Base transport in near-ideal graded-base Si/Si/sub 1-x/Ge/sub x//Si heterojunction bipolar transistors from 150 K to 370 K

A detailed study of electron base transport in Si/Si/sub 1-x/Ge/sub x//Si graded-base n-p-n heterojunction bipolar transistors is presented. The temperature dependence from 150 to 370 K of the collector current in near-ideal devices with various base gradings is examined, and it is shown that this collector current can be modeled over the entire temperature range by a simple analytical formula. It is also shown that graded base devices with an estimated room-temperature base spreading resistance of 7 k Omega / Square Operator have a gain of about 4000 at 89 K.<>