bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of Polycrystalline Silicon for Solar Cells by Small p-n Diode Array
Authors: Tanaka Satoshi , Imai Keita , Ogura Atsushi , Ohshita Yoshio , Arafune Koji , Kawai Hideaki , Kusuoka Futoshi , Tajima Michio , Inoue Masaaki
Published: April 2011

A small p-n diode array was fabricated on a polycrystalline Si substrate and the electrical characteristics were measured for each small diode to evaluate the distribution of energy conversion efficiency in the substrate. The crystal qualities in conjunction with the electrical characteristics were also evaluated. We found large variations in measuring the current-voltage (I-V) characteristics of the p-n diode. We also observed variations in quality even in diodes without any grain boundaries at the p-n junction. Therefore, we evaluated crystalline quality using various techniques to compare the diode characteristics. We found clear evidence in photo-luminescence (PL) mapping, where grains, including degraded diodes, were darker in the mapping, implying lower PL intensities than the others. The PL spectra obtained from the “dark grains” included D-lines indicating the existence of dislocations. We could conclude that the electrical characteristics of p-n diodes were not only affected by grain boundaries but also by crystalline defects evaluation such as dislocations. We observed a Secco-etched surface for crystalline defects evaluation using an optical microscope. The origins of etch pits were also determined by transmission electron microscope (TEM) and three different types of defects were confirmed.
Silicide Mediated Grown Silicon Thin Films for Photodiodes
Authors: Kim Joondong , Anderson Wayne A. , Han Chang-Soo , Lee Eung-Sug
Published: April 2011

Quality Si thin films were grown by the metal-induced growth (MIG) method. Metal (Co, Ni, or mixing of Co and Ni) was thermally evaporated on a 200 nm-SiO2 coated Si wafer. Si sputtering was performed at 600 – 620 °C in a dc magnetron system. The reaction of Si and metal first formed a silicide (CoSi2 or NiSi2) layer and further Si sputtering grew a Si film above it. The grown Si films were practically fabricated for Schottky photodiodes and electrically measured under one sun scan illumination (100 mW/cm2).
Characteristics of Chemically Deposited Thin Film Solar Cells using SnS and Sb2S3 Absorbers
Authors: Nair M. T. Santhamma , Avellaneda David , Messina Sarah , Nair P. K.
Published: April 2011

We use SnS and Sb2S3 thin films of about 500 nm in thickness deposited on glass substrates by chemical deposition to develop solar cell structures: glass-SnO2:F/CdS/SnS/CuS/silver paint and SnO2:F/CdS/Sb2(S/Se)3/PbS/silver paint. Here, SnS and Sb2S3, and PbS are absorber materials suitable for large scale production, considering their abundance at 0.2 ppm (Sb) and 2 ppm (Sn) and 8ppm (pb) in the earth's crust according to published data. SnS films deposited through distinct reaction routes have optical band gap of 1.1 eV or 1.7 eV. In SnO2:F/CdS/SnS(1.1eV)/SnS(1.7 eV)/CuS/silver paint, open circuit voltage (Voc) of ≈ 400 mV, and short circuit current (Jsc)of 7 mA/cm2 are obtained with a cell efficiency of 1%. Sb2S3 thin films have optical band gap 1.7 eV, but could be reduced through reaction in Se-vapor, upon which solid solutions of Sb2(S/Se)3 are formed. In SnO2:F/CdS/Sb2(S/Se)3/PbS/silver paint, Voc of ≈ 640 mV, Jsc of 7 mA/cm2 and conversion efficiency of 1.5% are obtained.
Comparison of Common Segmentation Techniques Applied to Transmission Electron Microscopy Images
Authors: Sadowski Thomas , Broadbridge Christine C. , Daponte John
Published: April 2011

Nanoparticles are of interest in many applications since their decreased size may give them properties that are very different from bulk material. Often nanoparticle properties such as size (diameter) and size distribution are evaluated using transmission electron microscopy (TEM). These parameters, size and size distribution, can be more easily obtained from digitized TEM images by mapping particle signal to black and background pixel to white in a process known as thresholding then performing an algorithm known as a particle analysis. The goal of this study was to compare the ability of several popular thresholding algorithms to segment TEM images. Performance of the thresholding algorithms was evaluated through qualitative and quantitative measures. Results show that the choice of a thresholding algorithm will strongly affect the results obtained from particle analysis.
Determination of Inelastic Mean Free Path by Electron Energy-Loss Spectroscopy in TEM: A Model Study Using Si and Ge
Authors: Wang Chongmin , Cannon Bret D.
Published: April 2011

Although the inelastic mean free path for Si and Ge have been measured previously, reported experimental values for silicon range from 121 nm to 160 nm for 200 keV and a large collection angle. A key factor responsible for this uncertainty is the lack of an accurate measurement of the specimen thickness at the point at which the EELS spectra are obtained. In this research, we have evaluated a systematic methodology for determination of the specimen thickness. In the thickness measurement based on converging beam electron diffraction, CBED, instead of the classic “trial and error” straight-line-fitting method to either the maxima or minima, a non-linear least square fitting of the theoretical diffraction profile to the energy filtered two-beam CBED is used. The low-loss EELS spectrum is also obtained from the same location. The inelastic mean free path was determined using the measured thickness and EELS data. Furthermore, attempt is also made to obtain the dielectric function from the low-loss spectrum. The established method will be extended to other materials and the results will be compared with numerical simulations.
Enhancing Light-trapping and Efficiency of Solar Cells with Photonic Crystals
Authors: Biswas Rana , Zhou Dayu
Published: April 2011

A major route to improving solar cell efficiencies is by improving light trapping in solar absorber layers. Traditional light trapping schemes involve a textured metallic back reflector that also introduces losses at optical wavelengths. Here we develop alternative light trapping schemes with a-Si:H thin film solar cells, that do not use metallic components, thereby avoiding losses. We utilize low loss one-dimensional photonic crystals as distributed Bragg reflectors (DBR) at the backside of the solar cells. The DBR is constructed with alternating layers of crystalline Si and SiO2. Between the DBR and the absorber layer, there is a layer of 2D photonic crystal composed of amorphous silicon and SiO2. The 2D photonic crystal layer will diffract light at oblique angles, so that total internal reflection is formed inside the absorber layer. We have achieved enhanced light-trapping in both crystalline and amorphous silicon solar cells at near-infrared wavelengths where absorption lengths are very large. Very high absorption is achieved throughout optical wavelengths. The optical modeling is performed with a rigorous 3 dimensional scattering matrix approach where Maxwell¡¯s equations are solved in Fourier space.
Dielectric Properties of Ultra Dense (3 g/cm3) Silicon Nitride Deposited by Hot Wire CVD at Industrially Relevant High Deposition Rates
Authors: Houweling Zomer Silvester , Verlaan Vasco , van der Werf Karine , Goldbach Hanno D. , Schropp Ruud E I
Published: April 2011

For silicon nitride (SiNx) deposited at 3 nm/s using hot wire chemical vapor deposition (HWCVD), the mass-density reached an ultra high value of 3.0 g/cm3. Etch rates in a 16BHF solution show that the lowest etch rate occurs for films with a N/Si ratio of 1.2, the ratio where also the maximum in mass density occurs. The thus found etch rate of 7 nm/min is much better than that for PECVD layers, even when made at a much lower deposition rate. The root-mean-square (rms) roughness measured on 300 nm thick SiN1.2 layers is only about 1 nm, which is advantageous for obtaining high field-effect mobility in thin-film transistors. SiN1.2 films have succesfully been tested in “all hot wire” thin film transistors (TFTs). SiNx films with various x values in the range 1.0 < × <1.5 have been incorporated in metal-insulator-semiconductor structures with n-type c-Si wafers to determine their electrical properties from C-V and I-V measurements. We analyzed the behavior of the static dielectric constant, fixed nitride charges and trapped nitride charges as function of N/Si ratio. I-V measurements show that the HW SiNx films with N/Si ≥ 1.33 have high dielectric breakdown fields that exceed 5.9 MV/cm. For these films we deduce a low positive fixed nitride charge density of 6.2-7.8 × 1016 cm-3 from the flat band voltage and from the small hysteresis in the backward sweep we deduce a low fast trapped charge density of 1.3-1.7 × 1011 cm-2. The dielectric constant ε for different compositions is seen not to change appreciably over the whole range and amounts to 6.3 ± 0.1. These high-density SiNx films possess very low tensile stress (down to 16 MPa), which will be helpful in for instance, plastic electronics applications. HWCVD provides high quality a-SiNx materials with good dielectric properties at a high deposition rate.
Effect of Boron Doping on Microcrystalline Germanium Carbon Thin Films
Authors: YASHIKI Yasutoshi , KOUKETSU Seiichi , MIYAJIMA Shinsuke , YAMADA Akira , KONAGAI Makoto
Published: April 2011

Effects of boron doping on microcrystalline germanium carbon alloy (μc-Ge1-xCx:H) thin films have been investigated. We deposited boron-doped p-type μc-Ge1-xCx:H thin films by hot-wire chemical vapor deposition technique using hydrogen diluted monomethylgermane (MMG) and diborane (B2H6). A dark conductivity of 1.3 S/cm and carrier concentration of 1.7 x 1020 cm-3 were achieved with B2H6/MMG ratio of 0.1. Furthermore, the activation energy decreased from 0.37 to 0.037 eV with increasing B2H6/MMG ratio from 0 to 0.1. We also fabricated p-type μc-Ge1-xCx:H/n-type c-Si heterojunction diodes. The diodes showed rectifying characteristics. The typical ideality factor and rectifying ratio were 1.4 and 3.7 x 103 at ¡Ó 0.5 V, respectively.
A Novel Bonding Technique Using Metal-Induced Crystallization of Amorphous Silicon
Authors: Ong Markus D. , Dauskardt Reinhold H.
Published: April 2011

This study investigates the used of aluminum-induced crystallization of amorphous silicon is a potential bonding mechanism for a sandwich stack of films between two silicon substrates. Similar procedures using copper diffusion bonds have been in use, but these require temperatures as high as 400°C. Using the crystallization of amorphous silicon as the bonding mechanism has allowed the bonding temperature to be lowered by more than 100 K. Fracture experiments for a low-k material were conducted, and the results using amorphous silicon bonding was compared to epoxy bonding control experiments. Essentially identical results were obtained for the two bonding mechanisms. Low-temperature bonding techniques are of great interest to future progress in the microelectronics industry, and these results are promising advances.
Deposition Uniformity Control in a Commercial Scale HTO-CVD Reactor
Authors: Sakai Shigeru , Ogino Masaaki , Shimizu Ryosuke , Shimogaki Yukihiro
Published: April 2011

High-temperature silicon dioxide chemical vapor deposition (HTOCVD), using SiH2Cl2 and N2O, can realize dense and conformal oxide film, not only on large size silicon wafers, but even inside of microscopic silicon trenches, at high-temperature around 800°C.

In this work, we investigated the kinetics of HTOCVD using a commercial scale low pressure (LP) CVD reactor, focusing on the correlation between deposition rate and surface-to-volume ratio (S/V ratio), which is a specific surface area of substrate wafer divided by the space volume between two adjacent wafers. We also investigated the deposition rate profile on wafers, and along the axial direction of the reactor near the region where one, two or three substrate wafers are extracted from the quartz holder. The deposition rate profiles on wafer characteristically change from skillet-like to pancake-like, according to the increase of wafer spacing. The influence on the deposition rate of wafer spacing spreads to ranges not only downstream, but also upstream in the gas flow. These experimental results strongly suggest that in the HTOCVD gas-phase reactions through intermediate states of active species contribute to deposition reaction as well as direct deposition reaction of source gases on Si surface.
Monolithic Integrated a-Si:H based pin-Diodes with Orthogonal Liquid Light Guidance Structures for Lab-on-Microchip Applications
Authors: Schäfer Heiko , Seibel Konstantin , Schöler Lars , Böhm Markus
Published: April 2011

We report the fabrication of an amorphous silicon based fluorescence sensor for miniaturized total analysis systems along with experimental results on optical excitation and detection elements. The pin-photodiode exhibits a dynamic range of 110dB and a room temperature dark current of less than 3000 charge carriers per ms according to a detector area of 0.1256mm2. The spectral response is ranging from 320nm to 780nm with a maximum at 600nm @ 80% quantum efficiency. To provide high sensitivity, the excitation light irradiates the fluid orthogonally to the active sensor detection direction by means of specifically designed microfluidic capillaries filled with e.g. methylene iodide or 1,2-o-dibrombenzene. The liquid core, which is enclosed by solid cladding materials, has been calculated to dimensions of a width of 16.75µm or 59.67µm with a height from 15µm to 50µm according to a number of propagating modes inside of 16 or 57, respectively.
Self-Aligned Nanocrystalline Silicon Thin-Film Transistor With Deposited n+ Source/Drain Layer
Authors: Cheng I-Chun , Wagner Sigurd
Published: April 2011

We demonstrated self-aligned nanocrystalline silicon (nc-Si:H) n-channel thin film transistors (TFTs) with directly deposited n+ layer. The silicon layers were deposited by plasma-enhanced chemical vapor deposition at a substrate temperature of 150°C. The TFTs were made in a staggered top-gate, bottom-source/drain geometry with a seed layer underneath. The self-alignment of top-gate to the bottom-source/drain was achieved by backside exposure photolithography through the glass substrate and the silicon layers, followed by a lift-off process. An extent of gate to source/drain overlap of 1.5 mm was obtained. The self-aligned TFTs have similar characteristics to their non-self-aligned counterpart. This result represents an important step toward directly deposited nc-Si:H TFT backplanes on plastic substrates.
Segmented Amorphous Silicon n-i-p Photodiodes on Stainless-Steel Foils for Flexible Imaging Arrays
Authors: Vygranenko Yuriy , Kerr R. , Kim K. H. , Chang J. H. , Striakhilev D. , Nathan A. , Heiler G. , Tredwell T.
Published: April 2011

This paper reports the first successful attempt to fabricate amorphous silicon (a-Si:H) n-i-p photodiodes on a thin stainless-steel foil substrate for medical X-ray imaging applications. Two architectures of the n-i-p-photosensor, where the top electrode is based on amorphous or polycrystalline ITO, have been developed and characterized. The impact of critical fabrication steps including the deposition of semiconductor layers, dry etch of the NIP stack, diode passivation and encapsulation, as well as a contact formation on the device performance is presented and discussed. The test structures comprising segmented photodiodes with an active area ranged from 0.126 × 0.126 to 1 × 1 mm2 have been fabricated on stainless-steel foils and on glass substrates for the purposes of process characterization. The fabricated samples are evaluated in terms of current-voltage, capacitance-voltage, and spectral response characteristics.
Germanium-Silicon Separate Absorption and Multiplication Avalanche Photodetectors Fabricated with Low Temperature High Density Plasma Chemical Vapor Deposited Germanium
Authors: Carroll Malcolm , Childs Kent , Serkland Darwin , Jarecki Robert , Bauer Todd , Saiz Kevin
Published: April 2011

A desire to monolithically integrate near infrared (NIR) detectors with silicon complementary metal oxide semiconductor (CMOS) technology has motivated many investigations of single crystal germanium on silicon (Ge/Si) diodes [1-3]. Reduction of the epitaxy thermal budget below the typical chemical vapor deposition (CVD) in-situ clean temperature (Tin-situ clean > 780°C) is also increasingly desired to reduce integration complexity. Reduced temperature growth approaches have included p+-Ge/n-Si detectors formed with low temperature poly-Ge (e-beam evaporation) or heavily dislocated single crystal germanium (molecular beam epitaxy, T ~ 450°C), which have had dark currents of ~5 mA/cm2 and responsivities of ~15 mA/W at 1310 nm, despite the large number of defects in and at the Ge/Si interface. Responsivities in these materials are however low and believed to be limited by a small diffusion length (i.e., 5-30 nm [2, 4]) due to fast electron recombination in the defect rich germanium. In this paper, we evaluate a commercially available high density plasma chemical vapor deposition (HDP-CVD) process to grow low temperature (i.e., Tin-situ & Tepitaxy < ~450°C) germanium epitaxy for a p+-Ge/p-Si/n+-Si NIR separate absorption and multiplication avalanche photodetectors (SAM-APD). This device structure is of interest both to examine ways to enhance the responsivity with internal gain as well as to examine alternatives to InGaAs-InP structures for NIR Geiger mode (GM) detection. A silicon avalanche region is highly desirable for GM to reduce after-pulsing effects, which are related to defect density that are smaller in Si than in InP [5]. Despite the high defect densities in the Ge and at the interface, the Ge-Si APDs in this work are found to have relatively low dark count rates in Geiger mode.
Drain Bias Dependent Threshold Voltage Shift of a-Si:H TFT Due to the Pulsed Stress
Authors: Park Sang-Geun , Lee Jae-Hoon , Han Sang-Myen , Kim Sun-Jae , Han Min-Koo
Published: April 2011

We have investigated the shift of threshold voltage in the a-Si:H TFT due to the various negative pulse width stress. The drain bias dependent threshold voltage shift in the pulsed stress of a-Si:H TFT for AMOLED backplane is also measured and analyzed. When a positive gate and drain bias is applied to a-Si:H TFT (W/L = 200/4 Ým), VTH of a-Si:H TFT is increased during the stress time due to the defect state creation and charge trapping. VTH of a-Si:H TFT is increased from 1.645V to 2.53V (δVTH=0.885V) after the DC gate bias stress of VGS=15V, VDS=0V for 20,000sec. When the pulsed negative bias stress is applied to the gate electrode of the current driving a-Si:H TFT with the drain bias, VTH shift is considerably reduced due to the hole trapping into the gate insulator during the stress. When a negative pulse width is 16msec (pulse of 60Hz), the VTH is increased form 1.594V to 2.195V (δVTH=0.601V). When a negative pulse width increases from 16msec to 5sec without drain bias (VDS=0V), VTH is increased from 1.615V to 2.055V (δVTH=0.44V). When a drain bias is increased from 0V to 15V, VTH is slightly decreased from 1.58V to 1.529V (δVTH=-0.051V) due to large (-30V) VGD (VG=-15V, VD=15V) bias, while it is increased from 1.66V to 2.078V (δVTH=0.418V) width DC gate bias stress of VGS=15V, VDS=15V for 20,000sec.
Noise Performance of High Fill Factor Pixel Architectures for Robust Large-Area Image Sensors using Amorphous Silicon Technology
Authors: Lai Jackson , Vygranenko Yuri , Heiler Gregory , Safavian Nader , Striakhilev Denis , Nathan Arokia , Tredwell Timothy
Published: April 2011

Large area digital imaging made possible by amorphous silicon thin-film transistor (a-Si TFT) technology, coupled with a-Si photo-sensors, provides an excellent readout platform to form an integrated medical image capture system. Major development challenges evolve around

optimization of pixel architecture for detector fill factor, signal propagation performance, and manufacturability, while suppressing noise stemming from pixel array and external electronics. This work analyzes a novel vertically integrated pixel design based on signal readout and noise performance, and compares with conventional co-planar and continuous detector architectures. In addition, the analysis will consider various substrate options including glass and robust substrates such as polymer and metal foil. Our evaluation have demonstrated state-of-the-art radiographic detector system with electronic noise under 2000 electrons at 150 µs frame time for an imaging arrays on robust substrate.
Triple Junction n-i-p Solar Cells with Hot-Wire Deposited Protocrystalline and Microcrystalline Silicon
Authors: Schropp Ruud E.I. , Li Hongbo , Franken Ronald H.J. , Rath Jatindra K. , van der Werf Karine , Schüttauf Jan Willem , Stolk Robert L.
Published: April 2011

We have implemented a number of methods to improve the performance of proto-Si/proto-SiGe/μc-Si:H triple junction n-i-p solar cells in which the top and bottom cell i-layers are deposited by Hot-Wire CVD. Firstly, a significant current enhancement is obtained by using textured Ag/ZnO back contacts developed in house instead of plain stainless steel. We studied the correlation between the integrated current density in the long wavelength range (650-1000 nm) with the back reflector surface roughness and clarified that the rms roughness from 2D AFM images correlates well with the long wavelength response of the cell when weighted with a Power Spectral Density function. For single junction 2-μm thick μc-Si:H n-i-p cells we improved the short circuit current density from the value of 15.2 mA/cm2 for plain stainless steel to 23.4 mA/cm2 for stainless steel coated with a textured Ag/ZnO back reflector.

Secondly, we optimized the μc-Si:H n-type doped layer on this rough back reflector, the n/i interface, and in addition used a profiling scheme for the H2/SiH4 ratio during i-layer deposition. The H2 dilution during growth was stepwise increased in order to prevent a transition to amorphous growth. The efficiency that was reached for a single junction μc-Si:H n-i-p cell was 8.5%, which is the highest reported value for hot-wire deposited cells of this kind, whereas the deposition rate of 2.1 Å/s is about twice as high as in record cells of this type so far. Moreover, these cells show to be totally stable under light-soaking tests.

Combining the above techniques, a rather thin triple junction cell (total silicon thickness 2.5 μm) has been obtained with an efficiency of 10.9%. Preliminary light-soaking tests show that this type of triple cells degrades by less than 4%.
Fabrication and Optimization of a-Si:H n-i-p Single-junction Solar Cells with 8 Å/s Intrinsic Layers of Protocrystalline Si:H Materials
Authors: Cao Xinmin , Du Wenhui , Ishikawa Y. , Liao Xianbo , Collins Robert W. , Deng Xunming
Published: April 2011

At the University of Toledo (UT), we have investigated hydrogenated amorphous silicon (a-Si:H) n-i-p solar cells with intrinsic layers deposited at high rates, ~ 8 Å/s, using our UT multi-chamber load-locked PECVD system. a-Si:H i-layers were grown with a VHF plasma density of ~ 0.2 W/cm2 and a frequency of 70 MHz using various hydrogen dilution levels. It is observed from the current-voltage (I-V) device performance characteristics that the open-circuit voltage (Voc) increases with increasing hydrogen dilution reaching a maximum and then decreasing. This drop in Voc can be attributed to the transition region (or protocrystalline regime) from an amorphous phase into a mixed amorphous+nanocrystalline (a + nc) phase for the i-layer. An initial efficiency of 9.99% (Voc = 0.986 V, Jsc = 13.98 mA/cm2, FF = 72.5%) was obtained. Quantum efficiency (QE) measurement has shown that the blue light response increases as the hydrogen dilution increases. Very good blue light spectral response with QE values over 0.7 at the wavelength of 400 nm have been obtained for a-Si:H cells made under specific deposition conditions in which tailored protocrystalline silicon materials were incorporated at the i/p interface region.
High-Performance, Tandem-Type Amorphous Silicon Solar Cell
Authors: Sichanugrist Porponth , Pingate Nirut , Piromjit Channarong
Published: April 2011

Microcrystalline silicon oxide (μc-SiO) deposited from the gas mixture of silane and carbondioxide using VHF plasma was reported by authors to be the promising material for thin-film silicon solar cell fabricated on glass substrate, comparing with the conventional amorphous silicon oxide or microcrystalline silicon p-layer. High-performance, tandem-type solar cell with amorphous and microcrystalline cells (double cells) has been achieved by ap-plying this μc-SiO to the p-layer of both cells.

Further work has been extended to a-Si tandem type solar cell with triple cell configu-ration using amorphous silicon oxide (a-SiO), amorphous silicon germanium (a-SiGe) and microcrystalline Si (μc-Si) as the top, middle and bottom cells, respectively. Up to now, cell efficiency of 15.7 % has been achieved using this novel μc-SiO.
Study of a Fabrication Process and Characterization of One Dimensional Array of Un-cooled Micro-bolometers Based on Germanium Films Deposited by Plasma
Authors: Moreno Mario , Kosarev Andrey , Torres Alfonso , Ambrosio Roberto
Published: April 2011

In our previous works we have studied the fabrication process and characterization of single cell micro-bolometers based on germanium thin films deposited by low frequency (LF) PECVD technique at low temperature and fully compatible with the IC fabrication technology. We have demonstrated promising properties of those devices for further development of IR imaging systems.

In this work we report the study of a fabrication process and characterization of one dimensional array of 32 un-cooled micro-bolometers. We have used surface micro-machining techniques for the array fabrication onto a silicon wafer. The micro-bolometers in the array have a “bridge type” configuration, in which a SiNx supporting film is suspended 2.5 μm from the substrate by two legs forming the bridge in order to provide sufficient thermo-isolation for thermo-sensing layer, which is deposited by LF PECVD over it. The a-GexSiy:H film used in this devices showed high activation energy Ea= 0.34 eV, providing high thermal coefficient of resistance, TCR=α=0.043 K-1 and improved but still high resistance. We studied the effect of include boron in the a-GexSiy:H film deposition process in order to reduce its undesirable high resistance and we used this layer (a-GexBySiz:H) as thermo-sensing film in the micro-bolometers arrays also. The active area of the cells in the array is Ab=70×66 μm2 and the area of the array including interconnection lines and pads is A=1600×3120 μm2. The temperature dependence of conductivity σ(T), current-voltage characteristics I(U) and spectral noise density have been measured in the micro-bolometers in the array in order to characterize and compare their performance characteristics, such as responsivity and detectivity.
High Performance Hydrogenated Amorphous Silicon n-i-p Photo-diodes on Glass and Plastic Substrates by Low-temperature Fabrication Process
Authors: Kim Kyung Ho , Vygranenko Yuriy , Bedzyk Mark , Chang Jeff Hsin , Chuang Tsu Chiang , Striakhilev Denis , Nathan Arokia , Heiler Gregory , Tredwell Timothy
Published: April 2011

We report on the fabrication and characterization of hydrogenated amorphous silicon (a-Si:H) films and n-i-p photodiodes on glass and PEN plastic substrates using low-temperature (150°C) plasma-enhanced chemical vapor deposition. Process conditions were optimized for the i-a-Si:H material which had a band gap of ~1.73 eV and low density of states (of the order 1015 cm-3). Diodes with 0.5 μm i-layer demonstrate quantum efficiency ~70%. The reverse dark current of the diodes on glass and PEN plastic substrate is ~10-11 and below 10-10 A/cm2, respectively. We discuss the difference in electrical characteristics of n-i-p diodes on glass and PEN in terms of bulk- and interface-state generation currents.
Evolution of Structural and Electronic Properties in Boron-doped Nanocrystalline Silicon Thin Films
Authors: Lee Hyun Jung , Sazonov Andrei , Nathan Arokia
Published: April 2011

We report on the boron-doping dependence of the structural and electronic properties in nanocrystalline silicon (nc-Si:H) films directly deposited by plasma- enhanced chemical vapor deposition (PECVD). The crystallinity, micro-structure, and dark conductivity of the films were investigated by gradually varying the ratio of trimethylboron [B(CH3)3 or TMB] to silane (SiH4) from 0.1 to 2 %. It was found that the low level of boron doping (< 0.2 %) first compensated the nc-Si:H material which demonstrates slightly n-type properties. As the doping increased up to 0.5 %, the maximum dark conductivity (ód) of 1.11 S/cm was obtained while high crystalline fraction (Xc) of the films (over 70 %) was maintained. However, further increase in a TMB-to-SiH4 ratio reduced ód to the order of 10-7 S/cm due to a phase transition of the films from nanocrystalline to amorphous, which was indicated by Raman spectra measurements.

P-channel nc-Si:H thin film transistors (TFTs) with top gate and staggered source/drain contacts were fabricated using the developed p+ nc-Si:H layer. The fabricated TFT exhibits a threshold voltage (VTp) of -26.2 V and field effective mobility of holes (μp) of 0.24 cm2/V·s.
Wafer Level Modeling of Electrochemical-Mechanical Polishing (ECMP)
Authors: Truque Daniel , Xie Xiaolin , Boning Duane
Published: April 2011

In this work, we propose a wafer level dynamic ECMP model based on time-evolving current density distributions across the wafer. The copper layer on the wafer surface is discretized, and the potential and current density distributions are calculated based on the applied voltage zones and metal film thicknesses across the wafer. The copper removal rate is proportional to the current density, and thus the copper thickness (and conductance) can be calculated as a function of position on the wafer and polish time. Using a time-stepping simulation, the model is able to capture the wafer level non-uniformity and time-dependence of ECMP removal. The model is also able to capture the time-varying voltage zones used in ECMP, and can be used to find optimal voltage zone control schemes to achieve improved wafer-level uniformity.
Supercritical Fluid Deposition of Ruthenium Thin Films: A Kinetic Study
Authors: Karanikas Christos F. , Watkins James J.
Published: April 2011

The kinetics of the deposition of ruthenium thin films from the hydrogen assisted reduction of bis(2,2,6,6-tetramethyl-3,5-heptanedionato)(1,5-cyclooctadiene)ruthenium(II), [Ru(tmhd)2cod], in supercritical carbon dioxide was studied in order to develop a rate expression for the growth rate as well as to determine a mechanism for the process. The deposition temperature was varied from 240°C to 280°C and the apparent activation energy was 45.3 kJ/mol. Deposition rates up to 30 nm/min were attained. The deposition rate dependence on precursor concentrations between 0 and 0.2 wt. % was studied at 260°C with excess hydrogen and revealed first order deposition kinetics with respect to precursor at concentrations lower then 0.06 wt. % and zero order dependence at concentrations above 0.06 wt. %. The effect of reaction pressure on the growth rate was studied at a constant reaction temperature of 260°C and pressures between 159 bar to 200 bar and found to have no measurable effect on the growth rate.
Novel [Topography-Sensitive] Bottom-Up Growth of Ruthenium and Copper for Filling Nano-Features Using Supercritical Co2 Fluids: Beyond Scalability
Authors: Kondoh Eiichi , Hirose M. , Ukai E. , Nagano K.
Published: April 2011

A novel selective and bottom-up deposition process from supercritical CO2 is proposed and demonstrated. Supercritical CO2 fluids are dense media, and a deposition precursor dissolving wherein can easily condences in hollow/concave features. By combining this capillary condensation phenomenon with proper reaction chemistry, it was realized to deposit Ru an Cu in holes and trenches structures preferentially. The capillary condensation occurs better in the narrower features, we call this method “gtopography-sensitive” selective deposition technique.
Novel vapor phase method for making ultra thin conformal films of polytetrafluoroethylene (PTFE)
Authors: Gupta Sushant , Chakkaravarthi Arul Arjunan , Singh Rajiv , Opalko Jeff , Singh Deepika
Published: April 2011

Ultra-thin conformal polytetrafluoroethylene (PTFE) films were prepared by a novel physical vapor technique i.e., pulsed electron deposition (PED) technique. Prepared PTFE or Teflon thin films show high degree of conformity on patterned substrates. Under optimized deposition conditions the films exhibit superhydrophobicity. The PED processed films were characterized using scanning electron microscopy (SEM) and atomic force microscopy (AFM) micrographs and the surface morphology and the conformal nature of the films were studied. The chemical nature and hydrophobicity were studied by FTIR and contact angle measurements, respectively.
Paramagnetic Defects and Photoluminescence in Carbon Rich a-SiC:H Films: Role of Hydrogen and Excess of Carbon
Authors: Vasin A. V. , Konchits A.A. , Kolesnik S.P. , Rusavsky A.V. , Lysenko V.S. , Nazarov A.N. , Ishikawa Y. , Ashok S.
Published: April 2011

The effect of excess of carbon in a-Si1−xCx:H has been studied with regard to local structure reconstruction, evolution of paramagnetic defects and photoluminescence (PL) after vacuum annealing over the temperature range 300–850°C. Two series of samples with stoichiometric (Si0.5C0.5) and carbon-rich (Si0.3C0.7) compositions were studied by Electron Paramagnetic Resonance (EPR), Photoluminescence (PL) and Raman scattering. It is found that there exist two effects responsible for the PL efficiency of a-Si1-xCx:H films: “killing” effect of carbon-related paramagnetic defects and “enhancing” effect of carbon-hydrogen bonds in Si:C-Hn configuration. A microstructure model is proposed for explaining the non-monotonic behavior of integrated PL intensity and concentration of paramagnetic centers and Si:C-Hn bonds as a function of annealing temperature. This model evolves from the following principal processes during thermal treatment of a-Si1−xCx:H: thermally activated release of weakly bonded hydrogen, migration of hydrogen within material and interaction of hydrogen with carbon-related defects.
Application of Computational Intelligence to Investigation of Defect Centers in Semi-Insulating Materials by Photoinduced Transient Spectroscopy
Authors: Kaminski Pawel , Jankowski Stanislaw , Kozlowski Roman , Bedkowski Janusz
Published: April 2011

A computational intelligence algorithm has been applied to extracting trap parameters from the photocurrent relaxation waveforms recorded at the temperature range of 20-320 K for semi-insulating (SI) InP samples. Using the inverse Laplace transform procedure, the spectral surfaces, visualized in the three dimensional space as functions of temperature and emission rate, are calculated. The processes of thermal emission of charge carriers from defect centers manifest themselves as the sharp folds on the spectral surface. Using a set of Gaussian functions, the approximating surface is created and the ridgelines of the folds, giving the temperature dependences of the emission rate for the detected traps, are determined. The approximation is performed using the support vector machine (SVM) algorithm which allows for trading off between the model complexity and fitting accuracy. The new approach is exemplified by comparing the defect structure of SI InP wafers after annealing in iron phosphide and pure phosphorous atmospheres.
Comparative Analysis of Process of Diffusion of Interstitial Oxygen Atoms and Interstitial Hydrogen Molecules in Silicon and Germanium Crystals: Quantumchemical Simulation
Authors: Gusakov Vasilii
Published: April 2011

A theoretical modeling and comparative analysis of the process of diffusion of the interstitial oxygen atoms and interstitial hydrogen molecules (H2) in silicon and germanium crystals at normal and hydrostatic pressure (HP) have been performed. The process of diffusion of particle with a strong interaction with a crystal lattice (interstitial oxygen atom) is a cooperative process. Three nearest Si (Ge) atoms of crystal lattice are involved in an elementary oxygen jump from a bond-center site to another bond-center site along a path in the (110) plane. It is precisely their optimum position (corresponding to a local minimum of the crystal total energy) determines the value of the diffusion parameters of an interstitial oxygen atom in silicon and germanium crystals. In a sense, the diffusion process may be considered as a diffusion process of qwasiparticle – (Oi+3Si). In the case of a particle weakly interacting with a crystal lattice (interstitial hydrogen molecules) we come up against the opposite case – the diffusion of H2 is not a cooperative process. The calculated values of the activation energy and pre-exponential factor for an interstitial oxygen atom δE(Si) = 2.59 eV, δE(Ge) = 2.05 eV, D0 (Si)= 0.28 cm2 s−1, D0 (Ge)= 0.39 cm2 s−1 and interstitial hydrogen molecule δE(Si) = 0.79 – 0.83 eV, δE(Ge) = 0.58 – 0.62 eV D0 (Si)= 7.4 10−4 cm2 s−1, D0 (Ge)= 6.510−4 cm2 s−1 are in an excellent agreement with experimental ones and for the first time describe perfectly an experimental temperature dependence of an interstitial oxygen atom and hydrogen molecules diffusion constant in Si crystals.
Effect of Strain and Polarization Grading on Hole Transport across Tunneling Barriers between Metals and Wurtzite Indium Gallium Nitride
Authors: Praharaj Choudhury Jayant
Published: April 2011

We theoretically model the transport of holes across graded wurtzite Indium Gallium Nitride layers with large barriers to metals of the order of 2 electron volts. The effect of continuous strain grading and the resulting piezoelectric grading is explicitly taken into account. As data about critical thicknesses for dislocation creation are scarce for these materials, the grading widths considered for the calculations are deliberately kept small to ensure that the layers are below theoretically predicted critical thickness limits. The spatial variation of spontaneous and piezoelectric polarization creates bulk bound polarization charges that have a strong effect on the electrostatics of the layers, and creates the optimum conditions for efficient tunneling of holes. We also explicitly model the effect of the different hole masses for the valence band. Three orders of magnitude increase of tunneling intensity is seen for split-off holes with effective masses of 0.15 for the case of moderate grading from 30 % Indium to 0% Indium over 30 angstroms, compared to the case without grading. The case of very aggressive grading of the same change in composition over 10 angstroms does not lead to any extra benefits and leads to a decrease in tunneling intensity. The electric field for more aggressive grading dominates the electric field for the moderate grading both near the top and the bottom of the barrier. However, the effective barrier width at the valence band edge becomes higher for the case of aggressive grading, and most of the carriers see a damped tunneling amplitude.
Fabrication of Strain Relaxed Silicon-Germanium-on-Insulator (Si0.35Ge0.65OI) Wafers using Cyclical Thermal Oxidation and Annealing
Authors: Wang Grace Huiqi , Toh Eng-Huat , Tung Chih-Hang , Foo Yong-Lim , Tripathy S. , Lo Guo-Qiang , Samudra Ganesh , Yeo Yee-Chia
Published: April 2011

A novel scheme for the fabrication of SiGe-on-insulator (SGOI) substrates comprising a thin and relaxed silicon-germanium (SiGe) layer with high Ge mole fraction is reported. A cyclical thermal oxidation and annealing (CTOA) process is introduced to alleviate issues associated with surface roughening and non-uniformity in Ge content. A systematic study of the stress developed in the SiGe layer as condensation takes place is presented. A clear understanding of the strain evolution enables the SGOI substrate fabrication to be tailored according to the requirements of strain engineering in high mobility MOSFETs.
Deep Level Transient Spectroscopy Study of Dislocations in SiGe/Si Heterostructures
Authors: Lu Jinggang , Park Yongkook , Rozgonyi George A
Published: April 2011

Examination of dislocations in the as-grown and annealed SiGe/Si heterostructures by DLTS indicates the three strong DLTS bands from 70 to 270K in the as-grown sample are likely related to intrinsic point defects or dislocation trails. A small amount of Fe at dislocations dramatically increases their electrical activity, and the trap concentration due to Fe-decorated dislocations can well exceed the total Fe impurities presented along dislocations. Through examining the competitive trapping of Fe at boron and dislocations, it is suggested that Fe trapping only happens at disordered sites along dislocations, such as kinks.
Germanium Layer Exfoliation by Ion-Cut Processes
Authors: Job Reinhart , Düngen Wolfgang
Published: April 2011

(100)–oriented Czochralski germanium (Cz Ge) wafers were implanted with hydrogen at en-ergies up to 100 keV (related to H+) at a doses of D = 4·106 H+/cm2. Post-hydrogen annealing in normal air atmosphere on a hotplate was employed for 10 min at various temperatures between 350 °C and 600 °C to investigate the samples with regard to blistering and layer exfoliation having in mind the Smart-Cut™ technology for GOI structure formation. The generation and evolution of blisters and craters (“exploded” blisters demonstrating layer exfoliation) were investigated in dependence on the annealing temperature by atomic force microscopy and μ-Raman spectroscopy. The latter method points out the appearance of strong tensile stress upon H+ implantation and subsequent annealing. If the tensile stress exceeds about 1.2 GPa layer exfoliation occurs.
Investigation of Biaxial Strain in Strained Silicon on Insulator (SSOI) Using High-Resolution X-ray Diffraction
Authors: Zoo Yeongseok , Theodore N. D. , Alford Terry L.
Published: April 2011

Intrinsic biaxial strain values of strained Si on insulator (SSOI) layers were measured using symmetric Bragg-Brentano configuration (i.e., {004} θ-2θ scans) and asymmetric {224} rocking curves. We confirmed that the twist angle between the layer and substrate can be incorporated into the biaxial strain equations for epitaxial layers. Moreover, as the samples were annealed up to 1200°C, the tensile parallel strains increased from 0.56% to 0.7%. Since both the overlying strained Si and underlying substrate maintained a stressed state in the buried SiO2, the compressively strained oxide retained the lattice expansion of the overlying strained Si and resulted in the increasing parallel strains after annealing.
Sub 50nm Strained n-FETs Formed on Silicon-Germanium-on-Insulator Substrates and the Integration of Silicon Source/Drain Stressors
Authors: Wang Grace Huiqi , Toh Eng-Huat , Hoe Keat-Mun , Tripathy S. , Lo Guo-Qiang , Samudra Ganesh , Yeo Yee-Chia
Published: April 2011

Silicon (Si) source and drain (S/D) regions have been successfully integrated in thin-body silicon-germanium-on-insulator (SGOI) n-FETs. The selectively grown Si S/D induces uniaxial tensile strain in the SiGe channel. Devices with gate length LG down to 50 nm were fabricated. The Si S/D gives rise to 40% higher saturation drive current IDsat for transistors fabricated on Si0.60Ge0.40-on-insulator substrates. For n-FETs fabricated on Si0.75Ge0.25-on-insulator substrates, a 27% IDsat enhancement was observed. Lattice mismatch between the silicon S/D region and the SiGe channel was exploited to induce lateral tensile strain and vertical compressive strain in the channel, leading to enhancement in electron mobility. Analyses of contributions from the tensile strain to mobility enhancement and performance improvement are discussed
Material and Electrical Characterization of Nickel Silicide-Carbon as Contact Metal to Silicon-Carbon Source and Drain Stressors
Authors: Lee Rinus Tek Po , Yang Li-Tao , Ang Kah-Wee , Liow Tsung-Yang , Tan Kian-Ming , Wong Andrew See-Weng , Samudra Ganesh S. , Chi Dong-Zhi , Yeo Yee-Chia
Published: April 2011

In this paper, the material and electrical characteristics of Nickel-Silicon-Carbon (NiSi:C) films were investigated for the first time to ascertain the compatibility of NiSi:C contacts to silicon-carbon (Si:C) source/drain stressors. The incorporation of 1 atomic percent of carbon was found to increase both the Ni2Si-to-NiSi and NiSi-to-NiSi2 transformation temperatures. Our results show that the incorporation of carbon stabilizes the interfacial and surface morphology of NiSi:C films. We speculate that the incorporated carbon segregates into the NiSi:C grain boundaries and suppresses film agglomeration and NiSi-to-NiSi2 phase transformation. X-ray diffraction analysis further revealed that the formed NiSi:C films possessed a preferred orientation. Current-voltage measurements for NiSi and NiSi:C n+/p junctions exhibit similar cumulative distribution for junction leakage indicating that carbon incorporation does not have a detrimental impact on the n+/p junction integrity. Our results suggest that NiSi:C is a suitable self-aligned contact metal silicide to n-channel MOSFETs with SiC S/D stressors in a similar manner to the way in which NiSiGe is used for p-channel MOSFETs with SiGe S/D stressors.
Effect of Oxidizer on Chemical Vapor Deposited Hafnium Oxide-Based Nanostructures and the Engineering of their Interfaces with Si(100)
Authors: Singh Manish K. , Katamreddy Rajesh , Takoudis Christos G.
Published: April 2011

Thin films of hafnium oxide were deposited on silicon substrates using tetrakis-diethylamino hafnium as precursor. Two different oxidizers: (a) ozone/oxygen mixture, and (b) dry oxygen were used for comparative study of the effect of different oxidizers on the deposited films. The deposition using dry oxygen was carried out in a cold-wall rapid thermal processing metalorganic chemical vapor deposition (MOCVD) reactor, whereas ozone/oxygen mixture was used in a cold-wall atomic layer deposition (ALD) reactor. Annealing studies were carried out at 600 and 800°C in high-purity argon at atmospheric pressure. X-ray photoelectron spectroscopy (XPS) analyses of as-deposited and annealed films were performed to study the HfO2/Si interface. The films deposited using these two different oxidizers appeared to be of comparable quality. Silicon oxide formation at the interface occurred after annealing at 600°C and it increased upon further annealing at 800 °C.
Magnetic and Electronic Properties of n-type (Al,Ga) co-doped Zn(Cu)O based Dilute Magnetic Semiconductors
Authors: Chakraborti Deepayan , Prater John T. , Narayan Jagdish
Published: April 2011

Systematic studies on the epitaxial growth and the effect of n-type (Al,Ga) doping on the magnetic and electrical properties of 2.0 % Cu doped ZnO dilute magnetic semiconducting thin films deposited on c-plane sapphire single crystals by pulsed laser deposition are reported here. An decrease in more than 3 orders of magnitude in resistivity from 2×101 Ohm cm for the 2.0 % Cu doped ZnO to ~5×10-3 Ohm cm for Al and Ga codoped films is observed. This increase in conductivity does not show any effect on ferromagnetic ordering thus contradicting the claim of free carrier mediated exchange as being responsible for ferromagnetic ordering in these DMS systems. A bound magnetic polaron or F-center mediated exchange is a possible explanation for the origin of ferromagnetism in these ZnO based DMS thin films.