New self-aligned InP/InGaAs HBTs with InGaAs dummy emitter for crystallographically defined emitter contact

A new self-alignment technology for InP/InGaAs heterojunction bipolar transistor (HBT) has been investigated based on crystallographically defined emitter contact (CDC) technology using anisotropic wet etching characteristics of an InGaAs layer. In the CDC technology, the InGaAs dummy emitter layer, which is used to obtain the crystallographically etched sidewalls, is incorporated into between the InGaAs/InP transfer layers and the InP emitter layer. The CDC technology provides a damage-free self-alignment, while producing precisely controlled undercut profiles. A self-aligned emitter-to-base contact spacing can be optimized by adjusting the InGaAs dummy emitter layer´s thickness. The fabricated HBTs exhibited excellent high-frequency performances with f_T of 88 GHz and f_max of 312 GHz, respectively, demonstrating that the new CDC technology is very effective in fabricating high-speed InP/InGaAs HBT.