Si/Si/sub 1-x/Ge/sub x/ heterojunction bipolar transistors produced by limited reaction processing

Si/Si/sub 1-x/Ge/sub x/ heterojunction transistors (HBTs) fabricated by a chemical vapor deposition (CVD) technique are reported. A rapid thermal CVD limited-reaction processing (LRP) technique was used for the in situ growth of all three device layers, including a 20-mm Si/sub 1-x/Ge/sub x/ layer in the base. The highest current gains observed ( beta =400) were for a Si/Si/sub 1-x/Ge/sub x/ HBT with a base doping of 7*10/sup 18/ cm/sup -3/ near the junction and a shallow arsenic implant to form ohmic contacts and increase current gain. Ideal base currents were observed for over six decades of current and the collector current remained ideal for nearly nine current decades starting at 1 pA. The bandgap difference between a p-type Si layer doped to 5*10/sup 17/ cm/sup -3/ and the Si/sub 1-x/Ge/sub x/(x=0.31) base measured 0.27 eV. This value was deduced from the measurements of the temperature dependence of the base current and is in good agreement with published calculations for strained Si/sub 1-x/Ge/sub x/ layers on Si.<
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