InGaP-based HBTs for high-temperature and microwave power applications

The heterojunction bipolar transistors (HBTs) based on AlGaAs/GaAs are the most wildly investigated and have shown good RF performance. However, this structure has many well known disadvantages. An alternative to this structure is to use the aluminium-free InGaP/GaAs HBTs which are lattice matched to GaAs substrates. We have used DLTS measurements, on the emitter/base junction of InGaP/GaAs and AlGaAs/GaAs N-p-n HBTs, to compare the presence of as-grown defect levels by MOCVD in these two heterojunctions. It is shown that although the DX-centre, with an apparent activation energy of 0.42 eV, is present in the AlGaAs emitter region no electron trapping defect levels are observed in the InGaP emitter. In addition, the temperature dependencies of current gains are investigated for both AlGaAs/GaAs and InGaP/GaAs HBTs, fabricated with identical processing steps. Measured results show that base bulk recombination current plays an important role in maintaining the current gain at high temperature. Theoretical modelling of current gains with temperature on these two HBTs was also presented which explains well the experimental data