0.25-µm-Emitter InP Heterojunction Bipolar Transistors with a Thin Ledge Structure

Abstract

This paper describes 0.25-µm-emitter InP heterojunction bipolar transistors (HBTs) with a thin ledge structure. The HBTs consist of a degenerately-doped n+-InGaAs/15-nm-thick undoped InP emitter, a 25-nm-thick p+-In0.53Ga0.47As base, and a 75-nm-thick In0.53Ga0.47As collector. The emitter enables fabrication of a 15-nm-thick ledge structure simply by wet etching the n+-InGaAs emitter. The emitter mesa and base metal were scaled down to 0.25 and 0.3 µm, respectively. The fabricated HBT with a 0.25-µm emitter provides a current gain of 62 at a collector current density, Jc, of 10 mA/µm2. With the thin ledge structure, the current gain is virtually independent of emitter size and emitter–base spacing. The HBT also exhibits an ft of 442 GHz and an fmax of 214 GHz at a Jc of 12 mA/µm2. The results of bias-temperature stress tests show that base and collector currents are stable up to 1042 h at a Jc of 5 mA/µm2.