Monolayer Be delta -doped heterostructure bipolar transistor fabricated using doping selective base contact

A heterostructure bipolar transistor (HBT) with a base delta -doping of 6*10¹⁴ cm^-2, near the physical limit of one monolayer (ML) is reported. The devices exhibits a current gain of 15. The doping confinement of the delta layer is 15 AA. To fabricate the HBT without inducing dopant diffusion or using sensitive etching, a new low-temperature base-contacting procedure (T_max=420 degrees C) which requires no base-emitter etching has been developed. This has the additional benefits of greatly reducing surface recombination and yielding a planar structure.