You and the parent poster are probably thinking of heterojunction SiGe bipolar transistors. SiGe bipolar transistors are fabricated on top of old CMOS processe

You and the parent poster are probably thinking of heterojunction SiGe bipolar transistors. SiGe bipolar transistors are fabricated on top of old CMOS processes and are relatively cheap from a fixed-cost perspective but not highly integrated and only cost/power-efficient for niche PHY layer applications.