Bandgap and transport properties of Si/sub 1-x/Ge/sub x/ by analysis of nearly ideal Si/Si/sub 1-x/Ge/sub x//Si heterojunction bipolar transistors

Abstract

Si/Si/sub 1-x/Ge/sub x//Si N-p-N heterojunction bipolar transistors (HBTs) produced by a chemical vapor deposition technique, limited-reaction processing, were analyzed using electrical measurements to determine properties of strained Si/sub 1-x/Ge/sub x/. The band discontinuities between Si and strained Si/sub 1-x/Ge/sub x/ were found by measuring the collector and base currents as a function of temperature. The electron diffusion coefficient in p-type Si/sub 1-x/Ge/sub x/ was extracted by measuring the change in collector current with Si/sub 1-x/Ge/sub x/ base width. The electron diffusion coefficient perpendicular to the heterointerface in the strained Si/sub 1-x/Ge/sub x/ layers studied here is smaller than that in Si doped to the same level. The reverse leakage currents at the base-emitter junction of the HBTs are smaller than the leakage at the collector-base junction, but in Si control transistors the situation is reversed. The high leakage currents at the collector-base junction in the HBTs are believed to result from the preferred accumulation of misfit dislocations at the strained interface closest to the substrate.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>