Bi/Tm共掺TiO2-BaO-SiO2-Ga2O3玻璃光谱特性与能量转换机理研究

用高温熔融法制备了Bi、Tm、Bi/Tm掺杂TiO₂-BaO-SiO₂-Ga₂O₃玻璃系统。在808 nm激光激发下, 与Tm单掺杂玻璃相比, Bi/Tm共掺玻璃中Tm³⁺的³H₄→³F₄跃迁荧光(~1485 nm)得到了显著的增强, 而Tm³⁺的³F₄→³H₆跃迁荧光(~1810 nm)减弱。在980 nm激光激发下, Tm单掺玻璃中没有观察到Tm离子的特征发光, 而在Bi/Tm共掺玻璃中观察到Tm³⁺的³F₄→³H₆跃迁荧光(~1810 nm)。这是由于在808和980 nm激光二极管(LD)各自激发下, Bi/Tm共掺玻璃中活性Bi离子的近红外发光能量传递给Tm³⁺, 分别产生³F₄→³H₄与³H₆→³H₅跃迁所致。采用Inokuti-Hirayama模型, 分析了该玻璃体系中Bi→Tm的能量传递机理。结果表明, Bi→Tm的能量传递属于电偶极–偶极相互作用。     

Optically active Er–Yb codoped Y2O3 films produced by pulsed laser deposition

Optically active Er³⁺:Yb³⁺ codoped Y₂O₃ films have been produced on c-cut sapphire substrates by pulsed laser deposition from ceramic Er:Yb:Y₂O₃ targets having different rare-earth concentrations. Stoichiometic films with very high rare-earth concentrations (up to 5.5 × 10²¹ at cm^− 3) have been achieved by using a low oxygen pressure (1 Pa) during deposition whereas higher pressures lead to films having excess of oxygen. The crystalline structure of such stoichiometric films was found to worsen the thicker the films are. Their luminescence at 1.53 μm and up-conversion effects have been studied by pumping the Yb³⁺ at 0.974 μm. The highest lifetime value (up to 4.6 ms) is achieved in films having Er concentrations of ≈ 3.5 × 10²⁰ at cm^− 3 and total rare-earth concentration ≈ 1.8 × 10²¹ at cm^− 3. All the stoichiometric films irrespective of their rare-earth concentration or crystalline quality have shown no significant up-conversion.     

Effects of reduction treatment on the photorefractive properties of Pb0.5Ba0.5Nb2O6

Lead barium niobate is a new photorefractive material of high interest for a variety of applications including holographic storage. Pb_0.5Ba_0.5Nb₂O₆ crystals have been grown by the Bridgman method, and the effects of heat treatments on their photorefractive properties were investigated using Ar ion laser at λ=514.5 nm. The color and absorption spectrum of the crystals varied depending on the oxygen partial pressure during heat treatment. The oxygen diffusivity was estimated to be in the order of 10⁻⁶ and 10⁻⁵ cm²/h at 425 and 550 °C, respectively. Reduction treatment at an oxygen pressure of 215 mTorr increased the effective density of photorefractive charges about three times from 8.0×10¹⁵ to 2.2×10¹⁶ cm⁻³ and made the charge transport more electron-dominant. As a result, the maximum gain coefficient improved from 5.5 to 13.8 cm⁻¹. A diffraction efficiency as high as 70% was achieved in a reduced crystal.     

Al2O3 formation on Si by catalytic chemical vapor deposition

Catalytic chemical vapor deposition (Cat-CVD) has been developed to deposit alumina (Al₂O₃) thin films on silicon (Si) crystals using N₂ bubbled tri-methyl aluminum [Al(CH₃)₃, TMA] and molecular oxygen (O₂) as source species and tungsten wires as a catalyzer. The catalyzer dissociated TMA at approximately 600 °C. The maximum deposition rate was 18 nm min⁻¹ at a catalyzer temperature of 1000 °C and substrate temperature of 800 °C. Metal oxide semiconductor (MOS) diodes were fabricated using gates composed of 32.5-nm-thick alumina film deposited at a substrate temperature of 400 °C. The capacitance measurements resulted in a relative dielectric constant of 7.4, fixed charge density of 1.74×10¹² cm⁻², small hysteresis voltage of 0.12 V, and very few interface trapping charges. The leakage current was 5.01×10⁻⁷ A cm⁻² at a gate bias of 1 V.     

Enhancement of Er I13/2 population in Y2O3 by energy transfer to Ce

We report measurements of the energy transfer between Er³⁺ and Ce³⁺ in Y₂O₃. The transition between the Er^{3+ 4}I_11/2 and ⁴I_13/2 excited states can be stimulated by energy transfer to Ce³⁺, augmenting the population in the ⁴I_13/2 state at the expense of that in the ⁴I_11/2 state. Experiments were performed on Y₂O₃ planar waveguides doped with 0.2 at.% erbium and 0–0.42 at.% cerium by ion implantation. From measurements of Er³⁺ decay rates as a function of cerium concentration we derive an energy transfer rate constant of 1.3×10⁻¹⁸ cm³/s. The efficiency of the energy transfer amounts to 0.47 at 0.42 at.% cerium. The energy transfer rate constant measured in Y₂O₃ is two times smaller for Er³⁺→Ce³⁺ than that for Er³⁺→Eu³⁺ in the same material.     

Implantation effect of diamond-like carbon films by 110 keV nitrogen ions

Diamond-like carbon films, grown on microscope slides by a dual-ion beam sputtering system, were implanted by 110 keV N⁺ under the doses of 1 × 10¹⁵, 1 × 10¹⁶ and 1 × 10¹⁷ions cm⁻² respectively. The implantation induced changes in electrical resistivity of the films and in infrared (IR) transmittance of the specimens were investigated as a function of implantation dose. The structural changes of the films were also studied using IR spectroscopy and Raman spectroscopy. It was observed that, with the increase of implantation dose, the diamond-like carbon films display two different stages in electrical and optical behaviours. The first is the increase of both the film resistivity and the IR transmittance of specimen at the dose of 1 × 10¹⁵ ions cm⁻² which, we consider, is attributed to the implantation-induced increase sp³ C---H bonds. However, when the doses are higher than 1 × 10¹⁵ ions cm⁻², the film resistivity and the IR transmittance of specimen decrea significantly and the decrease rates at dose range of 1×10¹⁶ to 1×10¹⁷ ions cm⁻² are smaller than those between 1×10¹⁵ and 1 × 10¹⁶ ions cm⁻². We conclude that the significant reductions of the two parameters at high doses are caused by the decreases of bond-angle disorder and of sp³ C---H bonds, the increases of sp² C---C bonds dominated the crystallite size and/or number and also the sp² C---H bonds. The smaller decrease rates at a dose range of 1 × 10¹⁶ to 1 × 10¹⁷ ions cm⁻² may be caused by further recombination of some retained hydrogen atoms to carbon atoms.     

Photoluminescence of Ga0.94In0.06As0.13Sb0.87 solid solution lattice matched to InAs

The lattice matched Ga_0.94In_0.06As_0.13Sb_0.87 quaternary solid solutions were grown by liquid phase epitaxy on (1 0 0) oriented InAs substrates from In rich melt. The p-type GaIn_0.06As_0.13Sb layers were intentionally undoped and their hole concentration was about p5×10¹⁶ cm⁻³, while n-type GaIn_0.06As_0.13Sb layers were slightly doped with Te and their electron concentration was about n10¹⁷ cm⁻³. Photoluminescence spectra exhibit single unresolved emission band in the spectral region from 0.65 to 0.8 eV for both types. Spectra were decomposed to elementary Gaussian components. The main mechanisms of radiative recombination were determined for both types of material.     

Crystal growth and spectral properties of pure and Co-doped Mg3B2O6 crystal

Novel pure and cobalt-doped magnesium borate crystals (Mg₃B₂O₆) have been grown successfully by the Czochralski technique for the first time. Crystal growth, X-ray powder diffraction (XRD) analysis, absorption spectrum, fluorescence spectrum as well as fluorescence decay curve of Co²⁺:Mg₃B₂O₆ (MBO) were described. From the absorption peaks for the octahedral Co²⁺ ions, the crystal-field parameter Dq and the Racah parameter B were estimated to be 943.3 cm⁻¹ and 821.6 cm⁻¹, respectively. The fluorescence lifetime of the transition ⁴T₁(⁴P) → ⁴T₂ centered at 717 nm was measured to be 9.68 ms.     

Temperature dependencies of excited states lifetimes and relaxation rates of 3–5 phonon (4–6 μm) transitions in the YAG, LuAG and YLF crystals doped with trivalent holmium, thulium, and erbium

The temperature dependencies of the nanosecond multiphonon relaxation (MR) rates of the ³F₃ state of Tm³⁺ in the YLF crystal and of the ⁵F₅ state of Ho³⁺ ion in the YAG and LuAG crystals and of the microsecond MR rates of the ⁴F_9/2 (²H_9/2) state of Er³⁺ ions in YLF were measured in the wide temperature range using direct laser excitation and selective fluorescence kinetics decay registration. For YLF the observed relations are explained by 4-phonon process in the frame of a single-frequency model with hω_eff=450±30 cm⁻¹ for the ³F₃ state of Tm³⁺ and by 5-phonon process with hω_eff=445 cm⁻¹ for the ⁴F_9/2 (²H_9/2) state of Er³⁺. For YAG and LuAG crystals these dependencies are explained by the 3-phonon process with hω_eff=630 cm⁻¹. The decrease of the relaxation rate with the temperature in the range from 13 to 80 K was observed for the ⁴F_9/2 (²H_9/2) state of Er³⁺ in the YLF crystal. It is explained by the redistribution of excited electronic states population of erbium ions over the higher lying Stark levels with different MR probabilities. A good fit of experimental temperature dependence (including the dropping part of the experimental curve) was obtained for single-frequency model (hω_eff=450 cm⁻¹) with W₀₁=8.0×10⁴ s⁻¹ and W₀₂=4.7×10⁴ s⁻¹ accounting Boltzmann distribution of population over two excited Stark levels of the excited state of erbium ions. Employment of this model improves the fit between the experiment and the theory for the ⁵F₅ state of Ho³⁺ ion in YAG as well. Strong influence of the parameters of the non-linear theory of MR, i.e. the reduced matrix elements U^(k) of electronic transitions and the phonon factor of crystal matrix η on the spontaneous MR rates was observed experimentally. The smaller these parameters the slower the spontaneous MR W₀. This fact can be used for searching new active crystal laser media for the mid-IR generation.     

Electrical and optical characteristics of molecular beam epitaxial Be-doped In0.53Ga0.26Al0.21As layers grown lattice-matched on InP (100) substrates

This paper reports the effects of beryllium (Be) doping in In_0.53Ga_0.26Al_0.2As layers grown lattice-matched to InP (100) substrates by molecular beam epitaxy (MBE). Hall effect measurements showed that hole concentrations as high as 2.94×10¹⁹ cm⁻³ was achieved, and the concentration decreased with further increase in the Be cell temperature. Depending on the hole concentration, good optical quality was achieved as verified by photoluminescence (PL) measurements. X-ray diffraction (XRD) measurements showed lattice mismatch values of lower than 8.6×10⁻⁴ in most samples. An intense PL peak (5 K) at 1.089 eV which is attributed to band-acceptor recombination was observed from the sample with the lowest hole concentration of 2.28×10¹⁶ cm⁻³. This sample exhibited the lowest PL full-width at half maximum (FWHM) of 8 meV (at 5 K) for the free exciton recombination. To the best of our knowledge, this is the lowest value reported to date. An increase in the hole concentration caused a merging of the band-acceptor and free excitor recombination lines to form a broad PL spectrum. A shift in the free exciton peak position in the PL spectrum was observed following an increase in the hole concentration, an effect which was probably due to degeneracy.     

Surface physical and chemical changes of pure iron after molybdenum ion implantation and their effects on the tribological behaviour I: Physical and chemical analysis

Molybdenum ions generated by a metal vapour vacuum arc (MEVVA) ion source were implanted into pure iron at doses of 1 × 10¹⁷ and 3 × 10¹⁷ ions cm⁻² with an extraction voltage of 45 kV. Auger electron spectroscopy (AES) sputtering depth profiles, X-ray photoelectron spectroscopy (XPS) analysis, X-ray diffraction (XRD) analysis, microhardness and the residual stress of the implanted specimen were studied. The results show that molybdenum atoms exist in the implanted layer at a maximum concentration 20 at.%. A new phase (Fe₃C) is formed in the specimens implanted higher doses due to carbon incorporation during sputtering of the natural oxide film from the implanted surface. The Fe₂Mo phase is formed in both dose regimes. Residual compressive stresses of 310 and 560 MPa were measured on the surfaces of the specimens after molybdenum ion implantation at 1 × 10¹⁷ and 3 × 10¹⁷ ions/cm² respectively due to a local expansion of the lattice in the near-surface region. Due to the existence of residual compressive stress and the formation of the new phases, the microhardness of pure iron specimens was increased from 264 to 325 and 333 kgf mm⁻² by molybdenum ion implantation at 1 × 10¹⁷ and 3 × 10¹⁷ ions cm⁻² respectively.     

Influence of Si doping level on the Raman and IR reflectivity spectra and optical absorption spectrum of GaN

The optical absorption (hν) and Raman and Infra Red (IR) spectra of Si doped GaN layers deposited on sapphire through buffer layers have been recorded for electron concentrations from 5×10¹⁷ to 5×10¹⁹ cm⁻³. The (hν) values deduced from photothermal deflection spectroscopy (0.5–3.5 eV) and IR absorption (0.15–0.5 eV) vary between 50 and 10⁴ cm⁻¹ showing doping dependant free electron absorption at low energy, doping independant band gap at high energy, and slowly doping dependant defect absorption in the medium energy range. In our micro Raman geometry, maxima appear or can be deduced near the frequency expected for either the A₁(LO⁻) or the A₁(LO⁺) modes split from the A₁(LO) mode by plasmon phonon interaction. There is a large systematic evolution in the expected way for the IR reflectivity.     

Deep levels in GaInAs grown by molecular beam epitaxy and their concentration reduction with annealing treatment

X-ray diffraction (XRD), current–voltage (IV), capacitance–voltage (CV), deep-level transient Fourier spectroscopy (DLTFS) and isothermal transient spectroscopy (ITS) techniques are used to investigate the thermal annealing behaviour of three deep levels in Ga_0.986In_0.014As heavily doped with Si (6.8 × 10¹⁷ cm⁻³) grown by molecular beam epitaxy (MBE). The thermal annealing was performed at 625 °C, 650 °C, 675 °C, 700 °C and 750 °C for 5 min. XRD study shows good structural quality of the samples and yields an In composition of 1.4%. Two main electron traps are detected by DLTFS and ITS around 280 K, with activation energies of 0.58 eV and 0.57 eV, capture cross sections of 9 × 10⁻¹⁵ cm² and 8.6 × 10⁻¹⁴ cm² and densities of 2.8 × 10¹⁶ cm⁻³ and 9.6 × 10¹⁵ cm⁻³, respectively. They appear overlapped and as a single peak, which divides into two smaller peaks after annealing at 625 °C for 5 min.

Annealing at higher temperatures further reduces the trap concentrations. A secondary electron trap is found at 150 K with an activation energy of 0.274 eV, a capture cross section of 8.64 × 10⁻¹⁵ cm² and a density of 1.38 × 10¹⁵ cm⁻³. The concentration of this trap level is also decreased by thermal annealing.     

P-type InP grown by liquid phase epitaxy with rare earths: not intentional Ge acceptor doping

InP single crystal layers were grown by liquid phase epitaxy (LPE) on semi-insulating InP:Fe substrates with praseodymium added to the melt. Room temperature Hall effect measurements revealed p-type conductivity of the layers with the hole concentration 6×10¹⁴ cm⁻³ and mobility 150 cm² V⁻¹ s⁻¹. By measuring temperature dependence of the hole concentration the binding energy of the dominant acceptor was determined as 223 meV. A photoluminescence line was found at 1.195 eV, close to the previously estimated no-phonon line of Ge acceptor transitions in Ge doped n-type InP. It was concluded that Ge acceptors cause the p-type conductivity of the grown layers.     

Control of Al-implantation doping in 4H–SiC

We report results of high-dose Al-ion implantation in 4H–SiC. Using multiple energy implantation techniques, box profiles were realized with targeted concentrations: 3.33×10¹⁸ to 10²¹ cm⁻³. The depths were 190 and 420 nm. The implantation energies ranged from 30 to 200 keV. The implantation and annealing temperatures were 650 and 1670°C, respectively. First, infrared investigations were done to assess the surface quality of the samples before and after annealing. Next, the conduction mechanism was investigated. Performing Hall measurements, we found that the room temperature free hole concentration varies like p_H=C_t/105 (cm⁻³), where C_t is the targeted Al-concentration, with a high level of electronic mobility. For the targeted concentration 10²¹ cm⁻³, this resulted in an active layer with 95 mΩ cm resistivity and, at room temperature, a free hole concentration of 10¹⁹ cm⁻³.     

Chemical effect of CH4 implantation into iron, nickel and aluminum thin films

Polycrystalline thin films of iron, nickel and aluminium were bombarded with CH₄⁺ ions in the dose range from 1 × 10¹⁶ to 1.2 × 10¹⁸ ions cm⁻² at room temperature and with energies between 15 and 50 keV. The formation of carbides was indicated in the cases of both iron and nickel from high voltage transmission electron micrographs and selected area diffraction patterns. No such compound formation in the case of aluminium could be detected. The carbides of iron and nickel were found to be stable on annealing up to 350 °C for 2 h.     

Ion-activated interface adsorption of oxygen during silver deposition on silicon

The process of ion-activated oxygen adsorption on silicon has been investigated using an experimental concept with simultaneous deposition of silver films. Auger electron spectroscopy in combination with sputter depth profiling is subsequently performed to determine the amount of oxygen adsorbed at the Ag---Si interface. Noble gas ions (⁴He⁺, ²⁰Ne⁺ and ⁴⁰Ar⁺)with energies between 50 and 175 keV were used, and it was found that for substrate temperatures of 300–700 K the oxygen adsorption depends strongly on ion mass, ion energy and ion flux density. For flux densities of 5 × 10¹¹ cm⁻² s⁻¹ or less, adsorption dominates and, in particular, for light-ion bombardment the majority of adsorbed oxygen atoms form chemical bonds with the silicon surface atoms (Si---O). However, for heavy ions, physical sputtering starts to compete and limits the effective rate of adsorption. At sufficiently high ion fluxes the adsorption starts to decrease, and for all ions and energies used in this work it is found that, if the electronic energy deposition density exceeds a critical value of about 1.2 × 10²¹ eV cm⁻² s⁻¹, dissociation of the Si---O bonds prevails with a corresponding loss in the adsorbed oxygen quantity.     

Synthesis and the luminescent properties of europium-activated Ca2SnO4 phosphors

The synthesis and photoluminescent (PL) properties of calcium stannate crystals doped with europium grown by mechanically activated in a high energy vibro-mill have been investigated. The characteristics of Ca₂SnO₄:Eu³⁺ phosphors were found to depend on the amounts of europium ions. The XRD profiles revealed that the system, (Ca_1−xEu_x)₂SnO₄, could form stable solid solutions in the composition range of x = 0–7% after being calcined at 1200 °C. The calcined powders emit bright red luminescence centered at 618 nm due to ⁵D₀ → ⁷F₂ electric dipole transition. Both XRD data and the emission ratio of (⁵D₀ → ⁷F₂)/(⁵D₀ → ⁷F₁) reveal that the site symmetry of Eu³⁺ ions decreases with increasing doping concentration. The maximum PL intensity has been obtained for 7 mol% concentration of Eu³⁺ in Ca₂SnO₄.     

Transparent conductive In2O3:Mo thin films prepared by reactive direct current magnetron sputtering at room temperature

An amorphous transparent conductive oxide thin film of molybdenum-doped indium oxide (IMO) was prepared by reactive direct current magnetron sputtering at room temperature. The films formed on glass microscope slides show good electrical and optical properties: the low resistivity of 5.9 × 10^− 4 Ω cm, the carrier concentration of 5.2 × 10²⁰ cm^− 3, the carrier mobility of 20.2 cm² V^− 1 s^− 1, and an average visible transmittance of about 90.1%. The investigation reveals that oxygen content influences greatly the carrier concentration and then the photoelectrical properties of the films. Atomic force microscope evaluation shows that the IMO film with uniform particle size and smooth surface in terms of root mean square of 0.8 nm was obtained.     

Dielectric properties of AlN films prepared by laser-induced chemical vapour deposition

The dielectric properties and electrical conductivity of AlN films deposited by laser-induced chemical vapour deposition (LCVD) are studied for a range of growth conditions. The static dielectric constant is 8.0 ± 0.2 over the frequency range 10²−10⁷ Hz and breakdown electric fields better than 10⁶ V cm⁻¹ are found for all films grown at temperatures above 130°C. The resistivity of the films grown under optimum conditions (substrate temperature above 170°C, NH₃/TMA flow rate ratio greater than 300 and a deposition pressure of 1–2 Torr) is about 10¹⁴ Ω cm and two conduction mechanisms can be identified. At low fields, F < 5 × 10⁵ V cm⁻¹ and conductivity is ohmic with a temperature dependence showing a thermal activation energy of 50–100 meV, compatible with the presumed shallow donor-like states. At high fields, F > 1 × 10⁶ V cm⁻¹, a Poole-Frenkel (field-induced emission) process dominates, with electrons activated from traps at about 0.7–1.2 eV below the conduction band edge. A trap in this depth region is well-known in AlN. At fields between 4 and 7 × 10⁵ V cm⁻¹ both conduction paths contribute significantly. The degradation of properties under non-ideal growth conditions of low temperature or low precursor V/III ratio is described.