Germanium negative-ion implantation into SiO2 layer on Si: Photoluminescence properties and oxidation state of Ge atoms in subsequent heat treatment

Photoluminescence properties (PL) and oxidation state of Ge atoms implanted into a thermally grown SiO2 layers have been investigated. The samples were prepared by Ge negative-ion implantation at multi-energies of 10–50 keV with various Ge concentrations of 0.5–6 at.% and subsequent two-stage annealing in N2 at a flow rate of 50 ml/min and in decompressed air at flow rate of 10 ml/min at temperatures of 600 °C–900 °C for 1–3 h. Results showed that the PL emission with a peak at 390 nm depended on both Ge concentration and subsequent annealing temperature. For the low Ge concentrations of 1–1.4 at.%, the strong PL emission could be obtained just after 1 h annealing in N2 at 700–800 °C. For the high Ge concentration of 3 at.%, the PL emission was improved and increased after annealing in decompressed air, but it still was weaker than that of the Ge sample at 1.4 at.%. XPS analysis showed that almost 60% of Ge atoms were oxidized to form GeO and GeO2, even as implanted sample and this oxidation decreased to 35% after N2 annealing. The induced defects of SiO2 as absorption center recovered while the oxygen defects (ODC) of GeO2 were reduced during annealing in N2. The deoxidation of GeO2 is suppressed by annealing in decompressed air flow. Based on the obtained results, we have discussed the best way of heat treatment to increase ODC by two-stage annealing in N2 and in decompressed air.