BREAKDOWN SPEED CONSIDERATIONS IN INP/INGAAS SINGLE-HETEROSTRUCTURE AND DOUBLE-HETEROSTRUCTURE BIPOLAR-TRANSISTORS

The breakdown and speed characteristics of InP/InGaAs single and double HBT's are presented. Temperature-dependent two- and three-terminal measurements suggest that avalanche impact ionization is the dominant breakdown mechanism in InGaAs collector HBT's. 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 HBT's (SHBT's) with conventional uniformly doped InGaAs collectors. Double HBT's (DHBT's) outperform all SHBT's 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 DHBT's and breakdown voltages up to 4.6 V were evaluated with 3000-angstrom-thick collector. Nongraded DHBT's can be optimized to perform better in terms of speed-breakdown tradeoffs provided that a high collector doping is used.