Experimental studies and fabrication process development of aluminum gallium arsenide/gallium arsenide heterojunction bipolar transistors

Hak-Lay Harry Chuang, Purdue University

Abstract

This thesis describes the development of a fully self-aligned fabrication process for AlGaAs/GaAs heterojunction bipolar transistors (HBTs). It also presents the experimental studies of heavy doping effects on p$\sp{+}$ and n$\sp{+}$ GaAs, and the experimental study of the surface passivation effects of As$\sb2$S$\sb3$ on the self-aligned HBTs. Heavy doping effects on p$\sp{+}$ and n$\sp{+}$ GaAs were experimentally investigated using homojunction barriers to confine minority carriers, so that the effects of band-gap shrinkage can be measured, and hence such effects on the electrical performance of AlGaAs/GaAs HBTs can be deduced. Evidence is presented to show that the effects of band-gap shrinkage due to heavy doping are strong on p$\sp{+}$ GaAs, but not on n$\sp{+}$ GaAs. The As$\sb2$S$\sb3$ chemical treatment is found to have significantly reduced the surface recombination at the perimeter of the emitter-base junction and lowered the base current. Furthermore, no decay has been observed in the treated HBT characteristics after two months of exposure to room temperature and atmospheric conditions.

Degree

Ph.D.

Advisors

Melloch, Purdue University.

Subject Area

Electrical engineering

COinS