Study On Luminescence Of Silicon Riched Silica Films Prepared By Ion Implantation

Integrated optoelectronics thoroughly based on silicon are not now available, because efficiency of luminescence originated from inter-band transition of bulk crystal silicon is 3-5 orders lower than compound semiconductor such as GaAs. Implantating surplus silicon ions into SiO2 substrate is an effective method to introduce new defect luminescence centers in the substrate for higher efficiency luminescence with expanded wave band. Hence, ion implantation has emerged as a useful tool to obtain Si based luminescence which is compatible with ULSI semiconductor technology; furthermore, it is ease to control distribution and concentration of implanted ions and the thickness of implanted layer by selecting appropriate implantation energy and dose.Two kind SiO2 films were prepared using dry and wet thermal oxidation. Si ions with varied implantation doses(2×1016,4×1016,6×1016,8×1016, 1×1017/cm2) and energies(28,42,56,70keV) were implanted into SiO2 films using metal vapor vacuum arc (MEVVA) implantation technology to investigate the influence of dose and energy on the photoluminescence of the implanted SiO2 films. The as-implanted samples were labeled as Group1-3(G1,G2,G3) with the varied implantation parameters. Annealing of the as-implanted SiO2 films were conducted at low tempreture(200-500℃) and high tempreture(200-500℃) repectively for different time(1～4h), the as-annealed samples were labeled as group 4-6 (G4,G5,G6) with the varied annealing conditions.Simulation results of TRIM indicated thickness of implanted layers and total atom displacements increased with increacing of implantation energies, and the average stoichiometric proportions in samples differed with implantation doses. FTIR test revealed that the quantity of Si-H and O-H in wet oxidation films was more than dry oxidation samples; as well as the Si-H bending mode and O-H stretching mode vibrations become notable stronger in the as-implanted samples than in the primitive thermal oxidized SiO2 films. XRD pattern showed SiO2:Si films were amorphous and microscale silicon nanocrystals would be formed when annealed at high temperature. Occurrence of silicon nanocrystals after annealing at high temperature was also confirmed by Laser Raman spectra tests. XPS pattern indicated the component of SiO2:Si films were Si and O, and there exist both oxygen deficient and oxygen sufficient structure in the as-implanted samples.PL spectra of all samples were composed of four photoluminescence bands whose peak positions ranged from the wavelength of 560nm to 700nm. Integrated PL intensity of SiO2:Si films increased firstly and then decreased with implantation doses, this trend can be explained by total atomic displacements and concentration quenching effect. The integrated PL intensity of the impanted dry oxidation layers increased with the implantation energy, while wet SiO2:Si films have inverse relationship with the implantation energy. Variation trend of the integrated PL intensity of dry oxidation SiO2:Si films with implantation energy was consistent with the total displacements variation trend. Different dependences of two typical PL bands of the SiO2:Si films on annealing temperature were observed, which indicated corresponding luminescence center have different thermodynamic stability. After annealing at different high tempreture PL intensity decreased significantly, none of emission peak attribute to silicon nanocrystals was observed, indicating that the defect centers responsible for luminescence have been passivated by high temperature annealing.Silicon nanocrystals luminescence were observed in Si ions of high doses and energies implanted samples after various anealing times at 1100℃, that indicated the important role of Si implantation dose and energy.According to discussions of the literatures and the results of XPS spectra, it can be confirmed that 560～600nm luminescence bands originated from peroxy defects SPR (small peroxy radicle) in silicon oxide layer, while 620～700nm bands originated from non bridge oxygen hole centre (NBOHC). The relationship of luminous intensity between each group of samples, as well as variation trend with the implantation parameters were attributed to ionization effect of ion implantation and diffusional limitation mechanisms of defect formation. It was observed that SPR and NBOHC defects exhibit different anneal characteristics at both high and low annealing temperature. Quantity of SPR defects decreased with elevation of annealing temperature and its concentration would be stable at a certain value eventually regardless of temperature elevation, revealing that this kind defects can not be passivated thoroughly by high temperature annealing, PL intensity of NBOHC defects experienced a first increase and then decrease process when annealing temperature rising, and annealing at high temperature of 1100℃resulted in completely disappearing of luminescence actvity of NBOHC defects.