Growth and Characterization of Self-Assembled InAs Quantum Dots on Si (100) for Monolithic Integration by MBE

High-density, self-assembled InAs quantum dots were grown on Si (100) substrates without any buffer layer by solidsource molecular beam epitaxy, following Volmer-Weber growth mode. The reconstructed (2 × 1) Si surface and growth transition from two-dimensional (2-D) to three-dimensional (3-D) were observed by in situ reflection high energy electron diffraction (RHEED). Surface morphology, shape, and chemical composition of these dots were investigated through scanning electron microscopy (SEM), atomic force microscopy (AFM), and energy dispersive X-ray (EDX) analysis, respectively. The dot densities were found to be 4 × 1014 m^-2 for the samples grown at 380°C with a V/III ratio of 13. Optical properties of InAs quantum dots were observed by photoluminescence (PL) spectroscopy both at room and low temperatures. Room-temperature PL (RTPL) peak was observed at 1.016 eV (~1220 nm) and 1.05 eV (~1180.95 nm) presumably originating from the ground state (GS) and excited state (ES), respectively. The 3-D carrier confinement rather than the strain is found to have the dominating role, which causes blueshift of 0.662 eV. The theoretical PL spectrum of dots was obtained by using Gaussian size distribution where the dots were assumed to be cubic in shape. The low-temperature PL (LTPL) peak position was observed at 1.16 eV. The experimentally observed variation of the bandgap with temperature was in close proximity with both Varshini and Vina model. Raman spectroscopic analysis confirms the carrier confinement in the InAs quantum dots by the downward frequency shift at 216.57 and 237.96 cm^-1 corresponding to the transverse optical (TO) and longitudinal optical (LO) phonon modes, respectively. The qualitative strain analysis was investigated by high-resolution X-ray diffractions (HRXRD) where the strain state was observed from the reciprocal space mapping in symmetric (004), as well as grazing exit and grazing incidence mode at (224)- plane.