Luminescence and Structural Properties of Silicon-Germanium Quantum Structures Fabricated by Ion Implantation

Matheus Coelho Adam, Western University

Abstract

The advancement of semiconductor materials has played a crucial role in driving positive technological breakthroughs that impact humanity in numerous ways. The presence of defects significantly alters the physical properties of semiconductors, making their analysis essential in the fabrication of semiconductor devices. I presented a new method to quantify surface and near-surface defects in single crystal semiconductors. Epitaxially-grown silicon was measured by low energy electron diffraction (LEED) to obtain the surface Debye temperature (θ_D). The results showed the surface θ_D of bulk Si (001), 1.0 μm, and 0.6 μm Si on sapphire of 333 K, 299 K, and 260 K, respectively. Complementary measurements using Rutherford backscattering spectrometry (RBS) and positron annihilation spectroscopy (PAS) showed a correlation between the concentration of defects N_d and the change in the surface θ_D, expressed by the empirical relation θ_D = (365 ± 14) − (8.1 ± 1.5) × 10⁻¹³N_d for silicon. Arrays of SiGe quantum dots (QDs) ranging from 1.7 to 5.7 nm in diameter were fabricated using two methods: co-implantation of Si and Ge into an SiO₂ matrix, and a hybrid method involving plasma-enhanced chemical vapor deposition (PECVD) of Si-rich SiO_x deposition plus Ge implantation. Ion implantation conditions allowed incorporation of up to 8.0 peak Ge at.% and identical thermal procedures were used in both methods. SiGe QD arrays in both methods exhibited photoluminescence in the visible and near-infrared spectra, with emissions from 780 nm to about 1020 nm. Incorporation of Ge, confirmed by Raman spectroscopy, induced a shift towards higher wavelengths in the light emission. Time-resolved photoluminescence measurements indicated average-weighted lifetimes ranging from 34 μs to 220 μs, with a decreasing trend noted with increasing Ge concentrations. Experimentally observed differences in PL peak intensity and width for the two fabrication approaches can be connected to SiGe QD size distributions and matrix effects.