Eur. Phys. J. D 8, 395–398 (2000) T HE EUROPEAN P HYSICAL JOURNAL D c  EDP Sciences Societ` a Italiana di Fisica Springer-Verlag 2000 Temperature behaviour of optical properties of Si + -implanted SiO 2 J. Valenta 1, a , J. Dian 1 , K. Luterov´ a 2 , P. Kn´ apek 2 , I. Pelant 2 , M. Nikl 2 , D. Muller 3 , J.J. Grob 3 , J.-L. Rehspringer 4 , and B. H¨ onerlage 5 1 Charles University Prague, Faculty of Mathematics and Physics, Department of Chemical Physics and Optics, Ke Karlovu 3, 12116 Prague, Czech Republic 2 Institute of Physics, Academy of Sciences of the Czech Republic, Cukrovarnick´a 10, 16253 Prague, Czech Republic 3 Laboratoire PHASE b , 23 rue du Loess, 67037 Strasbourg, France 4 IPCMS, Groupe des mat´ eriaux inorganiques c , UPL, 23 rue du Loess, 67037 Strasbourg, France 5 IPCMS, Groupe d’optique non lin´ eaire et d’opto´ electronique, 23 rue du Loess, 67037 Strasbourg, France Received 1st September 1998 and Received in final form 7 September 1999 Abstract. Silicon nanocrystals were prepared by Si + -ion implantation and subsequent annealing of SiO2 films thermally grown on a c-Si wafer. Different implantation energies (20–150 keV) and doses (7 × 10 15 – 2 × 10 17 cm -2 ) were used in order to achieve flat implantation profiles (through the thickness of about 100 nm) with a peak concentration of Si atoms of 5, 7, 10 and 15 atomic%. The presence of Si nanocrystals was verified by transmission electron microscopy. The samples exhibit strong visible/IR photoluminescence (PL) with decay time of the order of tens of μs at room temperature. The changes of PL in the range 70–300 K can be well explained by the exciton singlet-triplet splitting model. We show that all PL char- acteristics (efficiency, dynamics, temperature dependence, excitation spectra) of our Si + -implanted SiO2 films bear close resemblance to those of a light-emitting porous Si and therefore we suppose similar PL origin in both materials. PACS. 78.55.Hx Other solid inorganic materials – 61.46.+w Clusters, nanoparticles, and nanocrystalline materials – 78.45.+h Stimulated emission Different types of silicon-based nanostructured materials exhibiting efficient photoluminescence (PL) and electrolu- minescence have been developed in the course of the last decade. One of the most promising methods to prepare Si nanocrystals is the Si + -ion implantation of SiO 2 [1]. This technique is compatible with the integrated circuit tech- nology and provides nanocrystals with better passivation, durability, long-term stability and controlled size as com- pared with other Si-based light emitting materials, e.g. light-emitting porous silicon. In this communication we present results obtained on a set of four samples prepared by Si + -ion implantation of thermally grown SiO 2 layers on a c-Si wafer. Time- resolved PL as well as steady-state PL and PL-excitation (PLE) spectra were measured and compared to the red “S band” from typical light-emitting porous Si [2]. Our SiO 2 layers (500 nm thick) were thermally grown on c-Si wafers (〈100〉 n-type, resistivity 75 Ωcm) and im- planted with Si + ions at different energies and differ- ent doses in order to obtain layers with different atomic a e-mail: valenta@karlov.mff.cuni.cz b UPR 292 du CNRS c UMR 7504 du CNRS Si content: 5, 7, 10 and 15 at%. To realize a flat im- plantation profile, a summing of several subsequent im- plantations was used (see Tab. 1). The total doses vary between 1−2.8 × 10 17 ions/cm 2 . After implantation, the samples were annealed at 1100 ◦ C in a N 2 atmosphere for 4 hours. During this procedure a formation of spherical- like Si nanocrystals in a SiO 2 matrix is supposed [3]. The presence of nanocrystals in our films was evidenced by us- ing the transmission electron microscopy (TEM). Figure 1 presents a high resolution TEM image of one Si nanocrys- tal (5 nm in diameter) observed in the 10 at% Si + /SiO 2 layer. Steady-state PL measurements were performed under excitation with a high-pressure Xe lamp filtered by an ex- citation monochromator. PL emission was dispersed in an emission monochromator and detected with a photomul- tiplier connected to a photon counting system. In order to study PL spectra as a function of temperature, the sam- ples were fixed in a temperature variable gas flow cryostat. PL data were corrected for the spectral response of the de- tection system. A flash Xe-lamp (pulse duration of ∼ 2 μs) was used to excite PL in time-resolved PL measurements. The PL decay was detected by a time-correlated photon counting system.