Energy Levels of Defects in a-Si:H From Optical and Electrical Characteristics

1996 ◽  
Vol 424 ◽  
Author(s):  
T. Globus
Keyword(s):  
Thin Films ◽  
Energy Levels ◽  
Thin Film Transistor ◽  
Close Correlation ◽  
Device Fabrication ◽  
Defect States ◽  
Optical Interference ◽  
Hydrogenated Silicon ◽  
Transfer Characteristics ◽  
Wide Range

AbstractTwo novel characterization techniques for hydrogenated silicon thin films have been recently proposed which show promise in providing critical feedback for evaluating materials and monitoring the device fabrication process. The first technique is the optical interference spectroscopy for a quick non-destructive measurement of absorption coefficient and refractive index spectra of amorphous- and poly-Si thin films in a wide range of the incident photon energies (0.5–3.5 eV) [1]. By using this technique, the absorption related to defects in the subgap energy region has been determined for device quality thin films. The second technique is the novel version of the field effect conductivity (FEC) method for the direct density-of-states (DOS) determination from analysis of thin film transistor (TFT) quasi-static transfer characteristics [2]. This sensitive, fast, and easy to use, method makes it possible to resolve fine-scale features in the midgap DOS of a-Si:H. In this work, data from two methods of spectroscopy are analyzed together. Very close correlation of results is demonstrated which provides a unique opportunity to identify midgap defect states and to understand the fundamental physics of hydrogenated silicon films. The energy map of defect states in the upper half of a-Si:H bandgap is presented. These results permits to use TFT transfer characteristics and optical interference technique measurements as effective tools to control the quality of TFF manufacturing process.

Optical Characterization of Hydrogenated Silicon Films in the Extended Energy Range

1995 ◽  
Vol 406 ◽  
Author(s):  
T. Globus ◽  
S. J. Fonash ◽  
G. Gildenblat
Keyword(s):  
Thin Films ◽  
Refractive Index ◽  
Absorption Coefficient ◽  
Film Growth ◽  
Optical Measurement ◽  
Specular Reflection ◽  
Device Fabrication ◽  
Hydrogenated Silicon ◽  
Wide Range

AbstractThis work introduces a new interference technique for the diagnostic characterization of hydrogenated silicon thin films. The interference technique is based on new self-consistent data analysis algorithms for simultaneous optical transmission and specular reflection using exact interference equations for the system of a film on a substrate. It provides a quick non-destructive optical measurement of absorption coefficient and refractive index spectra of amorphous silicon (a-Si:H) and polycrystalline silicon (poly-Si:H) thin films in a wide range of the incident photon energies (0.5–3.5 eV). This non-contacting, high sensitivity method is a powerful probe of various material properties including thickness, refractive index and absorption spectra, hydrogen content, alloy fraction, energies of localized defect states and their concentrations. Experimental results for optical study of hydrogenated Si films indicate that the proposed method makes possible high precision measurements of the absorption in the region near the fundamental edge. In this region the absorption coefficient varies over several orders of magnitude. Also, the absorption related to impurities and defects in the subgap energy region at least from 102 cm−1 can be detected. As a result, the interference technique shows promise in providing feedback for monitoring film growth and device fabrication processes.

ATOMIC LAYER DEPOSITION OF SiO2 USING CATALYZED AND UNCATALYZED SELF-LIMITING SURFACE REACTIONS

1999 ◽  
Vol 06 (03n04) ◽  
pp. 435-448 ◽  
Author(s):  
J. W. KLAUS ◽  
O. SNEH ◽  
A. W. OTT ◽  
S. M. GEORGE
Keyword(s):  
Thin Films ◽  
Dielectric Breakdown ◽  
Substrate Surface ◽  
Surface Reactions ◽  
Atomic Layer ◽  
Device Fabrication ◽  
Initial Substrate ◽  
Wide Range ◽  
Limiting Surface ◽  
Layer Control

SiO 2 thin films were deposited with atomic layer control using self-limiting surface reactions. The SiO 2 growth was achieved by separating the binary reaction SiCl 4+ 2H 2 O → SiO 2+ 4HCl into two half-reactions. Successive application of the half-reactions in an ABAB… sequence produced atomic-layer-controlled SiO 2 deposition. SiO 2 films were grown at temperatures of 600–800 K, with SiCl 4 and H 2 O reactant exposures of ~109 L ( 1 L = 10-6 Torr s). Employing pyridine ( C 5 H 5 N ) as a catalyst, the SiO 2 films could be deposited at much lower temperatures and reactant exposures. The pyridine catalyst lowered the required SiO 2 deposition temperature from 600 K to 300 K and reduced the reactant exposure required for complete reactions from ~109 L to ~ 104 L. In addition, the SiO 2 growth rates increased from 0.75 Å per AB cycle at 800 K to 2.1 Aring; per AB cycle at 300 K. The deposited films were stoichiometric SiO 2 and were extremely flat, with a roughness nearly identical to the initial substrate surface. The films also displayed dielectric breakdown strengths similar to thermally deposited SiO 2 films. The ability to deposit conformal SiO 2 thin films with atomic layer control over a wide range of temperatures should find numerous applications in thin film device fabrication.

Characterization of Gap Defect States in Hydrogenated Amorphous Silicon Materials

2008 ◽  
Vol 1066 ◽  
Author(s):  
Lihong Jiao ◽  
C. R. Wronski
Keyword(s):  
Amorphous Silicon ◽  
Energy Levels ◽  
Hydrogenated Amorphous Silicon ◽  
Defect States ◽  
Wide Range ◽  
Silicon Materials ◽  
Energy Dependent ◽  
Hydrogenated Amorphous ◽  
Dependent Density ◽  
Gap State

ABSTRACTAn enhanced simulation model based on the carrier recombination through these states was developed to characterize the gap defect states in hydrogenated amorphous silicon materials (a-Si:H). The energy dependent density of electron occupied gap states, kN(E), was derived directly from Dual Beam Photoconductivity (DBP) measurements at different bias currents. Through Gaussian de-convolution of kN(E), the energy peaks of the multiple defect states, including both neutral and charged states, were obtained. These energy levels, together with the information on the capture cross sections, were used as known input parameters to self-consistently fit the subgap absorption spectra, the electron mobility-lifetime products over a wide range of generation rates, as well as the energy dependent density of electron occupied gap state spectra. Accurate gap state information was obtained and the nature of the defect states was studied. Simulation results on light degraded hydrogen diluted, protocrystalline a-Si:H show that the density of charged states is 2.3 times that of neutral states. The two states close to the midgap act as effective recombination centers at low generation rates and play key roles in photoconductivity studies.

scholarly journals The Growth of Photoactive Porphyrin-Based MOF Thin Films Using the Liquid-Phase Epitaxy Approach and their Optoelectronic Properties

Materials ◽  
2019 ◽  
Vol 12 (15) ◽  
pp. 2457 ◽  
Author(s):  
Ngongang Ndjawa ◽  
Tchalala ◽  
Shekhah ◽  
Khan ◽  
Mansour ◽  
...  
Keyword(s):  
Thin Films ◽  
Solar Cells ◽  
Liquid Phase ◽  
Liquid Phase Epitaxy ◽  
Metal Organic Framework ◽  
Device Fabrication ◽  
Optoelectronic Properties ◽  
Molecular Alteration ◽  
Wide Range ◽  
Light Absorbers

This study reports on the optoelectronic properties of porphyrin-based metal–organic framework (MOF) thin films fabricated by a facile liquid-phase epitaxy approach. This approach affords the growth of MOF thin films that are free of morphological imperfections, more suitable for optoelectronic applications. Chemical modifications such as the porphyrin ligand metallation have been found to preserve the morphology of the grown films making this approach particularly suitable for molecular alteration of MOF thin film optoelectronic properties without compromising its mesoscale morphology significantly. Particularly, the metallation of the ligand was found to be effective to tune the MOF bandgap. These porphyrin-based MOF thin films were shown to function effectively as donor layers in solar cells based on a Fullerene-C60 acceptor. The ability to fabricate MOF solar cells free of a liquid-phase acceptor greatly simplifies device fabrication and enables pairing of MOFs as light absorbers with a wide range of acceptors including non-fullerene acceptors.

scholarly journals A Slot-Die Technique for the Preparation of Continuous, High-Area, Chitosan-Based Thin Films

Polymers ◽  
2021 ◽  
Vol 13 (10) ◽  
pp. 1566
Author(s):  
Oliver J. Pemble ◽  
Maria Bardosova ◽  
Ian M. Povey ◽  
Martyn E. Pemble
Keyword(s):  
Thin Films ◽  
Mechanical Properties ◽  
High Volume ◽  
Mechanical Anisotropy ◽  
Diverse Range ◽  
Direction Parallel ◽  
High Area ◽  
Wide Range ◽  
Slot Die ◽  
Potential Applications

Chitosan-based films have a diverse range of potential applications but are currently limited in terms of commercial use due to a lack of methods specifically designed to produce thin films in high volumes. To address this limitation directly, hydrogels prepared from chitosan, chitosan-tetraethoxy silane, also known as tetraethyl orthosilicate (TEOS) and chitosan-glutaraldehyde have been used to prepare continuous thin films using a slot-die technique which is described in detail. By way of preliminary analysis of the resulting films for comparison purposes with films made by other methods, the mechanical strength of the films produced was assessed. It was found that as expected, the hybrid films made with TEOS and glutaraldehyde both show a higher yield strength than the films made with chitosan alone. In all cases, the mechanical properties of the films were found to compare very favorably with similar measurements reported in the literature. In order to assess the possible influence of the direction in which the hydrogel passes through the slot-die on the mechanical properties of the films, testing was performed on plain chitosan samples cut in a direction parallel to the direction of travel and perpendicular to this direction. It was found that there was no evidence of any mechanical anisotropy induced by the slot die process. The examples presented here serve to illustrate how the slot-die approach may be used to create high-volume, high-area chitosan-based films cheaply and rapidly. It is suggested that an approach of the type described here may facilitate the use of chitosan-based films for a wide range of important applications.

scholarly journals The Growth of Semiconductor Thin Films Studied by RHEED

1990 ◽  
Vol 43 (5) ◽  
pp. 583
Author(s):  
GL Price
Keyword(s):  
Thin Films ◽  
Surface Science ◽  
High Vacuum ◽  
High Energy ◽  
Ultra High Vacuum ◽  
Large Area ◽  
Growth Modes ◽  
Semiconductor Thin Films ◽  
Wide Range ◽  
Recent Developments

Recent developments in the growth of semiconductor thin films are reviewed. The emphasis is on growth by molecular beam epitaxy (MBE). Results obtained by reflection high energy electron diffraction (RHEED) are employed to describe the different kinds of growth processes and the types of materials which can be constructed. MBE is routinely capable of heterostructure growth to atomic precision with a wide range of materials including III-V, IV, II-VI semiconductors, metals, ceramics such as high Tc materials and organics. As the growth proceeds in ultra high vacuum, MBE can take advantage of surface science techniques such as Auger, RHEED and SIMS. RHEED is the essential in-situ probe since the final crystal quality is strongly dependent on the surface reconstruction during growth. RHEED can also be used to calibrate the growth rate, monitor growth kinetics, and distinguish between various growth modes. A major new area is lattice mismatched growth where attempts are being made to construct heterostructures between materials of different lattice constants such as GaAs on Si. Also described are the new techniques of migration enhanced epitaxy and tilted superlattice growth. Finally some comments are given On the means of preparing large area, thin samples for analysis by other techniques from MBE grown films using capping, etching and liftoff.

Heat transfer characteristics of nanofluids from a sinusoidal corrugated cylinder placed in a square cavity

2021 ◽  
pp. 095440622110272
Author(s):  
Salaika Parvin ◽  
Nepal Chandra Roy ◽  
Litan Kumar Saha ◽  
Sadia Siddiqa
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Rayleigh Number ◽  
Aspect Ratio ◽  
Average Nusselt Number ◽  
Numerical Study ◽  
Heat Transfer Characteristics ◽  
Number Range ◽  
Transfer Characteristics ◽  
Wide Range

A numerical study is performed to investigate nanofluids' flow field and heat transfer characteristics between the domain bounded by a square and a wavy cylinder. The left and right walls of the cavity are at constant low temperature while its other adjacent walls are insulated. The convective phenomena take place due to the higher temperature of the inner corrugated surface. Super elliptic functions are used to transform the governing equations of the classical rectangular enclosure into a system of equations valid for concentric cylinders. The resulting equations are solved iteratively with the implicit finite difference method. Parametric results are presented in terms of streamlines, isotherms, local and average Nusselt numbers for a wide range of scaled parameters such as nanoparticles concentration, Rayleigh number, and aspect ratio. Several correlations have been deduced at the inner and outer surface of the cylinders for the average Nusselt number, which gives a good agreement when compared against the numerical results. The strength of the streamlines increases significantly due to an increase in the aspect ratio of the inner cylinder and the Rayleigh number. As the concentration of nanoparticles increases, the average Nusselt number at the internal and external cylinders becomes stronger. In addition, the average Nusselt number for the entire Rayleigh number range gets enhanced when plotted against the volume fraction of the nanofluid.

scholarly journals Light- and Melanin Nanoparticle-Induced Cytotoxicity in Metastatic Cancer Cells

Pharmaceutics ◽  
2021 ◽  
Vol 13 (7) ◽  
pp. 965
Author(s):  
Victoria R. Gabriele ◽  
Robabeh M. Mazhabi ◽  
Natalie Alexander ◽  
Purna Mukherjee ◽  
Thomas N. Seyfried ◽  
...  
Keyword(s):  
Cancer Cells ◽  
Metastatic Cancer ◽  
Energy Levels ◽  
Nanoparticle Concentration ◽  
Visible Radiation ◽  
Laser Illumination ◽  
Wide Range ◽  
Low Glucose ◽  
Melanin Nanoparticles ◽  
Metastatic Cancer Cells

Melanin nanoparticles are known to be biologically benign to human cells for a wide range of concentrations in a high glucose culture nutrition. Here, we show cytotoxic behavior at high nanoparticle and low glucose concentrations, as well as at low nanoparticle concentration under exposure to (nonionizing) visible radiation. To study these effects in detail, we developed highly monodispersed melanin nanoparticles (both uncoated and glucose-coated). In order to study the effect of significant cellular uptake of these nanoparticles, we employed three cancer cell lines: VM-M3, A375 (derived from melanoma), and HeLa, all known to exhibit strong macrophagic character, i.e., strong nanoparticle uptake through phagocytic ingestion. Our main observations are: (i) metastatic VM-M3 cancer cells massively ingest melanin nanoparticles (mNPs); (ii) the observed ingestion is enhanced by coating mNPs with glucose; (iii) after a certain level of mNP ingestion, the metastatic cancer cells studied here are observed to die—glucose coating appears to slow that process; (iv) cells that accumulate mNPs are much more susceptible to killing by laser illumination than cells that do not accumulate mNPs; and (v) non-metastatic VM-NM1 cancer cells also studied in this work do not ingest the mNPs, and remain unaffected after receiving identical optical energy levels and doses. Results of this study could lead to the development of a therapy for control of metastatic stages of cancer.

Irradiation Induced Changes in Semiconducting Thin Films

2013 ◽  
Vol 341 ◽  
pp. 181-210 ◽  
Author(s):  
S.K. Tripathi
Keyword(s):  
Thin Films ◽  
Solar Cells ◽  
Heavy Ions ◽  
Semiconductor Device ◽  
High Energy ◽  
Device Fabrication ◽  
Electrical Performance ◽  
Radiation Environment ◽  
Extended Defects ◽  
Semiconducting Thin Films

High-energy electron, proton, neutron, photon and ion irradiation of semiconductor diodes and solar cells has long been a topic of considerable interest in the field of semiconductor device fabrication. The inevitable damage production during the process of irradiation is used to study and engineer the defects in semiconductors. In a strong radiation environment in space, the electrical performance of solar cells is degraded due to direct exposure to energetically charged particles. A considerable amount of work has been reported on the study of radiation damage in various solar cell materials and devices in the recent past. In most cases, high-energy heavy ions damage the material by producing a large amount of extended defects, but high-energy light ions are suitable for producing and modifying the intrinsic point defects. The defects can play a variety of electronically active roles that affect the electrical, structural and optical properties of a semiconductor. This review article aims to present an overview of the advancement of research in the modification of glassy semiconducting thin films using different types of radiations (light, proton and swift heavy ions). The work which has been done in our laboratory related to irradiation induced effects in semiconducting thin films will also be compared with the existing literature.

scholarly journals Conduction and convection heat transfer characteristics of water-based au nanofluids in a square cavity with differentially heated side walls subjected to constant temperatures

2014 ◽  
Vol 18 (suppl.1) ◽  
pp. 189-200 ◽  
Author(s):  
Primoz Ternik ◽  
Rebeka Rudolf
Keyword(s):  
Heat Transfer ◽  
Rayleigh Number ◽  
Base Fluid ◽  
Volume Fraction ◽  
Heat Transfer Characteristics ◽  
Square Cavity ◽  
Onset Of Convection ◽  
Transfer Characteristics ◽  
Wide Range ◽  
Water Based

The present work deals with the natural convection in a square cavity filled with the water-based Au nanofluid. The cavity is heated on the vertical and cooled from the adjacent wall, while the other two horizontal walls are adiabatic. The governing differential equations have been solved by the standard finite volume method and the hydrodynamic and thermal fields were coupled together using the Boussinesq approximation. The main objective of this study is to investigate the influence of the nanoparticles? volume fraction on the heat transfer characteristics of Au nanofluids at the given base fluid?s (i.e. water) Rayleigh number. Accurate results are presented over a wide range of the base fluid Rayleigh number and the volume fraction of Au nanoparticles. It is shown that adding nanoparticles in a base fluid delays the onset of convection. Contrary to what is argued by many authors, we show by numerical simulations that the use of nanofluids can reduce the heat transfer rate instead of increasing it.

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