bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Si Doping on The Structure of Gan
Authors: Liliental-Weber Zuzanna , Ruvimov S. , Suski T. , Ager J. W. , Swider W. , Chen Y. , Kisielowski Ch. , Washburn J. , Akasaki I. , Amano H. , Kuo C. , Imler W.
Published: April 2011

The influence of Si doping on the structure of GaN grown by metal-organic chemicalvapor deposition (MOCVD) has been studied using transmission electron microscopy (TEM), x-ray diffraction and Raman spectroscopy. Undoped and low Si doped samples were compared with samples of increased dopant concentration. In addition, defect reduction due to different buffer layers (AIN and GaN) is discussed. Silicon doping improves surface morphology and influences threading dislocation arrangement. High doping leads to a more random distribution of dislocations. Based on this study it appears (for the same dopant concentration) that an AIN buffer layer can significantly reduce the number of threading dislocations, leaving the samples more strained. However, no significant reduction of threading dislocations could be observed in the samples with GaN buffer layer. These samples are the least strained.
OBIC Measurements on 6H-SiC Schottky Diodes
Authors: Rottner K. , Schöner A. , Frischholz M. , Helbig R.
Published: April 2011

The OBIC (Optical Beam Induced Current) technique is a powerful method to investigate the electric field distribution of p-n junctions in SiC. In a previous work we found strong indications for the presence of a high density of negative surface charge in n-type SiC. In order to study samples of both conductivity types under similar conditions we prepared Schottky contacts on ntype and p-type 6H-SiC CVD epitaxial layers.

OBIC measurements show an extension of the depletion region of several hundreds of microns from the edge of the contact on n- and p-type samples, thus interconnecting diodes on an area up to several mm2. Our results imply that there is no fixed surface charge but a high density of both acceptor- and donorlike surface states leading to a dependence of the net surface charge on the Fermi energy, in which case the sign of the surface charge reverses from negative on ntype material to positive on p-type 6H-SiC.
Deep Level Defects in Mg-Doped GaN
Authors: Yi Gyu-Chul , Wessels Bruce W.
Published: April 2011

Deep level defects in Mg compensated GaN grown by metal-organic vapor phase epitaxy were investigated using photocapacitance spectroscopy measurements on Schottky barrier diodes. Addition of magnesium resulted in the formation of a series of deep centers with optical threshold energies of 1.0, 1.2, 1.8, and 3.1 eV. Upon annealing the epitaxial GCN in nitrogen at 850°C the ind-gap levels disappeared and only the trapping level at 3.1 eV remained. The mid-gap levels are ascribed to Mg dopant complexes which may in part be responsible for low doping efficiency of Mg in the as-grown, doped GaN. The deep level at 3.1 eV commonly observed from all Mgdoped GaN most likely involves the Mg acceptor. The photo-excited state of the 3.1 eV level had relaxation times of the order of 103 sec at 295 K.
Dlts and CV Analysis of Doped and N-Implanted GaN
Authors: Haase D. , Schmid M. , Dörnen A. , Härle V. , Bolay H. , Scholz F. , Burkard M. , Schweizer H.
Published: April 2011

We studied by deep level transient spectroscopy (DLTS) and capacitance-voltage (CV) measurements the effects of doping (Zn, S), nitrogen implantation and annealing of n-type GaN grown on sapphire by MOVPE. The DLTS spectra of the as grown samples show two defect levels which are assumed to be identical with recently reported levels [10, 11]. In N-implanted GaN a third level is introduced which is not detectable in our as grown samples. This levels concentration follows the increasing N-implantation density. The depth profiles of its concentration correlate with the distribution of implantation defects expected from Monte-Carlo simulation. After annealing at 900°C for 60s the additional defect level vanishes. The DLTS spectrum then resembles those of annealed as grown samples. The n-type carrier concentration (CV measurements) increases in samples with low N-implantation dose. This implantation effect can be removed also with the RTA step. The increasing carrier concentration provides evidence that the N vacancy is a donor in GaN. For Zn and S doped GaN deep defect levels has been found, which are reported here.
Extrapolation of critical thickness of GaN thin films from lattice constant data using synchrotron X-ray
Authors: Kim Chinkyo , Robinson I. K. , Myoung Jaemin , Shim Kyuhwan , Kim Kyekyoon , Yoo Myung-Cheol
Published: April 2011

In some materials, Van der Merwe's equilibrium theory of strain relief is believed to explain the sudden transition from pseudomorphic growth of a thin film to a progressively relaxed state. We show, for the first time for GaN, how an accurate estimate of the critical thickness of a thin film can be extrapolated from suitable measurements of lattice constants as a function of film thickness using synchrotron X-ray. We do this both for an elementary elastic energy function, in which the interactions between the dislocations are ignored, and for a more realistic energy estimate due to Kasper. The method is found to work quantitatively for thin films of GaN on AIN. The critical thickness is determined to be 29 ± 4 Å.
Ex Situ and In Situ Methods for Complete Oxygen and Non-Carbidic Carbon Removal from (0001)SI 6H-SiC Surfaces
Authors: King Sean W. , Benjamin Mark C. , Kern Richard S. , Nemanich Robert J. , Davis Robert F.
Published: April 2011

Comparisons between the wetting characteristics of (0001)si 6H-SiC and (111) Si surfaces in various acids and bases were made. It was found that 10:1 HF dipped Si (111) surfaces were hydrophobic where as the (0001)si 6H-SiC surfaces were hydrophilic. (0001)si 6H-SiC surfaces capped with a 20Å Si layer, however, were hydrophobic after HF dipping and exhibited outgassing levels on annealing which were several orders of magnitude lower than SiC wafers dipped in HF without the capping layer. Annealing the Si capped (0001)si 6H-SiC surfaces in UHV at 1100°C for 5 min. was found to be sufficient to thermally desorb the Si capping layer and produce a (3×3) Si rich, oxygen free (0001)si 6H-SiC surface.
Electrical Characterization of Magnesium-Doped Gallium Nitride Grown by Metalorganic Vapor Phase Epitaxy
Authors: Huang J. W. , Lu H. , Cederberg J. G. , Bhat I. , Kuech T. F.
Published: April 2011

We have applied frequency-dependent capacitance measurements and admittance spectroscopy on metalorganic vapor phase epitaxy GaN:Mg to study the electronic states associated with Mg doping. Samples with different Mg doping levels were grown and annealed in nitrogen. Lateral dot-and-ring Schottky diodes using Au/Ti were fabricated. After a 800 °C anneal, frequency-dependent measurements show that the capacitance is reduced at a higher frequency, most likely due to the inability of a deep center to maintain an equilibrium ionization state under a high frequency modulation. The net ionized acceptor concentrations was found to be greater at a higher Mg doping level. Admittance spectroscopy, in which the conductance is monitored as a function of temperature, verifies the existence of at least one impurity-related acceptor level with an activation energy of ∼ 140 meV. A reduction in the annealing temperature was found to lead to a lower net ionized acceptor concentration, as well as a higher activation energy.
Impurity Conduction in n-Type 4H-SIC
Authors: Evwaraye A. O. , Smith S. R. , Mitchel W. C. , Roth M. D.
Published: April 2011

Impurity conduction (or hopping conduction) has been observed in the more heavily n-type 4H-SiC samples by both temperature dependent resistivity measurements and thermal admittance spectroscopy. The measured activation energies ɛ 3 for hopping were 4–5 meV and 2.3–3.0 meV respectively. No evidence of hopping conduction was seen by either method in the sample where ND-NA < 1018 cm-3. The thermal admittance spectrum of the lightly n-type sample showed the two nitrogen levels at 53 and 100 meV.
Raman Spectroscopy Investigation of (SiC)1-x (Ain)x, Layers Formed by Ion Implantation in 6H-SiC
Authors: Zahn D. R. T. , Werninghaus T. , Thümer M. , Pezoldt J. , Heera V.
Published: April 2011

6H silicon carbide (SiC) substrates were implanted with nitrogen and aluminum at different doses and annealed in the temperature range from 1300°C-1700°C. Micro-Raman Spectroscopy (μ-RS) measurements were performed in two sample geometries (conventional plane-view and cross-sectional). Changes of the polytype from 6H- to a cubic (SiC)1-xAIN)x, and influences in the 6H-SiC wafer up to depths of 2μm were detected. The results obtained by crosssectional μ-RS are discussed in comparison to other results from Reflection High Electron Energy Diffraction (RHEED), Rutherford Backscattering (RBS), Auger Electron Spectroscopy (AES), Transmission Electron Microscopy (TEM), and Positron Annihilation Spectroscopy (PAS) measurements.
Low Energy Ion Doping Technology for Poly-Si TFTs
Authors: Mimura A. , Nagai M. , Shinagawa Y.
Published: April 2011

Ion doping technology using a bucket-type ion source to fabricate low temperature poly-Si TFTs is presented. Low energy and high ion density conditions are applied to realize the short doping time and resist mask doping for large area glass substrates. A novel CMOS doping technology with one resist mask process is proposed using compensation and inversion of the shollow doped layer. In combination with excimer laser crystallization and activation below 450°C, high performance CMOS TFTs are produced.
Electrical Performance Of an N-Channel TFT Fabricated on a Quartz Substrate by ZMR
Authors: Leeo Si-Woo , Joo Seung-Ki , Lee Byung-Il , Lim In-Gon
Published: April 2011

Single crystalline silicon thin films were formed on a transparent quartz substrate by zone melting recrystallization for the application of flat panel display. The recrystallized film shows a perfect (100) texture and the main defects are subgrainboundaries. High residual tensile stress, which can cause the film cracking, can be successfully eliminated by post-annealing. The nchannel thin film transistors fabricated on a recrystallized film showed excellent device characteristics: carrier mobility ˜ 420cm2/Vsec, subthreshold slope ˜ 100mV/dec and off-state leakage current < 0.2pA.
Ecr Plasma Oxidation of Amorphous Silicon for Improvement of The Interface State in a Poly Silicon Thin Film Transistor
Authors: Ihn Tae-Hyung , Lee Seok-Woon , Lee Byung-Il , Jeon Yoo-Chan , Joo Seung-Ki
Published: April 2011

A new oxidation process of the poly Silicon thin films has been demonstrated, where the amorphous silicon thin film was oxidized by ECR plasma at room temperature and then crystallized at 600°C for 30hrs(pre-oxidation). For comparison, amorphous silicon thin film was oxidized after crystallization(post-oxidation). The interface roughness turned out to be only 3Å in case of the pre-oxidation process, while the post-oxidation showed about 8Å of the interface roughness. The pre-oxidized TFT showed the constant mobility at high gate voltages, the post-oxidized TFT showed serious degradation of the mobility at high gate voltages.
Device Characteristics of a Poly-Silicon Thin Film Transistor Fabricated by Milc at Low Temperature
Authors: Lee Seok-Woon , Lee Byung-IL , Ihn Tae-Hyung , Kim Tae-Kyung , Kang Young-Tae , Joo Seung-Ki
Published: April 2011

High performance poly-Si thin film transistors were fabricated by using a new crystallization method, Metal-Induced Lateral Crystallization (MILC). The process temperature was kept below 500°C throughout the fabrication. After the gate definition, thin nickel films were deposited on top of the TFT's without an additional mask, and with a one-step annealing at 500°C, the activation of the dopants in source/drain/gate a-Si films was achieved simultaneously with the crystallization of the a-Si films in the channel area. Even without a post-hydrogenation passivation, mobilities of the MILC TFT's were measured to be as high as 120cm2/Vs and 90cm2/Vs for n-channel and p-channel, respectively. These values are much higher than those of the poly-Si TFT's fabricated by conventional solid-phase crystallization at around 6001C.
Effects of Germanium on Grain size and surface roughness of the solid phase crystallized polycrystalline Si1−xGex films
Authors: Kim Jin-Won , Ryu Myung-Kwan , Kim Tae-Hoon , Kim Ki-Bum , Kim Sang-Joo
Published: April 2011

Si1−xGex (x≤0.5) films were deposited by using Si2H4 and GeH4 source gases in a low pressure chemical vapor deposition (LPCVD). The deposition temperature was varied from 375 °C for Si0.5Ge0.5 to 450 °C for Si film in order to deposit amorphous Si1−xGex films and the deposition pressure was about 1 Torr. The grain size of polycrystalline Si1−xGex films made by solid phase crystallization (SPC) decreases with germanium content in the films, and the activation energy obtained from the dependence of grain size on annealing temperature was 0.4 eV for Si and 0.45 eV for Si0 69Ge0.31. From obtaining a similar activation energy irrespective of Ge content in the film, the decrease of grain size with germanium content is attributed to the difference of the asdeposited film conditions. The surface roughness of Si1−xGex films investigated by atomic force microscope (AFM) increases with germanium content in the film before and after SPC. For instance, the root-mean square (rms) values of the surface roughness of the as-deposited Si and Si0.5Ge0.5 films were 2.3 and 17 Å, while those values were increased to 2.6 and 41 Å, respectively, after SPC. In order to reduce the surface roughness of Si0.5Ge0.5 film, we have deposited a thin Si capping layer on top of the Si1−xGex layer and identified that this capping layer effectively reduces the increase of surface roughness after SPC.
Low Resistivity Transparent Indium Tin Oxide (Ito) Films Sputtered At Room Temperature With H2O Addition
Authors: Onisawa Ken-Ichi , Nishimura Etsuko , Ando Masahiko , Satou Takeshi , Takabatake* Masaru , Minemura Tetsuroh
Published: April 2011

A new kind of amorphous indium tin oxide (ITO) film with good pattern delineation properties and mass production capability, as well as low resistivity and high transparency has been developed. The film was prepared by a cluster-type DC magnetron sputtering apparatus at room temperature with H2O addition to the argon sputtering gas. The amorphous ITO film quality was improved by effective termination of oxygen vacancies with -OH species generated by enhanced decomposition from the added H2O in the plasma.
Atomic Hydrogen Effects on the Optical and Electrical Properties of Transparent Conducting Oxides For a-Si:H TFT-LCDs
Authors: Lan Je-Hsiung , Kanicki Jerzy
Published: April 2011

The effects of the atomic hydrogen treatment (H-treatment) of indium-tin oxide (ITO) and aluminum-doped zinc oxide (AZO) films have been investigated. The atomic hydrogen was generated by hot-wire chemical vapor deposition (HW-CVD) technique. Experimental results have shown that AZO films are chemically very stable under the H-treatment; almost no variation in the optical transmittance and electrical resistivity was observed. On the contrary, ITO films, either prepared by sputtering with ex-situ or in-situ thermal-annealing, have shown severe optical and electrical degradation and surface whitening after the H-treatment. SEM studies of the H-treated ITO surfaces have revealed that the surface whitening was due to the increase in surface roughness and the formation of granule-like metallic balls. Auger electron spectroscopy has indicated that the balls were mainly composed of indium atoms and the areas between balls were rich in oxygen atoms. These results were confirmed by X-ray diffraction and X-ray photoelectron spectroscopy measurements done on ITO before and after the H-treatment. Finally, we have demonstrated that a-SiO, deposited by PECVD will completely suppress the chemical reaction between ITO surfaces and atomic hydrogen generated by HW-CVD technique.
Electron Emission From Diamond and Carbon Nitride Grown by Hot Filament Cvd or Helical Resonator Pecvd
Authors: Chi Eung Joon , Shim Jae Yeob , Rho Soon Joon , Baik Hong Koo
Published: April 2011

To improve silicon field emitters, diamond and carbon nitride coatings were applied by hot filament CVD and helical resonator CVD, respectively. Helical resonator CVD was first proposed as a new method to grow carbon nitride on silicon tips without damage. Diamond and carbon nitride coatings lowered turn-on voltage and increased emission current. Microstructural and electronic investigations of carbon nitride film were performed. The negative electron affinity of carbon nitride is suggested for enhancing emission current.
Degradation Mechanisms and Vacuum Requirements for Fed Phosphors
Authors: Holloway Paul H. , Sebastian Joe , Trottier Troy , Jones Sean , Swart Hendrik , Petersen Ronald O.
Published: April 2011

Degradation of phosphors in field emission displays (FED's) is described and related to electron beam stimulated surface reactions between ZnS and residual gas in the vacuum system. The requirements for producing and maintaining vacuums in FED packages is reviewed and limitations associated with the size of the FED's are discussed. It is concluded that vacuum production and maintenance is critical to the performance of FED's, and this is not a simple task.
Cross-Sectional Observations of Molecular Orientation in LCDs using a UV Curable Liquid Crystal
Authors: Masuda Shin , Nose Toshiaki , Sato Susumu
Published: April 2011

Cross-sectional observations of the molecular orientation in typical display modes are demonstrated. ECB (Electrically Controlled Birefringence), Bend and TN (Twisted Nematic) cells are fabricated using a UV curable liquid crystal material. LC cells are photo-polymerized with applying appropriate AC voltages and cut into slices to obtain the cross-sectional images. As a result, frozen molecular orientation states in a cross section of the LC cell are successfully visualized clearly using a polarizing microscope.
Spatially Resolved Characterization of the Electroclinic Effect in Chiral Smectic a Liquid Crystals
Authors: Lindle J. R. , Flom S. R. , Bartoli F. J. , Harter A. T. , Geer R. E. , Ratna B. R. , Shashidhar R.
Published: April 2011

The electro-optical properties of an electroclinic liquid crystal have been investigated using a spatially resolved technique which measures the birefringence, optical tilt angle and extinction within adjacent stripe domains. A comparison of these results with the data obtained from standard optical and X-ray measurements suggests the presence of substripes or an angular distribution of molecular directors within the stripe domains.
Novel Memory Effect Found in Nematic Liquid Crystal/Clay Mineral Composites
Authors: Kawasumi M. , Hasegawa N. , Usuki A. , Okada A. , Kurauchi T.
Published: April 2011

Novel liquid crystalline composites composed of a nematic two-frequency-addressing liquid crystal and organized clay mineral have been prepared. The particles of the clay mineral were dispersed homogeneously in the liquid crystal. The composite cells displayed a reversible and multistable electro-optical effect between transparent and turbid light scattering states by changing the frequency of the electric field. The light transmittances of both transparent and light scattering memory states did not change after 15 hrs without the electric field applied.
The Effect of Hydrogen Bonding on the Mesomorphic Properties for Side Chain Type Liquid Crystalline Polyurethanes
Authors: Mihara T. , Koide N.
Published: April 2011

Mesomorphic properties and temperature dependence of the hydrogen bonding between urethane bonds (H-bonding) for side chain type liquid crystalline polyurethane(SLCPU)s were studied by thermally controlled FT-IR spectroscopy. A remarkable change in the strength of H-bonding for SLCPUs with a flexible chain in the polymer backbone(flexible SLCPUs) was displayed near the phase transition temperatures, while small changes in the strength of H-bonding for SLCPUs with a rigid moiety in the polymer backbone(rigid SLCPUs) was influenced by a mesogenic group in the side chain and the flexible chain length in the polymer backbone. Furthermore, in order to study the influence of H-bonding in rigid SLCPUs, polyurethane derivatives with methyl group were synthesized replacing hydrogen in urethane bonds. No mesomorphic properties for polyurethane derivatives obtained were exhibited. It was concluded that H-bonding played an important role to exhibit mesomorphic properties of rigid SLCPUs.
Synthesis and Study of 4'-Acyl-4-Biphenylol Esters
Authors: Lu Wan-Fang , Zhang Zhi-Yong , Ding Hui , Shi Yao-Zeng
Published: April 2011

Eight new 4'-acyl-4-biphenylol esters 5a∼h were synthesized and their mesomorphic properties were tested by PM and DSC. These compounds have wider mesomorphic transition temperature ranges and higher clearing points. The compound 5g in which there is no chiral carbon exhibits a stripped focal conic texture in its Sc mesophase. The effect of the molecular structure on the liquid crystal properties was discussed.
Comparison of Vapor Phase and Liquid Phase Epitaxy for Deposition of Crystalline Si on Glass
Authors: Kühnle J. , Bergmann R. B. , Krinke J. , Werner J. H.
Published: April 2011

We compare the suitability of vapor phase and liquid phase epitaxy in a two step deposition process for the formation of thin crystalline Si films on glass substrates. In a first deposition step, we form polycrystalline Si seeding layers on glass. In a second step, we increase the thickness either by vapor phase or liquid phase epitaxy. Liquid phase epitaxy leads to growth of faceted grains of more than 100 μm in diameter but the films are not continuous. In contrast, chemical vapor deposition results in continuous, smooth films with grain sizes up to 7 μm. This difference of morphology originates from the influence of supersaturation and growth rate anisotropy. Chemical vapor deposited films exhibit surface morphologies and electrical properties that are promising for the preparation of crystalline thin film Si solar cells.
Development of Cu(InGa)Se2 Thin Film Solar Cells with Cd-Free Buffer Layers
Authors: Konagai M. , Ohtake Y. , Okamoto T.
Published: April 2011

Cu(InGa)Se2(CIGS) thin film absorbers were fabricated by a three-stage method using a coevaporation apparatus. As a Cd-free buffer layer, ZnSe, InxSe, GaxSey and ZnInxSey buffer layers have been deposited on the CIGS absorber continuously in the same apparatus. Atomic layer deposition (ALD) was employed as a growth technique for ZnSe. This technique offers a good thickness control as well as a good surface coverage. By irradiating with a solar simulator, all the solar cell parameters increased drastically for the first 50 minutes of the irradiation and then saturated at longer irradiation times. This phenomenon did not appear for the cells with a CdS buffer layer. The best efficiency of ZnO/ZnSe/CIGS thin film solar cells with about 10 nm thick ZnSe buffer layer was 11.6%. On the other hand, ZnO/InxSey/CIGS thin film solar cells showed very stable characteristics under the light illumination, and initial measurements show an efficiency of 13.0%.
Measured and Simulated Temperature Dependence of A-Si:H Solar Cell Parameters
Authors: Stiebig H. , Eickhoff Th. , Zimmer J. , Beneking C. , Wagner H.
Published: April 2011

In contrast to the successful application of analytic equations to the current-voltage behaviour of crystalline silicon solar cells in the dark and under AM1.5 illumination, the description of a-Si:H solar cells parameters requires device modelling concepts taking the full set of semiconductor equations into account. This in particular holds for the explanation of the temperature dependence (225–400K) of experimentally determined a-Si:H p-i-n solar cell parameters. Device modelling calculations show that the observed decrease of the short circuit current at AM 1.5 with lower T is much more effected by the additional charge trapped in the tail states and recharging of defect states than by the broadening of the gap. The induced electric field distortion blocks the extraction of photo generated holes. The open circuit voltage Voc increases with lower T which is caused by the same trapping effect.
Use of Super-Thin Modulated Reactants to Influence Binary Intermediate Formation in Thin Film CuInSe2 Synthesis
Authors: Musialowski M. , Guffey S. , Hornbostel M. D. , Johnson D. C.
Published: April 2011

A multilayer synthesis of polycrystalline CuInSe2 has been performed by vacuum evaporation with repeat layers thinner than 225Å. Samples deposited with different elemental sequences and repeat layer thicknesses were analyzed by x-ray diffraction as a function of annealing temperature. Samples with 225Å layers produce multiple phases in the synthetic pathway. In samples with thinner layers small amounts of In2Se3 were detected but CuInSe2 predominated. Diffraction and calorimetry data indicate that CuInSe2 and In2Se3 crystallites begin growth at room to moderate temperatures. Layering of samples was probed by grazing angle x-ray diffraction and similarly indicates interdiffusion of layers at room to moderate temperatures.
Growth and Characterization of Copper Indium Diselenide Thin Films by Molecular Beam Deposition
Authors: Ueng H. Y. , Chang D. Y. , Lin J. L.
Published: April 2011

CuInSe2 thin films grown on Corning 7059 glass substrates were prepared by molecular beam deposition method with various Cu/In ratios in order to study the relationship between composition and material properties. Under a fixed copper beam flux intensity and overpressure selenium environments, the composition of films was modulated by changing the indium beam flux: intensity to obtain Cu-rich or In-rich films. The X-ray diffraction patterns show that the epitaxy films grown onto glass substrates are the polycrystalline structure. The grain size of polycrystalline films indicate that the surface morphology of the films are varied as a function of Cu/In ratio.
The Effects of Air Annealing on Cuinse2 Thin Films Grown by Molecular Beam Fpitaxy
Authors: Kim I. , Niki S. , Fons P. J. , Kurafuji T. , Okutomi M. , Yamada A.
Published: April 2011

High quality epitaxial CuInSe2 (CIS) films with a range of Cu/In ratios (γ) = 0.80∼2.24 grown by molecular beam epitaxy (MBE) have been post-annealed at temperatures of TA=200∼400°C in both dry-air and Ar atmospheres. Changes in the structure and composition due to annealing have been investigated. The only oxide observed experimentally for both the In-rich, and the Cu-rich CIS films was In2O3. This is consistent with equilibrium thermodynamic calculations which indicate that In2O3 is the mnst stable solid oxide phase. During annealing some reac-tions arc probably kinetically limited making the annealing process a function of time and temperature. but the equilibrium thermodynamic results reported here simplify interpretation of phase space.
Surface Characterization of Cu(In, Ga)Se2 Thin Films Treated by Various Solutions
Authors: Wada T. , Hashimoto Y. , Kusao K. , Kohara N. , Negami T. , Nishitani M.
Published: April 2011

Cu-rich Cu(In, Ga)Se2 (CIGS) films were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive x-ray fluorescence spectroscopy (EDX) and x-ray photoelectron spectroscopy (XPS). The Cu-rich CIGS film were treated in KCN and NH3 solutions. In the as-deposited Cu-rich CIGS film, the cation ratio of Cu/(In+Ga) at the surface exceeded the bulk value. Cross-sectional TEM of the KCN-treated film suggested that Cu2-xSe existed both at the grain boundaries and on the grains near the surface of the Cu-rich CIGS film. The Cu2-xSe was completely removed by the treatment in the KCN solution and was removed only at the front surface by treatment in the NH3 solution.
Electrical Properties of Coevaporated CuInS2 Films by in-situ Conductivity Measurements
Authors: Scheer R. , Alt M. , Luck I. , Schieck R. , Lewerenz H. J.
Published: April 2011

The conductivity σ of CuInS2 films grown by coevaporation is investigated by in-situ measurements during the deposition and ex-situ measurements. During the controlled cool-down period of the grown films, σ vs l/T data are obtained for films with Cu-rich and In-rich composition. Furthermore, first experiments on the effect of extrinsic dopants such as P, N, and Na on the conductivity of In-rich films are reported.
CdTe Thin Films: Spray Deposition Using a Nanoparticle Ink Precursor
Authors: Schulz Douglas L. , Pehnt Martin , Curtis Calvin J. , Ginley David S.
Published: April 2011

CdTe thin film growth using nanoparticle precursors and spray deposition has been investigated. Employing a metathesis approach, cadmium iodide was reacted with sodium telluride in methanol solvent resulting in the formation of soluble Nal and insoluble CdTe nanoparticles. After appropriate chemical workup, methanol-capped CdTe colloids were isolated. CdTe colloids prepared by this method exhibit a dependence of the nanoparticle diameter upon reaction temperature as determined by transmission electron microscopy (TEM) and UV-Visible spectroscopy (UV-Vis). CdTe thin film formation was achieved by spray depositing the nanoparticle colloids (25–75 Å diameter) onto substrates at elevated temperatures (T = 280–440 °C) with no further thermal treatment. These films were characterized by XRD, x-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Cubic CdTe phase formation was observed by XRD with a contaminant oxide phase also detected. XPS analysis showed that CdTe films produced by this one-step method contained no Na or C, but substantial O. AFM gave CdTe grain sizes of ˜0.1–0.3 pim for films sprayed at 400 °C. A layer-by-layer film growth mechanism proposed for the one-step spray deposition of nanoparticle precursors will be discussed.
Effects of Rapid Thermal Annealing on CdTe/CdS Solar Cell Fabrication
Authors: Cho Y. A. , Nam W. J. , Kim H. S. , Yeom G. Y. , Yoon J. K. , Oho K. H. , Shin S. H. , Park K. J.
Published: April 2011

Rapid thermal annealing (RTA) was applied to anneal polycrystalline CdTe thin films evaporated on CdS/ITO substrate and the effects of rapid thermal annealing temperatures and gas environments were studied. X-ray diffractometer (XRD), X-ray photoelectron spectroscopy(XPS), energy dispersive X-ray spectroscopy(EDX), cross-sectional transmission microscopy(TEM), and micro-EDX in TEM were used to characterize physical and chemical properties of rapid thermal annealed CdTe thin films. Complete CdTe/CdS photovoltaic cells were fabricated and I-V characteristics of these cells were measured under the illumination. Results showed that the bulk composition of CdTe remained stoichiometric to 550°C in the air environment and surface composition became Cd-rich. Cross-sectional TEM and micro-EDX showed columnar grains and micro-twins remained even after RTA, however, sulfur content in rapid thermal annealed CdTe caused by sulfur diffusion from CdS during the annealing was much smaller than that by furnace annealing. Among the investigated RTA temperatures and gas environments, the cell made with CdTe annealed at 550°C in the air showed the best solar energy conversion efficiency.
Effect of CdTe Stoichiometry on the Electrical Properties of CdTe Films
Authors: Chung Gil Yong , Song Jin Soo , Ahn Byung Tae
Published: April 2011

CdTe films have been prepared by a close-spaced sublimation (CSS) process with screenprinted CdTe layers as a source. The electrical resistivity of the CdTe film deposited in O2 was about one order of magnitude lower than that of the film deposited in He. The Cd content in the CdTe films deposited in O2 was smaller than that in the CdTe films deposited in He. No oxygen was detected in the CdTe films deposited in O2. As the Cd/Te ratio decreased, the resistivity of the CdTe films decreased and reached at about 3×104 Ω2.cm. The resistivity decrease by oxygen flow was diminished when the CdTe composition was limited by solid solubility. The above results indicated that the resistivity decrease of CdTe films deposited in O2 was not by due to the oxygen doping but by due to the CdTe stoichiometry change.
Hydrogen Treatment of Undoped Zno Thin Film Using Photo-Chemical Vapor Deposition
Authors: Baik Seung Jae , Song Jinsoo , Lim Koeng Su
Published: April 2011

To obtain high quality ZnO thin films for use as transparent electrodes of amorphous silicon solar cells, hydrogen treatment of the films using photo-chemical vapor deposition was performed for the first time. The as-deposited ZnO thin film was irradiated by UV light during the flow of hydrogen molecules in the presence of photo-sensitizers of mercury. As the treatment time increased, resistivity decreased from 1 × 10−2Ωcm to 2 × 10−3Ωcm. Moreover, haze ratio increased from 20% to 48%. Hydrogen radicals were thought to be playing various roles on the neighborhood of the surface region and the grain boundary region.
This new trial gave us new understanding into the relation between hydrogen and ZnO. Moreover, these results could be applied to the process of amorphous silicon solar cells and a possible increase of efficiency is expected.
Photoinduced Reversible Conductivity and Photoconductivity Changes in Transparent Amorphous and Micro-Crystalline In2O3-X Films
Authors: Stradins P. , Fritzsche H. , Claflin B.
Published: April 2011

The dark conductivity σ of poorly conducting In2O3-x films can be enhanced by orders of magnitude by blue or UV light exposure at any temperature between 4.2K and 300K. The resulting high σ state of amorphous films reverts back to its original low σ state upon heating to 400K in an inert gas and can be repeated many times. In crystalline films the high σ state is stable to higher temperatures where annealing leads to some outdiffusion of oxygen and hence to a conductivity increase which can only be reversed by external re-oxidation. The photoinduced increase in dark conductivity is accompanied by an increase in photoconductivity at hv = 0.6 or 2eV by a factor of 107 at 4.2K.
Ale Growth of Transparent Conductors
Authors: Rit Mikko , Asikainen Timo , Leskelä Markku , Skarp Jarmo
Published: April 2011

Owing to its self-limiting growth mechanism the Atomic Layer Epitaxy (ALE) technique is capable of growing uniform high quality thin films on large area substrates. Therefore, ALE is an attractive choice for depositing transparent electrically conducting films for large area applications, such as solar cells and flat panel displays. In this paper studies on ALE growth of In2O3 and ZnO based transparent conducting thin films will be presented. In2O3, In2O3:Sn and In 2O3:F films were grown at 500 °C and their lowest resistivities were about 3 x 10-3, 2 x 10-3 and 6 x 10-4 Ωcm, respectively. Low temperature (120 - 350 °C) ALE deposition processes were developed for ZnO and ZnO:AI films, the latter having resistivities as low as 8 x 10-4 Ωcm. A straightforward scale-up of the ZnO process from 5 x 5 to 30 x 30 cm 2 substrate size was also demonstrated.
Nano-Scale Resolved Detection of Photo-Current in a-Si:H Films
Authors: Koida Takashi , Kawasaki Masashi , Maruyama Ryuichiro , Matsuse Mitsutaka , Koinuma Hideomi
Published: April 2011

The growth mode of a-Si:H plasma CVD film was observed by AFM to range from homogeneous deposition to heterogeneous island formation depending on the substrate material and deposition temperature. The correlation between the grain-like structure and electric property of the film deposited on transparent conductive SnO2 substrates has been elucidated by using an AFM with a conductive cantilever. The local distribution of photo-current in the a-Si:H films was found to agree well with the topographic image; the photo-current around the grain boundaries was lower than that on the grains. The effect of surface treatment with an aqueous HF solution indicates that the imhomogeneity in the photo-current originates from the preferential oxidation around the grain boundaries rather than intrinsic electric property.
A Simple Optical Properties Modeling of Microcrystalline Silicon by the Effective Medium Approximation Method
Authors: Cho Woo Yeong , Lim Koeng Su , Cho Hyun-Mo
Published: April 2011

The optical properties of microcrystalline silicon (µc-Si) were estimated using the EMA (Effective Medium Approximation) method. This modeling was based on two-phase mixture, amorphous silicon (a-Si) and crystalline silicon (c-Si) with volume fractions of fa and fc respectively. From this modeling, it could be possible to understand thatµc-Si has lower light absorption characteristics than a-Si over all solar spectrum by considering hydrogen involvement in embedded a-Si part of iic-Si and crystalline volume fraction. Also, it is proposed that p-type pe- Si is superior to n-type tic-Si because of its high optical gap of Eo4 and its low absorption coefficient spectrum shape.
Porous Semiconductor Films For Photo-Electrical Applications
Authors: Könenkamp R. , Hoyer P.
Published: April 2011

We report on the preparation and characterization of semiconductor devices based on porous nano-crystalline TiO2 films. We present experimental results on photoconduction to elucidate the role of trap states in this material. We then analyse the behavior of a SnO2/TiO2/Pt Schottkydiode and finally present spectral photoresponse data obtained on a hetero-junction between TiO2 films and PbS quantum dots. We find that the porous films hold some promise for electronic applications, in which fast reponse times are not required.
Monograin Powders And Layers For Photovoltaic Application
Authors: Altosaar M. , Mellikov E. , Hie J. , Meissner D. , Varema T.
Published: April 2011

The recrystallization of CdTe powders in different fluxes was studied and the possibility to grow p- and n - type CdTe monograin powders of high conductivity was shown. It was determined that very important technological factors for creating p - type conductivity in CdTe are the cooling rate and the presence of Te in flux. NaCl content in CdCl2 flux was found to inhibit the crystal growth and to allow for doping CdTe with Na that acts as an effective acceptor impurity in CdTe. The region of most effective added Na concentrations was found.
A New Confocal Scanning Laser MACROscope/Microscope Applied to the Characterization of Solar Cells
Authors: Ribes A. C. , Damaskinos S. , Tiedje H. F. , Dixon A. E. , Brodie D. E. , Duttagupta S. P. , Fauchet P. M.
Published: April 2011

Scanning stage microscopes have traditionally been used to provide high resolution, large area photocurrent mapping of solar cells and detectors. This imaging method, while very useful in the characterization and quality control of solar cells, is unfortunately slow (image acquisition takes several minutes). This paper describes a confocal scanning beam MACROscope-Microscope which can image specimens from 25×25 μm up to 7.5×7.5 cm in size, a zoom factor of 3000, using reflected light, photoluminescence, and optical beam induced current in less than 10s. Resolutions range from 0.25 to 10 μ;m laterally and 0.5 to 300 pm axially depending upon whether microscope or MACROscope mode is used. This instrument can therefore be used to characterize and provide quick and efficient quality control for solar cells and detectors at a microscopic and macroscopic level.

A brief description of the MACROscope-Microscope is given. The MACROscope- Microscope's many abilities are highlighted by showing various reflected-light, photolhminescence and optical beam induced current images from CdZnS/CulnSe2 thin film solar cells and porous silicon devices.
Photovoltaic Effect in a-Si/c-Si Heterostructure Prepared by RF Magnetron Sputtering Technique
Authors: Budaguan B. G. , Sherchenkov A. A. , Aivazov A. A.
Published: April 2011

Photosensitivity spectral dependencies of the a-Si(n-type)/c-Si(p-type) heterostructure for the different reverse biases, Vb, amorphous Si film thickness, substrate predeposition temperatures, Ts, and annealing conditions, Ta, were investigated in the wavelengths range of 500–1200 nm It was found that the position of the relative photosensitivity maximum depends on Ts, and Vb and can be varied in the wavelengths range of 840–1080 nm. The energy band diagram of the heterostructure was analyzed to explain the observed results. It was shown that the photosensitivity properties of the a-Si/c-Si heterostructure depend on the interfacial condition. The perspective application of the structures investigated is IR detector fabrication.
Current Dependence of Reversible Electromigration Induced Resistance Changes in Short Al Lines and Interpretation of Irreversible Effects
Authors: Verbruggen A. H. , Van Den Homberg M. J. C. , Kalkman A. J. , Kraayeveld J. R. , Willemsen A. W.-J. , Radelaar S.
Published: April 2011

Changes in the electrical resistance induced by electromigration in short (< 20 μm) Al lines show a rather well-defined behavior. For current densities j below a critical value jc the resistance change saturates with time and the resistance fully recovers when the current is switched off. Above the critical current density the induced resistance changes do not saturate and vary approximately linearly with time. In this case the resistance changes recover only partially after removal of the current. We report (i) measurements of the current dependence of the magnitude of the reversible resistance changes and (ii) the results of atomic force microscopy (AFM) inspection of the lines after stressing with current densities above jc. The resistance measurements were made with a high-resolution AC bridge technique. The samples were pure, unpassivated Al lines with a film thickness of 100 nm and a line width of 2 gm. The results show a linear dependence between the magnitude of the reversible changes and the current density. The linear dependence is predicted by two models. The first is based on a description of the vacancy flux and the second on a description of the build-up of mechanical stress during an electromigration experiment. To study the origin of the irreversible effects, samples were stressed at current densities above jc, and the induced irreversible changes in the resistance were recorded. Both negative and positive changes of the resistance were observed. After six hours the experiment was stopped and the lines were inspected by atomic force microscopy. It was always possible to observe a void, a hillock or a hillock/void pair that was created during the passage of the DC current. Moreover, lines with decreasing resistance during stress always showed a hillock and lines with an increased resistance always showed a void.
Oxidation Resistant Dilute Copper (Boron) Alloy Films Prepared by DC-Magnetron Cosputtering
Authors: Hymes S. , Kumar K. S. , Murarka S. P. , Wang W. , Lanford W. A.
Published: April 2011

To enhance the corrosion resistance and reliability of the proposed copper interconnections in silicon integrated circuits, alloying with small amounts thermodynamically favorable elements has been pursued. In the present investigation dilute copper (boron) alloy thin films (in boron concentration range of 0–4 at % in copper) were deposited by DC magnetron co-sputtering using a high purity copper and Cu-4 at. % B targets. Films were then annealed in Ar-3% H2, pure Ar, vacuum, and air ambients in the temperature range of 200–500°C. Sheet resistance, Rutherford backscattering, x-ray diffraction measurements were made to characterize the films. The residual resistivity of the as-deposited alloy films was found to be 5.3 μΩ-cm/at %. To obtain sufficiently low working resistivity, an alloy content below 0.5 at % is suggested for application as a potential metallization material. The addition of boron, which is the common dopant in Si. to the copper films offers considerable oxidation protection. The resulting oxidation rates are considerably lower than that for pure copper films. All this will be presented and discussed.
The Improvement of Immunity to Electromigration by Means of Microstructural Design
Authors: Kononenko O. V. , Matveev V. N.
Published: April 2011

It is known from literature that the properties of thin films greatly depend on their structuare. Therefore, the microstructural design is attractive for control over the properties of thin metal films used for interconnect metallization.

In this paper we discuss the potentialities of the self-ion assisted deposition technique for control over the grain and grain boundary structures of thin metal films and their properties such as resistivity and immunity to electromigration.

It was found that resistivity of aluminum films deposited at the 6 kV bias was virtually equal to resistivity of bulk aluminum. Films deposited at the less bias or without it had higher resistivities. Abnormal grain growth was found in 6 kV-films. In films prepared without bias normal grain growth proceeds.
Analysis of Geometrical and Microstructural Effects on Void Formation in Metallization: Observation and Modelling
Authors: Shih W. C. , Ghiti A. , Low K. S. , Greer A. L. , O'Neill A. G. , Walker J. F.
Published: April 2011

This paper reports the analysis of geometrical and microstructural effects on void formation in interconnects. Ion-beam machining is used to define segments for study at the cathode end of test lines. Scanning electron microscopy is used to observe damage development, focused ion beam microscopy to observe the corresponding grain structure. Finite-element calculations of self-consistent current density and temperature distributions in the conductor are used to predict damage locations both for a continuum material and for simulated grain structures. Cross-section changes in the line give temperature variations leading to divergences in atomic flux. Regions of
high flux divergence are favoured for electromigration damage, but the precise sites of damage are determined by the grain structure, as shown both in the experiment and in the modelling.
In-Situ UHV Electromigration in CU Films
Authors: Vook R. W. , Jo B. H.
Published: April 2011

Copper stripes, current stressed under UHV, clean surface conditions, have an activation energy Q for electromigration (EM) of 0.5 eV, significantly lower than the 0.8 eV reported when the surface has been exposed to air. Application of positive or negative potentials to the stripes during EM testing raises or lowers the clean surface Q in a linear relationship in the range of 0.2 to 1. 0 eV. These results were obtained from in-situ electrical resistance measurements during which potentials up to +/− 800 volts were applied to the stripe. Thus the rate at which surface EM takes place is influenced by the sign and magnitude of the applied potential. The low Q for the in-situ clean surface studies also implies that surface diffusion is the dominant physical mechanism whereby EM damage occurs. Ex-situ SEM studies support this conclusion. This work has important implications for ULSI since numerous recent studies have indicated that surface and/or interface diffusion are present during current stressing of passivated and unpassivated fine line stripes.
Limitations of Plasma Charging Damage Measurements Using MOS Capacitor Structures
Authors: Shawming M A , Abdel-Ati Wael L. N. , Mcvittie James P.
Published: April 2011

This paper investigates the sensitivity and limitation of capacitor testing for measuring potential charging damage to gate oxides in a given plasma step. While C-V measurements are the most directly related to transistor threshold voltage (Vth) and transconductance (gm), C-V measurements are slow, difficult to automate and not usable for large antenna structures without a fuse link. In contrast, ramp breakdown measurements are quick and easy to automate but lack sensitivity. Charge-to-breakdown offers better sensitivity but with long measurement times. A more promising method is the V-t measurement where the slope dV/dt after initial charging is a measure of the trapping generation rate and is found to be very sensitive to charge damage. The damage sensitivity of this method is high and involves tradeoffs between antenna ratio, testing current and testing time. All of which are critical to damage testing. Leakage measurements are another method which offers short measurement times and high sensitivity. Their limitations are the noise level of the measurement system and the making of good probe contact to the gate material.