Bandgap and transport properties of Si1-xGex by analysis of nearly ideal Si/Si1-xGex/Si heterojunction bipolar transistors

Si/Si_1-xGe_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_1-xGe_x. The band discontinuities between Si and strained Si_1-xGe_x were found by measuring the collector and base currents as a function of temperature. The electron diffusion coefficient in p-type Si _1-xGe_x was extracted by measuring the change in collector current with Si_1-xGe_x base width. The electron diffusion coefficient perpendicular to the heterointerface in the strained Si_1-xGe_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