Ion-implanted SiO2 Research Articles

Visible room-temperature emission and excitation photoluminescence in In+- and As+-co-implanted SiO2 films

The visible room-temperature emission and excitation photoluminescence spectra were studied as a function of the indium and arsenic profiles in the In+ and As+ ion-implanted thermally grown SiO2 films before and after the annealing at the temperature of 900 °C. As+ ions at the energy of 40 or 135 keV and In+ ions at the energy of 50 keV, providing a projective range ratio RpAs/RpIn of 1 or 3, respectively, were used. Four emission photoluminescence bands, peaked at ∼347 nm (3.57 eV), ∼440 nm (2.81 eV), ∼450 nm (2.75 eV) and ∼500 nm (2.48 eV), were obtained from the 40 keV As+ and 50 keV In+ ion-implanted samples under the excitation wavelength of 300 nm (4.13 eV), 350 nm (3.54 eV), 400 nm (3.10 eV) and 450 nm (2.75 eV), respectively. As the As+ energy increased to 135 keV, under the same excitation conditions, the emission bands peaked at 370 nm (3.35 eV), 420 nm (2.95 eV), 460 nm (2.69 eV) and 505 nm (2.45 eV) dominated in the photoluminescence spectra. The excitation spectra of the observed emission peaks were studied, too. We preliminarily interpret the observed photoluminescence peaks as a result of the T1 → S0 transition of molecular-like clusters associated with the oxygen deficiency provided by In or In–As in ion-implanted SiO2.

Raman scattering and photoluminescence in In+ and As+ ion-implanted SiO2 layers encapsulated with Si3N4

Raman and photoluminescence spectra were investigated in the In+ and As+ ion-implanted SiO2 films encapsulated with Si3N4 layers as a function of annealing temperature. The optical phonon frequency, as a function of the InAs nanocrystal size, was also calculated within the confined phonon model. The Raman scattering band of around 231 cm−1, close to the low-frequency shifted longitudinal optical phonon mode in the InAs matrix, was observed as the annealing temperature increased to 900 °C. The InAs nanocrystal size of 3 nm was estimated. The strong room-temperature photoluminescence peaking at 550 nm (2.25 eV) was also obtained under the 473 nm wavelength excitation. Its intensity reached a maximum value as the annealing temperature increased to 1000 °C. Its peak position was blue-shifted as the excitation wavelength decreased. The direct irradiative electron and hole recombination in the InAs nanocrystals was proposed as a possible mechanism of this photoluminescence.

Enhanced InAs phase formation in the In+- and As+-implanted SiO2 films covered with Si3N4 layers

The Raman spectroscopy and room-temperature photoluminescence were used to study the properties of the In+ and As+ ion-implanted SiO2 films as a function of annealing temperature Ta at 700–1100 °C. No features of the InAs phase were obtained in the Raman spectra of the native SiO2 films irrespective of Ta. In the ion-implanted SiO2 films encapsulated with Si3N4, three Raman peaks at 202 cm−1, 256 cm−1 and 232 cm−1 corresponding to transverse and longitudinal optical phonons in black As and to longitudinal optical phonons in InAs, respectively, were detected. The SiO2 encapsulation effect on the enhanced InAs phase formation is discussed. A photoluminescence of around 556 nm was observed from the encapsulated ion-implanted SiO2 films and reached its intensity maximum after the annealing at 1000 °C.

Ion-beam synthesis of InSb nanocrystals at the Si/SiO2 interface

The formation of InSb nanocrystals at the bonding Si/SiO2 interface of silicon-on-insulator structure was obtained as a result of the In and Sb atom diffusion from the ion-implanted SiO2 and Si regions, respectively, toward the interface. After the annealing at 1000 °C, the Raman scattering peaks corresponding to the transverse and longitudinal optical phonon mode in the monocrystalline InSb matrix were obtained. As the annealing temperature grew to 1100 °C, the transverse optical phonon mode vanished and the longitudinal optical phonon mode dominated in the spectrum. This effect is explained by matching InSb and Si lattice constants under ion-beam synthesis conditions.

XAFS and TEM Investigation of Nanocluster Formation in 64Zn+ Ion-Implanted and Thermo-Oxidized SiO2 Film

Due to their tunable current–voltage characteristics, Zn-doped thin SiO2 films are promising for microelectronic devices, e.g., memristors. In this work we studied single-crystal Si (100) substrates with 200 nm SiO2 surface layers implanted with 64Zn+ using Zn K-edge x-ray absorption spectroscopy (XAS), transmission electron microscopy (TEM) and electron diffraction. We used two specimens: as-implanted and annealed in oxygen at 700°C. Cross-section TEM analysis showed that 64Zn+ implantation leads to the formation of a subsurface layer consisting of Zn nanoparticles approximately 7 nm in size. The nanoparticles are distributed in depths from 10 nm to 90 nm, with a concentration peak at 45 nm. Electron microscopy showed that most of the Zn nanoparticles are amorphous. However, XAS data indicated that almost all the Zn atoms are coordinated with oxygen. Thus, only a small fraction of zinc atoms are involved in the formation of nanoclusters. Annealing at 700°C leads to the oxidation of particles with the formation of the Zn2SiO4 phase. The particle sizes in the surface layer of SiO2 after annealing vary from 3 nm to 20 nm.

Enhanced germanium precipitation and nanocrystal growth in the Ge+ ion-implanted SiO2 films during high-pressure annealing

Abstract The effect of pressure employed during subsequent annealing of the Ge + -ion implanted SiO 2 layers on the Ge nanocrystal formation was studied. Ge + ions implanted in the thin SiO 2 layers formed Gauss-like profiles with a Ge peak concentration varied from 1 to 12 at%. Subsequent annealing was carried out at temperature 600–1130 °C under pressures 1–1.2×10 4 bar. Strong effect of the pressure on the Ge atom distribution was obtained. High-temperature annealing under pressure within the range of 1–10 3 bar resulted in the out-diffusion of germanium from the SiO 2 layer to the Si substrate. As the pressure reached 1.2×10 4 bar, Ge migration to the Si/SiO 2 interface was prevented. At that, the Ge nanocrystal growth within the ion-implanted region of the SiO 2 film took place. The nanocrystal size was investigated as a function both of the Ge atom concentration and the annealing temperature. The obtained results show a diffusion-controlled nanocrystal growth mechanism. The high-pressure (1.2×10 4 bar) diffusion coefficient of germanium in silicon dioxide was estimated as a function of the temperature and expressed by D= 1.1×10 −10 exp ( −1.43 eV/kT) cm 2 /s.

Electronic band gap reduction and intense luminescence in Co and Mn ion-implanted SiO2

Cobalt and manganese ions are implanted into SiO2 over a wide range of concentrations. For low concentrations, the Co atoms occupy interstitial locations, coordinated with oxygen, while metallic Co clusters form at higher implantation concentrations. For all concentrations studied here, Mn ions remain in interstitial locations and do not cluster. Using resonant x-ray emission spectroscopy and Anderson impurity model calculations, we determine the strength of the covalent interaction between the interstitial ions and the SiO2 valence band, finding it comparable to Mn and Co monoxides. Further, we find an increasing reduction in the SiO2 electronic band gap for increasing implantation concentration, due primarily to the introduction of Mn- and Co-derived conduction band states. We also observe a strong increase in a band of x-ray stimulated luminescence at 2.75 eV after implantation, attributed to oxygen deficient centers formed during implantation.

Formation of nickel germanide on SiO2-capped n-Ge to lower its Schottky barrier height

In this Letter, NiGe/SiO2/n-Ge ohmic contacts were demonstrated with Ge, rather than Ni, diffusion through the ion-implanted SiO2 films to form NiGe. The equivalent Schottky barrier height reduced from 0.58 eV for NiGe/n-Ge to ohmic contact. The anomalous diffusion behavior and accumulation of Ge in the SiO2 near the NiGe/SiO2 interface can be explained by vacancy-enhanced Ge diffusion. It is proposed that the presence of vacancies and Ge atoms embedded in the SiO2 layer play a significant role in the current enhancement by generation of multiple levels in the SiO2 band gap.

The microstructure, optical and magnetic property of nitrogen implanted SiO2

The microstructure, optical property and magnetism of nitrogen ion-implanted SiO2 were studied. The nitrogen incorporation into SiO2 was confirmed by means of x-ray photoelectron spectra and a Fourier-transform infrared absorption spectrum. The bond angle of Si–O–Si is decreased by nitrogen implantation. The absorption in the ultraviolet region is enhanced, which may be due to the band gap narrowing effect. Room-temperature ferromagnetic-like behavior is obtained in the nitrogen-implanted sample with a nominal dose of 1 × 1018 ions cm−2.

Low-temperature photoluminescence of ion-implanted SiO2:Sn+ films and glasses

Low-temperature photoluminescence spectroscopy with pulsed synchrotron excitation is applied to study the regularities of excitation and relaxation of both point defects and nanoparticles formed by tin implantation into SiO2 films and glasses. It has been found that tin implantation followed by air and nitrogen annealing yields the formation of α-Sn nanoclusters and nonstoichiometric SnO x nanoparticles, while a stable phase of SnO2 does not appear. Alternative channels of luminescence excitation are revealed for nanoclusters, including energy transfer from excitons and electron-hole pairs of the host SiO2 matrix.

Si and Ge nanocluster formation in silica matrix

High resolution transmission electron microscopy, scanning transmission electron microscopy, and cathodoluminescence have been used to investigate Si and Ge cluster formation in amorphous silicon-dioxide layers. Commonly, cathodoluminescence emission spectra of pure SiO2 are identified with particular defect centers within the atomic network of silica including the nonbridging oxygen hole center associated with the red luminescence at 650 nm (1.9 eV) and the oxygen deficient centers with the blue (460 nm; 2.7 eV) and ultraviolet band (295 nm; 4.2 eV). In Ge+ ion-implanted SiO2, an additional violet emission band appears at 410 nm (3.1 eV). The strong increase of this violet luminescence after thermal annealing is associated with formation of low-dimension Ge aggregates such as dimers, trimers, and higher formations, further growing to Ge nanoclusters. On the other hand, pure silica layers were modified by heavy electron beam irradiation (5 keV; 2.7 A/cm2), leading to electronic as well as thermal dissociation of oxygen and the appearance of under-stoichiometric SiOx. This SiOx will undergo a phase separation and we observe Si cluster formation with a most probable cluster diameter of 4 nm. Such largely extended Si clusters will diminish the SiO2-related luminescence and Si-crystal-related luminescence in the near IR.

Effect of indentation and annealing on 2 MeV Cu ion-implanted SiO2

Enhancement of surface plasmon resonance (SPR) in optical absorption has been found on Cu ion-implanted SiO2 substrate modified by micro-indentation and post annealing. The SiO2was firstly implanted with 2MeV Cu2+ ions, at an ion flux of 4μA/cm2, up to a fluence of 6×1016ions/cm2 at room temperature. After the ion implantation, dot-array patterns of micro-indents were made by a micro-Vickers machine, and annealed at 600°C, 700°C and 800°C in vacuum for 1h. The optical absorption spectra of the indented region and the non-indented flat region were measured by a dual beam spectrometer. After post annealing at different temperatures, all the indented areas showed higher absorbance of SPR at 2.2eV, comparing to the flat region annealed under the same annealing conditions. In particular, the SPR enhancement reached maximum after 600°C annealing, and decreases with further increasing annealing temperature. The result of SPR enhancement by the micro-indentation suggests that the indentation-induced deformation enhances the atomic migration, resulting in promoting the precipitation under thermal annealing.

Influence of in situ ultrasound treatment during ion implantation on formation of silver nanoparticles in silica

We report on the effect of in situ ultrasound treatment on the clustering process of silver atoms in ion-implanted SiO2. Cross-sectional transmission electron microscopy shows single-crystal Ag spheres with an increased cluster size when prepared using ultrasound vibrations. Time-of-flight secondary-ion-mass spectrometry demonstrates an enhanced yield of [Ag2]216 complexes in structures treated with acoustic waves. An analysis of the influence of ultrasound on defect reaction kinetics as well as on different stages of the clustering process is performed.

Influence of the Ge Dose in Ion-implanted SiO2 Layers on the Related Nanocrystal-memory Properties

ABSTRACTThin silicon dioxide (SiO2) on Si layers with embedded germanium nanocrystals (Ge-ncs) were fabricated using 74Ge+-implantation at 15 keV and subsequent annealing. Transmission electron microscopy and Rutherford backscattering spectrometry have been used to study the Ge redistribution in the SiO2 films as a function of implantation dose under specific annealing conditions. At low implantation doses, Germanium is found to segregate at the Si/SiO2 interface leading to poor electrical properties. At higher doses and when the disorder limit of one displacement per atom is reached at the interface, transmission electron microscopy revealed the formation of a Ge-nc layer array located close to the Si/SiO2 interface and an another one inside the SiO2 host material. This near-interface high density (>1012 ncs/cm2) nc-layer is found to act as a floating gate embedded within the silicon dioxide. Capacitance-voltage measurements performed on metal-oxide-semiconductor structures containing such implanted SiO2 layers show significant memory properties (few volts hysteresis) at low programming voltages (<|10V|) due to the presence of Ge-ncs near the Si/SiO2 interface

White luminescence from Si+ and C+ ion-implanted SiO2 films

The microstructural and optical analysis of SiO2 layers emitting white luminescence is reported. These structures have been synthesized by sequential Si+ and C+ ion implantation and high-temperature annealing. Their white emission results from the presence of up to three bands in the photoluminescence (PL) spectra, covering the whole visible spectral range. The microstructural characterization reveals the presence of a complex multilayer structure: Si nanocrystals are only observed outside the main C-implanted peak region, with a lower density closer to the surface, being also smaller in size. This lack of uniformity in their density has been related to the inhibiting role of C in their growth dynamics. These nanocrystals are responsible for the band appearing in the red region of the PL spectrum. The analysis of the thermal evolution of the red PL band and its behavior after hydrogenation shows that carbon implantation also prevents the formation of well passivated Si/SiO2 interfaces. On the other hand, the PL bands appearing at higher energies show the existence of two different characteristics as a function of the implanted dose. For excess atomic concentrations below or equal to 10%, the spectra show a PL band in the blue region. At higher doses, two bands dominate the green–blue spectral region. The evolution of these bands with the implanted dose and annealing time suggests that they are related to the formation of carbon-rich precipitates in the implanted region. Moreover, PL versus depth measurements provide a direct correlation of the green band with the carbon-implanted profile. These PL bands have been assigned to two distinct amorphous phases, with a composition close to elemental graphitic carbon or stoichiometric SiC.

XPS investigation with factor analysis for the study of Ge clustering in SiO2

The change of the depth profile and chemical bond character of Ge in Ge+ ion-implanted SiO2 layers during annealing in an O2 atmosphere has been studied by x-ray photoelectron spectroscopy (XPS). The Ge depth profiles in as-implanted and annealed samples as measured by XPS are in agreement with profiles measured by Rutherford backscattering spectroscopy (RBS). At interfaces, XPS gives more information about the Ge depth distribution than RBS. Thus, other than RBS, XPS could prove that the fraction of implanted Ge, which moves during annealing to the SiO2/Si interface region, resides on the Si side of this interface. Additionally, the high- and low-contrast nanoclusters in Ge-implanted samples, which have been found recently in cross-section transmission electron microscopy images, could be identified by XPS, in combination with data analysis by factor analysis, to consist mainly of elemental Ge and GeO2, respectively. Copyright © 2000 John Wiley & Sons, Ltd.

Characterization of Si+ ion-implanted SiO2 films and silica glasses

We report here electron spin resonance (ESR), Raman scattering, photoluminescence (PL), and absorption studies of Si+ ions implanted into silica glasses and thermally grown SiO2 films on Si wafers. The aim is to understand the defect formation and luminescence mechanism as the films were annealed at several temperatures. In as-grown Si-implanted films, paramagnetic defects in the form of Si–E′ and nonbridging oxygen hole centers (NBOHC) were detected by ESR. A luminescence band, centered at 650 nm, was observed in these samples. The E′ and NBOHC defects were annealed out in samples annealed above 500 °C, but Si dangling bonds in the form of Pb centers were observed. In films annealed above 800 °C, Si nanocrystals of varying size between 1 and 5 nm were formed, as detected by transmission electron microscopy. A red PL band (>700 nm) and a Si-phonon band at 510 cm−1, gradually evolved as a function of anneal temperature. The observation of the Si-phonon mode with a 15 cm−1 shift in the peak position from the bulk affirms the presence of Si clusters in the annealed ion-implanted SiO2 films and silica glasses. We attribute this red PL band to excitonic recombination in Si nanocrystals. The peak position of this PL band was found to shift with excitation wavelength. The shift of the PL spectra as a function of excitation energy was interpreted as the emission from Si particles of certain sizes that are excited by the incident energy. An energy band gap distribution due to a size distribution was used to model the PL spectra at each excitation energy.

Enhancement of the intensity of the short-wavelength visible photoluminescence from silicon-implanted silicon-dioxide films caused by hydrostatic pressure during annealing

We have studied the influence of the hydrostatic pressure during annealing on the intensity of the visible photoluminescence (PL) from thermally grown SiO2 films irradiated with Si+ ions using double-energy implants at 100 and 200 keV and ion doses ranging from 1.2×1016 to 6.3×1016 cm−2. Postimplantation anneals have been carried out in an Ar ambient at temperatures Ta of 400 and 450 °C for 10 h at both atmospheric pressure and hydrostatic pressures of 0.1, 10, 12, and 15 kbar. It has been found that the intensity of the ultraviolet (∼360 nm), blue (∼460 nm), and red (∼600 nm) PL emission bands increases with raising hydrostatic pressure whereby the PL peaks retain their wavelength positions. The results obtained have been interpreted in terms of enhanced, pressure-mediated formation of ≡Si–Si≡ centers and small Si clusters within metastable regions of the ion-implanted SiO2.

Evaluation of microscopic structural randomness in SiO2 by analysis of photoluminescence decay profiles

Microscopic structural randomness in SiO2, a typical electrical insulating material, was evaluated by observing the decay profile of the photoluminescence due to oxygen vacancies (≡Si-Si≡). As samples with different degrees of randomness, an ion-implanted thermal SiO2 film, SiO2 films formed by plasma-enhanced chemical vapor deposition of tetraethoxysilane with and without doped fluorine, a buried oxide film prepared by SIMOX (separation by ion-implanted oxygen), and a bulk silica glass prepared by the soot-remelting method were tested. By analyzing the decay profile with a stretched exponential function, it was found that the deviation of the decay profile from a single exponential function is larger in the samples whose infrared absorption properties and HF etch rate suggest greater structural randomness. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 119 (3): 1–6, 1997

Effect of implanted ion species on the decay kinetics of 2.7 eV photoluminescence in thermal SiO2 films

Decay kinetics of photoluminescence (PL) existing around 2.7 eV has been studied in various ion-implanted thermal SiO2 films as a function of implantation conditions. The PL observed in many samples shows decay constants shorter than 10 ms, which is a well-observed decay constant for silica glass. The change in the decay constant and that in the PL intensity have been found to be systematically related with the mass and the dose of the implanted ions. Therefore, despite the short decay constant, the present 2.7 eV PL is attributable to a triplet-to-singlet transition of oxygen deficient centers, as in the case of silica glass. The rapid decay is interpreted as the increase in spin-orbit coupling interaction due to structural deformations by ion implantation such as the formation of paramagnetic defects and/or densification.