Defect Contribution to the Photoluminescence from Embedded Germanium Nanocrystals Prepared by Ion Implantation and Sputter Deposition Methods

摘要

In this work, we present a comparative study of vibrational and luminescent properties of Ge nanocrystals (NCs) prepared by ion implantation (Process I) and radio frequency (RF) sputter deposition techniques (Process II). Optical Raman studies reveal presence of strain in the Ge NCs embedded in SiO_2 in both cases. Polarization dependent Raman scattering studies show that process I yields NCs with surface symmetrical Raman modes only, whereas process II yields additional surface quadrupolar Raman modes. Photoluminescence studies using 488 nm excitation show broad PL emissions peaked at ～2.3 in all the samples with varying intensities. PL studies on Ar implanted and similarly annealed SiO_2 layers confirm that the 2.3 eV emission is originated from oxygen deficient defects in the SiO_2 matrix. PL studies with 325 nm excitation show additional strong peaks at higher energies, which are believed to be due to Ge/O interface defects. It is concluded that room temperature visible light emission from embedded Ge NCs is primarily dominated by the oxygen deficient defects in SiO_x matrix and non-bridging oxygen surrounding the Ge NCs, while light emission due to quantum confined carriers in the NCs are quenched perhaps due to inherent strain in the embedded NCs.