ABSTRACT
Very high dc current gain in InGaP/GaAs heterojunction bipolar transistors (HBTs) was demonstrated. The dc current gain/base sheet resistance ratio (4E19 cm-3 @700 Å) in large area devices (L = 5625 μm2) was 0.6. A comparison of low and high gain HBT devices clearly showed an enhancement in the effective minority carrier lifetime of the base layer. Small area devices (L = 4 μm2) exhibited a current gain of 132 at 60 kA/cm2. The base current at low current densities was low indicating low space charge recombination which is one of the key characteristics of InGaP/GaAs HBTs. Selected devices were tested for extended reliability under high junction temperatures of up to 363°C and at a high current density (60 kA/cm2). The MTTF (mean time to failure) was extrapolated to 5 × 105 hours at 150°C junction temperature (Ea = 0.68 eV). These results are attributed to the superior material parameters of InGaP in the HBT (high valence band offset (△Ev >0.30 eV), low surface recombination, high energy gap, and long minority carrier lifetime).
