Al Thickness Research Articles

Computational modeling of optical properties in aluminum nanolayers inserted in ZnO for solar cell electrodes.

Numerical simulations were used to study the transmittances (Ts) of ZnO/Al/ZnO (ZAZ) films with Al thicknesses between ∼1 and 40nm. The simulations are validated using previously reported experimental results. Multilayers with Al thicknesses between ∼1 and 10nm are shown to have average Ts between ∼75% and 90%, which decreased farther to ∼63 and 41% for the Al layer thicknesses of 20 and 40nm, respectively. Variations in the ZnO thickness between ∼10 and 100nm are shown to have little effect on the optical properties of the model multilayers for a given Al thickness. The reliability of the numerical simulations is tested by comparing them with experimental measurements on films produced using similar interlayer thicknesses. These are also shown to be comparable to the performance characteristics of indium tin oxide (ITO) anodes that are used currently in organic solar cells (OSCs) and organic light emitting diodes (OLEDs).

Influence of Al Composition Thickness on Critical Current Density in Transformation-Processed <inline-formula> <tex-math notation="TeX">$\hbox{Nb}_{3}\hbox{Al}$</tex-math></inline-formula> Superconductors

The influence of the Al layer thickness on the critical current density $J_{c}$ of transformation-processed $\hbox{Nb}_{3}\hbox{Al}$ superconductors was investigated. The Al layer thickness in the jerry-roll filaments of precursor wires was varied from 120 to 250 nm; the Nb layer thickness is proportional to the Al thickness, keeping the Nb–Al composition ratio to 3. The rapid heating and quenching (RHQ) operation condition was varied within a range of the conditions to form the ductile body-centered cubic (BCC) Nb–Al phase. The RHQ wires were also followed by an areal reduction process prior to the $\hbox{Nb}_{3}\hbox{Al}$ phase transformation. Thinner Al thickness wires show a steeper increase in $J_{c}$ with reduction in the area, whereas thicker Al thickness wires show a slower increase. The best $J_{c}$ performance was obtained for the thinnest Al thickness sample. Without areal reduction, there was not much difference in the optimum $J_{c}$ with respect to the Al thickness.

A simulation study on the electrical structure of interdigitated back-contact silicon solar cells

In this paper, a simulation for interdigitated back-contact (IBC) silicon solar cells was performed by using Silvaco TCAD ATLAS to investigate the cell’s electrical properties. The impacts of various parameters, including the depth of the front surface field(FSF), the FSF peak doping concentration, the depths of the emitter and the back surface field(BSF), the peak doping concentrations of the emitter and BSF, the base doping, and the bulk lifetime on the output characteristics like the light current-voltage curves and the internal quantum efficiency of the IBC solar cell, were investigated. The light absorption was determined by adjusting the antireflection coating and the Al thickness. The FSF must be thin and have a low doping concentration for high-efficiency IBC cells. If the conversion efficiency is to be improved, a thick emitter and a high doping concentration are needed. Because of the low resistivity of the Si substrate, the series resistance was reduced, but recombination was increased. With a high-resistivity Si substrate, the opposite trends were observed. By counter-balancing the series resistance and the recombination, we determined by simulation that the optimized resistivity for the IBC cells was 1 Ω·cm. Because all metal electrodes in the IBC cells are located on the back side, a higher minority carrier lifetime showed a higher efficiency. After the various parameters had been optimized, texturing and surface recombination were added into the simulation. The simulated IBC cells showed a short-circuit current density of 42.89 mA/cm2, an open-circuit voltage of 714.8 mV, a fill factor of 84.04%, and a conversion efficiency of 25.77%.

Microstructure of V-based ohmic contacts to AlGaN/GaN heterostructures at a reduced annealing temperature

Ohmic contacts with V/Al/Ni/Au and V/Ni/Au metalization schemes were deposited on AlGaN/GaN heterostructures. The dependence of the specific contact resistance on the annealing conditions and the V:Al thickness ratio was shown. For an optimized electrode stack, a low specific contact resistance of 8.9 × 10−6 Ω cm2 was achieved at an annealing temperature of 650 °C. Compared to the conventional Ti/Al/Ni/Au contact, this is a reduction of 150 K. The microstructure and contact formation at the AlGaN/metal interface were investigated by transmission electron microscopy including high-resolution micrographs and energy dispersive X-ray analysis. It was shown that for low-resistive contacts, the resistivity of the metalization has to be taken into account. The V:Al thickness ratio has an impact on the formation of different intermetallic phases and thus is crucial for establishing ohmic contacts at reduced annealing temperatures.

Broadband and wide-angle antireflective characteristics of nanoporous anodic alumina films for silicon-based optoelectronic applications

Nanoporous anodic alumina (NPAA) films are fabricated on silicon (Si) surfaces by the anodization of aluminum (Al). Effect of the thickness of initial Al films on the antireflective characteristics of NPAA films consisting of random pore structures is investigated in the wavelength range of 300–1,100 nm at incident light angles (θ inc) of 3°–70°, together with theoretical analysis using a rigorous coupled-wave analysis method. The reflectance strongly depends on the thickness and porosity of NPAA films, resulting from anodization parameters such as applied voltage, anodization time, and pore widening time. For the obtained NPAA film at the initial Al thickness of 100 nm and the applied voltage of 30 V, the surface reflectance is reduced over a wide wavelength region of 300–1,100 nm at normal incidence of ~3°, exhibiting the relatively lower average reflectance (R avg) of ~19 % (i.e., R avg ~ 39 % for the bare Si substrate). The lower angle-dependent reflective properties are observed compared to the bare Si substrate at θ inc = 20°–70° for unpolarized light. The calculated reflectance results of NPAA films show similar trends to the measured data.

Optical properties of ZnO/Al/ZnO multilayer films for large area transparent electrodes

Abstract

Current Transport in Al-Diffused ZnO/Si Heterostructures

The current–voltage–temperature (I-V-T) characteristics of transparent Al-doped ZnO (AZO) on n-Si heterojunction structures were analyzed with respect to two different Al diffusion temperatures, 200°C and 600°C. Thin films of Al were deposited on top of the ZnO/Si structures, followed by introducing the Al atoms into the ZnO to form AZO through a process of thermal diffusion. Measurements at temperatures of 150–400 K were carried out in order to understand the temperature dependence of the heterostructure diode characteristics for photovoltaic applications. The results indicated the difference in current mechanisms observed in the two diodes with different Al-diffusion temperatures and Al thicknesses. The charge transport mechanism in the 200°C diodes indicated thermionic field emission (TFE) as the dominating mechanism, whereas the 600°C diodes resulted in field emission (FE) as the dominating current transport. The differences in conduction mechanisms explain the better solar cell performance using the 200°C process.

Voltage polarity manipulation of the magnetoresistance sign in organic spin valve devices

The spin transport in organic spin valve (OSV) devices has been systematically investigated by inserting a low work function material Al between ferromagnetic electrode and organic layer. The resistance and current-voltage curve symmetry are dramatically altered as increasing Al thickness, indicating that an electron-unipolar OSV is obtained. Moreover, the magnetoresistance sign depends on the voltage polarity for certain Al thickness. We attribute this phenomenon to the Fermi and the lowest unoccupied molecular orbits energies of the two electrodes responding to the spin injection and detection, respectively. These findings provide a simple approach to control both the carrier type and the spin direction simultaneously.

Physicochemical properties and osteogenic activity of radiopaque calcium silicate-gelatin cements.

The purpose of this study is to evaluate the physicochemical properties and in vitro osteogenic activity of radiopaque calcium silicate-gelatin cements. The radiopacity, setting time, working time, flow, diametral tensile strength, pH value, washout resistance and morphology of the cements with gelatin (0, 5 and 10% by weight) were measured, which compared to a popular endodontic material, ProRoot white-colored mineral trioxide aggregate (WMTA). The cell morphology, cell attachment and proliferation, alkaline phosphatase and osteocalcin levels on the cements were measured by culturing the specimens with dental pulp cells. The results indicated that the presence of gelatin significantly (P < 0.05) reduced radiopacity and diametral tensile strength and prolonged setting time. Nevertheless, the 5 wt% gelatin cement had a radiopacity (5.1 mm of Al thickness) higher than ISO 6876:2001 standards (3 mm of Al thickness). The setting time (33 min), working time (9 min) and flow value (17.4 mm) of the 5 wt% gelatin cement were significantly (P < 0.05) better than those of WMTA (corresponding 165, 6 min and 14.2 mm). The fresh WMTA completely degraded after soaking in a physiological solution for 1 h, while the gelatin cements resisted washout, showing no noticeable breakdown even after 1 day of soaking. The gelatin cement enhanced the higher expression of cell attachment, proliferation and differentiation as compared to WMTA. It was concluded that the 5 wt% gelatin-calcium silicate hybrid cement appears to be promising as a radiopaque biomaterial for medical applications such as endodontics and vertebroplasty.

Aluminum-thin-film packaged fiber Bragg grating probes for monitoring the maximum tensile strain of composite materials.

In this paper, new fiber Bragg grating (FBG) sensor probes are designed to intermittently detect the maximum tensile strain of composite materials, so as to evaluate the structural health status. This probe is fabricated by two thin Al films bonded to an FBG optical fiber and two supporting brackets, which are fixed on the surface of composite materials. The residual strain of the Al packaged FBG sensor probe is induced by the strain of composite materials. This residual strain can indicate the maximum strain of composite materials. Two types of sensor probes are prepared-one is an FBG with 18 μm thick Al films, and the other is an FBG with 36 μm thick Al films-to compare the thickness effect on the detection sensitivity. These sensor probes are bonded on the surfaces of carbon fiber reinforced plastics composite specimens. In order to determine the strain sensitivity between the residual strain of the FBG sensor probe and the maximum strain of the composite specimen, tensile tests are performed by universal testing machine, under the loading-unloading test condition. The strain sensitivities of the probes, which have the Al thicknesses of 18 and 36 μm, are determined as 0.13 and 0.23, respectively.

Formation of Ta/Ti/Al/Mo/Au ohmic contacts to an AlGaN/AlN/GaN heterostructure grown on a silicon substrate

The features of the formation of Ta/Ti/Al/Mo/Au ohmic contacts to a Al0.26Ga0.74N/AlN/GaN heterostructure grown on semi-insulating Si(111) substrates are studied. The dependences of the contact resistance on the Al (90, 120, 150, 180 nm) and Ti (15, 30 nm) layer thickness and optimal temperature-time annealing conditions are determined for each studied metallization scheme. It is shown that the minimum achievable contact resistance monotonically increases from 0.43 to 0.58 Ω mm as the Al layer thickness increases from 90 to 180 nm at unchanged Ta, Ti, Mo, Au layer thicknesses. A change in the Ti layer thickness from 15 to 30 nm has no significant effect on the minimum contact resistance. The least contact resistance of 0.4 Ω mm is achieved for Ta/Ti/Al/Mo/Au layers with thicknesses of 10/15/90/40/25 nm, respectively. The optimal annealing temperature for this metallization variant is 825°C at a process duration of 30 s. The grown ohmic contacts have smooth contact-area edges and flat morphology of their surface.

Simulation study of two-dimensional electron gas in N-polar GaN/AlGaN heterostructure

By the self-consistent solution of the Schrödinger and poisson equations, the effects of GaN channel layer, AlGaN back barrier layer with and without Si doping and AlN interlayer on two-dimensional electron gas in N-polar GaN/AlGaN heterostructure are systematically studied. The results indicate that the increases of the thickness values of GaN channel layer and AlGaN back barrier layer and Al content value can improve the density of 2DEG to a certain degree, and the influences of different Si doping forms on 2DEG sheet density are not the same, also the confinement of 2DEG could be strengthened by increasing Al content value and thickness value of the AlGaN barrier layer. The AlN interlayer is a comparatively outstanding one in improving the performance of the 2DEG such as the 2DEG sheet density and confinement. When GaN channel layer thickness is less than 5 nm, there is no 2DEG in the simulation, when it exceeds 20 nm the 2DEG sheet density tends to be saturated. 2DEG has a tendency to be saturated when the thickness value of AlGaN back barrier is more than 40 nm. 2DEG sheet densities with uniform doping and delta doping in AlGaN back barrier are saturated when the doping concentration is more than 5×1019 cm-3. The 2DEG sheet density could be increased from 0.93×1013 cm-2 without AlN interlayer to 1.17×1013 cm-2 with 2 nm AlN interlayer.

Creep behavior of pack cementation aluminide coatings on Grade 91 ferritic–martensitic alloy

The creep behavior of various pack cementation aluminide coatings on Grade 91 ferritic–martensitic steel was investigated at 650°C in laboratory air. The coatings were fabricated in two temperature regimes, i.e., 650 or 700°C (low temperature) and 1050°C (high temperature), and consisted of a range of Al levels and thicknesses. For comparison, uncoated specimens heat-treated at 1050°C to simulate the high temperature coating cycle also were included in the creep test. All coated specimens showed a reduction in creep resistance, with 16–51% decrease in rupture life compared to the as-received bare substrate alloy. However, the specimens heat-treated at 1050°C exhibited the lowest creep resistance among all tested samples, with a surprisingly short rupture time of <25h, much shorter than the specimen coated at 1050°C. Factors responsible for the reduction in creep resistance of both coated and heat-treated specimens were discussed.

Leakage-Assisted Transverse Mode Selection in Vertical-Cavity Surface-Emitting Lasers With Thick Large-Diameter Oxide Apertures

Cold-cavity 3-D transverse-vertical modes of 850 nm GaAs/AlGaAs vertical-cavity surface-emitting lasers with thick oxide aperture layers were simulated. Single fundamental mode operation at large aperture diameters is achieved by proper positioning of the layer with low Al content and thickness beyond a quarter-wavelength in the top distributed Bragg reflector above the aperture layers. This modification promotes the lateral leakage of the transverse higher-order modes along the oxidized layers and their discrimination due to increased gain thresholds at certain aperture diameters. At high leakage, even the fundamental mode exhibits confined spatially-modulated states due to coupling with the leakage field component.

Effect of Ge/Al thickness on Al‐induced crystallization of amorphous Ge layers on glass substrates

AbstractLow‐temperature (350 °C) crystallization of amorphous Ge films on SiO2 was investigated using Al‐induced layer exchange (ALILE) process. Thicknesses of Ge and catalytic Al layers were varied in the range of 30‐300 nm, which strongly influenced the ALILE growth morphology. Based on the study, the Ge thickness was adjusted to 40 nm while the Al thickness was adjusted 50 nm. This sample satisfied both of the surface coverage of polycrystalline‐Ge and the annihilation of randomly oriented Ge regions. Moreover, the enhancement of the heterogeneous Ge nucleation improved the (111) orientation and the grain size. As a result, the area fraction of the (111)‐orientation reached as high as 97% and the average grain size as large as 70‐μm diameters. This (111)‐oriented Ge layer with large‐grains promises to be the high‐quality epitaxial template for various functional materials to achieve next‐generation devices. (© 2013 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Very thin, highly‐conductive ZnO:Al front electrode on textured glass as substrate for thin‐film silicon solar cells

AbstractA very thin (250 nm), highly conductive (annealed), non‐texturized DC‐sputtered aluminum‐doped zinc oxide layer (ZnO:Al) deposited on a textured glass is used as substrate for thin‐film silicon solar cells. Compared to the classical approach, where wet‐chemically texturized ZnO:Al on planar glass is used, this approach allows a reduction in the as‐deposited ZnO:Al thickness of almost 70% while at the same time, thanks to the good light trapping capability of the glass texture the efficiency of the cells was maintained at the high level of 10.9%.magnified image(© 2014 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Instability of Nonequilibrium Superconducting State and the Proximity Effect in MoRe/Al Sandwiches

The proximity effect in MoRe/Al sandwiches with different critical temperatures T c of MoRe films has been studied. The estimation of the proximity effect parameters has been made and their dependence on the Al thickness built. Features associated with instability of nonequilibrium superconducting state have been observed in the current-voltage characteristics of MoRe/Al–I–Pb tunnel junctions as a result of quasiparticle tunnel injection into the MoRe/Al sandwich. The estimation of the parameter of tunnel injection has been made and its impact on instabilities emergence studied. MoRe–I–Pb tunnel junctions have been produced and their current-voltage characteristics studied to be compared with the results obtained.

Simulation analysis of the aluminum thin film thickness measurement by using low energy electron beam

This paper indicates a simulation analysis for estimating the aluminum (Al) thin film thickness measurements by using the low energy electron beam. In order to calculate the Al thickness estimation, the energy of the incident electron beams was varied from 10 to 30keV, while the thickness of the Al film was varied between 6 and 14μm. From the simulation results it was found that electron transmittance fraction in 14μm sample is about nine orders of magnitude more than 6μm sample at the same incident electron beam energy. Simulation results show that maximum transmitted electrons versus Al layer thickness has a parabolic relation and by using the obtained equation, it is possible to estimate unknown thickness of the thin film Al layer. All calculations here were done by CASINO numerical simulation package.

Piezoresistive pressure sensor using low-temperature aluminium induced crystallization of sputter-deposited amorphous silicon film

In the present work, we have investigated the piezoresistive properties of silicon films prepared by the radio frequency magnetron sputtering technique, followed by the aluminium induced crystallization (AIC) process. Orientation and grain size of the polysilicon films were studied by x-ray diffraction analysis and found to be in the range 30–50 nm. Annealing of the Al–Si stack on an oxidized silicon substrate was performed in air ambient at 300–550 °C, resulting in layer exchange and transformation from amorphous to polysilicon phase. Van der Pauw and Hall measurement techniques were used to investigate the sheet resistance and carrier mobility of the resulting polycrystalline silicon film. The effect of Al thickness on the sheet resistance and mobility was also studied in the present work. A piezoresistive pressure sensor was fabricated on an oxidized silicon substrate in a Wheatstone bridge configuration, comprising of four piezoresistors made of polysilicon film obtained by the AIC process. The diaphragm was formed by the bulk-micromachining of silicon substrate. The response of the pressure sensor with applied negative pressure in 10–95 kPa range was studied. The gauge factor was estimated to be 5 and 18 for differently located piezoresistors on the diaphragm. The sensitivity of the pressure sensor was measured to be ∼ 30 mV MPa−1, when the Wheatstone bridge was biased at 1 V input voltage.

Gap Layer Effect on Performances of Differential Dual Spin Valve

Several materials (Ta, Cu, Al, Ru) are investigated for the gap layer (GL) in a differential dual spin valve (DDSV) as a function of GL thickness in terms of the differential effect and interlayer coupling. High field measurements in current in the plane geometry show that similar GMR effect can be obtained for two spin valves (SVs) with Ta, Ru, and Cu GLs, while for Al GL, GMR ratio of the upper SV decreases as Al thickness increases. For Ta GL, the two free layers (FLs) may switch either simultaneously or separately, depending on which FL switches first due to the weak ferromagnetic (FM) Neel coupling between the FLs. For Ru GL, the switching behavior depends on the thickness of Ru, due to the oscillation of interlayer exchange coupling. Cu GL causes additional GMR resulted from the FL/GL/FL structure. Detailed investigation on thickness dependence of Ru GL shows that FM interlayer coupling is achieved with Ru thickness of 1.6, 2.4, and 4 nm. The good differential effect can be obtained till Ru = 8 nm, above which MR of the upper SV decreases. Patterned DDSV sensors with Ru GL = 2.4 nm shows an overall FM coupling between the FLs, implying FM exchange coupling is larger than the antiferromagnetic magnetostatic coupling at edges.