Yen-Po Lin

Investigation of the Luminescent Properties of Tb3 + -Substituted YAG:Ce, Gd Phosphors

Generation of white light closer to daylight with good color-rendering index properties can be achieved with the proper combination of emissions from the phosphor system consisting of semiconductor diode and Ce 3 + /Gd 3 + -doped yttrium aluminum garnet (YAG: Ce, Gd). Here, we report crystal structure and luminescent properties of Tb 3 + -substituted YAG: Ce, Gd. The values of lattice constant increases and the photoluminescent spectrum shows red emission shift, as the Tb 3 + content increases in YAG. We also studied luminescent properties of these phosphors using vacuum ultraviolet excitation for future plasma display panel applications. We propose a possible mechanism for the energy migration from YAG host to Tb 3 + and Ce 3 + ions.

Luminescent Properties and Structure Investigation of Y3Al5O12 ∕ Ce Phosphors with Si Addition

of YAG + xSi3N4 x = 0, 0.2, 0.3, and 0.4. The mixtures were well ground in an agate mortar and sintered in a reducing atmosphere 5% H2 in N2 at 1400°C for 5 h. Characterization.— The crystal structure and phase of the synthesized samples were analyzed using a PANalytical X’Pert PRO X-ray powder diffractometer XRD with a wavelength of Cu K = 1.5406 A at 45 kV and 40 mA. The luminescence spectra were measured using a SPEX Fluorolog-2 spectrometer with a Xe lamp as the light source. NMR characterization.— All the experiments were carried out on a Bruker DSX-300 spectrometer at 27 Al frequency of 78.2 MHz. Isotropic chemical shifts were referenced to 1.0 M aqueous AlCl3. The 27 Al TQMAS 22 spectrum was obtained at a spin rate of 12 kHz using the z-filtering sequence. 23 The pulse sequence and coherencelevel diagram were shown in Fig. 1. The nutation frequencies of the first two hard pulses and the third soft pulse were 120 and 20 kHz, respectively. Quadrature detection in the F1 dimension was achieved by the hypercomplex approach. For each t1 increment 468 transients were accumulated, and a total of 63 increments were done at steps of 83.3 s. Recycle delay was set to 1 s. Data analyses of the 2D spectra were based on the procedure described earlier. 24 The extracted NMR parameters include the isotropic chemical shift iso and the second-order quadrupolar effect

energy transfer in Ce3+-doped Y3−xTbxGd0.65Al5O12

Photoluminescence of Y2.3−x Tbx Ce0.05Gd0.65Al5O12 (x = 0.575, 1.15, 1.725 and 2.3) has been measured at room temperature at high hydrostatic pressure. Under excitation at 457 nm, the broad band emission related to interconfigurational transition from the lowest state of excited electronic configurations 5d 1 to the ground state split by spin–orbit interaction into 2 F5/2 and 2 F7/2 components of Ce 3+ ions, peaked at 550 nm, is seen. Under excitation with 325 nm one observes mainly the sharp luminescence lines related to 5 D4 → 7 F6, 5 D4 → 7 F5, 5 D4 → 7 F4 and 5 D4 → 7 F3 transitions in Tb 3+ ions. One observes a strong pressure induced red-shift of the Ce 3+ emission approximately equal to −20 cm −1 kbar −1 and much smaller shifts (approximately − 1c m −1 kbar −1 ) of the energies of the sharp lines related to Tb 3+ luminescence. It has been found that the efficiency of Tb 3+ → Ce 3+ energy transfer depends on Tb content and excitation energy; specifically, it is less effective when Tb 3+ is excited to the lowest state of the excited 5d 1 4f 7 electronic configuration. This effect has been tentatively attributed to the nonradiative de-excitation of the Tb 3+ ion to the metastable 5 D4 state. A configurational model has been developed, which explains peculiarities of relaxation in the excited states of Tb 3+ and Tb 3+ → Ce 3+ energy transfer.

Using Anodization to Oxidize Ultrathin Aluminum Film for High-k Gate Dielectric Application

Very low cost room-temperature process to fabricate ultrathin Al 2 O 3 high-k gate dielectrics with equivalent oxide thickness of 10 to 35 A was studied in this work. Anodic oxidation (anodization) in deionized water followed with rapid thermal annealing was used to oxidize ultrathin aluminum film. Unlike thermal oxidation, anodic Al 2 O 3 possesses a speciality of self-limited oxide thickness. This work also demonstrated that the anodic Al 2 O 3 exhibits gate dielectric quality characteristics, including low gate leakage current, low interface states, and low bulk trap density. The dielectric constant of anodic Al 2 O 3 is estimated to be 9.7. In addition, the gate current density, Jg, is almost independent of the measurement temperature, revealing a low trap density and high thermal stability. These good insulator characteristics are believed to be related to the leakage path self-readjustment nature under electric field influence in liquid during anodization.

Oxide-Thickness-Dependent Suboxide Width and Its Effect on Inversion Tunneling Current

Suboxide between SiO 2 and Si examined by current-voltage (I-V) measurement was found to exhibit the thickness-dependent inversion current property. In this work, oxides with thickness ranging from 20 to 40 A were grown on a single wafer. It was found that in gate injection bias, currents decrease with oxide thickness (T ox ). However, in the substrate injection region, currents saturate and the saturated levels increase with T ox . From the X-ray photoelectron spectroscopy results, suboxide width was observed to increase with T ox . We believe the minority carriers generated from the suboxide region contributes to the additional current source that lead to the polarity-dependent I-V characteristics in MOS diode.

Suboxide characteristics in ultrathin oxides grown under novel oxidation processes

Interfacial suboxide (SiOx,0<x<2) between Si and its stable SiO2 is observed to be a key factor to affect the ultrathin-oxide quality. SiO2 grown by anodic oxidation (anodization) or by repeated-spike oxidation (RSO) presents a better dielectric characteristic than conventional rapid-thermal oxidation (RTO). This improvement can be attributed to two reasons: (1) A thinner transition region and/or (2) more stoichiometric S–O bonds under the same oxide thickness. Anodic SiO2 presents a thinner suboxide width (interface region) and RSO SiO2 demonstrates the existence of less suboxide existence at the near-surface region (oxide bulk). The reduction of the imperfect bonding structure in suboxide gives an abrupt Si–SiO2 interface and consequently, the reduction of electron tunneling probability through oxide.

Application of anodization to reoxidize silicon nitride film

Anodic reoxidation of ultrathin Si3N4 film in deionized (DI) water followed by rapid thermal annealing (RTA) in N2 (ANO) was for the first time studied in this work. The Si3N4 film directly reoxidized in O2 by RTA (O2RTA) was used for comparison. It was found that the reoxidation process could significantly improve the characteristics of chemical-vapor-deposited (CVD) Si3N4 in terms of both the interface and bulk qualities. The ANO samples show lower leakage current, lower interface trap and bulk trap densities, and higher breakdown field than O2RTA of the same equivalent oxide thickness (EOT). The better electrical characteristics of ANO are due to more oxygen atoms incorporated into the Si3N4 films during the anodic reoxidation.

SiO2/Si Suboxide Characteristics of Ultra-Thin Gate Oxides Prepared by Room Temperature Anodic Oxidation and Rapid Thermal Oxidation

l. Introduction Ultrathin SiO2 under 204 will be adopted as a gate dielectric of CMOS transistor for sub-O.lpm technology node. It is known that oxides below l5A thickness can result in high leakage current. Generally, the SiOz/Si interface is not perfectly flat, a ffansition region (suboxide region, SiOx, x<2) exists within the interfacial region of about 30 A [U. Since the suboxide layer may broadly distribute in this ultrathin region, an atomic scale variation in the effective oxide layer can lead to an order of magnitude variation in local tunneling current. It is therefore of importance to improve the suboxide quality. In this work, room temperature anodic oxidation and conventional rapid thermal oxidation (RTO) are used to study ultrathin SiO2 layers. The anodic oxide presents less leakage characteristic and less barrier height lowering effect than RTO SiO2. A sharper transition from SiO2 to Si was observed for anodic oxides.