A Route to Obtaining Low-Defect III-V Epilayers on Si(100) Utilizing MOCVD
Low-defect III-V multilayer structures grown on Si(100) open opportunities for a wide range of cost-effective high-performance photovoltaic and optoelectronic devices. For that, (Al)GaP epilayers prepared almost lattice-matched on Si(100) substrates can serve as high-quality virtual substrates for subsequent heteroepitaxial growth. The evolution of crystal defects, such as stacking fault pyramids or threading dislocations, needs to be impeded already during the first preparation step, the III-V-on-Si nucleation, as they tend to propagate into the subsequently grown layers and increase nonradiative electron-hole recombination rates, which finally degrade the device performance. We establish a ternary GaP/AlP pulsed nucleation process on Si(100) substrates fabricated by metalorganic chemical vapor deposition, and compare it to the defect evolution from pure GaP nucleation layers (NLs). The entire procedure was optically monitored in situ using reflection anisotropy spectroscopy. Crystal defects were investigated by electron channeling contrast imaging. GaP grown on GaP/AlP NLs exhibits drastically reduced densities of threading dislocations and stacking faults by 1 and 2 orders of magnitude, respectively, compared to buffer layers grown on binary GaP NLs. We observed that the surface morphology at the initial stage of growth of these buffer layers is significantly smoother compared to the buffer layers grown on pure GaP NLs using atomic force microscopy. The proposed nucleation procedure here is supposed to substantially improve the crystalline quality of III-V buffer layers integrated on Si(100) wafers.