InP double heterostructure bipolar transistors with a quaternary collector for improved breakdown behavior

The authors have fabricated double heterostructure bipolar transistors (HBTs) which use an InP wide band-gap emitter and a quaternary collector. The quaternary composition was chosen to be that which gives a 1.13 eV bandgap used in lasers which operate at 1.1 μm. This gap compares with the 1.35eV bandgap of the InP emitter and 0.75 eV for lattice-matched InGaAs. The composition for the quaternary was In: 0.87, Ga: 0.13, As: 0.29; P: 0.71. The collector was moved away from the base-collector junction to help improve the characteristics of the HBT. The devices exhibited good ideality factors with a gain of up to approximately 60 and breakdown voltages of about 8 V. Derived electron ionization coefficients are lower than literature values but depend strongly on the estimated fields in the collector