The origin of photoluminescence In Ge - implanted SiO/sub 2/ layer

Abstract

The study of semiconductor nanocrystals embeded in Si02 is becoming an expanding field of interest because of their potential as optoelectronic emission devices directly coupled with Si integrated circuits. These nanocrystals emit luminescence that usually doesn't appear in the bulk materials. For fabrication technique of these nanocrystals, ion implantation is a good candidate in that it produces a controlled depth distribution of desired species and is extensively used in semiconductor technology. In this work, we present possible luminescence origins observed from Ge implanted Si02 layers. The Si02 layer with a thickness of 300 nm was grown by wet oxidation of Si(100). Ge negative ions were implanted into Si02 layer at room temperature(RT) with an energy of 100 keV. The employed dose of Geion was 5 X 10l6 ions/cm2. After implantation, the samples were annealed in nitrogen ambient for 2 hour at various temperatures. X-ray photoelectron spectroscopy(XPS) measurements were performed using a standard A1 K a (1486.7 eV) excitation source in an electron spectrometer ESCA 5700(PHI Ldt.) at a residual gas pressure of 2 X lo-'' torr. The photoemitted electrons were detected by hemispherical analyzer with a pass energy of 23.5 eV. Photoluminescence spectra were obtained at RT in a conventional way. An Ar-ion laser (457.9 nm) was used as an excitation source and the luminescence was detected by a cooled photomultiplier tube employing the photon counting technique. Figure 1 shows the PL spectra of an as-implanted sample and samples annealed for 2 hours at 900, 1000, and 1100 "C . After annealing at 900 "C in nitrogen ambient for 2 hours, the PL peak around 2.0 eV observed from as implanted sample disappeares. It implies that the luminescence from the as-implanted sample is related to some radiative defects formed by Ge implantation. However, after annealing at temperature higher than 900 C , the luminescence with the same peak position as that of the as-implanted sample shows up again, and its intensity increases with temperature. Hence, the PL from the annealed sample should be regarded as a luminescence emitted from the Ge nanocrystal. Similar results of luminescence from Ge nanocrystals were reported by others.[ 1,2] In order to confirm the origin of PL, we carried out XPS analysis for both asimplanted sample and the other samples annealed at 1 100 "C . In the case of the asimplanted sample, Ge-0 bond appears dominant, but the annealed sample shows mainly Ge-Ge bond with small amount of Ge-0 bond near the projected range of iplanted Ge.