Heterojunction bipolar transistor using a (Ga,In)P emitter on a GaAs base, grown by molecular beam epitaxy

We report the first N-p-n heterojunction bipolar transistor (HBT) using a (Ga,In)P/GaAs heterojunction emitter on a GaAs base. This combination is of interest as a potential alternate to (Al,Ga)As/GaAs, because of theoretical predictions of a larger valence band discontinuity and a smaller conduction band discontinuity, thus eliminating the need for grading of the emitter/base junction. The structure was grown by molecular beam epitaxy, with the base doping (∼10¹⁹cm^-3) far exceeding the n-type doping ∼5¹⁷cm^-3) of the (Ga,In)P wide gap emitter (Eg= 1.88 eV). Common-emitter current gains of 30 were attained at a current density of 3000 A/cm², the highest current density achieved without burnout.