Ultraviolet-photon emitted GeO2/Ge quantum dots fabricated using hot Ge+-ion implantation into SiO2 layer

Using simple hot Ge+-ion implantation into an SiO2 layer at a substrate temperature T, followed by post-N2 annealing at 850 °C for an annealing time tN, we successfully fabricated GeO2/Ge quantum dots (GeO2/Ge-QDs) embedded in the SiO2 layer. The Ge+ ion dose (DGe) was varied from 1 × 1015 to 6 × 1015 cm−2 at 400 ≤ T ≤ 800 °C. Using transmission electron microscopy (TEM) observation, the diameter (Φ) of GeO2/Ge-QDs and surface density (NQD) increased drastically as T and tN increased, because of the increase in the formation rate of the QDs at a higher T, resulting in 1.9 ≤ Φ ≤ 3.2 nm and 1 × 1012 ≤ NQD ≤ 3 × 1012 cm−2. TEM observation revealed the partially crystallized rutile-GeO2-QDs and Ge-QDs. Hard x-ray photoelectron spectroscopy also revealed Ge–O2 and Ge–Ge bonds, which verified the formation of both GeO2-QDs and Ge-QDs. We also verified photoluminescence (PL) of the QDs with ultra-violet peaks of higher and lower energy peaks at approximately 4.4 eV (NHI) and 3.2 eV (NLO), whose spectra were assumed to originate from the GeO2- and Ge-QDs, respectively, because the PL peak energies of NHI and NLO were nearly equal to the bandgaps of rutile GeO2 and approximately 1.5-nm Ge-QDs. The PL intensity increased drastically as T and tN increased, which was attributed to an increase in the surface area of the QDs. The PL peak energy of NHI was roughly proportional to Φ−2, which was attributed to the quantum confinement effects of the carriers.