Nitrogen incorporation in GaInP for novel heterojunction bipolar transistors

Abstract

Novel device structures using GaInNP in a thin layer at the base-collector (BC) junction of a heterojunction bipolar transistor (HBT) are described. The proposed devices, blocked hole bipolar transistors (BHBTs) combine the benefits of single and double heterojunction bipolar transistors (DHBTs). In DHBTs there is typically a barrier to electrons at the BC junction. In the BHBT the barrier is eliminated by the incorporation of nitrogen into GaInP. In the new structures the majority of the collector remains GaAs, which yields a device with a higher cutoff frequency than achievable with GaInP collectors. Since the reduction in bandgap energy is primarily in the conduction band from the incorporation of nitrogen, there will remain a substantial valence band discontinuity. This will yield reduced saturation charge storage. The offset voltage will also be reduced by the greater symmetry of the base-emitter (BE) and BC junctions. Additionally, the eliminated barrier at the BC junction will yield devices with a reduced knee voltage. These attributes make the proposed devices very well suited for microwave power amplifiers.