Development of a Planar Heterojunction Bipolar Transistor for Very High Speed Logic.

Abstract

Abstract : The following describes the results of research on III-V molecular beam epitaxial (MBE) growth, material characterization and the fabrication of heterostructure bipolar transistors (HBT) for very-high-speed logic applications. Work on the InGaP/GaAs heterojunction (HJ) was completed. Isotype HJs were grown and evaluated by a CV reconstruction method in order to determine the energy band offsets. It was found that delta Ec = 0.22 eV and delta Ev = 0.24 eV for the lattice matched composition. An inverted AlGaAs/GaAs HBT was investigated, and it was shown that an undoped, graded region between emitter and base would eliminate the conduction band spike and provide a buffer for Be diffusion. A new direction toward improvement in performance and fabrication techniques for the AlGaAs/GaAs HBT was successfully demonstrated. Graded-bandgap nonalloyed ohmic contacts using n+ InAs for the AlGaAs emitter and p+ GaSb for the GaAs base were provided by selective epitaxial regrowth. The MBE growth conditions for grading from GaAs to InAs and GaAs to GaSb were determined. Low specific contact resistances were observed for both contact types. A self-aligned AlGaAs/GaAs HBT with graded-gap contacts to both base and emitter was demonstrated.