Structural properties of SiGe nanoparticles in LPCVD Si3N4

(1) Department of Electronic Materials Engineering, The Australian National University, Canberra, ACT, Australia
(2) Department of Nuclear Science and Technology, Brookhaven National Laboratory, Upton, New York, USA

Semiconductor nanoparticles (NPs) are novel material systems that lie between the molecular and solid-state regimes with unique properties largely controlled by their size and shape. Due to their exceptional optical and electrical properties, semiconductor NPs have direct applications in optoelectronic and non-volatile memory devices. Of particular interest are Ge NPs embedded in a dielectric matrix due to their ability to both emit light [1] and store charge [2].

Previous studies have investigated the structural and vibrational properties of Ge NPs embedded in SiO2 [3]. Here, we discuss the structural properties of SiGe NPs synthesised by ion implantation in amorphous Si3N4.

Ge ions, were implanted into a 2µm amorphous Si3N4 films were grown on Si (100) substrates. Implantations were performed at temperatures of 400 °C. The resulting peak Ge concentrations ranged from 0.3 to 12 at.%. In order to promote the growth of NPs, samples were annealed post-implantation at 700, 900 and 1100 °C for 1-10 hours under an N2 ambient.

Multiple techniques were used to characterise the evolution of the structural properties of samples. The crystalline and amorphous components both as a function of concentrations, and post-implantation annealing were quantified by X-ray Absorption Spectroscopy. The formation of a Si-Ge bonding environments with different composition, for all examined concentrations and temperatures was readily evident. Complementary Raman spectroscopy measurements were also used to quantify the vibrational properties and composition of each sample and confirmed the post-implantation annealing and atomic concentration concentration-dependent structure. Rutherford backscattering spectrometry and transmission electron microscopy measurements also show evidence of a phase transition of the host matrix, independent of atomic concentration, after post-implant annealing at 1100 °C. Crystallisation of the nitride matrix was found to facilitate the rapid diffusion of Ge atoms to the Si/Si3N4 interface. Here, we discuss the role of implantation and post-implantation conditions on the growth of NPs in a Si3N4 matrix and compare the differences to that previously observed for Ge in SiO2. We find that both implantation and chemical-induced defects appear to be responsible for the various structures that ensue with processing conditions. The complex mechanisms responsible for crystallisation of the matrix, including consideration of structure disorder, loss of N2, and non-stoichiometry will be discussed.  

[1] S. K. Ray et al., Opt. Mater. 27, 948 (2005).
[2] C. J. Park et al., Appl. Phys. Lett. 88, 071916 (2006).
[3] L. L. Araujo et al., Physical Review B, (2008).