Vertical scaling in heterojunction bipolar transistors with nonequilibrium base transport

We experimentally measure a departure from conventional scaling of current gain β with base thickness xB in abrupt junction n-p-n heterojunction bipolar transistors. It is empirically established that extreme nonequilibrium electron transport in the base causes β to vary as approximately 1/xB. In our AlInAs/InGaAs transistors this new behavior occurs for base thickness xB≲1000 Å.