Proposal of buried metal heterojunction bipolar transistor and fabrication of HBT with buried tungsten

We propose a buried metal heterojunction bipolar transistor (BM-HBT), in which buried metal in the collector layer could reduce the total base-collector capacitance. To show the possibility of making a BM-HBT, we fabricated an InP-based HBT with buried tungsten mesh replacing the subcollector layer, where tungsten mesh works as a Schottky collector electrode. A flat heterostructure on the InP collector layer of the buried tungsten mesh was confirmed by a cross-sectional SEM view. A DC current gain of 12 was measured from the common-emitter collector I-V characteristics.