Wide bandgap collectors in GaInP/GaAs heterojunction bipolar transistors with increased breakdown voltage

Al0.11Ga0.89As in the base, adjacent to the collector has been used to eliminate the conduction band spike and demonstrate double HBTs with high breakdown voltages, BVCEO and BVBCO, of 44V (current gain of 20) and 54V respectively with a 1 mu m thick GaInP collector doped to 2x10(16)cm(-3) without any voltage dependence on the gain. The inferred electron lifetime in the AlGaAs base was found to be approximately ten times smaller than the equivalently doped GaAs. Analysis of the Kirk effect yielded an estimate of the effective velocity in the GaInP collector of 4.3x10(6)cms(-1) at room temperature. A graded AlGaAs base and graded transition from GaInP at the base/collector junction to AlInP demonstrated a record breakdown voltage, BVBCO=74V, for the same collector doping and thickness. Electron impact ionisation coefficients were measured for use in an Ebers-Moll model to predict breakdown voltage.