High-gain n-p-n and p-n-p InGaAs/InAlAs double-heterojunction bipolar transistors with InAs cap layers by molecular-beam epitaxy

The vertical and lateral diffusion of the contact metal during thermal processing become increasingly critical as device dimensions shrink. To alleviate these problems while achieving low contact resistances, InAs contact layers have been used to facilitate the formation of nonalloyed ohmic contacts in n-p-n and p-n-p double-heterojunction bipolar transistors (DHBTs) grown by MBE on