Fabrication and Characterization of InP Heterojunction Bipolar Transistors with Emitter Edges Parallel to [001] and [010] Crystal Orientations

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Abstract
We present a study of fully-self aligned InP-based heterojunction bipolar transistors (HBTs) with the emitter edges oriented parallel to the [0,0,1] and [0,1,0] crystal orientations. A technology based on vertical and lateral wet etching of InP was developed to fabricate emitter-up and collector-up InP/InGaAs HBTs with reduced parasitic resistances and capacitances. For emitter-up HBTs, the undercut distance between the base contact and the emitter active area was f T=105 GHz and f MAX=82 GHz were obtained for a 4×12 µm2 emitter area. For collector-up metal HBTs (MHBTs), emitter widths as small as 0.5 µm were formed by lateral wet etching with a relative area fluctuation less than 10%, and high frequency performance of f T=40 GHz and f MAX=160 GHz were obtained for a 0.5×52 µm2 emitter area.