GaP collector development for SiGe heterojunction bipolar transistor performance increase: A heterostructure growth study

To develop a III/V wide bandgap collector concept for future SiGe heterobipolar transistor performance increase, a heterostructure growth study of GaP on pseudomorphic 4° off-oriented Si0.8Ge0.2/Si(001) substrates was performed. For pseudomorphic GaP/Si0.8Ge0.2/Si(001) heterostructure growth, critical thickness of GaP on Si and maximum thermal budget for GaP deposition were evaluated. A detailed structure and defect characterization study by x-ray diffraction, atomic force microscopy, and transmission electron microscopy is reported on single crystalline 170 nm GaP/20 nm Si0.8Ge0.2/Si(001). Results show that 20 nm Si0.8Ge0.2/Si(001) can be overgrown by 170 nm GaP without affecting the pseudomorphism of the Si0.8Ge0.2/Si(001) layer. The GaP layer grows however partially relaxed, mainly due to defect nucleation at the GaP/Si0.8Ge0.2 interface during initial island coalescence. The achievement of 2D GaP growth conditions on Si0.8Ge0.2/Si(001) systems is thus a crucial step for achieving fully pseudomorphic heterostructures. Anti-phase domain-free GaP growth is observed for film thicknesses beyond 70 nm.