Lattice-engineered Si1−xGex-buffer on Si(001) for GaP integration

XRD techniques determined that 270 nm GaP grown on 400 nm Si_0.85Ge_0.15/Si(001) substrates by MOCVD is single crystalline and pseudomorphic, but carry a 0.07% tensile strain after cooling down to room temperature due to the bigger thermal expansion coefficient of GaP with respect to Si (Fig. 2). TEM and AFM examinations indicated a closed but defective GaP layer (Fig. 3(a)) with low root mean square of roughness (rms) of 3.0 nm for 1 μm² surface area (Fig. 3(b)). Although TEM studies confirm the absence of misfit dislocations in the pseudomorphic GaP film, growth defects (e.g. stacking faults, microtwins, and anti-phase domains) are detected, concentrating at the GaP/SiGe interface (Fig. 3(c)-(d), Fig. 4). We interpret these growth defects as a residue of the initial 3D island coalescence phase of the GaP film on the Si_0.85Ge_0.15 buffer. TEM-EDX studies reveal that the observed growth defects are often correlated with stoichiometric inhomogeneities in the GaP film (not shown here). Finally, ToF-SIMS detects sharp heterointerfaces between GaP and SiGe films with a minor level of Ga diffusion into the SiGe buffer (Fig. 5).