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ABSTRACT: The atomic layer deposition (ALD) of HfO2 and ZrO2 thin films is investigated using (MeCp)2HfMe2, (MeCp)2Hf(OMe)(Me), (MeCp)2ZrMe2, and (MeCp)2Zr(OMe)(Me) as the precursors at deposition temperatures between 300 and 500 °C, with water vapor as the oxygen source. A self-limiting growth mechanism is confirmed at 350 °C for all the metal precursors examined. The processes provide nearly stoichiometric HfO2 and ZrO2 films with carbon and hydrogen concentrations below 0.5 and 1.0 at.-%, respectively, for representative samples. All films are polycrystalline as deposited, and possess a thin interfacial SiO2 layer. The capacitance-voltage (C-V) and current density-voltage (I-V) behavior is reported and discussed for capacitor structures containing films from this study.
Chemical Vapor Deposition 12/2008; 14(11‐12):358 - 365. · 1.80 Impact Factor
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Journal of the American Chemical Society 11/2007; 129(41):12370-1. · 9.91 Impact Factor
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ABSTRACT: Atomic layer deposition (ALD) of HfO2 thin films was studied using four novel cyclopentadienyl precursors, namely, (CpMe)2HfMe2, Cp2Hf(OMe)2, (CpMe)2Hf(OMe)Me, and (CpMe)2Hf(OMe)2. Ozone was used as the oxygen source. Among the cyclopentadienyl precursors, (CpMe)2HfMe2 and (CpMe)2Hf(OMe)Me were the most promising, showing ALD-type growth characteristics at high temperatures as the self-limiting growth mode was confirmed at 400 °C. ALD-type growth was verified also on 60:1 aspect ratio trench structures even at 450 °C, where perfect conformality was obtained. The growth rate stayed nearly constant at around 0.5 Å/cycle at substrate temperatures between 350 and 500 °C. When Cp2Hf(OMe)2 and (CpMe)2Hf(OMe)2 were applied, slight decomposition of the precursor was detected at 350−400 °C, and thus a self-limiting growth mode was not achieved. Time-of-flight elastic recoil detection analyses demonstrated stoichiometric HfO2 films, where impurity concentrations were below 0.1 at % for C, H, and N in films deposited from each of the four Hf precursors. In addition, thin HfO2 films showed good dielectric properties such as low hysteresis, nearly ideal flatband voltage, and effective permittivity values similar to previously reported HfO2 films obtained by the alkylamide-based processes.
05/2007;
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ABSTRACT: The principles of Atomic Layer Deposition(ALD) for thin film growth are briefly introduced, emphasizing the aspects of a
self-limiting mechanism. Binary rare earth oxide(REO) thin films have been grown by ALD using various precursor approaches,
which are discussed starting with the β-diketonates (thd-complexes) which require ozone to form the oxide. The focus of this review is on the most recent developments
in the precursor chemistry, viz. the use of precursors which coordinate to the trivalent RE ions through carbon or nitrogen
and react with water at reasonable temperatures, generally below 350°C, to produce the oxide. The growth rates obtained with
RE-cyclopentadienyl complexes together with water as oxygen source are significantly higher than those observed in the conventional
β-diketonate/ozone system, e.g., for Y2O3 using (CpMe)3Y/H2O and Y(thd)3/O3 the observed growth rates were 1.2–1.3 and 0.23Å cycle–1, respectively. Furthermore, the resulting REO films from the organometallics and nitrogen-coordinated precursors have lower
carbon and hydrogen impurity levels and good electrical characteristics. However, poor thermal stability of the novel carbon-
or nitrogen-coordinated precursors may restrict their use as ALD precursors.
In addition to the desired ALD-mode reactions, other reactions may occur causing some deleterious effects on the REO films.
In particular, the large and basic La3+ ion tends to adsorb and react with environmental water and carbon dioxide to form hydroxide and carbonate phases, respectively.
Generally, dielectric properties may be improved by annealing, e.g., the permittivity for as-deposited Gd2O3 film was 10.4 but annealing in oxygen at 700°C raised it to 15.4.
The ALD processes for the binary REOs form the basis for depositing multi-component RE-containing films. Besides ternary oxides
with the perovskite structure, e.g., LaAlO3 and LaGaO3, phases with two REOs can be processed as solid solutions. An example thereof is YScO3 having permittivity above 15 and remaining amorphous up to 800°C to 1000°C, depending on the ALD process selected, thus offering
a very attractive alternative to the existing high-κ gate dielectrics.
11/2006: pages 15-32;
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ABSTRACT: The atomic layer deposition of W2O3 films was demonstrated employing W2(NMe2)6 and water as precursors with substrate temperatures between 140 and 240 degrees C. At 180 degrees C, surface saturative growth was achieved with W2(NMe2)6 vapor pulse lengths of >/=2 s. The growth rate was about 1.4 A/cycle at substrate temperatures between 140 and 200 degrees C. Growth rates of 1.60 and 2.10 A/cycle were observed at 220 and 240 degrees C, respectively. In a series of films deposited at 180 degrees C, the film thicknesses varied linearly with the number of deposition cycles. Time-of-flight elastic recoil analyses demonstrated stoichiometric W2O3 films, with carbon, hydrogen, and nitrogen levels between 6.3 and 8.6, 11.9 and 14.2, and 4.6 and 5.0 at. %, respectively, at substrate temperatures of 160, 180, and 200 degrees C. The as-deposited films were amorphous. Atomic force microscopy showed root-mean-square surface roughnesses of 0.7 and 0.9 nm for films deposited at 180 and 200 degrees C, respectively. The resistivity of a film grown at 180 degrees C was 8500 microhm cm.
Journal of the American Chemical Society 08/2006; 128(30):9638-9. · 9.91 Impact Factor
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ABSTRACT: The atomic layer deposition growth of Ga2O3 films was demonstrated using Ga2(NMe2)6 and water with substrate temperatures between 150 and 300 °C. At 250 °C, surface saturative growth was achieved with Ga2(NMe2)6 vapor pulse lengths of ≥1.5 s. The growth rate was 1.0 Å/cycle at substrate temperatures between 170 and 250 °C. Growth rates of 1.1 and 0.89 Å/cycle were observed at 150 and 275 °C, respectively. In a series of films deposited at 250 °C, the film thicknesses varied linearly with the number of deposition cycles. Time-of-flight elastic recoil detection analyses demonstrated stoichiometric Ga2O3 films, with carbon, hydrogen, and nitrogen levels between 1 and 2.1, 4.8−5.4, and 0.6−0.9 at. %, respectively, at substrate temperatures of 170, 200, and 250 °C. The as-deposited films were amorphous, but crystallized to β-Ga2O3 films upon annealing between 700 and 900 °C under a nitrogen atmosphere. Atomic force microscopy showed root-mean-square surface roughnesses of 0.4 and 0.6 nm for films deposited at 170 and 250 °C, respectively.
12/2005;
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ABSTRACT: L., Exploiting volatile lead compounds as precursors for the atomic layer deposition of lead dioxide thin films, Thin Solid Films 497 (2006) 77-82. Abstract Lead dioxide thin films were grown by atomic layer deposition on Si(100) substrates. Lead diethyl-dithiocarbamate (Pb(dedtc) 2), lead 2,2,6,6-tetramethyl-3,5-heptadione (Pb(thd) 2) and tetraphenyl-lead (Ph 4 Pb) were used as lead precursors, and ozone as oxygen source. The depositions were carried out at 300 – 350 -C, 150 – 300 -C and 185 – 400 -C for Pb(dedtc) 2 , Pb(thd) 2 and Ph 4 Pb, respectively. Attempts to use Pb(dedtc) 2 as a lead-containing precursor for lead oxide thin films resulted in lead sulphate films, which reacted with the substrate and formed lead silicate during annealing. According to X-ray diffraction, films deposited from Pb(thd) 2 /O 3 or from Ph 4 Pb/O 3 were crystalline either orthorhombic or tetragonal lead dioxide. Surface morphology of the films were characterized by atomic force microscopy while time-of-flight elastic recoil detection analysis was used to analyse stoichiometry and possible impurities. D 2005 Elsevier B.V. All rights reserved.
12/2005;
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ABSTRACT: Reactions during the atomic layer deposition (ALD) process of ZrO(2) from Cp(2)Zr(CH(3))(2) and deuterated water as precursors were studied with a quadrupole mass spectrometer (QMS) at 210-440 degrees C. The detected reaction byproducts were CpD (m/z = 67) and CH(3)D (m/z = 17). Almost all (90%) of the CH(3) ligands were released during the Cp(2)Zr(CH(3))(2) precursor pulse because of exchange reactions with the OD-terminated surface, and the rest, during the D(2)O pulse. About 40% of the CpD was released during the metal precursor pulse, and 60%, during the D(2)O pulse. ALD-type self-limiting growth was confirmed from 210 to 400 degrees C. However, below 300 degrees C the growth rate was low. Precursor decomposition affected the film growth mechanism at temperatures exceeding 400 degrees C.
Langmuir 09/2005; 21(16):7321-5. · 4.19 Impact Factor
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ABSTRACT: This review introduces the possibilities of ion-beam techniques for the analysis of thin films and thin-film structures processed by atomic layer deposition (ALD). The characteristic features of ALD are also presented. The analytical techniques discussed include RBS, NRA and ERDA with its variants, viz. the TOF-ERDA and HI-ERDA. The thin film examples are taken from flat-panel display technology (TFEL structures) and the semiconductor industry (high-k insulators).
Analytical and Bioanalytical Chemistry 09/2005; 382(8):1791-9. · 3.78 Impact Factor
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ABSTRACT: This review describes the principles and practice of atomic layer deposition (ALD) for thin-film
growth emphasising recent progress in precursor chemistry. Various types of metal-containing precursors
including conventional volatile inorganic compounds and chelates are introduced with the main emphasis
on true organometallics where the metal alkyls and cyclopentadienyl compounds seem most suitable for
ALD deposition technology. Organometallic compounds as precursors offer distinct advances in the
ALD growth of metals and metal oxides, for instance. Higher precursor reactivity compared to conventional
precursors may be utilised in ALD due to separate surface reactions. The advantages compared to conventional
precursors often include lower deposition temperatures and lower impurity levels.
08/2005: pages 125-145;
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ABSTRACT: Yttrium oxide thin films were deposited in a flow-type ALE reactor from Y(thd)3 (Hthd 2,2,6,6-tetramethyl-3,5-heptanedione) and either ozone or oxygen. The influence of the substrate and source temperatures, pressure and pulse durations on the film growth on soda-lime and silicon substrates was studied. Films were also grown on Corning glass, sapphire and Si/CeO2 substrates to study the effect of the substrate on the growth rate and crystallinity of the films. Spectrophotometry, XRD and AFM were used to determine the optical properties, thickness, crystallinity and surface morphology of the films. All the films deposited with ozone were crystalline, but differences in preferential orientation depending on the substrate were observed. The growth rate with ozone was about 0.8 Å cycle−1 on all substrates except sapphire where it was higher. The films deposited with oxygen were less crystalline and the growth rate was significantly lower than in depositions with ozone under the same growth conditions.
Advanced Materials for Optics and Electronics 09/2004; 4(6):389 - 400.
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ABSTRACT: The aim of the present solid-state NMR study was to characterize the surface species of γ-aminopropyltriethoxysilane (APTS), γ-aminopropyltrimethoxysilane (APTMS), and γ-aminopropyldiethoxymethylsilane (APDMS) on porous silica when the deposition was performed via the gas phase. The reaction temperature used, that is, 150−300 °C, in an atomic layer deposition reactor at a pressure of 20−50 mbar, was observed to distinctly affect the surface species of aminopropylalkoxysilanes on silica. The gas−solid reactions of the precursors with the silica surface were observed to be surface-limiting at the deposition temperatures of ≤150 °C. On the basis of 29Si CP/MAS NMR, the amino ends of APTS and APTMS molecules were observed to react both with alkoxy groups of other precursor molecules and silanols of silica at deposition temperatures of ≥150 °C forming Si−N linkages. The amino groups of APDMS molecules were observed to react at 150 °C only on silica heat-treated at 200 °C in a similar way. The reaction of amino groups affected also the chemical shifts of the carbon atoms in the propyl chain causing splitting of the peaks in the 13C CP/MAS NMR spectra. At still higher reaction temperatures, especially at 300 °C, decomposition of the surface structures was observed to occur. The bonding modes of trifunctional APTS and bifunctional APDMS on silica heat-treated at 200−800 °C were systematically studied by 29Si and 13C NMR when the deposition was performed at 150 °C. Bi- and tridentate species of APTS were observed on silica pretreated at 200 °C, and mono- and bidentately bound surface structures were observed when silica was heat-treated at 450−800 °C. APTMS was also observed to attach onto silica pretreated at 600 °C in a similar way. APDMS was bound both mono- and bidentately on silica pretreated at 200 °C and at 600−800 °C but solely bidentately on silica pretreated at 450 °C.
07/2004;
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ABSTRACT: Y2O3 thin films were grown onto Si(100) substrates by atomic layer deposition (ALD) using organometallic precursors, viz. tris(cyclopentadienyl)yttrium, Cp3Y, and tris(methylcyclopentadienyl)yttrium, (CpCH3)3Y (Cp = cyclopentadienyl). Water was used as oxygen source. The deposition rate of yttria in the Cp3Y/H2O process slightly increased as a function of the deposition temperature, viz. from 1.5 to 1.8 Å/cycle at temperatures from 250 to 400 °C. With the (CpCH3)3Y/H2O process, a constant growth rate of 1.2−1.3 Å/cycle was achieved in a wide deposition temperature range of 200−400 °C. The ALD-type growth mode was corroborated in both processes at 250 and 300 °C. The deposited films were characterized by XRD, AFM, and TOF-ERDA for crystallinity, morphology, and chemical composition, respectively. Carbon impurity levels for films deposited at 300 °C from (CpCH3)Y and Cp3Y were 0.2 and 0.5 atom %, respectively. (CpCH3)3Y/H2O-processed film contained 3.1 atom % of hydrogen, whereas the Cp3Y/H2O-processed film contained 1.8 atom %. With both processes the smoothest films were obtained at or below the deposition temperature of 250 °C.
07/2004;
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ABSTRACT: Atomic layer deposition (ALD) technique can be used for the preparation of amino-functionalized silica surfaces and for the study of the gas−solid reactions. In the present study N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (AAPS) was used as a silylating agent. The characterization of aminosilylated silica samples was performed by elemental analyses, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and solid-state 13C NMR. Under saturation conditions, viz. at 180 °C and at a pressure of 20−50 mbar, vaporized AAPS molecules were observed to react with the silanols of silica at the silane end of the molecule forming siloxane bridges. Thus, one surface-saturated molecular layer was deposited on the surface. Under these conditions indication of the gas-phase reaction of terminal amino groups with methoxy groups of other AAPS molecules or silanol groups of silica was observed. The surface density of amino groups on the silica surface could be controlled within 2.0−3.4 amino groups/nm2 silica through the pretreatment temperature of silica, i.e., 200−800 °C. The amino group density on silica could also be controlled through a procedure based on sequential gas-phase reactions of AAPS and water. Thus, a high-density aminopropylsiloxane network was grown on the silica surface. With this procedure a surface density of 3.0−5.4 amino groups/nm2 of silica (pretreated at 450 °C) could be obtained depending on the number of AAPS/water cycles. The surface was observed to be saturated with the precursor molecules after four AAPS/water cycles. The gas−solid reactions of AAPS on silica were also compared with those of single-amino-group precursors, viz. γ-aminopropyltrialkoxysilanes.
06/2004;
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ABSTRACT: A novel gas-phase procedure for the control of amino group density on porous silica through consecutive reactions of aminopropylalkoxysilanes and water vapor was developed. First heat-treated silica was saturated with trifunctional γ-aminopropyltrimethoxysilane (APTMS) or γ-aminopropyltriethoxysilane (APTS) in an atomic layer deposition reactor. During this step, precursor molecules were bound onto the surface both mono- and bidentately forming siloxane bridges with the silanol groups of silica. Then surface densities of 1.8 APTMS or 2.0 APTS molecules/nm2 were achieved. Next the aminosilylated surface was treated with water vapor in order to hydroxylate the free alkoxy groups of chemisorbed aminosilane molecules. At the same time, the silanol groups on the silica surface, which had remained unreacted during the first step, were revealed below the hydrolyzed alkoxy groups. These silanol groups of silica and hydrolyzed alkoxy groups were able to react further with the next feed of aminosilane molecules. The above-mentioned aminosilane/water vapor cycles, that is, two consecutive steps, could be repeated several times, and the amino group content on silica could be controlled through the number of aminosilane/water cycles. After four cycles, the surface was observed to be saturated and maximum amino group density was achieved. Then, by performing four or five cycles, surface densities of up to 3.0 APTS or APTMS molecules/nm2 were obtained. With this procedure, a high-density aminopropylsiloxane network is grown through horizontal polymerization of aminosilane molecules on the surface. With bifunctional γ-aminopropyldiethoxymethylsilane (APDMS), the repetition of aminosilane/water cycles did not increase the amino group content because of a lack of free and reactive ethoxy groups on the aminosilylated silica surface due to the bidentate bonding of APDMS molecules on silica.
11/2003;
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ABSTRACT: Besides the well-known reaction between the ethoxy groups of the silane end of the gamma-aminopropyltriethoxysilane (APTS) molecule and the silanols of silica, the amino ends of APTS molecules were observed to react in the gas phase with ethoxy groups of other APTS molecules and silanols of silica at elevated temperatures on the silica surface, dehydroxylated at 600 degrees C, forming Si-N linkages, as established by 29Si CP/MAS NMR.
Chemical Communications 09/2003; · 6.17 Impact Factor
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ABSTRACT: Modification of porous silica with aminopropylalkoxysilanes was studied under an inert atmosphere by a gas-phase technique, atomic layer deposition. Trifunctional γ-aminopropyltrimethoxysilane and γ-aminopropyltriethoxysilane (APTS), bifunctional γ-aminopropyldiethoxymethylsilane (APDMS), and monofunctional γ-aminopropyldimethylethoxysilane were used as precursors to deposit surface-saturated molecular layers onto dehydroxylated silica surfaces. A silica bed was saturated with each of the vaporized aminosilanes studied using a reaction temperature of 150 °C and a pressure of 20−50 mbar. At higher reaction temperatures, viz., 280−300 °C, decomposition of aminosilanes was observed on the surface. Aminosilanes were observed to interact with the silica surface through a site adsorption mechanism. Elemental analyses and DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy) were used for the characterization of aminosilylated silica samples. The pretreatment temperature of silica, 200−800 °C, and the precursor used were observed to affect the surface density and the bonding mode of aminosilanes on the surface. The surface densities of amino groups on silica decreased when the pretreatment temperature of silica was increased. Tri- and bifunctional aminosilanes were bound onto the silica surface through fewer alkoxy groups when the heat-treatment temperature of silica was increased. The most dense molecular layers were achieved with APDMS and APTS (2.0−2.1 molecules/nm2 on silica heat-treated at 200 °C) even though the differences between the precursors were not large. A linear correlation between the surface densities of amino groups and the number of isolated silanol groups on silica was observed.
03/2003;
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ABSTRACT: Scandium oxide thin film deposition by atomic layer epitaxy was studied at 175−500 °C using Sc(thd)3 (thd = 2,2,6,6-tetramethyl-3,5-heptanedione) and (C5H5)3Sc as scandium precursors. A constant deposition rate of 0.125 Å (cycle)-1 was observed at 335−375 °C on Si(100) and soda lime glass substrates with Sc(thd)3 and O3. The use of H2O2 as an additional oxidizer slightly increased the deposition rate to 0.14 Å (cycle)-1. When (C5H5)3Sc and H2O were used as precursors, the growth rate of Sc2O3 was significantly higher, viz., 0.75 Å (cycle)-1 at 250−350 °C. The effects of growth parameters such as reactant pulsing times were investigated in detail to confirm the surface-controlled growth mechanism. The crystallinity and surface morphology of the films were characterized by XRD and AFM, while ion-beam analysis (time-of-flight elastic recoil detection analysis) was used to determine the stoichiometry and impurity levels. Crystalline thin films with (111) as the dominant orientation were obtained on Si(100) when depositions were carried out at 300 °C or above from Sc(thd)3 and O3 precursors, while films deposited from (C5H5)3Sc and H2O were polycrystalline regardless of the deposition temperature. When films were deposited at 300 °C onto Si(100), the preferred orientation changed from (111) to (100) when the film thickness exceeded 200 nm. Films were stoichiometric when deposited from Sc(thd)3/O3 below 450 °C or from (C5H5)3Sc/H2O at 250 °C or above. When the films were deposited from Sc(thd)3/O3, the carbon content was below 0.1 atom % regardless of the deposition temperature, whereas the hydrogen content decreased to below 0.1 atom % when the deposition temperature was increased to 375 °C. The C and H contents of the films, deposited from (C5H5)3Sc/H2O at 300−400 °C, were around 0.1 and 0.5−0.3 atom %, respectively.
10/2001;
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ABSTRACT: Photoluminescence (PL) and electroluminescence (EL) of blue and green SrS:Cu thin films prepared by atomic layer epitaxy and molecular beam epitaxy, and blue SrS:Ag,Cu,Ga thin films prepared by sputtering were studied in a temperature range of 80–320 K. Two bands are present both in the PL and EL spectra of SrS:Cu films. The low energy band (L band) at about 520 nm can be observed throughout the temperature range studied. The high energy band (H band) at about 460 nm is seen only at higher temperatures and it disappears at 80 K. Decay studies at 80 K reveal at least two types of centers having lifetimes of 100 and 17 μs with a 10% variation. Several luminescence processes are proposed for further discussions. The L band may be attributed to the emission from an isolated Cu+ ion replacing the host Sr2+ ion but at an off-center site, and it undergoes a redshift caused by aggregated Cu centers. The H band is tentatively described as due to the Cu+ ion at different site symmetry. Blue luminescence of SrS:Ag,Cu,Ga most probably originates from Ag+ pairs. There is no direct evidence of energy transfer from Cu+ to Ag+ but Cu does contribute to the EL. © 1999 American Institute of Physics.
Journal of Applied Physics 10/1999; 86(9):5017-5025. · 2.17 Impact Factor
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ABSTRACT: Silver ions were implanted into SrS:Ce3+ thin films grown by atomic layer epitaxy (ALE) to examine the effects of Ag+ codoping on the luminescence of SrS:Ce3+ used in thin-film electroluminescent (TFEL) devices. High-temperature annealing (800 °C) of the standard ALE SrS:Ce prepared at 510 °C caused a pronounced blueshift of the photoluminescence (PL) emission, but the intensity was decreased. Codoping by ion implantation of Ag+ and high-temperature annealing (800 °C) caused no further blueshift but the PL intensity was more than double that of the nonimplanted samples. The implanted SrS:Ce, Ag also exhibited the longest decay value (SN = 22 ns at 520 nm with 420 nm excitation) reported for ALE SrS:Ce thin films. The improved PL properties show that codoping with Ag+ can be advantageous in ALE SrS:Ce3+ thin films used for electroluminescent multicolor and full-color flat panel displays. The results also suggest the potential of the ion implantation technique in TFEL device preparation. © 1999 American Institute of Physics.
Applied Physics Letters 04/1999; 74(16):2298-2300. · 3.84 Impact Factor
