Amorphous-Si emitter heterojunction UHF power transistors for handytransmitter

A UHF silicon heterojunction bipolar power transistor with a heavily doped amorphous-silicon emitter is reported. The fabrication process utilized an improved glow discharge technique. The deposition rate of amorphous silicon is 0.3-0.4 Å/s, which is slower than that of conventional a-Si:H. The average carrier density in the amorphous-silicon film is estimated to be about 1.5×10¹⁹ cm^-3. The present device can deliver 4.0-W output power with 72% collector efficiency and 8.2-dB gain at 470 MHz for 9.0-V low supply voltage. These preliminary results make the use of n⁺ a-Si:H as a wide-bandgap emitter material for high-frequency and high-power heterojunction bipolar transistors (HBTs) very attractive