Improved InGaP/GaAs HBTs AC performance and linearity with collector design

An additional thin high-doping layer within the collector of InGaP/GaAs HBTs has been designed and fabricated to improve the Kirk effect threshold current, cutoff frequency, and power distortion, while keeping a high breakdown voltage. The proposed structure effectively relieves the Kirk effect and results in a higher current drive and cut-off frequency. From the extracted C/sub BC/ with V/sub CB/, HBTs with non-uniform collector doping demonstrate less base-collector capacitance variation than that in baseline HBTs, due to the depletion region limited by the thin, high-doping layer. The experimental results on third-order intermodulation demonstrate a significant improvement in OIP3 by as large as 6 dB. This proposed InGaP/GaAs HBT, with non-uniform collector doping, is well suited to replace current InGaP/GaAs HBTs for power amplifier applications, due to its significantly improved linearity and current/frequency capability, with negligible impact on DC characteristics and fabrication.