Breakdown-speed considerations in InP/InGaAs single- and double-heterostructure bipolar transistors

The breakdown and speed characteristics of InP/InGaAs single and double HBTs are presented. Temperature-dependent two- and three-terminal measurements suggest that avalanche impact ionization is the dominant breakdown mechanism in InGaAs collector HBTs. Monte Carlo techniques and 1D drift-diffusion modeling are used for speed and breakdown simulation, respectively. Special doping profiles are evaluated for improving the breakdown-speed characteristics of single HBTs (SHBTs) with conventional uniformly doped InGaAs collectors. Double HBTs (DHBTs) outperform all SHBTs in terms of speed-breakdown tradeoffs as long as they use graded base-collector junctions or they operate under sufficiently high collector-emitter voltage conditions. A cutoff frequency of 200 GHz was found to be feasible with graded DHBTs, and breakdown voltages up to 4.6 V were evaluated with a 3000-AA-thick collector. Nongraded DHBTs can be optimized to perform better in terms of speed-breakdown tradeoffs provided that a high collector doping is used.>