightly doped emitter (LDE) and a strategically placed /spl delta/-doping layer. Device simulations were used to optimize the LDE length and location of the /spl delta/-doping. The experimental results of a fabricated device with a 1370 /spl Aring/ LDE+/spl delta/-doping yielded a 3.3x reduction in C/sub be/, a 2.7x increase in f/sub t/, and a 2x increase in /spl beta/ over the baseline device at low J/sub c/ (J/sub cspl les/10/sup 3/ A/cm/sup 2/).<>