GaN nanocrystals obtained by Ga and N implantations and thermal treatment under N2 into SiO2/Si and SiNx/Si wafers

Abstract

The formation of GaN nanocrystals in SiO2/Si and SiNx/Si dielectric layers implanted with Ga + and N + ions, followed by annealing at 950 °C for 60–120 min in N2, has been studied by high resolution transmission electron microscopy (HRTEM), synchrotron radiation X-ray diffraction (XRD), X-ray absorption fine structure (XAFS) technique at the Ga K-edge, as well as by Rutherford Backscattering spectrometry (RBS), X-Ray photoelectron spectroscopy (XPS), Raman spectroscopy (RS) and Scanning electron microscopy (SEM). The effect of the dielectric matrix, of the gas annealing environment (N2) and of the annealing time at 950 °C have been investigated. GaN nanocrystals implanted near the surface are observed in SiO2/Si only. The hexagonal wurtzite crystalline structure was confirmed by HRTEM, XRD and Raman spectroscopy. However, the synthesis process is multiphasic as elemental Ga0 nanoparticles at larger depths and Ga2O3 rods (~200–300 nm) on the surface were formed in addition to implanted h-GaN, as shown by TEM, XAFS, SEM, XPS and Raman spectroscopy. Moreover, Ga atoms are always remaining on some vacant Si sites in the SiO2 matrix. The local environment around Ga is quite different in the SiNx matrix, as seen by XAFS. This difference can be explained by the gallium and nitrogen diffusions which are much faster in the case of the SiO2 matrix, as shown by RBS profiles. Results are discussed in close comparison with existing literature.