Electron lifetime of heavily C-doped InGaAs and GaAsSb as a function of doping density

The In_0.53Ga_0.47As and GaAs_0.51Sb_0.49 alloys, both lattice-matched on InP, are competing materials for the heavily p-type doped base layer in high-speed heterojunction bipolar transistors (HBT). If the growth of the InGaAs alloy is certainly more mature, the InP/GaAsSb staggered band line-up presents a potential advantage over the InP/InGaAs one for the base/collector junction. Heavy doping of the base is required to keep the base resistance as low as possible with very thin bases, carbon being the preferred dopant to get an abrupt doping profile. Activated carbon densities exceeding 10²⁰ cm^-3 have been demonstrated for InGaAs as well as for GaAsSb grown by molecular beam epitaxy. It has been shown that the heavy p-type doping of InGaAs:Be results in an Auger-dominated electron lifetime: it is inversely proportional to the square of the hole density, which in turn should reduce the current gain of the InGaAs HBT. This should apply for InGaAs:C as well. On the contrary, it has recently been claimed from indirect measurements that the Auger effect was suppressed in p+ GaAsSb:C, resulting in an electron lifetime inversely proportional to the hole density. It is the purpose of this study to describe direct electron lifetime measurements on the GalnAs and GaAsSb alloys, both heavily carbon-doped in the range 10¹⁹-10²⁰ cm^-3.