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We report on the development of a novel laser crystal with broadband emission properties at similar to 2 mu m - a Tm3+, Li+-codoped calcium tantalum gallium garnet (Tm:CLTGG). The crystal is grown by the Czochralski method. Its structure (cubic, sp. gr . la (3) over bard, a = 12.5158(0) angstrom) is refined by the Rietveld method. Tm:CLTGG exhibits a relatively high thermal conductivity of 4.33 Wm(-1) K-1. Raman spectroscopy confirms a weak concentration of vacancies due to the charge compensation provided by Li+ codoping. The transition probabilities of Tm3+ ions are determined using the modified Judd-Ofelt theory yielding the intensity parameters Omega(2) = 5.185, Omega(4) = 0.650, Omega(6) = 1.068 [10(-20) cm(2)] and alpha = 0.171 [10(-4) cm]. The crystal-field splitting of the Tm3+ multiplets is revealed at 10 K. The first diode-pumped Tm:CLTGG laser generates 1.08 W at similar to 2 mu m with a slope efficiency of 23.8%. The Tm3+ ions in CLTGG exhibit significant inhomogeneous spectral broadening due to the structure disorder (a random distribution of Ta5+ and Ga3+ cations over octahedral and tetrahedral lattice sites) leading to smooth and broad gain profiles (bandwidth: 130 nm) extending well above 2 mu m and rendering Tm:CLTGG suitable for femtosecond pulse generation. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

We analyze the internal structure and hydration properties of poly(diallyl dimethyl ammonium chloride)/poly(styrene sulfonate sodium salt) oligoelectrolyte multilayers at early stages of their layer-by-layer growth process. Our study is based on large-scale molecular dynamics simulations with atomistic resolution that we presented recently [Sánchez et al., Soft Matter 2019, 15, 9437], in which we produced the first four deposition cycles of a multilayer obtained by alternate exposure of a flat silica substrate to aqueous electrolyte solutions of such polymers at 0.1M of NaCl. In contrast to any previous work, here we perform a local structural analysis that allows us to determine the dependence of the multilayer properties on the distance to the substrate. We prove that the large accumulation of water and ions next to the substrate observed in previous overall measurements actually decreases the degree of intrinsic charge compensation, but this remains as the main mechanism within the interface region. We show that the range of influence of the substrate reaches approximately 3 nm, whereas the structure of the outer region is rather independent from the position. This detailed characterization is essential for the development of accurate mesoscale models able to reach length and time scales of technological interest. © 2020 by the authors.

Here we report a detailed structural analysis, and properties of the cathodoluminescence (CL), photo-luminescence (PL) and 3D thermoluminescence spectra of the Tm3þincorporated ZnB2O4phosphorsuccessfully synthesized through wet-chemical synthesis. The formation of a single-phase compound isverified through X-ray diffraction (XRD) studies. The phosphor shows an efficient blue emission locatedat 458 nm corresponding to1D2/3F4under both a low voltage electron beam and UV excitation. Theoptimal concentration of the doped Tm3þis 0.5 mol% in CL and PL measurements. The correspondingconcentration quenching mechanism is confirmed to be a multipole-multipole interaction, and thecritical distance between Tm3þions is estimated to be 34 Å. Incorporating Liþremarkably enhances theluminescence intensity probably because of the charge compensation effect. Li ions are speculated tofillthe defects in the ZnB2O4host and then the excitation energy transfers from the host to Tm3þ. Sur-prisingly, the thermoluminescence spectra of ZnB2O4:Tm3þand Liþco-doped ZnB2O4:Tm3þrecorded inthe temperature range 30e400 C follow a different pattern compared with PL and CL data. The domi-nant signals come from Tm3þsites. Above room temperature, the Tm3þions do not show the peaktemperature movement, but do exhibit a different pattern with the addition of co-doped Liþions. Theseresults indicate that these phosphors are promising candidates for luminescence-based optoelectronicdevices.

This work addresses the formation and the internal morphology of polyelectrolyte layers obtained by the layer-by-layer method. A multimodal characterization showed the absence of stratification of the films formed by the alternate deposition of poly(diallyldimethylammonium chloride) and poly(sodium 4-styrenesulfonate). Indeed the final organization might be regarded as threedimensional solid-supported inter-polyelectrolyte films. The growth mechanism of the multilayers, followed using a quartz crystal microbalance, evidences two different growth trends, which show a dependency on the ionic strength due to its influence onto the polymer conformation. The hydration state does not modify the multilayer growth, but it contributes to the total adsorbed mass of the film. The water associated with the polyelectrolyte films leads to their swelling and plastification. The use of X-ray photoelectron spectroscopy has allowed for deeper insights on the internal structure and composition of the polyelectrolyte multilayers., Ministerio de Economía y Competitividad (MINECO), ESA, EU, ESFCOST, Depto. de Química Física, Fac. de Ciencias Químicas, TRUE, pub

Strong Stark effects are visible in the spectra of the organic donor-pi-acceptor dye D35 when it is adsorbed onto mesoporous TiO2, both under steady state conditions and under modulated light conditions. The addition of lithium cations to the electrolyte results in a significant red shift of the D35 absorption spectrum, which is attributed to adsorption of Li+ at the TiO2 surface, resulting in a change of the electric field across the adsorbed dye molecules. The dye molecules must therefore be located inside the Helmholtz double layer at the TiO2/electrolyte interface. In photoinduced absorption (PIA) spectroscopy, modulated light is used to excite dye molecules. A significant Stark bleach is found in PIA spectra, which corresponds to a blue shift of the dye absorption spectrum upon addition of electrons to TiO2, due to an electric field across the dye monolayer. The observed bleach is reduced when the concentration of supporting electrolyte is increased, indicating local charge compensation of the electrons in TiO2 by adsorbed cations. Transient absorption studies reveal that screening of the interfacial electric field is faster at lower dye coverage compared to full monolayer coverage. Analysis of the Stark effect in dye-sensitized solar cell gives valuable information on the mechanism of charge compensation of electrons in mesoporous electrodes.

We investigate in detail the influence of AlN passivation on dynamic ON-resistance (R-ON) and electric field (E-field) distribution in high-voltage AlGaN/GaN high electron mobility transistors (HEMTs) on a Si substrate based on pulsed I-V measurements, electroluminescence (EL) microscopy, and 2-D physics-based numerical device simulations. It is found that the dynamic R-ON increase has been significantly suppressed to below 10% at various temperatures ranging from -50 to 200 degrees C owing to the effective and robust compensation of deep acceptor-like trap states at the AlN/GaN (passivation/cap) interface by the additional positive polarization charges induced in the epitaxial AlN thin passivation layer grown in a plasma-enhanced atomic layer deposition system. To the best of our knowledge, this is the first time that highly suppressed current collapse in an AlGaN/GaN HEMT on a Si substrate within a wide temperature range is ever reported. By monitoring the dynamic R-ON for 100 consecutive 133-kHz switching cycles, its variation is observed to be less than 2.5%, indicating excellent stability of the passivation effectiveness. The electric field in an AlN-passivated device is found to be well confined at the drain-side gate edge, as shown in EL measurement and numerical simulation results. This phenomenon directly suggests that the virtual gate effect arising from surface trap charging has been effectively alleviated by the AlN passivation technique.

We investigate in detail the influence of AlN passivation on dynamic ON-resistance (R-ON) and electric field (E-field) distribution in high-voltage AlGaN/GaN high electron mobility transistors (HEMTs) on a Si substrate based on pulsed I-V measurements, electroluminescence (EL) microscopy, and 2-D physics-based numerical device simulations. It is found that the dynamic R-ON increase has been significantly suppressed to below 10% at various temperatures ranging from -50 to 200 degrees C owing to the effective and robust compensation of deep acceptor-like trap states at the AlN/GaN (passivation/cap) interface by the additional positive polarization charges induced in the epitaxial AlN thin passivation layer grown in a plasma-enhanced atomic layer deposition system. To the best of our knowledge, this is the first time that highly suppressed current collapse in an AlGaN/GaN HEMT on a Si substrate within a wide temperature range is ever reported. By monitoring the dynamic R-ON for 100 consecutive 133-kHz switching cycles, its variation is observed to be less than 2.5%, indicating excellent stability of the passivation effectiveness. The electric field in an AlN-passivated device is found to be well confined at the drain-side gate edge, as shown in EL measurement and numerical simulation results. This phenomenon directly suggests that the virtual gate effect arising from surface trap charging has been effectively alleviated by the AlN passivation technique.

We investigate in detail the influence of AlN passivation on dynamic ON-resistance (R-ON) and electric field (E-field) distribution in high-voltage AlGaN/GaN high electron mobility transistors (HEMTs) on a Si substrate based on pulsed I-V measurements, electroluminescence (EL) microscopy, and 2-D physics-based numerical device simulations. It is found that the dynamic R-ON increase has been significantly suppressed to below 10% at various temperatures ranging from -50 to 200 degrees C owing to the effective and robust compensation of deep acceptor-like trap states at the AlN/GaN (passivation/cap) interface by the additional positive polarization charges induced in the epitaxial AlN thin passivation layer grown in a plasma-enhanced atomic layer deposition system. To the best of our knowledge, this is the first time that highly suppressed current collapse in an AlGaN/GaN HEMT on a Si substrate within a wide temperature range is ever reported. By monitoring the dynamic R-ON for 100 consecutive 133-kHz switching cycles, its variation is observed to be less than 2.5%, indicating excellent stability of the passivation effectiveness. The electric field in an AlN-passivated device is found to be well confined at the drain-side gate edge, as shown in EL measurement and numerical simulation results. This phenomenon directly suggests that the virtual gate effect arising from surface trap charging has been effectively alleviated by the AlN passivation technique.

The combined luminescence and Raman-scattering microspectroscopy technique allows separate spectroscopic studies on several crystal phases in mixed compounds. A mixed sample of LiBaAlF6 and Ba3Al 2F12 doped with Pr was studied. The Pr3+ concentration was found to be much higher in the Ba3Al 2F12 phase. Several non-equivalent Pr3+ centers are present in both compounds, however, only in Ba3Al 2F12 there are several non-equivalent crystallographic positions of Ba. In LiBaAlF6 non-equivalent Pr3+ centers appear because of complicated scheme for charge compensation of ( PrBa3+)+. Possible reasons of Ba3Al2F 12 formation in the process of Pr3+:LiBaAlF6 growth are discussed. An excess of LiF in melt is assumed to produce ( LiBa+)- antisite defects as a charge compensation for ( PrBa3+)+ substitution. © 2013 Elsevier Ltd. All rights reserved.

The combined luminescence and Raman-scattering microspectroscopy technique allows separate spectroscopic studies on several crystal phases in mixed compounds. A mixed sample of LiBaAlF6 and Ba3Al 2F12 doped with Pr was studied. The Pr3+ concentration was found to be much higher in the Ba3Al 2F12 phase. Several non-equivalent Pr3+ centers are present in both compounds, however, only in Ba3Al 2F12 there are several non-equivalent crystallographic positions of Ba. In LiBaAlF6 non-equivalent Pr3+ centers appear because of complicated scheme for charge compensation of ( PrBa3+)+. Possible reasons of Ba3Al2F 12 formation in the process of Pr3+:LiBaAlF6 growth are discussed. An excess of LiF in melt is assumed to produce ( LiBa+)- antisite defects as a charge compensation for ( PrBa3+)+ substitution. © 2013 Elsevier Ltd. All rights reserved.

English: Red glowing phosphors were prepared by adding Pr3+ ions as activators to several oxide host matrixes; CaTiO3, LaTaO4, YTaO4, and GdTaO4. The perovskite CaTiO3:Pr3+ compound is a phosphor that glows with a single red emission around 613 nm at room temperature upon irradiation with UV light of 230 – 360 nm wavelengths or an electron beam. The source of the single red emission is the intervalence charge transfer between Pr3+ and Ti4+ ions, which opens up a channel to completely depopulate the 3P0 state, by populating the 1D2 state. This leads to a dominant emission coming from the 1D2 → 3H4 transition. The dynamics of Pr3+ in YTaO4, LaTaO4, and GdTaO4 have not been explored excessively, and the resulting emission of these compounds doped with Pr3+ comes from both 3P0 and 1D2 states of Pr3+. The compounds were prepared by solid state reaction at 1200 oC and CaTiO3 was prepared by directly firing TiO2 (Anatase phase) and CaCO3 for 4 hours. The compound was doped with several mol% concentrations of Pr3+ from PrCl3 compound to optimize the output emission intensity. The rare-earth tantalate phosphors were prepared by directly firing Ta2O5 with Y2O3, La2O3, or Gd2O3 for 4h to obtain LaTaO4, YTaO4, and GdTaO4 respectively. The tantalates were doped with 0.5 mol% concentration of Pr3+ from PrCl3 and the synthesis was carried through in the presence of 30 wt% Li2SO4 flux agent. The role of the flux agent in this instant was to increase the reaction rate by acting as an intermediate that converts the reagents to reactive species, lower the reaction temperature required for the final compound to form and to facilitate crystallinity and to control particle sizes. The phase of the phosphor compounds was identified by using X-ray diffraction (XRD, Bruker AXS D8 Advance). The XRD patterns of CaTiO3 with different Pr3+ concentrations match that of the standard orthorhombic CaTiO3 (JCPDS card no. 22-0153). The XRD patterns of LaTaO4, YTaO4, and GdTaO4 with 0.5 mol % of Pr3+ s, National Research Foundation (NRF)

Samples of epitaxially grown n-type silicon have been implanted at room temperature with low doses (10(6)-10(9) cm(-2)) of He, C, Si, and I ions using energies from 2.75 to 46 MeV. Deep level transient spectroscopy studies reveal that the generation of divacancy (V-2) and vacancy-oxygen (VO) pairs has a distinct ion mass dependence. Especially, the doubly negative charge state of the divacancy, V-2(=/-), decreases in intensity with increasing ion mass compared to that of the singly negative charge state of the divacancy, V-2(-/0). In addition, the measurements show also a decrease in the intensity of the level assigned to VO compared to that of V-2(-/0) with increasing ion mass. Carrier capture cross-section measurements demonstrate a reduction in the electron capture rate with increasing ion mass for all the three levels V-2(-/0), V-2(=/-), and VO; but a gradual recovery occurs with annealing. Concurrently, the strength of the V-2(-/0) level decreases in a wide temperature range starting from below 200 degrees C, accompanied by an increase in the amplitudes of both the VO and V-2(=/-) peaks. In order to account for these results a model is introduced where local carrier compensation is a key feature and where two modes of V-2 are considered: (1) V-2 centers located in regions with a high defect density around the ion track (V-2(dense)) and (2) V-2 centers located in regions with a low defect density (V-2(dilute)). The V-2(dense) fraction does not give any contribution to the V-2(=/-) signal due to local carrier compensation, and the amplitude of the V-2(=/-) level is determined by the V-2(dilute) fraction only. The spatial distributions of defects generated by single-ion impacts were simulated by Monte Carlo calculations in the binary collision approximation, and to distinguish between the regions with V-2(dense) and V-2(dilute) a threshold for the defect generation rate was introduced. The model is shown to g

The optimized values for the physical and geometrical parameters of the p- and n-regions used in the voltage-sustaining layer of the COOLMOS(TM)(1) are presented. Design of the parameters is aimed to produce the lowest specific on-resistance, R-on, for a given breakdown voltage, V-B. A new relationship between the R-on and V-B for the COOLMOS(TM) is developed as R-on = C.V-B(1.32), where the constant C is dependent on the cell dimension and pattern geometry. It is also found that by putting a thin layer of insulator between the p-region and its neighboring n-regions, the value of R-on can be further reduced. The possibility of incorporating the insulating layer may open up opportunities for practical implementation of the COOLMOS(TM) for volume production.

A novel silicon RF lateral double-diffused metal oxide semiconductor field effect transistor (LDMOSFET) structure, using a simple vet effective concept of stacked lightly doped drain (LDD), is proposed. The stacked lavers of LDD minimizes the on-state resistance of the transistor due to the nt doping used in the top LDD layer, and also raises the device breakdown voltage due to the charge compensation in the composite LDD region. Therefore, for the same blocking voltage rating, the stacked LDD structure allows the LDMOSFET to have a higher current handling capability, This in turn causes the transconductance Gm to be higher, leading to higher RF performance for the power device. Measured results show that a 67\% improvement in I-dsat and a 16\% improvement in forward blocking voltage are obtained. Furthermore, the new device achieves an increase in transconductance of 145\% and improves cut-off frequency by 108\% at a gate voltage of 10 V.

The optimized values for the physical and geometrical parameters of the p- and n-regions used in the voltage-sustaining layer of the COOLMOS(TM)(1) are presented. Design of the parameters is aimed to produce the lowest specific on-resistance, R-on, for a given breakdown voltage, V-B. A new relationship between the R-on and V-B for the COOLMOS(TM) is developed as R-on = C.V-B(1.32), where the constant C is dependent on the cell dimension and pattern geometry. It is also found that by putting a thin layer of insulator between the p-region and its neighboring n-regions, the value of R-on can be further reduced. The possibility of incorporating the insulating layer may open up opportunities for practical implementation of the COOLMOS(TM) for volume production.

A novel silicon RF lateral double-diffused metal oxide semiconductor field effect transistor (LDMOSFET) structure, using a simple vet effective concept of stacked lightly doped drain (LDD), is proposed. The stacked lavers of LDD minimizes the on-state resistance of the transistor due to the nt doping used in the top LDD layer, and also raises the device breakdown voltage due to the charge compensation in the composite LDD region. Therefore, for the same blocking voltage rating, the stacked LDD structure allows the LDMOSFET to have a higher current handling capability, This in turn causes the transconductance Gm to be higher, leading to higher RF performance for the power device. Measured results show that a 67\% improvement in I-dsat and a 16\% improvement in forward blocking voltage are obtained. Furthermore, the new device achieves an increase in transconductance of 145\% and improves cut-off frequency by 108\% at a gate voltage of 10 V.

The optimized values for the physical and geometrical parameters of the p- and n-regions used in the voltage-sustaining layer of the COOLMOS(TM)(1) are presented. Design of the parameters is aimed to produce the lowest specific on-resistance, R-on, for a given breakdown voltage, V-B. A new relationship between the R-on and V-B for the COOLMOS(TM) is developed as R-on = C.V-B(1.32), where the constant C is dependent on the cell dimension and pattern geometry. It is also found that by putting a thin layer of insulator between the p-region and its neighboring n-regions, the value of R-on can be further reduced. The possibility of incorporating the insulating layer may open up opportunities for practical implementation of the COOLMOS(TM) for volume production.

A novel silicon RF lateral double-diffused metal oxide semiconductor field effect transistor (LDMOSFET) structure, using a simple yet effective concept of stacked lightly doped drain (LDD), is proposed. The stacked layers of LDD minimizes the on-state resistance of the transistor due to the n+ doping used in the top LDD layer, and also raises the device breakdown voltage due to the charge compensation in the composite LDD region. Therefore, for the same blocking voltage rating, the stacked LDD structure allows the LDMOSFET to have a higher current handling capability. This in turn causes the transconductance Gm to be higher, leading to higher RF performance for the power device. Measured results show that a 67% improvement in I/sub dsat/ and a 16% improvement in forward blocking voltage are obtained. Furthermore, the new device achieves an increase in transconductance of 145% and improves cut-off frequency by 108% at a gate voltage of 10 V.

The optimized values for the physical and geometrical parameters of the p- and n-regions used in the voltage-sustaining layer of the COOLMOS(TM)(1) are presented. Design of the parameters is aimed to produce the lowest specific on-resistance, R-on, for a given breakdown voltage, V-B. A new relationship between the R-on and V-B for the COOLMOS(TM) is developed as R-on = C.V-B(1.32), where the constant C is dependent on the cell dimension and pattern geometry. It is also found that by putting a thin layer of insulator between the p-region and its neighboring n-regions, the value of R-on can be further reduced. The possibility of incorporating the insulating layer may open up opportunities for practical implementation of the COOLMOS(TM) for volume production.

This research was aimed at advancing understanding and utilization of selected optical properties of semiconductors containing magnetic elements. Emphasis was placed on the interaction of such materials with ultrashort pulses of laser radiation in order to study coupled electronic and magnetic excitations under selected nonequilibrium conditions. We hoped to generate novel results through experimental research for applications to fast optoelectronic devices. The mixed crystal semiconductors (Cd, Mn)Se and (Cd, Mn)Te were used. The contract work has generated a number of 'firsts', e.g., we measured the formation of local, microscopic magnetically oriented domains through real-time spectroscopy with picosecond laser pulses. (Author)

The objective of this basic research effort is to demonstrate the feasibility of a new technology for all solid state large data base memories for airborne/spaceborne applications. The program scope is limited to demonstrating the feasibility of the device functions and bit density capabilities required to meet the system goals. It is the objective of this program to advance one technology into development. Based on an evaluation of the present and potential capabilities of candidate solid state technologies to meet the system goals, magnetic bubble domain technology has been selected as the one to be pursued on this program. The proposed approach makes use of small bubble materials, multilayer, self-biased materials and devices, wafer level integration using hybrid chip designs and fineline lithographic techniques for device fabrication. The effort on small bubble materials research was devoted to: (1) extending the useful temperature range of the 2 micrometers and 1 micrometer bubble diameter materials which were developed in the previous report internal, (2) investigating film growth on 76 mm dia substrates, and (3) demonstrating the capabilities of the materials by device operation. With the successful accomplishment of the above three tasks the small bubbles portion of the materials research effort has been concluded. Materials research has concentrated on the means for improving the performances of self-biased bubble films and on an alternate to CaGe substitution in bubble films.