Metal-oxide semiconductor light-emitting devices based on Ge nanocrystals co-implanted with Er ions

Si nanocrystals (NCs) have widely been used as sensitizers in Er-doped SiO2 layers where following the recombination of excitons (electron-hole pairs) in optically excited Si NCs energy is transferred to the higher energy levels of the 4f shell of Er3+ ions and subsequently decay radiatively via 4I13/2 → 4I15/2 transition. This as a result emits light at ~1.53 m, which coincides well the silica-based optical fibers. However, the temperature and concentration quenching of Er3+ ions in Si-rich SiO2 matrices are the basic obstacles for practical application. In the quest for an alternative host material, Ge-rich SiO2 layers have presently attracted a considerable interest due to strong quantum confinement effect and a better control of the surface oxidation of Ge NCs with respect to Si-NCs. In fact, the growth of Er-doped Ge nanoperticles embedded in a SiO2 layer and the photoluminescence (PL) properties have recently been studied. Despite progress in PL response, electrically pumped light-emitting devices (LEDs) are highly required from the optoelectronic standpoints.
We have investigated Ge NCs embedded in a metal-oxide semiconductor (MOS) structure co-doped with Er3+ ions and the corresponding electroluminescence (EL). Here we follow the two step implantation approach: (i) First, 130 keV Ge ions have been implanted (dose of 2–6E16 ions/cm2) into a thermally grown 200 nm thick SiO2 layer followed by furnace annealing (FA) at 950 C for 60 min, which is followed by (ii) 250 keV Er implantation (dose of 1-5E15 ions/cm2) combined with FA in the range of 800-1100oC for 30 min in nitrogen ambience. The MOS structures have been fabricated by depositing indium-tin-oxide (ITO) and aluminium in the front and rare sides of the samples, respectively, and patterning the ITO layer using photolithography. Interestingly, instead of electrically driven pumping of Er3+ ions by Ge NCs, we found that an EL band ~407 nm associated to the Ge-related oxygen-deficiency centres (GeODCs) have been pumped by Er3+ ions and discuss the observed phenomenon on the ground of an inverse energy transfer process. Concentration and temperature dependent modification of microstructure and the subsequent impact on EL response will also be discussed.