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During the fabrication of crystalline silicon solar cells, kerf-loss caused by the wire-sawing of silicon ingots to produce thin wafers inevitably limits the reduction of electricity production cost. To avoid the kerf-loss, direct growth of crystalline silicon wafers of 50-150 μm with a porous separation layer that can be mechanically broken during the exfoliation process, has been widely investigated. However, several issues including flattening of the surface after the exfoliation remain unsolved. In this work an alternative method that utilizes a water-soluble Sr3Al2O6 (SAO) sacrificial layer inserted between the mother substrate and the grown crystalline silicon layers is introduced. Polycrystalline silicon layers were grown on SAO/Si by plasma-enhanced CVD process and silicon membranes could be successfully obtained after the dissolution of SAO in the water. Same process could be applied to obtain flexible amorphous silicon membranes. Further research is being conducted to increase the size of the exfoliated wafer, which expects to reduce the production cost of crystalline silicon solar cells effectively.

Intrinsic hydrogenated amorphous silicon (i-a-Si:H) films lead to excellent surface passivation of crystalline silicon wafers. However, a-Si:H deposition on a crystalline silicon wafer often results in undesired epitaxy growth, which deteriorates the passivation property, In this paper, we studied the influence of varying plasma enhanced chemical vapor deposition (PECVD) parameters, such as the product of the gas pressure (P) and the electrode distance (Di) and the hydrogen dilution ratio (P = SiH4/(H2 + SiH4) × 100), on the passivation quality and the properties of silicon heterojunction (SHJ) solar cells. Measurements showed that proper combinations of high P × Di and large P values can yield high minority carrier lifetimes (MCLTs) of passivated silicon wafers. Also, the tendency of MCLTs measured from passivated wafers is the same as that for open circuit voltages (Voc) of fabricated SHJ solar cells. A high Voc is obtained from SHJ solar cells when unwanted epitaxial growth is minimized at the wafer surface.

The fabrication of ultrathin silicon wafers at low cost is crucial for advancing silicon electronics toward stretchability and flexibility. However, conventional fabrication techniques are inefficient because they sacrifice a large amount of substrate material. Thus, advanced silicon electronics that have been realized in laboratories cannot move forward to commercialization. Here, a fully bottom-up technique for producing a self-releasing ultrathin silicon wafer without sacrificing any of the substrate is presented. The key to this approach is a self-organized nanogap on the substrate fabricated by plasma-assisted epitaxial growth (plasma-epi) and subsequent hydrogen annealing. The wafer thickness can be independently controlled during the bulk growth after the formation of plasma-epi seed layer. In addition, semiconductor devices are realized using the ultrathin silicon wafer. Given the high scalability of plasma-epi and its compatibility with conventional semiconductor process, the proposed bottom-up wafer fabrication process will open a new route to developing advanced silicon electronics.

Microstructural, optical and electrical properties of Cl-doped CdTe crystals grown by the low pressure Bridgman (LPB) method were investigated for four different doping concentrations (unintentionally doped, 4.97 × 1019 cm−3, 9.94 × 1019 cm−3 and 1.99 × 1020 cm−3) and three different locations within the ingots (namely, samples from top, middle and bottom positions in the order of the distance from the tip of the ingot). It was shown that Cl dopant suppressed the unwanted secondary (5 1 1) crystalline orientation. Also, the average size and surface coverage of Te inclusions decreased with an increase in Cl doping concentration. Spectroscopic ellipsometry measurements showed that the optical quality of the Cl-doped CdTe single crystals was enhanced. The resistivity of the CdTe sample doped with Cl at the 1.99 × 1020 cm−3 was above 1010 Ω.cm.

Background: TlBr is of considerable technological importance for radiation detection applications where detecting high-energy photons such as X-rays and γ-rays are of prime importance. However, there were few reports on investigating optical properties of TlBr itself for deeper understandings of this material and for making better radiation detection devices. Thus, in this paper, we report on the optical characterizations of TlBr single crystals. Spectroscopic ellipsometry (SE) and photoluminescence (PL) measurements at RT were performed for this work. Materials and Methods: A 2-inch TlBr single crystalline ingot was grown by using the vertical Bridgman furnace. SE measurements were performed at RT within the photon energy range from 1.1 to 6.5 eV. PL measurements were performed at RT by using a home-made PL system equipped with a 266 nm-laser and a spectrometer. Results and Discussion: Dielectric responses from SE analysis were shown to be slightly different among the different samples possibly due to the different structural/optical properties. Also from the PL measurements, it was observed that the peak intensities of the middle samples were significantly higher than those of the other two samples. With the given values for permittivity of free space (e0 = 8.854x10-12 F·m-1), thickness (d = 1 mm), and area (A = 10x10 mm2) of the TlBr sample, capacitances of TlBr were 6.9 pF (at hν = 3 eV) and 4.4 pF (at hν = 6 eV), respectively. Conclusion: SE and PL measurement and analysis were performed to characterize TlBr samples from the optical perspective. It was observed that dielectric responses of different TlBr samples were slightly different due to the different material properties. PL measurements showed that the middle sample exhibited much stronger PL emission peaks due to the better material quality. From the SE analysis, optical, dielectric constants were extracted, and calculated capacitances were in the few pF range.

TlBr single crystals grown using the vertical Bridgman-Stockbarger method were characterized for semiconductor based radiation detector applications. It has been shown that the vertical Bridgman-Stockbarger method is effective to grow high-quality single crystalline ingots of TlBr. The TlBr single crystalline sample, which was located 6 cm from the tip of the ingot, exhibited lower impurity concentration, higher crystalline quality, high enough bandgap (>2.7 eV), and higher resistivity (2.5 × 1011Ω·cm) which enables using the fabricated samples from the middle part of the TlBr ingot for fabricating high performance semiconductor radiation detectors.

We studied the effects of precursor gas composition and the addition of dopant gas, PH3, on polycrystalline silicon films deposited using plasma-enhanced chemical vapor deposition. Spectroscopic ellipsometry measurement and modeling results revealed that the poly-Si films consist of a subsurface layer and a bulk layer. The sample deposited under greater hydrogen dilution exhibited a fully crystallized subsurface layer and a denser bulk layer. We also studied the effects of various dopant gas flow rates on structural and electrical properties of the poly-Si films. Ellipsometry, X-ray diffraction, and Raman analyses revealed that the film deposited using a large dopant-gas flow rate exhibits decreased grain size and increased void fraction. Furthermore, the doped poly-Si films show a trend of Raman peak shift, which was attributed to tensile stress. The stress of the doped poly-Si films increases with higher dopant-gas flow rate. Measurement of the temperature-dependent dark conductivity shows saturation of the electrical conductivity of heavily doped films.

Double deep diffused structured Si PIN diode having ALD Al 2 O 3 anti-reflection and passivation layer were fabricated and characterized. Detailed device fabrication process is described at the experimental section and electrical, optical and radiation response characteristics were characterized.

We investigated the electrical and optical properties of chemically stable nitride-based ZrON/Ag/ZrON multilayers for use in organic photovoltaics. As the ZrON layer thickness increases, the carrier concentration smoothly decreases and the transmission window region becomes wider and gradually shifts toward the lower energy-side. The optical bandgap also decreases with decreasing carrier concentration. The ZrON/Ag/ZrON samples exhibit somewhat lower transmittance in the region of ∼400–800 nm than the ITO/Ag/ITO samples. The aging test shows that the resistivity of the ZrON/Ag/ZrON samples remains almost the same even after aging for 1 month in air. It is shown that the ZrON/Ag interface is more chemically stable than the ITO/Ag interface. Simulation results exhibit that the ZnPc:C60 bulk hetero-junction organic solar cells fabricated with the ZrON(30 nm)/Ag/ZrON(70 nm) layers give a short circuit current of 9.54 mA/cm 2 , which is comparable to that (10.54 mA/cm 2 ) of the cells with 90-nm-thick ITO electrodes. The ZrON/Ag/ZrON samples experienced a large shift in the absorption edge. This behavior is explained in terms of the material characteristics of the ZrON layers and the higher refractive index of the ZrON/Ag/ZrON samples.

We investigated how mixtures of Ar and O 2 or N 2 gases affect the structural, electrical and optical properties of RF-magnetron-sputtered NiO films. It is shown that the addition of O 2 gas to Ar ambient (namely, Ar:O 2 =2:1 to 1:2) slightly reduces the (2 0 0) texturing of the NiO films. The introduction of N 2 gas (from 0 to 2 sccm) to Ar:O 2 (2:1) mixture enhances the (2 0 0) texturing, while the addition of N 2 gas (from 0 to 2 sccm) to Ar ambient slightly weakens the (1 1 1) texturing. The deposition rate is reduced from 6.1 to 1.5 nm/min when O 2 gas is added to Ar ambient. The addition of N 2 gas to the Ar:O 2 (2:1) mixture slightly increases the deposition rate from 1.8 to 2.6 nm/min, whereas adding N 2 gas to Ar only ambient somewhat reduces the rate from 6.1 to 4.4 nm/min. The carrier concentration of the films is increased and the mobility is decreased as the O 2 flow rate in the Ar:O 2 mixture is increased. The addition of N 2 gas to the Ar:O 2 (2:1) mixture increases the resistivity of the films, while adding N 2 gas to Ar ambient decreases the resistivity. The transmittance and optical bandgap of the films are reduced (from 58.4 to 45.5% at 550 nm and from 3.5 to 3.3 eV, respectively) with increasing O 2 flow to Ar ambient. When N 2 gas is added to the Ar:O 2 (2:1) mixture, the transmittance in the visible wavelength range increases from 58.4 to 71.3% and the optical bandgap increases from 3.5 to 3.6 eV. However, adding N 2 gas to the Ar only ambient results in decrease in the transmittance in the visible wavelength region (from 69.3 to 56%) and the optical bandgap (from 3.7 to 3.5 eV).

Photocatalytic and hydrophilic TiO2 thin-film applications include water purification, cancer therapy, solar energy conversion, self-cleaning devices, and antifogging windows. We demonstrate superhydrophilicity of aerosol-deposition (AD) TiO2 films on a glass substrate without use of a carrier solvent, thereby removing the possibility of impurity contamination. AD films exhibit high visible light transmittance (greater than 80%) and superhydrophilicity (0° contact angle) with even minimal UV-light irradiation exposure. This AD method represents a significant step toward the realization of economically viable, functional thin films for the aforementioned applications.

A tunable surface that promotes either hydrophobic or hydrophilic behavior of TiO2 films is produced with aerosol deposition. This process is capable of mass production by high-speed coating at room temperature without any wet chemicals, and therefore the process has the potential to be economically viable, energy efficient, and environmentally friendly. Functional TiO2 films between 1 and 18 μm thick are produced by directly depositing dry, 1-μm TiO2 powders accelerated through a supersonic nozzle. Tunable film morphology due to a rough honeycomb surface structure yields variable water contact angles. When plasma treated with CF4, the films exhibit superhydrophilicity despite the rough honeycomb surface structure. Superhydrophilicity is due to the incorporation of fluorine in the film as shown using XPS.

We report on the improvement in the performance of InGaN/GaN multi-quantum well-based solar cells by the introduction of a Cu-doped indium oxide (CIO) layer at the interface between indium tin oxide (ITO) p-electrode and p-GaN. The solar cell fabricated with the 3 nm-sample exhibits an external quantum efficiency of 29.8% (at a peak wavelength of 376 nm) higher than those (25.2%) of the cell with the ITO-only sample. The use of the 3-nm-thick CIO layer gives higher short circuit current density (0.72 mA/cm2) and fill factor (78.85%) as compared to those (0.65 mA/cm2 and 74.08%) of the ITO only sample. Measurements show that the conversion efficiency of the solar cells with the ITO-only sample and the 3 nm-sample is 1.12% and 1.30%, respectively. Based on their electrical and optical properties, the dependence of the CIO interlayer thickness on the efficiency of solar cells is discussed.

We investigate how TiO 2 nanopatterns formed onto ZnO:Al (AZO) films affect the performance of hydrogenated amorphous silicon (a-Si:H) solar cells. Scanning electron microscopy results show that the dome-shaped TiO 2 nanopatterns (300 nm in diameter) having a period of 500 nm are formed onto AZO films and vary from 60 to 180 nm in height. Haze factor increases with an increase in the height of the nanopatterns in the wavelength region below 530 nm. Short circuit current density also increases with an increase in the height of the nanopatterns. As the nanopatterns increases in height, the fill factor of the cells slightly increases, reaches maximum (0.64) at 100 nm, and then decreases. Measurements show that a-Si:H solar cells fabricated with 100 nm-high TiO 2 nanopatterns exhibit the highest conversion efficiency (6.34%) among the solar cells with the nanopatterns and flat AZO sample.

We investigate the effect of 1-(1-D) and 2-dimensional (2-D) patterned Ag grids combined with Al-doped ZnO contacts on the electrical and optical properties of GaN-based light-emitting diodes (LEDs). The ratio of the grid width to the gap between the grids varies from 2.8 for the 1-D to 38.7 for the 2-D grids. All of the patterned Ag grid/AZO contacts show transmittances in the range of 86.4-94.0%. The LEDs fabricated with the differently patterned Ag grid/AZO contacts exhibit forward-bias voltages ranging from 3.67 to 4.62V at an injection current of 20mA, which are much lower than those (7.44V) of the LEDs with the AZO only contacts. It is further shown that the LEDs with the patterned Ag grid/AZO contacts produce a 78.0-108.7% higher output power (at 20mA) than those with the AZO only contacts. The reason for the improved output performance of the LEDs with the Ag grid/AZO contacts is briefly described in terms of the contact areas and plasma-induced damage of p-GaN.

Polycrstalline zinc oxide (ZnO) thin films were fabricated on indium tin oxide (ITO) substrates by electrostatic spray deposition using propylene glycol as the solvent for potential use in bulk heterojunction polymer solar cells. The microstructure and characteristics of the ZnO/ITO bilayer have been investigated for various precursor concentrations using SEM, AFM, X-ray diffraction, and UV-Visible spectroscopy. The bandgap energy of the bilayer slightly decreases when the zinc acetate dihydrate concentration in the propylene glycol solvent increases from 0.1 to 0.3 M. The ZnO/ITO bilayer shows high figure of merit (12.4 × 10−3 −1) and low resistivity (3.78 × 10−3 -cm) for a Zn precursor concentration of 0.2 M. © 2012 The Electrochemical Society. [DOI: 10.1149/2.077208jes] All rights reserved.

Photocatalytic TiO2 films combined with Ag nanoparticles (NPs) embedded-SiO2 films were fabricated by means of a RF magnetron sputtering and subsequent rapid thermal annealing (RTA). X-ray diffraction results show that the TiO2 films have anatase phase when annealed at 500 °C. The Ag NPs were formed by deposition and subsequent annealing at 600 °C. Scanning electron microscopy (SEM) results show that the density of the NPs decreases with increasing Ag film thickness. For example, the average NP diameter varies from ~ 19.3 to ~ 55.9 nm as the film thickness increases from 2 to 12 nm. Transmittance measurements show that as the Ag NP size decreases, the plasmonic peaks shift towards the shorter-wavelength region and become narrower. It is further shown that under UV-illumination (352 nm), all the TiO2 films with the Ag NPs show higher methylene blue decomposition rates compared to the TiO2 only films and the TiO2 films with Ag NP (a 7 nm-thick Ag film) show the best decomposition rate among the samples possibly due to the combined effects of optimized localized field amplification and radiative efficiency.

We characterized the electrical and chemical properties of Cu-doped In2O3(CIO) (2.5 nm thick)/Sb-doped SnO2(ATO) (250 nm thick) contacts to p-type GaN by means of current-voltage measurement, scanning transmission electron microscope (STEM) and x-ray photoemission spectroscopy (XPS). The CIO/ATO contacts show ohmic behaviors, when annealed at 530 and 630°C. The effective Schottky barrier heights on diodes made with Ni (5 nm)/Au (5 nm) contacts decrease with increasing annealing temperature. STEM/energy dispersive x-ray (EDX) profiling results exhibit the formation of interfacial In-Ga-Sn-Cu-oxide. XPS results show a shift of the surface Fermi level toward the lower binding energy side upon annealing. Based on the STEM and XPS results, the ohmic formation mechanisms are described and discussed.

Al-doped ZnO (AZO, ZnO:Al2O3 = 98:2 wt%) films are deposited on different substrates by an RF magnetron sputtering and subsequently annealed at three different conditions to investigate the microstructural, electrical, and optical properties. X-ray diffraction and scanning electron microscope results show that all the samples are polycrystalline and the samples rapid-thermal-annealed at 900 °C in an N2 ambient contain larger grains compared to the furnace-annealed samples. It is shown that the sample deposited at room temperature on the sapphire gives a resistivity of 5.57 × 10−4 Ω cm when furnace-annealed at 500 °C in a mixture of N2:H2 (9:1). It is also shown that the Hall mobility vs. carrier concentration (μ–n) relation is divided into two groups, depending on the annealing conditions, namely, either rapid-thermal annealing or furnace annealing. The relations are described in terms of either grain boundary scattering or ionized impurity scattering mechanism. In addition, the samples produce fairly high transmittance of 91–96.99% across the wavelength region of 400–1100 nm. The optical bandgaps of the samples increase with increasing carrier concentration.

We have investigated the annealing-induced improved electrical properties of In(10 nm)/ITO(200 nm) contacts with p-type GaN. The contacts become ohmic with a specific contact resistance of 2.75×10–3 Ω cm2 upon annealing at 650 °C in air. X-ray photoemission spectroscopy (XPS) Ga 2p core levels obtained from the interface regions before and after annealing indicate a large band-bending of p-GaN, resulting in an increase in the Schottky barrier height. STEM/energy dispersive X-ray (EDX) profiling results exhibit the formation of interfacial In-Ga-Sn-oxide. Based on the STEM and XPS results, the ohmic formation mechanisms are described and discussed. It is also shown that patterning by nano-imprint lithography improves the light output power of blue LEDs by 18–28% as compared to that of LEDs fabricated with unpatterned In/ITO contacts.

We report on the formation of low-resistance and transparent p-type ohmic contact for green GaN-based light-emitting diodes (LEDs) using Ni–Co solid solution(5 nm)/Au(5 nm) scheme. The as-deposited Ni–Co solid solution(5 nm)/Au(5 nm) contact shows nonlinear current–voltage ( I – V ) characteristics. However, annealing the sample at 550 ∘C in air results in the formation of ohmic contacts with specific contact resistance of 6.5×10−4 Ω cm2. The annealed sample shows light transmittance of 71.7% at a wavelength of 530 nm, which is better than that (64.9%) of oxidized Ni/Au contacts. Based on Auger electron spectroscopy and x-ray photoemission spectroscopy results, the annealing-induced improvement of the contacts is described and discussed.

Resistiveswitchingbehaviorhasbeenobservedinbinaryoxides 1‐4 and perovskite oxides. 5‐9 In particular, Pr0.7Ca0.3MnO3 (PCMO)films have been studied extensively because they exhibit a reversible pulseinduced change in resistance, which is very useful for nonvolatile memory devices. 8 PCMO thin films are known to be p-type materials, andtheyshowbipolarresistiveswitchingbehavior. 5‐9 Recently,theinterestinReRAMdevicesfabricatedatlowtemperatures(≤200 ◦ C)has increased because these devices can be used in flexible electronics. 3,4 Moreover, films grown at low temperatures are preferred for integration of the oxide materials with existing technologies. The amorphous PCMO(APCMO)wasalsogrownontheITO/glasssubstrateandtheir switching properties have been investigated. 10 In this work, APCMO films were grown on TiN/SiO2/Si substrate under various oxygen pressures (OPs) using a pulsed laser deposition (PLD) method, and their microstructure and resistive switching behavior were investigated. Moreover, the resistive switching behaviors of the APCMO films were explained by the trap-charged space-charge-limited current (SCLC) mechanism. Experimental

We propose a dual-layer transparent Indium Tin Oxide (ITO) top electrode scheme and demonstrate the enhancement of the optical output power of GaN-based light emitting diodes (LEDs). The proposed dual-layer structure is composed of a layer with randomly distributed sphere-like nano-patterns obtained solely by a maskless wet etching process and a pre-annealed bottom layer to maintain current spreading of the electrode. It was observed that the surface morphologies and optoelectronic properties are dependent on etching duration. This electrode significantly improves the optical output power of GaN-based LEDs with an enhancement factor of 2.18 at 100 mA without degradation in electrical property when compared to a reference LED. (C) 2013 Optical Society of America

It has been shown that the laser shock cleaning (LSC) process is effective for removing nanoscale particles from solid surfaces and thus has various potential applications in microelectronic manufacturing. In this work, we propose a simple method to amplify the shock wave intensity generated by laser-induced breakdown (LIB) of air. The suggested scheme employs a plane shock wave reflector which confines the plasma expansion in one direction. As the half of the LIB-induced shock wave is reflected by the reflector, the intensity of the shock wave propagating in the opposite direction is increased significantly. Accordingly, the enhanced shock wave can remove smaller particles from the surface than the existing LSC process. The LSC process under geometrical confinement is analyzed both theoretically and experimentally. Numerical computation of the plasma/shock behavior shows about two times pressure amplification for the plane geometry. Experiments confirm that the shock wave intensity is enlarged by the effect of geometrical confinement of the plasma and shock wave. The result of cleaning tests using polystyrene particles demonstrates that the particle removal efficiency increases by the effect of geometrical confinement.

Amorphous Pr0.7Ca0.3MnO3 (APCMO) films, which were grown on indium tin oxide (ITO)/glass at room temperature (RT), were n-type materials. The APCMO/ITO/glass device exhibited an average transparency of 77% in the visible range with a maximum transparency of 84% at a wavelength of 530 nm. The Pt/APCMO/ITO device showed stable bipolar resistive switching behavior over 200 cycles that did not degrade after 105 s at RT. The resistance of the APCMO film decreased in both low- and high-resistance states with increasing device area. The resistive switching behavior of the Pt/APCMO/ITO device can be explained by the trap-charged space-charge-limited current mechanism.

We report a facile and reliable method to fabricate polymer-based monolithic nanofluidic channels. The nanochannels are obtained via three main steps: (1) fabrication of nanowire-transistor like structures, which are silver or zinc oxide nanowires horizontally bridging two electrodes made of zinc oxide on SiO(2)/Si substrates; (2) casting and curing polyimide solution on the nanowire structures; and (3) selective etching of the nanowire and electrode templates against the polyimide substrates. This process leads to the production of nanochannels with a diameter down to ∼ 50 nm. Our method is based on nanowires that are chemically synthesized whereas nanopattern fabrication conventionally relies on expensive equipment. Moreover, the polymer nanochannels are fabricated monolithically while a process of bonding two different materials is required in traditional methods where leakage problems are often identified at the interface. Construction of nanofluidic circuitry could be expected in the future based on the current work.

Surface cleaning based on the laser-induced breakdown of gas and subsequent plasma and shock wave generation can remove small particles from solid surfaces. Accordingly, several studies were performed to expand the cleaning capability of the process. In this work, the cleaning process using laser-induced plasma (LIP) under geometrical confinement is analyzed both theoretically and experimentally. Two-dimensional numerical analysis is conducted to examine the behavior of the LIP shock wave under geometrical confinement for several geometries. As a result of the analysis, we propose a simple and practical method to amplify the intensity of laser-induced shock. In the proposed method, a flat quartz plate placed close to the focal point of the laser pulse confines the expansion of the LIP, allowing the plasma to expand only in one direction. As a consequence of the plasma confinement, the intensity of the shock wave produced is increased significantly. Experiments demonstrate that the enhanced shock wave can remove smaller particles from the surface better than the existing process.