Silicon/silicon suboxide heterostructures grown by molecular beam epitaxy

Thin silicon suboxide (SiO_x) layers were fabricated in situ by molecular beam epitaxy. The layers were grown by introducing molecular oxygen up to a background pressure of 2 × 10^-6 mbar, while maintaining a silicon flux of 0.1 Å s^-1. The layer thickness was varied between 2 and 200 nm. Ellipsometry and SIMS measurements indicate an oxygen content x between 1 and 1.6. The suboxide layers were overgrown with polycrystalline silicon. Transmission electron microscopy (TEM) measurements reveal a uniform amorphous suboxide layer with a sharp interface on the substrate side and some roughness on the surface side. Current-voltage characteristics of transport through such a layer show current blocking behavior up to ≈ 1.5 V for 10 nm layer thickness at low temperatures. At higher temperatures, the current at fixed voltage increases with an activation energy of ≈ 120 meV. It is demonstrated that the suboxide potential barrier can be used to enhance impact excitation of erbium ions in silicon by increasing the number of hot electrons with energies > 0.8 eV.