Characterization of p-type multicrystalline silicon prepared by cold crucible continuous melting and directional solidification

A solar-grade boron doped silicon ingot with the cross section of 62 mm× 62 mm was cast by cold crucible continuous melting and directional solidification (CCDS). The characterization of this p-type multicrystalline silicon (mc-Si) was measured and evaluated. The results indicate that the ingot mainly consists of uniform columnar grains preferentially aligned parallel to the ingot growth direction. The average density of dislocations (N_dis) in the center area varies from 4 × 10⁴ cm⁻² to 4 × 10⁵ cm⁻², and it is much lower than that in the peripheral area. Comparing with the raw material, the oxygen concentration in the cast ingot is much lower while the carbon holds the same level. The electrical resistivity distributes uniformly and its average value is same as that of the raw material. The minority carrier lifetime (MCLT) is higher than that of the raw material and no region with obvious low MCLT is observed. CCDS has shown to be a potential process to produce mc-Si for solar cells with no crucible contamination and consumption, high production efficiency and uniform quality.     

Structural characterization of ultra-thin (0 0 1) silicon films bonded onto (0 0 1) silicon wafers:: a transmission electron microscopy study

Ultra-thin (0 0 1) silicon films (thickness less than 25 nm) directly bonded onto (0 0 1) silicon wafers have been investigated by transmission electron microscopy. Twist interfacial dislocations accommodate the twist between the two crystals, whereas tilt interfacial dislocations accommodate the tilt resulting from the residual vicinality of the initial surfaces. In low-twist angle grain boundaries, twist interfacial dislocations are dissociated and no precipitates are detected. In high-twist angle grain boundaries, there is no dissociation and a high density of silicon oxide precipitates is observed at the interface. Tilt interfacial dislocations are pinned by these precipitates, they are more mobile than precipitates. Without precipitates, their lines are straighter than those with precipitates, and this is especially when the bonded wafers are annealed at a high temperature. When no precipitates are present, tilt interfacial dislocations are associated by pairs, and we demonstrate that each tilt interfacial dislocations introduce a diatomic interfacial step at the interface.     

Properties of CdTe films brush plated on high temperature substrates

CdTe thin films were brush plated on substrates maintained at temperatures in the range 30–90 °C from the precursors. The films exhibited cubic structure. Optical band gap of 1.45 eV was obtained. XPS measurements indicated the formation of CdTe. AFM studies indicated the formation of fine grains of the order of 50 nm, for the films deposited on room temperature substrates. Hot probe measurements indicated films to be n-type. A mobility in the range of 5–60 cm² V⁻¹ s⁻¹ and a carrier density of 10¹⁵ cm⁻³ was obtained.     

Carrier gas and VI/II ratio effects on carbon clusters incorporation into ZnO films grown by MOCVD

Undoped ZnO films were deposited by atmospheric metal-organic chemical vapor deposition (MOCVD) on (0001) ZnO substrate. The films were grown at various partial pressure ratios of oxygen and zinc precursors (VI/II) using either N₂ or H₂ as carrier gas. Micro-Raman scattering was employed to study the effects of carrier gas, VI/II ratio and annealing on carbon impurity incorporation into the ZnO films. Besides the well known phonon modes of ZnO, Raman spectra of the samples grown with N₂ carrier gas show two additional broad peaks, which are ascribed to carbon sp² clusters related modes, spreading in the frequency range 1300–1600 cm^?1 and dominate the Raman spectrum of the sample grown under oxygen deficiency (VI/II=0.25). In addition, a band centered at ～520 cm^?1, considered as some defects related local vibrations, appears in the samples grown with N₂ as carrier gas and its intensity increases when the VI/II ratio decreases. The average cluster size, estimated from the intensity ratio of D over G bands of the carbon sp² clusters, ranges from 16.5 to 19.4 Å. However, in all the samples grown with H₂ as carrier gas, the bands related to carbon sp² clusters and defects, are largely suppressed and the second-order-Raman scattering band (1050–1200 cm^?1) is clearly observed in addition to the bulk ZnO lattice modes. After annealing the samples at 900 °C in oxygen ambient, the crystal quality has been improved for all the samples but the carbon related bands, formed in the as-deposited films grown with the N₂ carrier gas, were only weakened.     

Performance improvement of pentacene-doped P3HT:PCBM inverted polymer solar cells with AZO nanorod array passivated using photoelectrochemical technique

The pentacene-doped P3HT:PCBM inverted polymer solar cells (IPSCs) with Al-doped zinc oxide (AZO) nanorod array were fabricated. The AZO nanorod array could enhance the carrier collection and carrier extraction capability. The AZO nanorod array formed by the laser interference photolithography method and the wet etching process sequentially was used as the carrier collection and carrier transportation layers. The defects on the sidewall surface of the AZO nanorods were passivated by using the photoelectrochemical (PEC) method. It was demonstrated that the better performance of the IPSCs was obtained by PEC treatment. Compared with the IPSCs without PEC treatment, the short current density and power conversion efficiency of the IPSCs with PEC treatment for 60 s increased from 14.56 mA/cm² to 15.85 mA/cm² and 5.45% to 6.13%, respectively.     

Charge carrier mobility and lifetime of organic bulk heterojunctions analyzed by impedance spectroscopy

Charge carrier diffusion and recombination in an absorber blend of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C₆₁-butyric acid methyl ester (PCBM) with indium tin oxide (ITO) and aluminium contacts have been analyzed in the dark by means of impedance spectroscopy. Reverse bias capacitance exhibits Mott–Schottky-like behavior indicating the formation of a Schottky junction (band bending) at the P3H:PCBM-Al contact. Impedance measurements show that minority carrier (electrons) diffuse out of the P3HT:PCBM-Al depletion zone and their accumulation contributes to the capacitive response at forward bias. A diffusion–recombination impedance model accounting for the mobility and lifetime parameters is outlined. Electron mobility results to be 2 × 10⁻³ cm² V⁻¹ s⁻¹ and lifetime lies within the milliseconds timescale.     

Investigation of deep level defects in copper irradiated bipolar junction transistor

Commercial bipolar junction transistor (2N 2219A, npn) irradiated with 150 MeV Cu¹¹⁺-ions with fluence of the order 10¹² ions cm^?2, is studied for radiation induced gain degradation and deep level defects. I–V measurements are made to study the gain degradation as a function of ion fluence. The properties such as activation energy, trap concentration and capture cross-section of deep levels are studied by deep level transient spectroscopy (DLTS). Minority carrier trap levels with energies ranging from E_C ? 0.164 eV to E_C ? 0.695 eV are observed in the base–collector junction of the transistor. Majority carrier trap levels are also observed with energies ranging from E_V + 0.203 eV to E_V + 0.526 eV. The irradiated transistor is subjected to isothermal and isochronal annealing. The defects are seen to anneal above 350 °C. The defects generated in the base region of the transistor by displacement damage appear to be responsible for transistor gain degradation.     

Achieving high sensitivity in single organic submicrometer ribbon based photodetector through surface engineering

The performance of the single organic submicrometer ribbon based photodetector has been improved by one order of magnitude by combining a better crystalline structure with proper surface engineering, such as coating a dielectric layer PMMA or PS between the substrate and the organic semiconductor. The photoconductivity gain is as much as 1.3 × 10⁴, the responsivity is about 4372 A W^?1 at the field of about 2 × 10⁶ V m^?1, and the highest on/off ratio reaches 10⁴. The extremely high gain is attributed to the high mobility and the long photo carrier’s lifetime induced by the dielectric layer.     

Oxide precipitates in annealed nitrogen-doped 300 mm CZ-SI

The lateral distribution of oxide precipitates as well as the denuded zone were investigated in a set of 300 mm CZ silicon wafers containing different amounts of nitrogen. Two light scattering methods, infrared light scattering tomography (IR-LST) as well as scanning infrared microscopy (SIRM) were used to characterize the precipitation density and the spatial distribution. The obtained results show that under certain heat treatments a high density of oxide precipitates, more than 1×10⁹ cm⁻³, can be achieved in the depth of 300 mm wafers. With increasing nitrogen content the radial distribution of precipitates becomes more uniform. A 10–60 μm wide precipitation-free denuded zone was observed. A comparison between IR-LST and SIRM results was performed indicating the dominance of relatively small precipitates.     

Non-destructive diagnostic techniques for oxygen precipitates in Czochralski silicon

This work investigates the determination of oxygen precipitate density in silicon using non-destructive methods, based essentially on electrical and optical techniques. Regarding electrical techniques, minority carrier diffusion length measurements by means of surface photo voltage or electrolytical metal tracer methods to determine the density of oxygen precipitates in p-type silicon wafers is evaluated, taking advantage of the activity of oxygen precipitates as recombination centres for minority carriers. Regarding optical techniques, the scanning infra-red microscope is considered, which can detect oxygen precipitates in silicon exploiting their effectiveness as light scattering centres. These techniques are compared with the traditional etching technique, considering samples in a wide range of precipitate density (5×10⁶–10¹¹ cm⁻³) and submitted to a wide variety of thermal treatments. Correlations are discussed with the support of transmission electron microscopy, X-ray diffraction and infrared spectroscopy observations, which provide complementary information on size, morphology and matrix stress of the oxygen precipitates.     

Effects of oxygen content on the structural,optical, and electrical properties of NiO films fabricated by radio-frequency magnetron sputtering

Nickel oxide (NiO) films were deposited on Corning glass substrate with variable (0–100%) oxygen content by radio-frequency sputtering. Effects of different oxygen content on the structural, optical, and electrical properties of NiO films were studied. X-ray diffraction showed that the NiO film deposited on substrate with 0% oxygen content resulted in a random polycrystalline structure and small grain size. The introduction of oxygen gas leaded to a (200) preferential orientation and larger grain size. The transmittance decreases with oxygen content due to the increase of oxygen interstitials in NiO films. The 0%-O₂ deposited NiO film has a tensile strain and a small band gap. Upon introducing 33%-O₂ content, the NiO film exhibits a compressive strain, increasing the bandgap. However, the compressive strain is released and gradually turns into tensile strain, which leads to the narrowing of bandgap with the increase of oxygen content. Hall measurement shows the obtained NiO is p-type and the resistivity decreases from 4.3 × 10⁵ Ω-cm to 5.02 Ω-cm with increasing oxygen content from 0% to 100%. The carrier concentration increases from 6.3 × 10¹⁴ cm⁻³ to 4.6 × 10¹⁸ cm⁻³ and the mobility decreases from 26 cm²/V-s to 0.26 cm²/V-s for the NiO films deposited with oxygen content increasing from 50% to 100%. X-ray photoelectron spectroscopy showed that the Ni⁺³/Ni⁺² ratio is the origin of p-type NiO and the ratio increases from 1.32 to 2.63 by increasing the oxygen content from 0% to 100%, which caused more defects, oxygen interstitials and nickel vacancies.     

DC and microwave characteristics of Lg 50 nm T-gate InAlN/AlN/GaN HEMT for future high power RF applications

The DC and microwave characteristics of L_g = 50 nm T-gate InAlN/AlN/GaN High Electron Mobility Transistor (HEMT) on SiC substrate with heavily doped n+ GaN source and drain regions have demonstrated using Synopsys TCAD tool. The proposed device features an AlN spacer layer, AlGaN back-barrier and SiN surface passivation. The proposed HEMT exhibits a maximum drain current density of 1.8 A/mm, peak transconductance (g_m) of 650 mS/mm and ft/fmax of 118/210 GHz. At room temperature, the measured carrier mobility, sheet charge carrier density (n_s) and breakdown voltage are 1195 cm²/Vs, 1.6 × 10¹³ cm⁻² and 18 V respectively. The superlatives of the proposed HEMTs are bewitching competitor for future monolithic microwave integrated circuits (MMIC) applications particularly in W-band (75–110 GHz) high power RF applications.     

Carbon-related defects in microelectronics

In the present study electrically active carbon and hydrogen-related (CH) defects, which can act as strong recombination centers in high power devices and CMOS photodetectors, are investigated in n-type Si. Several different CH-related defects are observed by using the deep level transient spectroscopy (DLTS) technique on hydrogenated Si samples with different oxygen content. The concentration of these defects is determined as low as 10¹²–10¹³ cm^− 3. By comparing samples with different O, C, and H concentrations the origin of the CH-related defects is derived. We show that the concentration of the electrically inactive substitutional C can be estimated by a comparison of the depth profiles of the electrically active CH-related defects in a sample with those in a reference sample which has an identical oxygen and known carbon content. This approach is applicable even for concentrations of substitutional C lower than 10¹⁵ cm^− 3.     

Evolution in crystal structure and electrical performance of thiophene-based polymer field effect transistors: A remarkable difference between thermal and solvent vapor annealing

We report the various conformational structures of long pendant side-chains, and the effects of thermal and solvent vapor annealing (SVA) with the corresponding charge carrier mobilities of thiophene-based conjugated polymers, poly[5,5′-bis(3-dodecyl-2-thienyl)-2,2′-bithiophene] (PQT-12) and poly(4,4′-bis-decyloxymethylquaterthiophene) (POQT), by correlated study of their extraordinary polymorphic crystal structures. In substitution for alkyl chains in polythiophenes, ether alkyl chains induce a favorable non-covalent interaction between the oxygen and sulfur atoms and help the polymer chains planar with lower torsion angles between conjugated backbone units showing a reduced π–π stacking distance. However, the flexibility and conformational freedom with such long side-chains dominantly induce polymorphic crystallites from bent and extended side-chains. Especially, POQT exhibit two polymorphic crystallite phases in a similar ratio probably due to the increased freedom of ether alkyl chains. Therefore, the field effect mobility of POQT is decreased gradually with the increase of annealing temperature from 0.024 (at 80 °C) to 3.96 × 10⁻⁴ cm²/V s (at 170 °C). Contrary to the thermal annealing method, solvent-vapor-annealed POQT films show highly ordered and single-phase crystallites with edge-on orientation to the substrate, which ultimately provides an effectively improved charge carrier mobility from 0.023 (pristine) to 0.076 cm²/V s after adequate solvent vapor exposure.     

Electrical and optical properties of Cu2ZnSnS4 grown by a thermal co-evaporation method and its diode application

Cu₂ZnSnS₄ (CZTS) is low cost and constitutes non-toxic materials abundant in the earth crust. Environment friendly solar cell absorber layers were fabricated by a thermal co-evaporation technique. Elemental composition of the film was stated by energy dispersive spectroscopy (EDS). Some optical and electrical properties such as absorption of light, absorption coefficient, optical band gap charge carrier density, sheet resistance and mobility were extracted. Optical band gap was found to be as 1.44 eV, besides, charge carrier density, resistivity and mobility were found as 2.14×10¹⁹ cm⁻³, 8.41×10⁻⁴ Ω cm and 3.45×10² cm² V⁻¹ s⁻¹, respectively. In this study Ag/CZTS/n-Si Schottky diode was fabricated and basic diode parameters including barrier height, ideality factor, and series resistance were concluded using current–voltage and capacitance–voltage measurements. Barrier height and ideality factor values were found from the measurements as 0.81 eV and 4.76, respectively, for Ag/CZTS/n-Si contact.     

Efficient planar organic solar cells with the high near-infrared response

Efficient planar organic solar cells extending the response into the near-infrared (NIR) were fabricated using the highly ordered Titanyl phthalocyanines (TiOPc) films as the donor layer. This type of films obtained through the weak epitaxy growth (WEG) method presents good continuity and integrity with the low density of grain boundaries. More importantly the films own a strong absorption in the NIR (750–950 nm) and a broad absorption spectrum from 550 to 950 nm. Meanwhile the high external quantum efficiency (EQE) is obtained in the NIR with the peak value over 38% and the EQE is over 18% in the entire response range, which could benefit from the long exciton diffusion length and the high carrier mobility of the highly ordered films. Thereby the fabricated planar solar cells achieve a high short-circuit current density (J_sc) of 9.26 mA cm^?2 and a power conversion efficiency (PCE) of 2.67%.     

Characterization of MIS structures and thin film transistors using RF-sputtered HfO2/HIZO layers

MIS structures using HfO₂ and HIZO layers, both deposited by room temperature RF magnetron sputtering are fabricated for TFTs application and characterized using capacitance-voltage. The relative dielectric constant obtained at 1 kHz was 11, the charge carrier concentration of the HIZO was in the range of (2–3) × 10¹⁸ cm^− 3 and the interface trap density at flat band was smaller than 2 × 10¹² cm^− 2. The critical electric field of the HfO₂ layer was higher than 5 × 10⁵ V/cm, with a current density in the operating voltage range below 4 × 10^− 8 A/cm². The hysteresis and bias stress behavior of RF-sputtered HfO₂/HIZO MIS structures is presented. Fabricated HfO₂/HIZO TFTs worked in the operation voltage range below 8 V.     

Fabrication of high-mobility organic single-crystal field-effect transistors with amorphous fluoropolymer gate insulators

High-mobility rubrene single-crystal field-effect transistors are built on highly water- and oil-repellent fluoropolymer gate insulators. Roughness is introduced at the surface once to provide good adhesion to metal films and photoresist polymers for stable electrodes. Before constructing interfaces to crystals, smoothness of the fluoropolymer surface is recovered by annealing at a moderate temperature to maximize carrier mobility. Mobility values estimated in the saturation region reproducibly exceeded 15 cm²/V s for all the 10 devices, reaching 30 cm²/V s for the best two devices. The results demonstrate that the water-repellency and smoothness of the dielectric polymers are favorable for the excellent transistor performance.     

Positive bias temperature instabilities on sub-nanometer EOT FinFETs

PBTI degradation on FinFETs with HfO₂/TiN gate stack (EOT < 1 nm) is studied. Thinner TiN layer decreases interfacial oxide thickness, and reduces PBTI lifetime. This behavior is consistent with the results in planar devices. Corner rounding effect on PBTI is also analyzed. Finally, charge pumping measurements on devices with several fin widths devices apparently show a higher density of defects in the top-wall high-κ oxide than in the sidewall of the fin. This could explain more severe PBTI degradation.     

The influence of high energy electron irradiation on the Schottky barrier height and the Richardson constant of Ni/4H-SiC Schottky diodes

The influence of high energy electron (HEE) irradiation from a Sr-90 radio-nuclide on n-type Ni/4H–SiC samples of doping density 7.1×10¹⁵ cm⁻³ has been investigated over the temperature range 40–300 K. Current–voltage (I–V), capacitance–voltage (C–V) and deep level transient spectroscopy (DLTS) were used to characterize the devices before and after irradiation at a fluence of 6×10¹⁴ electrons-cm⁻². For both devices, the I–V characteristics were well described by thermionic emission (TE) in the temperature range 120–300 K, but deviated from TE theory at temperature below 120 K. The current flowing through the interface at a bias of 2.0 V from pure thermionic emission to thermionic field emission within the depletion region with the free carrier concentrations of the devices decreased from 7.8×10¹⁵ to 6.8×10¹⁵ cm⁻³ after HEE irradiation. The modified Richardson constants were determined from the Gaussian distribution of the barrier height across the contact and found to be 133 and 163 A cm⁻² K⁻² for as-deposited and irradiated diodes, respectively. Three new defects with energies 0.22, 0.40 and 0.71 eV appeared after HEE irradiation. Richardson constants were significantly less than the theoretical value which was ascribed to a small active device area.