Optical behavior of self-assembled high-density Ge nanoislands embedded in SiO2

The radio frequency magnetron sputtering method is used to prepare well-dispersed pyramidal-shaped Ge nanoislands embedded in amorphous SiO2sublayers of various thicknesses. The estimated size and number density of Ge nanoislands in SiO2sublayer thicknesses beyond 30 nm are approximately 15 nm and 1011cm 2, respectively. Atomic force microscopy(AFM) reveals root mean square(RMS) roughness sensitivity as the SiO2sublayer thickness varies from 30 to 40 nm. The formation of nanoislands with high aspect ratios is attributed to the higher rate of surface reactions between Ge adatoms and nucleated Ge islands than reactions associated with SiO2and Ge. The Ge nanoisland polyorientation on SiO2(50-nm thickness) is revealed by X-ray difraction(XRD) patterns. Photoluminescence(PL) peaks of 2.9 and 1.65 eV observed at room temperature(RT) are attributed to the radiative recombination of electrons and holes from the Ge nanoislands/SiO2and SiO2/Si interfaces, respectively. The mean island sizes are determined by ftting the experimental Raman profle to two models, namely, the phonon confnement model and the size distribution combined with phonon confnement model. The latter model yields the best ft to the experimental data. We confrm that SiO2matrix thickness variations play a signifcant role in the formation of Ge nanoislands mediated via the minimization of interfacial and strain energies.