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

Al_0.11Ga_0.89As in the base, adjacent to the collector has been used to eliminate the conduction band spike and demonstrate double HBTs with high breakdown voltages, BV_CEO and BV_BCO, of 44 V (current gain of 20) and 54 V respectively with a 1 μm thick GaInP collector doped to 2×10¹⁶cm ^-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 4.3×10⁶ 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, BV_BCO=74 V, for the same collector doping and thickness. Electron impact ionisation coefficients were measured for use in an Ebers-Moll model to predict breakdown voltage