Doping Concentration Ratio Research Articles

Energy transfer and color-tunable luminescence properties of YVO4:RE (RE = Eu3+, Sm3+, Dy3+, Tm3+) phosphors via molten salt synthesis

Single-phased YVO4:RE (RE = Eu3+, Sm3+, Dy3+, Tm3+) phosphors with high efficient photoluminescence properties have been successfully synthesized using NaNO3 as molten salt by the molten salt synthesis (MSS) method. The formation of a single YVO4 phase has been confirmed by X-ray diffraction (XRD) and the photoluminescence spectra of these phosphors have been characterized using photoluminescence spectroscopy. The results indicated that all phosphors showed rare earth ion characteristic emissions (Eu3+, Sm3+, Dy3+, Tm3+) in the YVO4 host. The dependency of the luminescence intensity on doping concentrations and annealing temperatures of YVO4:Eu3+ and YVO4:Sm3+ phosphors has been discussed. It was found that the emission of YVO4:Sm3+ at 647 nm due to 4G5/2 → 6H9/2 transition of Sm3+ ions was improved drastically by the MSS method, more than other methods. Moreover, the emission colors are tuned from blue to white and ultimately to yellow through concentration variation of the doping concentration ratio of Tm3+ and Dy3+ in YVO4:Dy3+/Tm3+, and a white light could be achieved from YVO4:1% (Dy0.3Tm0.7) phosphor with chromaticity coordinates of (0.32, 0.31) under excitation at 320 nm.

Preparation of Ho3+/Tm3+ Co-doped Lanthanum Tungsten Germanium Tellurite Glass Fiber and Its Laser Performance for 2.0\u2009\u03bcm

Ho3+/Tm3+ co-doped 50TeO2-25GeO2-3WO3-5La2O3-3Nb2O5-5Li2O-9BaF2 glass fiber is prepared with the rod-tube drawing method of 15 μm core diameter and 125 μm inner cladding diameter applied in the 2.0 μm-infrared laser. The 2.0 μm luminescence properties of the core glass are researched and the fluorescence intensity variation for different Tm3+ doping concentration is systematically analyzed. The results show that the 2.0 μm luminescence of Ho3+ is greatly influenced by the doping concentration ratio of Ho3+ to Tm3+ and that the maximum fluorescence intensity of the core glass can be obtained and its emission cross section can reach 0.933 × 10−21 cm2 when the sensitized proportion of holmium to thulium is 0.3 to 0.7 (mol%). Simultaneously, the maximum phonon energy of the core glass sample is 753 cm−1, which is significantly lower than that of silicate, gallate and germanate glass and the smaller matrix phonon energy can be conductive to the increase 2.0 μm-band emission intensity. The continuous laser with the maximum laser output power of 0.993 W and 2051 nm -wavelength of 31.9%-slope efficiency is output within the 0.5 m glass fiber and the experiment adopts 1560 nm erbium-doped fiber laser(EDFL) as the pump source and the self-built all-fiber laser. Therefore, the glass fiber has excellent laser characteristics and it is suitable for the 2.0 μm-band laser.

Bidirectional energy transfer induced single-band red upconversion emission of Ho3+ in KZnF3:Mn2+,Yb3+,Ho3+ nanocrystals

In contrast to common multiple upconversion (UC) emission characteristic from Ho3+, intense single-band red UC emission is realized in perovskite KZnF3: Mn2+,Yb3+,Ho3+ nanocrystals via controlling the doping concentration ratio of Mn2+ to Ho3+. Based on stokes emission, UC luminescence and energy levels of Mn2+ and Ho3+, a bidirectional energy transfer from the 5S2/5F4 state of Ho3+ to the 4T1(4G) state of Mn2+or |F27/2,T41(G4)〉 state of Yb3+-Mn2+ dimer, then to 5F5 state of Ho3+ (ET2) is provided to explain the unique UC emission behaviors of KZnF3: Mn2+,Yb3+,Ho3+. The effects of dopant concentration on the UC luminescence properties of KZnF3: Mn2+, Yb3+, Ho3+ is investigated in detail. Analysis of the dominant red UC emission of KZnF3: Mn2+, Yb3+, Ho3+ under different laser pulse width excitation indicates the energy transfer process. The special temperature dependent UC luminescence for Mn2+ doped and Mn2+ freely doped KZnF3:Yb3+, Ho3+ further confirm the bidirectional energy transfer mechanism in the UC process. The study of these single-band red UC nanocrystals provides deep insights into the understanding of bidirectional energy transfer in UC mechanism, offering the possibility for applications in biolabels and bioimaging.

White Light Emission and Luminescence Dynamics in Eu³⁺/Dy³⁺ Codoped ZnO Nanocrystals.

In order to expand the use of ZnO in advanced display and lighting device applications, such as distinguishable emissive flat panel displays and liquid crystal display backlights, Eu³⁺/Dy³⁺-codoped ZnO nanocrystals were synthesized using a low temperature wet chemical doping technique and chemical surface modification. X-ray diffraction patterns revealed that co-doping Eu³⁺ and Dy³⁺ does not change the wurtzite structure of ZnO. A high-resolution TEM image showing obvious lattice fringes confirmed the high crystallinity of the nanosized sample. The luminescence and dynam- ics of Eu³⁺/Dy³⁺-codoped ZnO nanocrystals of various doping concentrations were studied under ultraviolet excitation. Excitation into the ZnO conduction band was also studied. ZnO doped with Eu³⁺ and Dy³⁺ ions exhibited a strong blue (483 nm) emission from the ⁴F₉/₂ --> ⁶H₁₅/₂ transition of Dy³⁺ ions, a yellowish-green (575 nm) emission from the ⁴F₉/₂ --> ⁶H₁₃/₂ transition of Dy³⁺ ions and a red (612 nm) emission from the ⁵D₀ --> ⁷F₂ transition of Eu³⁺ ions, without a defect background. Undoped ZnO emitted a broadband green light, demonstrating an efficient energy transfer from the ZnO host to the Eu³⁺ and Dy³⁺ ions. Moreover, energy transfer from the Eu³⁺ ions to the Dy³⁺ ions in the ZnO host was also observed by analyzing luminescence decay curves. The luminescence dynamics of the Eu³⁺/Dy³⁺-codped ZnO sample indicate that as the Eu³⁺ concentration increased, both the rise and the decay time constants of the ⁴H₉/₂ level of the Dy³⁺ ions became longer, while the decay time constants of the ⁵D₀ level of the Eu³⁺ ions became shorter, suggesting an energy transfer from the Eu³⁺ ions to the Dy³⁺ ions in the ZnO host. Furthermore, by adjusting the doping concentration ratio of Eu³⁺ and Dy³⁺ ions, the Eu³⁺/Dy³⁺-codoped ZnO phosphors emitted strong white luminescence with a high color purity and high color rendering index. The results indicate that the Eu³⁺/Dy³⁺-codoped ZnO phosphors are promising light-conversion materials, and have the potential to be used in field emission display devices and LCD backlights.

Effects of doping concentration ratio on electrical characterization in pseudomorphic HEMT-based MMIC switches for ICT system

The effects of the doping concentration ratios between upper and lower silicon planar-doping layers on the DC and RF characteristics of the double planar doped pseudomorphic high electron mobility transistors (pHEMTs) are investigated. From the device simulation, an increase of maximum extrinsic transconductance and a decrease of total on- and off-state capacitances are observed, as well as an increase of the upper to lower planar-doping concentration ratios (UTLPDR), which give rise to an enhancement of the switching speed and isolation characteristics. On the basis of simulation results, two types of pHEMTs are fabricated with two different UTLPDRs of 4:1 and 1:2. After applying these two types’ pHEMTs, single-pole-double-throw (SPDT) transmitter/receiver monolithic microwave integrated circuit (MMIC) switches are also designed and fabricated. The SPDT MMIC switch with a 4:1 UTLPDR shows an insertion loss of 0.58dB, isolation of 40.2dB, and switching speed of 100ns, respectively, which correspondingly indicate a 0.23dB lower insertion loss, 2.90dB higher isolation and 2.5 times faster switching speed than those of 1:2 UTLPDR at frequency range of 2–6GHz. From the simulation results and comparative studies, we propose that the UTLPDR must be greater than 4:1 for the best switching performance. With the abovementioned excellent performances, the proposed switch would be quite promising in the application of information and communications technology system.

Characterization of Terbium and Samarium Co-Doped Ceria Films as SOFC Electrolyte Prepared by Using Ultrasonic Spray Pyrolysis Method

Because of the high ionic conductivity at intermediate temperatures (500–700 °C), doped ceria oxides are of special interest as the promising electrolyte materials for the intermediate temperature solid oxide fuel cells (IT-SOFC). However, main drawback of the ceria based solid electrolytes is the partial electronic conductivity at reducing conditions resulting in an internal partial short-circuiting of the cell and decreased total efficiency for SOFC. Tb, considered an electron trap, was found to suppress the partial electronic conductivity for microcrystalline ceria electrolyte. The aim of this work is to study the influence of Tb and Sm dopant concentration ratio on the microstructural and electrical properties of Ce0.9Sm0.1-xTbxO2-δ films. Tb and Sm cations binary co-doped ceria films were deposited using the ultrasonic atomizing spray pyrolysis method. The crack-free homogenous films with different dopant concentration were deposited and thereafter annealed at fixed temperatures 900, 1200 and 1300 °C, respectively. It was demonstrated that several microstructural parameters of oxide films are controlled by the sintering temperature. The Ce0.9Sm0.1-xTbxO2-δ films formed were analyzed using X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscopy, atomic force microscopy and four probe dc technique at different pO2 and T values. Based on the SEM analysis the average thickness of Ce0.9Sm0.1-xTbxO2-δ films were 700 nm. The XRD patterns for the Ce0.9Sm0.1-xTbxO2-δ films annealed at 1200 °C indicated the high degree of crystallinity. Tb dopant ions influence the microstructural properties like median diameter of grain, microstrain, lattice parameter and electrical properties like activation energies of ionic and electronic conductivity of the Ce0.9Sm0.1-xTbxO2-δ film. Significantly higher microstrain value for smallest Tb dopant concentration and strong dependence of electrical properties on that was observed. The activation energy of ionic conductivity was lowered in that case, while the activation energy of electronic conductivity was increased. The lower bound of electrolytic domain for Ce0.9Sm0.09Tb0.01O2-δ film was lowered by one order of magnitude toward lower oxygen partial pressures. Further increase of Tb amount increased the activation energy of ionic conductivity, shifting the lower bound of electrolytic domain toward higher oxygen partial pressures.

Gas Sensitivity and Morphologically Characterized of Nanostructure CdO Doped In2O3 Films Deposited by Pulsed Laser Deposition

In this work, films have been grown under various deposition conditions in order to understand the effect of processing on the film properties and to specify the optimum condition, different indium oxide (In2O3) contents (0, 1%, 3%, 5% and 7%) using double frequency pulse laser beam (Q-switching) Neodymium-yttrium aluminum garnet (Nd:YAG (wavelength 532 nm)), to deposit Cadmium Oxide: Indium oxide (CdO:In2O3) films on Aluminum Oxide (sapphire α-Al2O3 (006)) and quartz substrates. The structural properties of samples were investigated by using of surface morphology of the deposits materials has been studied by using atomic force microscopy (AFM). The samples are displayed granular structure. It was found that the grain size decreases with increasing of doping concentration ratio, the smallest grain size equal to (79.11 nm) and (82.99 nm) were achieved at ratio of doping (7%) for quartz and sapphire α-Al2O3 substrate, respectively. The sensitivity of undoped and doped CdO samples toward Nitric dioxide (NO2) gas in air ambient has been measured in the home building system. All samples were tested at mixing ratio (3% NO2:air). The optimal operating temperature is found to be 200-225°C for pure CdO and decreases to 175-200°C for samples. The maximum sensitivity is equal to (263.97%) with response time (13.5 s) and recovery time (15.5 s) are achieved at (3%) doping concentration level for sapphire α-Al2O3 substrate.

Gain-shift induced by dopant concentration ratio in a thulium-bismuth doped fiber amplifier

This paper details the effect of Thulium and Bismuth concentration ratio on gain-shift at 1800 nm and 1400 nm band in a Thulium-Bismuth Doped Fiber Amplifier (TBDFA). The effect of Thulium and Bismuth's concentration ratio on gain shifting is experimentally established and subsequently numerically modeled. The analysis is carried out via the cross relaxation and energy transfer processes between the two dopants. The energy transfer in this process was studied through experimental and numerical analysis of three samples with different Tm/Bi concentration ratio of 2, 0.5 and 0.2, respectively. The optimized length for the three samples (TBDFA-1, TBDFA-2 and TBDFA-3) was determined and set at 6.5, 4 and 5.5 m, respectively. In addition, the experimental result of Thulium Doped Fiber Amplifier (TDFA) was compared with the earlier TBDFA samples. The gain for TBDFA-1, with the highest Tm/Bi ratio, showed no shift at the 1800 nm region, while TBDFA-2 and TBDFA-3, possessing a lower Tm/Bi concentration ratio, shifted to the region of 1950 and 1960 nm, respectively. The gain shifting from 1460 nm to 1490 nm is also observed. The numerical model demonstrates that the common 3F4 layer for 1460 nm emission (3H4→3F4), and 1800 nm emission (3F4→3H6)inversely affects the 1460 nm and 1800 nm gain shifting.

Analytical Expression for Thermionic Transport Through Isotype Heterojunction Interfaces of Arbitrary Doping Ratio

We present an analytical expression for the current density across an isotype heterojunction valid for arbitrary doping concentration ratios. This result generalizes the standard expression found in the literature, which is limited by the assumption that the doping concentration ratio is equal to one. This result relies on the solution of a transcendental equation associated with the heterojunction boundary conditions by means of the Lambert W function. As done in the derivation of the standard expression, the generalization only considers thermionic emission, but the method can equally be applied for other transport mechanisms. The general result mathematically contains the expression for the current density across a metal-semiconductor Schottky contact as a limiting case, unifying the treatment of these two heterointerfaces into a single general analytical description.

Synthesis and luminescent properties of Eu3+ and Dy3+ doped BiPO4 phosphors for near UV-based white LEDs

The phosphors BiPO4:Eu3+ co-doped with Dy3+ were synthesized by the conventional solid-state reaction method. XRD and scanning electron microscopy results showed that the crystalline phase of the samples BiPO4:Eu3+ transforms from high-temperature monoclinic phase to low-temperature monoclinic phase with the increase of Dy3+ concentration. The photoluminescence properties of the samples showed that the colors shifting from red–orange area to blue–green area are close to those of ideal white light by readjusting the doping concentration ratio of Eu3+ and Dy3+. The Eu3+and Dy3+ doped BiPO4 phosphors may be potential applications in white light near-UV light-emitting diodes.

Influence of pH on the Morphology and Luminescence Properties of Europium-Doped Hydroxyapatite Nanoparticles

Luminescence behaviors and morphology of Eu3+doped hydroxyapatite synthesized under different pH values were well investigated by X-ray diffraction (XRD), scanning electronic microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Inductively Coupled Plasma (ICP) (ICP–PLASMA 1000), and photoluminescence (PL) spectroscopy. Results revealed that With pH values increased from 6.5 to 10.0, the morphology of nano-Eu:HA particles changes from rod particles to equiaxed particles. The actual doping concentration and aspect ratio of Eu3+-doped HA decreased with the increasing of pH value. At the same time, the fluorescence intensity also tends to weakly lower with the increasing of pH value, which indicated that the luminescence properties mainly depended on the actual Eu3+doping concentration, the influences of morphology on the luminescence properties were slight.

적색 도펀트가 도핑된 발광층을 갖는 유기발광다이오드에서의 컬러 시프트 메커니즘 연구

컬러 시프트 현상은 다양한 색상을 생성하는 유기발광다이오드 소자에 있어서 발광 색상의 순도를 저하시키는 주요 원인으로 작용되어지고 있다. 본 연구에 적용한 유기발광다이오드 소자의 기본 구조는 ITO/<TEX>${\alpha}$</TEX>-NPD/<TEX>$Alq_3$</TEX>:DCJTB [wt%]/<TEX>$Alq_3$</TEX>/Mg:Ag로 구성되어지며, 컬러 시프트가 일어나는 메커니즘을 규명하기 위하여 유기발광다이오드 소자 내에서의 전기광학적인 특성 요인들을 수치 해석하였다. 또한 DCJTB[wt%]의 도핑 농도 비율을 변화시켜 가면서 컬러 시프트의 원인을 조사하였다. 그 결과, 발광층과 정공 수송층의 경계면에서 발생되어지는 호스트에 트랩된 전자들과 자유 정공들 그리고 게스트에 트랩된 정공들과 자유 전자들에 의한 재결합율의 변화가 컬러 시프트 현상의 주요 요인들 중의 하나임을 확인하였다. The Color shift phenomenon is becoming a major degradation factor of the emitting color purity in the organic emitting diodes which is generating a plurality of colors. In this study, the basic structure of organic light emitting diode device is comprised of ITO/<TEX>${\alpha}$</TEX>-NPD/<TEX>$Alq_3$</TEX>:DCJTB[wt%]/<TEX>$Alq_3$</TEX>/Mg:Ag, we have carry out numerical simulation of the electric-optical characteristics in organic light emitting diode device to estimate the mechanism of color shift phenomenon. We have investigated the causes of the color shift through the change of DCJTB doping concentration ratio. As the result, we have confirmed that the changes of the recombination rate which generated by trapped electrons and holes is one of the major factors for the color shift phenomenon.

Physical properties of indium and fluorine codoped zinc oxide thin films deposited by chemical spray

Indium and fluorine codoped zinc oxide (ZnO:In + F) thin films were deposited on glass substrates by the chemical spray technique. The effect of the dopant concentration ratio in the starting solution, as well as the substrate temperature on the electrical, morphological, structural, and optical properties of ZnO:In + F thin films was studied. A minimum electrical resistivity, in the order of 3.4 × 10 −3 Ω cm, for as-grown films deposited at 475 °C from a starting solution containing [In]/[Zn] = 3 and [F]/[Zn] = 20 at.%, was obtained. All the films were polycrystalline, and some differences in the intensity of the peaks and preferential growth, depending on the doping ratios, were observed. The deposited ZnO:In + F thin films showed an average optical transmittance in the order of 85%, in the visible region (400–700 nm). The band gap values oscillated around 3.35 and 3.39 eV, and a shift towards higher values with the increase of the dopant concentration was observed. The surface morphology of the films was also strongly affected by the dopant concentration ratio, since a variation in both geometry and grain size was observed.

Photoluminescence properties of Sr 1– xSi 2O 2N 2: Eu 2+x as green to yellow-emitting phosphor for blue pumped white LEDs

This study evaluated potential applications of green to yellow-emitting phosphors (Sr 1− x Si 2O 2N 2: Eu 2+ x ) in blue pumped white light emitting diodes. Sr 1– x Si 2O 2N 2: Eu 2+ x was synthesized at different Eu 2+ doping concentrations at 1450 °C for 5 h under a reducing nitrogen atmosphere containing 5% H 2 using a conventional solid reaction method. The X-ray diffraction patterns of the prepared phosphor (Sr 1– x Si 2O 2N 2: Eu 2+ x ) were indexed to the SrSi 2O 2N 2 phase and an unknown intermediate phase. The photoluminescence properties of these phosphors (Sr 1− x Si 2O 2N 2: Eu 2+ x ) showed that the samples were excited from the UV to visible region due to the strong crystal field splitting of the Eu 2+ ion. The emission spectra under excitation of 450 nm showed a bright color at 545–561 nm. The emission intensity increased gradually with increasing Eu 2+ doping concentration ratio from 0.05 to 0.15. However, the emission intensity decreased suddenly when the Eu 2+ concentration ratio was >0.2. As the doping concentration of Eu 2+ was increased, there was a red shift in the continuous emission peak. These results suggest that Sr 1– x Si 2O 2N 2: Eu 2 + x phosphor can be used in blue-pumped white light emitting diodes.

Facile Mixed-Solvent-Thermal Synthesis and Characterization of Shape-Controlled Monodisperse CeF&lt;SUB&gt;3&lt;/SUB&gt;:Tb&lt;SUP&gt;3+&lt;/SUP&gt; Nanocrystals

Monodisperse CeF3:Tb3+ nanocrystals have been synthesized from mixed solvents-thermal synthesis under mild condition. The products have been characterized by High Resolution Transmission electron microscopy (HRTEM), X-ray diffraction (XRD), UV-visible Diffuse Reflectance spectra and luminescent spectra, respectively. Besides, different solvents ratio and different surfactants to synthesize CeF3:Tb3+ nanocrystals have been compared to investigate the influence on their microstructure and morphology. As a result, the HRTEM images reveal the products crystallize in the hexagonal structure corresponding to the XRD and illustrate the mean rod length of about 15 nm, whose preferred orientation is parallel to the growth direction, namely c axis direction. The solvent ratios have influence on the microstructure and morphology of the products to some extent. With the increase of DMF solvent, the shape of CeF3:10%Tb3+ changed from grain-like particles to rodlike ones. In addition, a disordered array of CeF3:10%Tb3+ nanocrystals can be obtained with the existence of oleic acid. The characteristic emissions of Tb3+ originated from (5)D4-->7F(J) (J = 6, 5, 4, 3) are observed, and the dominant peak was the green emission of 543 nm. Measurements of emission spectra have been performed to examine the effect of Tb3+ concentration quenching on spectroscopic properties. The optimum doping-concentration ratio of Tb3+ was found to be approximately 15 mol%.

Effects of Phosphorus Implantation on the Activation of Magnesium Doped in GaN

The effects of phosphorus implantation on the activation of magnesium doped in GaN at different dopant concentration ratios have been systematically investigated. Hall effect measurements show that P implantation improves the hole concentration, and that this improvement is dependent on P/Mg dopant concentration ratio and annealing conditions. This phenomenon is attributable to the reduction in self-compensation that results from the formation of deep donors and the enhanced Mg atom activation, which is in reasonable agreement with the optical properties observed by photoluminescence measurements. In addition, a new photoluminescence peak resulting from P-related transitions is also observed, evidently owing to the recombination of electrons from the shallow native donors with holes previously captured by isoelectronic P traps.

Magnesium/nitrogen and beryllium/nitrogen coimplantation into GaN

The nitrogen coimplantation characteristics in the Mg- and Be-implanted GaN with different dopant concentration ratios have been systematically investigated. The Hall-effect measurements show that the p-type characteristics are produced in the Mg- and Be-implanted GaN by the coimplantation of N atoms and subsequent annealing, which is essentially related to the column II/V dopant concentration ratio and annealing condition. This behavior may be attributed to the reduction of self-compensation induced by N vacancies and the enhanced acceptor substitution, which is in reasonable agreement with the surface stoichiometric switching determined by x-ray photoelectron spectroscopy measurements. From photoluminescence data, the activation energy of the Be acceptor level is evaluated to be about 145meV, which is shallower than that of the Mg acceptor. These experimental results indicate that the selective-area N coimplantation with Mg and Be atoms into GaN is an effective method to enhance the p-type conductivity and to improve the p-type Ohmic contact resistance.

C and N co-implantation in Be-doped GaN

Carbon and nitrogen co-implantation characteristics in Be-doped GaN with different dopant concentration ratios have been systematically investigated. It was found that the conductive characteristics of Be-doped GaN convert to p-type by co-implantation of C or N atoms and subsequent annealing, which are essentially related to the dopant concentration ratio and annealing conditions. The conversion could be attributed to the reduction of self-compensation and the shift of the surface Fermi level towards the valance band edge. The outcome was reasonably in agreement with the surface stoichiometric switching as determined by x-ray photoelectron spectroscopy measurements. From photoluminescence data, the activation energy of the Be acceptor level was evaluated to be about 145–155 meV, which is shallower than that of Mg acceptors. These experimental results indicated that co-implanting C or N with Be atoms into the selective area of GaN is an effective method to enhance the electrical activation efficiency of Be acceptors and to reduce the surface barrier height, which can help to decrease the metal contact resistivity to p-type GaN.

Study of the effect of gamma-irradiation on the emission spectra of poly(methylmethacrylate) doped with rhodamine dyes

The emission spectra of irradiated and non-irradiated thin films of poly (methyl methacrylate) (PMMA) matrices containing rhodamine B (RhB) or rhodamine 6G (Rh6G) as donors and chloranil (CA) as acceptor, have been investigated. A single radiophotoluminescence peak was recorded around 570 nm. The maximum fluorescence intensity was found to be at a doping concentration ratio of 6:4, acceptor: donor. The materials investigated, particularly Rh6G-CA, proved to be sensitive in absorbing UV light and re-emitting in the visible region, and hence, could be used as a luminescent concentrator for solar cells. Such materials may also find a useful field of application in radiation dose assessment.

Adaptive mesh refinement for multilayer process simulation using the finite element method

An adaptive mesh refinement technique is proposed for a two-dimensional finite-element multilayer process simulator. Mesh refinement is based on the dopant concentration ratio inside each element, together with a prediction technique, minimizing the interpolation errors. A significant reduction in CPU time is obtained by automatic grid refresh. Several methods were tested. The mesh adequacy is evaluated with bipolar test structures using analytical punch-through voltage calculations. Applications of these methods are presented in two ways. First, an advanced trench-isolated polysilicon bipolar transistor was simulated to show the general possibilities of the techniques, and second, a coupled process and device simulation approach allows the evaluation of the scheme on real structures in relation to experimental measurements.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>