Electrochemical polishing of monocrystalline silicon with specific crystallographic planes

In this study, an electrolytic polishing experimental system was developed to obtain a uniform, flat-surfaced monocrystalline silicon with specific crystallographic planes. Several key factors reflecting specific electrolytic polishing on monocrystalline silicon with specific crystallographic planes were summarized. These factors, including electrolyte, conduction mode, Schottky barrier, semiconductor body resistance, and unidirectional conductivity, were analyzed comprehensively through energy spectrum analysis, theoretical modeling, and potential simulation. The effects of electrolytic polishing process were obtained, and corresponding solutions were proposed. Finally, the electrolytic polishing experiment for monocrystalline silicon with specific crystallographic planes was conducted. A uniform, flat-surfaced monocrystalline silicon with no metamorphic layer was then obtained. The flatness error of the center area was less than 0.201 µm. Furthermore, the crystallographic planes of monocrystalline silicon wafers showed no change.     

Experimental optimization of solar cells edge junction passivation

We have developed in this study a simple procedure to determine the optimal etching time to passivate the parasitic edge junction of solar cells. The principle of the technique is based on the control of cells electrical characteristics evolution during the gradual elimination of this edge junction. Using plasma technique, the experiments were conducted on monocrystalline and multicrystalline 4 in silicon solar cells round and square in shape respectively. For monocrystalline silicon, the edge junction etch rates of 55.5 nm/min and 90.0–96.5 nm/min has been found for a batch of 20 cells with chemically phosphorus silica glass (PSG) etched and non-etched respectively. The deduced selectivity S=Si/PSG is about 10. For a batch of 100 multicrystalline silicon solar cells, 34 min were sufficient to remove 0.4 μm parasitic junction depth. For the three batches, the difference between the etch rates is explained by the phosphorus concentration and silicon loading effect. As well as for etching uniformities, they are considered good to acceptable.     

Contact resistance between pentacene and indium–tin oxide (ITO) electrode with surface treatment

Contact resistance between indium–tin oxide (ITO) electrode and pentacene was studied by transmission line method (TLM). Organic solvent cleaned, inorganic alkali cleaned, and self-assembled monolayer (with OTS: octadecyltrichlorosilane) modified ITO electrode structures were compared. Pentacene layer of 300 Å thickness was vacuum deposited on patterned ITO layer at 70 °C with a deposition rate of 0.3 Å/s. Alkali cleaned and SAM modified ITO gave a lower contact resistance of about 6.34 × 10⁴ Ω cm² and 1.88 × 10³ Ω cm², respectively than organic solvent cleaned ITO of about 6.58 × 10⁵ Ω cm². Especially with the SAM treatment, the work function of ITO increased closer to the highest occupied molecular orbital (HOMO) level of pentacene, which lowers the injection barrier between ITO and pentacene. It was also believed that pentacene morphology was improved on SAM modified ITO surface due to the lowering of the surface energy. We could obtain the low contact resistance with SAM treatment which is comparable to the measured value of gold–pentacene contact, 1.86 × 10³ Ω cm². This specific contact resistance is still much higher than that of amorphous silicon thin film transistor (0.1–30 Ω cm²).     

Synthesis of samarium telluride thin films by successive ionic layer adsorption and reaction (SILAR) method for supercapacitor application

The present paper deals with synthesis of samarium telluride (Sm₂Te₃) thin films using simple and low cost successive ionic layer adsorption and reaction (SILAR) method for supercapacitor application. The Sm₂Te₃ thin films are characterized by X-ray diffraction (XRD) for structural determination, energy dispersive analysis of X-ray (EDAX) for elemental composition, field emission scanning electron microscopy (FE-SEM) for surface morphological study and contact angle measurement for wettability study. The Sm₂Te₃ exhibits orthorhombic crystal structure with cloud like surface morphology. The film surface showed lyophilic behavior with contact angle of 5.7° for propylene carbonate (PC). Further, electrochemical measurements are carried out in LiClO₄–PC electrolyte using cyclic voltammetry (CV), galvanostatic charge discharge and electrochemical impedance spectroscopy (EIS) techniques. The Sm₂Te₃ film showed maximum specific capacitance and energy density of 144 F g⁻¹ and 10 W h kg⁻¹ respectively. The EIS study showed negligible change in resistive parameters after 1000 electrochemical cycles.     

Dependence of the optoelectronic properties of selenium-hyperdoped silicon on the annealing temperature

Selenium-hyperdoped silicon was prepared by ion implantation at 100 eV to a dose of 6×10¹⁵ Se/cm², followed by furnace annealing at 500–900 °C for 30 min. A phase transition from amorphous to crystalline was observed for the sample annealed at 600 °C. Carrier density in the Se doping layer gradually increases with the annealing temperature and a high carrier/donor ratio of 7.5% was obtained at 900 °C. The effects of annealing temperature on the rectifying behavior and external quantum efficiency of n⁺p junctions formed on Se-hyperdoped silicon were also investigated. We found that 700 °C was the optimal annealing temperature for improving the crystallinity, below-bandgap absorption, junction rectification and external quantum efficiency of Se-doped samples.     

Electromigration-induced failure in operando characterization of 3D interconnects: microstructure influence

An accurate knowledge of the phenomenon is required to develop a predictive modeling of the electromigration failure. Thus, a hitherto unseen SEM in operando observation method is devised. The test structure with “high density” through silicon vias (TSV) is tested at 623 K with an injected current density of 1 MA/cm². Regular shots of micrographs inform about the voids nucleation, forced in copper lines above the TSV, and about the scenario of their evolution. A clear relation is established between voids evolution and the one of the electrical resistance. The lack of impact of test conditions on the failure mechanism is demonstrated. Finally, the impact of microstructure on the depletion mechanism is discussed. Grain boundaries are preferential voids nucleation sites and influence the voids evolution. A probable effect of grain size and crystallographic orientation is revealed.     

Effect of electron-donating unit on crystallinity and charge transport in organic field-effect transistors with thienoisoindigo-based small molecules

We report the effect of an electron-donating unit on solid-state crystal orientation and charge transport in organic field-effect transistors (OFETs) with thienoisoindigo (TIIG)-based small molecules. End-capping of different electron-donor moieties [benzene (Bz), naphthalene (Np), and benzofuran (Bf)] onto TIIG (giving TIIG-Bz, TIIG-Np, and TIIG-Bf) is resulted in different electronic energy levels, solid-state morphologies and performance in OFETs. The 80 °C post-annealed TIIG-Np OFETs show the best device performance with a best hole mobility of 0.019 cm² V⁻¹ s⁻¹ and threshold voltage of −8.6 ± 0.9 V using top gate/bottom contact geometry and a CYTOP gate dielectric. We further investigated the morphological microstructure of the TIIG-based small molecules by using grazing incidence wide angle X-ray scattering, atomic force microscopy and a polarized optical microscope. The electronic transport levels of the TIIG-based small molecules in thin-film states were investigated using ultraviolet photoelectron spectroscopy to examine the charge injection properties of the gold electrode.     

Structural and electrical resistivity characteristics of vacuum arc ion deposited zirconium nitride thin films

Zirconium nitride (ZrN) thin films were grown on glass and aluminum substrates using a dual cathodic arc ion deposition technique. The effects of various negative bias voltages and flow ratios of N₂/Ar on the stoichiometric ratio of nitrogen to zirconium (N/Zr), deposition rate, structure, surface morphology and electrical resistivity of the ZrN layer were investigated. Rutherford backscattering spectroscopy measurements indicated a drop in the deposition rate and a slight increase in stoichiometric ratio (N/Zr) with the increase of bias voltage up to −400 V, although the latter still remained slightly less than unity (~0.92). Deposition rate of the film showed an increase with the argon addition. X-ray diffraction patterns depicted mostly polycrystalline nature of the films, with preferential orientation of (2 0 0) planes in the −100 V to −300 V bias voltage range. For 70–50% nitrogen and at a bias voltage of −400 V, the (1 1 1) orientation of ZrN film predominated. The films were smoother at a lower bias of −100 V, while the roughness increased slightly at a higher bias voltage possibly due to (increased) preferential re-sputtering of zirconium-rich clusters/islands. Changes in the resistivity of the films were correlated with stoichiometry, crystallographic orientation and crystalline quality.     

Dislocation-mediated plasticity in silicon during nanometric cutting: A molecular dynamics simulation study

The nucleation and propagation of dislocations and its consequence on the defect structure in silicon during nanometric cutting are not well known, although the amorphization and high pressure phase transformation studies on silicon have remained at the epicentre of research across various disparate disciplines for over a decade. This paper proposes a new mechanism of crystal plasticity identified by a fully automated dislocation extraction algorithm in molecular dynamics simulations of nanometric cutting of silicon for different cutting planes/directions at a wide range of temperatures (300–1500 K). Alongside amorphization of silicon, our simulations revealed nanoscale stochastic nucleation of dislocations and stacking faults, which serve as mediators of microscopic plasticity during various contact loading operations and manufacturing processes of silicon. Of interest is that, irrespective of the cutting temperature, the stacking faults, which were not formed for either the (010)[100] or (111)[$\bar{1}1$0] crystal setups, were generated with three atomic layers in the (110)[00$\bar{1}$] cutting.     

Fabrication of single crystal field-effect transistors with phenacene-type molecules and their excellent transistor characteristics

Single crystal field-effect transistors (FETs) using [6]phenacene and [7]phenacene show p-channel FET characteristics. Field-effect mobilities, μs, as high as 5.6 × 10^?1 cm² V^?1 s^?1 in a [6]phenacene single crystal FET with an SiO₂ gate dielectric and 2.3 cm² V^?1 s^?1 in a [7]phenacene single crystal FET were recorded. In these FETs, 7,7,8,8-tetracyanoquinodimethane (TCNQ) was inserted between the Au source/drain electrodes and the single crystal to reduce hole-injection barrier heights. The μ reached 3.2 cm² V^?1 s^?1 in the [7]phenacene single crystal FET with a Ta₂O₅ gate dielectric, and a low absolute threshold voltage |V_TH| (6.3 V) was observed. Insertion of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F₄TCNQ) in the interface produced very a high μ value (4.7–6.7 cm² V^?1 s^?1) in the [7]phenacene single crystal FET, indicating that F₄TCNQ was better for interface modification than TCNQ. A single crystal electric double-layer FET provided μ as high as 3.8 × 10^?1 cm² V^?1 s^?1 and |V_TH| as low as 2.3 V. These results indicate that [6]phenacene and [7]phenacene are promising materials for future practical FET devices, and in addition we suggest that such devices might also provide a research tool to investigate a material’s potential as a superconductor and a possible new way to produce the superconducting state.     

Deep Diffusion of Phosphorus in Silicon using Microsecond-pulsed Laser Doping

Deep diffusion of phosphorus atoms in monocrystalline silicon using laser doping process has been studied in this work. A pulse modulated CW fiber laser of wavelength 1070 nm with microsecond pulses has been used to diffuse phosphorus from pre-deposited spin-on-dopant film. The surface and cross-sectional morphology has been studied using SEM and AFM. The concentration-depth profiling was done using PP-TOFMS. Deep junctions of more than 10 µm have been obtained under various laser doping conditions while a maximum junction depth of 51.3 µm has been obtained through optimization. Diffusion depth enhancement is made possible by increasing the pulse length and reducing laser scan speed. Laser doping led to formation of n⁺ region with surface concentration varying in the range of 3×10²⁰–5×10²⁰ cm⁻³ for varying scan speed. Cross-sectional TEM and diffraction studies on laser irradiated samples show presence of only monocrystalline silicon phase after laser induced melting and solidification.     

New method for boron removal from silicon by electron beam injection

A new method for boron removal from silicon using electron beam injection (EBI) is proposed. After thermal oxidation on monocrystalline silicon (100) wafer at 1000 °C for 1 h, EBI was used to induce thermal and negative charging effects to enhance boron diffusion in the oxide film and the silicon substrate. This facilitates boron removal from the silicon substrate. The boron concentration in samples was measured by secondary ion mass spectrometry. The results show that EBI reduced the boron concentration in the silicon substrate by 4.83%.     

An investigation on capacitance-trigger ESD protection devices for high voltage integrated circuits

A novel cascaded complementary dual-directional silicon controlled rectifier (CCDSCR) structure has been proposed and implemented in a 0.5 μm 20 V Bipolar/CMOS/DMOS process as an ESD (electrostatic discharge) protection device. The ESD characteristics of the capacitance-trigger CCDSCR has been investigated by transmission line pulse (TLP) testing. Compared with the substrate-trigger insulated gate bipolar transistor with the enhanced substrate parasitic capacitance, the gate-driven trigger insulated gate bipolar transistor with the gate coupling capacitance and the normal dual-directional silicon controlled rectifier, the CCDSCR has the highest holding voltage of about 25.4 V and the best current conduction uniformity. In addition, it has the best figure of merit (FOM) with the value of about 0.64 mA/μm². The good current conduction uniformity in CCDSCR due to the enhanced substrate parasitic capacitance-trigger effect is finally confirmed by Sentaurus simulations.     

Residual strain and electrical resistivity dependence of molybdenum films on DC plasma magnetron sputtering conditions

Sputter deposited molybdenum (Mo) thin films are used as back contact layer for Cu(In_1−xGa_x)(Se_1−yS_y)₂ based thin film solar cells. Desirable properties of Mo films include chemical and mechanical inertness during the deposition process, high conductivity, appropriate thermal expansion coefficient with contact layers and a low contact resistance with the absorber layer. Mo films were deposited over soda-lime glass substrates using DC-plasma magnetron sputtering technique. A 2³ full factorial design was made to investigate the effect of applied power, chamber pressure, and substrate temperature on structural, morphological, and electrical properties of the films. All the films were of submicron thickness with growth rates in the range of 34–82 nm/min and either voided columnar or dense growth morphology. Atomic force microscope studies revealed very smooth surface topography with average surface roughness values of upto 17 nm. X-ray diffraction studies indicated, all the films to be monocrystalline with (001) orientation and crystallite size in the range of 4.6–21 nm. The films exhibited varying degrees of compressive or tensile residual stresses when produced at low or high chamber pressure. Low pressure synthesis resulted in film buckling and cracking due to poor interfacial strength as characterized by failure during the tape test. Measurement of electrical resistivity for all the films yielded a minimum _value of 42 μΩ cm for Mo films deposited at 200 W DC power.     

Source/drain metallization effects on the specific contact resistance of indium tin zinc oxide thin film transistors

We report on the specific contact resistance of interfaces between thin amorphous semiconductor Indium Tin Zinc Oxide (ITZO) channel layers and different source/drain (S/D) electrodes (Al, ITO, and Ni) in amorphous oxide thin film transistors (TFTs) at different channel lengths using a transmission line model. All the contacts showed linear current–voltage characteristics. The effects of different channel lengths (200–800 μm, step 200 μm) and the contact resistance on the performance of TFT devices are discussed in this work. The Al/ITZO TFT samples with the channel length of 200 μm showed metallic behavior with a linear drain current-gate voltage (I_D–V_G) curve due to the formation of a conducting channel layer. The specific contact resistance (ρ_C) at the source or drain contact decreases as the gate voltage is increased from 0 to 10 V. The devices fabricated with Ni S/D electrodes show the best TFT characteristics such as highest field effect mobility (16.09 cm²/V·s), ON/OFF current ratio (3.27×10⁶), lowest sub-threshold slope (0.10 V/dec) and specific contact resistance (8.62 Ω·cm² at V_G=0 V). This is found that the interfacial reaction between Al and a-ITZO semiconducting layer lead to the negative shift of threshold voltage. There is a trend that the specific contact resistance decreases with increasing the work function of S/D electrode. This result can be partially ascribed to better band alignment in the Ni/ITZO interface due to the work function of Ni (5.04–5.35 eV) and ITZO (5.00–6.10 eV) being somewhat similar.     

Nanostructured nickel oxide ultrafine nanoparticles: Synthesis,characterization, and supercapacitive behavior

Well-dispersed NiO nanoparticles were prepared via cathodic electrodeposition followed by a heat-treatment method. The supercapacitive performance of the prepared nanoparticles was analyzed by means of cyclic voltammetry (CV) and galvanostatic charge–discharge tests at −0.2–0.5 V potential windows in 1 M KOH. The nanoparticles exhibited high specific capacitance (1623.1 F g⁻¹ at the scan rate of 5 mV s⁻¹) and good long-term cycling stability (9.6% capacity decay after 1000 cycling at the current density of 2 A g⁻¹).     

Organic light-emitting diodes based on an ambipolar single crystal

Slice-like organic single crystals of 1,4-bis(2-cyano-2-phenylethenyl)benzene (BCPEB) are grown by the physical vapor transport (PVT) method, and exhibit a very high photoluminescence quantum efficiency (Φ_PL) of 75%. The ambipolar behavior of BCPEB single crystals are confirmed using the time of flight technique. The high efficiency and balanced (μ_h = 0.059 cm²/Vs and μ_e = 0.070 cm²/Vs) carriers’ mobility imply that the BCPEB single crystal is a promising light-emitting layer in the diodes structure. Intense green electroluminescence (EL) from a diode has been successfully demonstrated at an applied electric field of 2 × 10⁵ V/cm.     

Fabrication and application of temperature triggered MEMS switch for active cooling control in Solid State Lighting system

As the power of Solid State Lighting (SSL) system continuously rising and consequently high temperature occurred in the light source, active cooling solutions with controlling were widely used and smart controlling was indispensable for less energy consuming. In this work, a micro–electro-mechanical-system (MEMS) based, temperature triggered, switch was developed as a cost-effective solution for smart cooling control in SSL systems. The switch (1.0 × 0.4 mm²) was embedded in a silicon substrate and fabricated with a single-mask 3D micro-machining process. The device switched on at a designed temperature threshold with a contact resistance less than 2 ohm, and switched off when the temperature dropped below that limit. In this way, this device can enhance the automatic control of a cooling system without any need of additional electronic components and the used standard semiconductor manufacturing process gives highly possibility for integration and fabrication for future silicon based SSL systems.     

Enhancing charge transport in copper phthalocyanine thin film by elevating pressure of deposition chamber

Copper phthalocyanine (CuPc)-based thin film transistors were fabricated using CuPc films grown under different deposition pressure (P_dep) (ranging from 1.8 × 10⁻⁴ Pa to 1.0 × 10⁻¹ Pa). The transistor performance highly depended on P_dep. A field-effect mobility of 2.1 × 10⁻² cm²/(V s) was achieved under 1.0 × 10⁻¹ Pa. Detailed investigations revealed that P_dep modulates the molecular packing and orientation of the organic films grown on a SiO₂/Si substrate and influences the charge transport. Furthermore, from a device physics point of view, contact resistance of the fabricated transistors decreased when P_dep increased, which was beneficial in reducing energy consumption.     

Synthesis,characterization and high-efficiency blue electroluminescence based on coumarin derivatives of 7-diethylamino-coumarin-3-carboxamide

A novel tripodal compound, tris[2-(7-diethylamino-coumarin-3-carboxamide)ethyl]amine (tren-C), and a model compound, N-butyl-7-(diethylamino)-coumarin-3-carboxamide, were synthesized and characterized by elemental analysis, infrared and ¹H NMR spectra. The structure of the model compound was characterized by single crystal X-ray crystallography. The electroluminescence devices of ITO/2-TNATA (5 nm)/NPB (40 nm)/CBP: tren-C or model compound (wt%, 30 nm)/Bu-PBD (30 nm)/LiF (1 nm)/Al (100 nm) were fabricated and characterized. The EL spectra of the devices comprising vacuum vapour-deposited films using tren-C as a dopant are similar to the PL spectrum of tren-C in chloroform solutions. At the concentration of 0.5 wt% tren-C, a blue-emitting OLED with an emission peak at 464 nm, a maximum external quantum efficiency (EQE) of 1.39% and a maximum luminous efficiency of 2 cd/A at the current density of 20 mA/cm², and a maximum luminance of 1450 cd/m² at 12 V are achieved.