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

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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, $J_{\text{c}}$, 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 $ f_{\text{t}}$ of 442 GHz and an $ f_{\text{max}}$ of 214 GHz at a $J_{\text{c}}$ 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 $J_{\text{c}}$ of 5 mA/μm2.
2010-04-25