bluuebunny/crossref_metadata_2025 huggingface dataset:
Fabrication of High Quality Silicide Layers by Ion Implantation
Authors: Reeson Karen J , Veirman Ann De , Gwilliam Russell , Jeynes Chris , Sealy Brian J , Landuyt J , Bussmann Udo , Lindner J K N , Kaat E H te
Published: March 2011

Buried layers of CoSi2 have been successfully fabricated in (100) single crystal silicon by implanting 350 keV Co+ to doses in the range 2 - 7 × 1017 cm−2 at a temperature of ∼550°C. For doses ≥ 4 × 101759Co+ cm−2, a continuous buried layer of CoSi2 grows epitaxially, during implantation. After annealing (1000°C 30 minutes) continuous layers of stoichiometric CoSi2 which are coherent with the matrix are produced for doses ≥ 4 × 101759Co+ cm−2. For doses of ≤ 2 × 101759Co+, cm−2, discrete octahedral precipitates of monocrystalline CoSi2 are observed. Isochronal annealing (for 5s) at temperatures in the range 800–1200°C, shows that at temperatures ≥ 900°C there is significant redistribution of the Co from B-type or interstitial sites → substitutional A-type lattice sites. As the anneal temperature is increased there is a corresponding improvement in the crystallinity and coherency of the Si and CoSi2 lattices. This shows that at a given temperature much of the Co redistribution takes place within the first 5s of the anneal.
Formation of Buried Iridium Silicide Layer in Silicon by High Dose Iridium Ion Implantation
Authors: Yu K. M. , Katz B. , Wu I. C. , Brown I. G.
Published: March 2011

We have investigated the formation of IrSi3 layers buried in <111> silicon. The layers are formed by iridium ion implantation using a metal vapor vacuum arc (MEVVA) high current metal ion source at room temperature with average beam energy = 130 keV. Doses of the Ir ions ranging from 2×1016 to 1.5×1017/cm2 were implanted into <111> Si. The formation of IrSi3 phase is realized after annealing at temperatures as low as 500°C. A continuous IrSi3 layer of =200 Å thick buried under =400 Å Si was achieved with samples implanted with doses not less than 3.5×1016/cm2. Implantated doses above 8×1016/cm2 resulted in the formation of an IrSi3 layer on the surface due to excessive sputtering of Si by the TI ions. The effects of implant dose on phase formation, interface morphology and implanted atom redistribution are discussed. Radiation damage and regrowth of Si due to the implantation process was also studied.
Damage Removal of Low Energy Ion Implanted BF2 Layers in Silicon
Authors: Myers E. , Hren J. J.
Published: March 2011

Recent results indicate that thermal budgets associated with ion implantation induced end of range damage removal is affected by the presence of a free surface. Low energy BF2 implants (6 keV) were done into both single crystal and Ge preamorphized silicon substrates. Rapid thermal processing was used to study the residual end of range defect structure in the temperature range from 700 to 1000°C. 6 keV, 5E14 cm-2 BF2 implantation resulted in formation of continuous amorphous layers approximately 10 nm deep with a mean B penetration of approximately 7 nm. Conventional TEM analysis found the structures to be completely free of any spanning “hairpin” dislocations or stacking faults associated with the BF2 implant for all the annealing temperatures. For anneals between 700 °C and 900°C end of range damage formation resulted, but the size of the dislocation loops remained small. Annealing at 1000°C, 10 seconds showed no evidence of residual end of range damage. Location of the end of range damage region close to the free surface was found to decrease the thermal budget required for the removal of ion implantation induced radiation damage.
Correlation Between Defect Characteristics and Layer Intermixing in Si Implanted GaAs/AIGaAs Superlattices
Authors: Chen Samuel , Lee S.-Tong , Braunstein G. , Rajeswaran G. , Fellinger P.
Published: March 2011

Defects induced by ion implantation and subsequent annealing are found to either promote or suppress layer intermixing in Ill-V compound semiconductor superlattices (SLs). We have studied this intriguing relationship by examining how implantation and annealing conditions affect defect creation and their relevance to intermixing. Layer intermixing has been induced in SLs implanted with 220 keV Si+ at doses < 1 × 1014 ions/cm2 and annealed at 850°C for 3 hrs or 1050°C for 10 s. Upon furnace annealing, significant Si in-diffusion is observed over the entire intermixed region, but with rapid thermal annealing layer intermixing is accompanied by negligible Si movement. TEM showed that the totally intermixed layers are centered around a buried band of secondary defects and below the Si peak position. In the nearsurface region layer intermixing is suppressed and is only partially completed at ≤1 × 1015 Si/cm2. This inhibition is correlated to a loss of the mobile implantation-induced defects, which are responsible for intermixing.
Removal of End-of-Range Ion Implantation Defects in Silicon by Near Noble and Refractory Silicide Formation
Authors: Lur W. , Cheng J. Y. , Chen L. J.
Published: March 2011

Complete removal of end-of-range (EOR) defects in ion implanted silicon has been achieved by the formation and growth of near noble silicides (CoSi 2 and NiSi 2 ) and refractory silicides (MoSi 2 and WSi2). Continued generation of vacancies during the silicide growth was found to be essential to reduce EOR defects. The results are consistent with the suggestion of the presence of a vacancy diffusion barrier near the EOR defects
Observation of the Wurtzite Phase in OMVPE Grown ZnSe/GaAs: Effect on Implantation and Rapid Thermal Annealing
Authors: Jones K. S. , Yu J. , Lowen P. D. , Kisker D.
Published: March 2011

Transmission electron diffraction patterns of cross-sectional TEM samples of OMVPE ZnSe on GaAs indicate the existence of the hexagonal wurtzite phase in the epitaxial layers. The orientation relationship is (0002)//(111); (1120)//(220). Etching studies indicate the phase is internal not ion milling induced. The average wurtzite particle size is 80Å-120Å. Because of interplanar spacing matches it is easily overlooked. Electrical property measurements show a high resistivity (1010ω/square) which drops by four orders of magnitude upon rapid thermal annealing between 700°C and 900 °C for 3 sec. Implantation of Li and N have little effect on the electrical transport properties. The Li is shown to have a high diffusivity, a solid solubility of ≈1016/cm3 at 800°C and getters to the ZnSeA/aAs interface.
Diffusion, Segregation, and Recrystallization in High-Dose Ion-Implanted Si
Authors: Pennycook S. J.
Published: March 2011

Using the new technique of Z-contrast scanning transmission electron microscopy (STEM), we have been able to study the segregation of Sb at an advancing SPE growth interface and the resulting interface breakdown. The first direct information is obtained on Sb diffusion in the amorphous phase, which is many orders of magnitude enhanced over tracer crystalline values. This controls both the dopant incorporation and the stability of the resulting supersaturated alloy. These results are compared to the behavior of the low melting point substitutional diffusers and the interstitial diffusers.
Development of Thermally Stable Indium-Based Ohmic Contacts to N-Type GaAs
Authors: Murakami Masanori , Kim H. J. , Price W. H. , Norcott M. , Shih Y. C.
Published: March 2011

Development of low resistance ohmic contacts to n-type GaAs which withstand high temperature cycles without degrading their electrical properties is crucial for fabrication of high performance GaAs integrated circuits. Prior to our work, indium-based ohmic contact materials were not attractive for actual devices, because the contacts provided resistances higher than those of the widely used AuNiGe contacts, were thermally unstable after contact formation, and had rough surface morphology. Recently, based on analysis of the interfacial microstructure of these contacts, several thermally stable, low resistance In-based ohmic contacts to n-type GaAs have been developed in our laboratories using a standard evaporation and lift-off technique and annealing by a rapid thermal annealing method. The present paper points out the reasons for the poor electrical properties and thermal stability of the “traditional” In-based ohmic contacts, and reviews the recent progress.
The AuZn/GaAs Heterojunction: Evidence of Varying Solid State Reactions
Authors: Vendura George J. , Messier Russell , Spear Karl , Pantano Carlo , Drawl William
Published: March 2011

Au-Zn is one of several metal systems applied to p-GaAs to form ohmic contacts. Although it exhibits a fair degree of reliability, the thrust toward higher power and adverse environments raises concern. Observations indicate that the electrical and mechanical properties as well as the stability of AuZn/GaAs vary with Zn thickness. In this study devices with thin and thick layers were tested visually, mechanically and using SEM and X-ray diffraction techniques. Results revealed significantly different reactivity and product chemistry that could significantly affect overall device performance.
Methods to Decrease Defect Density in GaAs/Si Heteroepitaxy
Authors: Liliental-Weber Zuzanna
Published: March 2011

In this paper, the fundamental mechanisms of procedures improving the structural quality of GaAs grown on Si are discussed. Patterned growth, strained layer superlattices and proper thermal cycling are promising approaches to achieve a high quality of GaAs layers grown on Si substrates.
The Use of Superlattices to Block the Propagation of Dislocations in Semiconductors
Authors: Blakeslee A.E.
Published: March 2011

Since the discovery in 1973 that GaAs/GaAsP superlattices can be grown with low dislocation densities, considerable interest has developed in utilizing superlattices as dislocation filters in multilayer semiconductor device structures. Many attempts to implement this process have been described, with varying degrees of success being achieved. Some investigators have reported favorable results; some have observed no effect; and in some cases the situation was actually made worse. This paper analyzes these reports and attempts to clarify the confusion that has arisen. Suggestions are made for improved effectiveness. Factors considered include the strain between layers, the layer thickness, the concept of critical thickness, the dislocation geometry, and the influence of buffer layers and growth conditions.
Growth of Gaas on Si Using Algap Intermediate Layer
Authors: Noto N. , Nozaki S. , Egawa T. , Soga T. , Jimbo T. , Umeno K.
Published: March 2011

We have studied heteroepitaxial growth of GaAs on Si using an AlxGa1−xP intermediate layer in an atmospheric-pressure metal organic chemical vapor deposition (NOCVD) reactor. The crystallinity of the GaAs layer depends on AlP composition(x) of the intermediate layer. The bett crystal quality of GaAs layer is obtained when the AlP composition(x) of the intermediate layer is close to 0.5. The X-ray FWHX of 180 arcs and the etch pit density (EPD) of 2.5 × 107cm−2 were obtained in this GaAs/AlGaP/Si structure.
Nucleation Studies of Lattice Matched and Mis-Matched Heteroepitaxial Layers Using the GaAs/AlxGa1−xP/Si System.
Authors: George Thomas , Weber E. R. , Wu A.T. , Nozaki S. , Noto N. , Umeno M.
Published: March 2011

Heteroepitaxial growth of GaAs on Silicon substrates is being actively pursued, since this technology offers numerous potential benefits in terms of optoelectronic and high speed devices. However a complete understanding of the fundamental causes for film properties such as surface morphology and crystal quality is still lacking at the present time. We present here the results of a study of GaAs grown on Silicon substrates using AlxGa1−xP intermediate layers. This system offers the advantage of studying the effects of surface properties and bulk properties of heteroepitaxial films separately. Surface and interface properties are shown to be the dominant factors in the growth of AlxGa1−xP on Si, where the lattice match between the two materials is very good. For low Al mole fractions the layers tend to form islands indicative of 3D growth, whereas for x>0.4, the layers are planar indicative of 2D growth. Bulk properties such as the lattice constant mismatch are presumed to play a key role in the growth of GaAs on AlxGa1−xP intermediate layers, where it is shown that the GaAs still has an island type nucleation phase, even though surface and interface factors such as contamination and polar-on-nonpolar growth are avoided. In addition the nucleation of the GaAs on the AlxGa1−xP intermediate layers appears to be modified by the nature of the AlxGa1−xP layer i.e. whether the intermediate layer is in the form of islands or a planar layer. The final surface morphology and the crystalline quality of 3gtm GaAs films grown on AlxGa1−xP intermediate layers can be correlated to the initial nucleation.
Silicon Surface Passivation for Heteroepitaxy by Hydrogen Termination
Authors: Fenner D.B. , Biegelsen D.K. , Bringans R.D. , Krusor B.S.
Published: March 2011

Results are reported for XPS and LEED evaluations of Si(100) wafers cleaned, etched, andhydrogen terminated by various low — temperature, wet — chemical techniques. We have obtained especially promising results with the JPL spin — etch technique. Under quite practical tolerances for the spin etch, our XPS measurements indicate about lx10-2 monolayer (ML) of total residue. The LEED showed sharp spots in a (1x1) pattern. We review our experimental results and suggest an interpretation in termsof both the chemistry of silicon surfaces in contact with HF in a polar solvent, and thehydrodynamics of liquids on spinning surfaces.
Growth and Characterizations of Gaas on Inp with Different Buffer Structures by Molecular Beam Epitaxy
Authors: Liu Xiaoming , Lee Henry P. , Wang Shyh , George Thomas , Weber Eicke R. , Liliental-Weber Zuzanna
Published: March 2011

We report the growth and characterizations of 31μm thick GaAs films grown on (100) InP substrates by MBE employing different buffer layer structures during the initial deposition. The buffer layer structures under study are: 1) GaAs layer grown at low temperature; 2) GaAs layer grown at low temperature plus two sets of In0.08Ga0.92As/GaAs strained layer superlattices (SLS) and 3) a transitional compositionally graded InxGal-xAs layer between the InP substrate and the GaAs film. After the buffer layer deposition, the growth was continued by conventionalMBE to a total thickness of 3μm for all samples. From the 77K photoluminescence (PL) measurement, it was found that the sample with SLS layers has the highest PL intensity and the narrowest PL linewidth. Cross-sectional transmission electron microscopy (TEM) studies showed that the SLS is effective in reducing the propagation of threading dislocations and explains the observed superior optical quality from the PL measurement.
Effect of Strain and Interface Interdiffusion on the Valence Band Offset at Si/Ge Interfaces
Authors: Hybertsen Mark S.
Published: March 2011

The valence band offset for the Si/Ge interface is studied using the local density functional approach with a superlattice geometry. The effect of non-abrupt interfaces is modeled by including an interface layer of Si5 Ge0 5 ordered in a interface unit cell. The change in valence band offset is less than 0.01 eV. For an abrupt interface, the offset is found to be a function of strain in the Ge. The interface dipole is proportional to the perpendicular strain parameter which yields an interface contribution to the energy of the strained epitaxial Ge layers. The equilibrium strain parameter in epitaxial Ge differs from that in biaxially compressed bulk Ge.
The Growth Rates of Intermediate Phases in Co/Si Diffusion Couples: Bulk Versus Thin-Film Studies
Authors: Jan C. H. , Lin J. C. , Chang Y. A.
Published: March 2011

Bulk diffusion couples of Co/Si were annealed at 800, 900, 1000, 1050 and 1100°C for periods ranging from 24 hours to one month. Growth rates of the intermediate phases, Co2Si, CoSi and CoSi2, as well as the composition profiles across the couples were determined by optical microscopy and electron probe microanalysis (EPMA). Using the solution to the multiphase binary diffusion equations and the experimental data, the interdiffusion coefficients for Co2Si, CoSi and CoSi2 are obtained as a function of temperature. The activation energies obtained are 140, 160 and 190 KJ/mole for Co2Si, CoSi and CoSi2, respectively. The generally small interdiffusion coefficient of CoSi2 and its high activation energy cause the growth rate of CoSi2 to be extremely small at low temperatures.

The interdiffusion coefficients for Co2Si, CoSi and CoSi2 at 545°C are obtained by extrapolation of the high-temperatures data. Using these data and solving numerically the diffusion equations with the appropriate boundary conditions, the growth of Co2Si, CoSi and CoSi2 is calculated as a function of time. The calculated results are in good agreement with the experimental data reported in the literature. This study demonstrates clearly that the initial absence of the CoSi2 phase is due to diffusion-controlled rather than nucleation-controlled kinetics. This phenomenon may be quite common in many thin-fiflm metal/Si couples.
Investigation of the Interface Integrity of the Thermally Stable Wn/GaAs Schottky Contacts
Authors: Ding J. , Lee B. , Yu K. M. , Gronsky R. , Washburn J.
Published: March 2011

WNx,/GaAs Schottky contacts formed by reactive sputtering were found to be thermally stable up to an annealing temprature of ∼9400°C. The interface morphology and structure of this contact under high temperature annealing conditions ( > 700°C ) have been investigated by transmission electron microscopy (TEM) and x-ray diffractometry techniques. For the as-deposited samples, the thin film had an amorphous structure. After annealing at high temperatures, the amorphous phase transformed to α-W and W2N phases. However, the contact interface remained thermally stable up to 850°C. Cross-sectional TEM micrographs revealed that annealing at temperatures above 850°C resulted in the formation of ‘pockets’ beneath the interface. This phenomenon has been correlated with the electrical properties of the contacts, e. g., an enhancement of the barrier height of the contact. Comparisons between the interface morphology of this system and other refractory metal nitride contacts (e. g., TiN/GaAs) are also presented.
Phase Formation in the Pt/Inp Thin Film System
Authors: Olson D. A. , Yu K. M. , Washburn J.
Published: March 2011

InP substrates with 40nm metal films of Pt were encapsulated in SiO2, and isochronally annealed up to 600°C in flowing forming gas. The composition and morphology of the phases that formed were studied using x-ray diffraction, Rutherford Backscattering, and transmission electron microscopy.

Results show that the Pt/InP system begins interacting at 300°C. TEM analysis of the 350°C anneal shows unreacted Pt and and additional polycrystalline phases, with no observed orientation relationship with the substrate. The Pt layer has been completely consumed by 400°C, with a uniform reacted layer indicated by RBS. At high temperatures (between 500°C and 600°C), the reaction products are PtIn2 and PtP2. The two phases show a tendency for phase separation, with a higher concentration of PtP2 at the InP/reacted layer interface. The phosphide phase also shows a preferred orientation relationship with the substrate.
Kinetics and Thermodynamics of Amorphous Silicide Formation in Nickel/Amorphous-Silicon Multilayer Thin Films
Authors: Clevenger L.A. , Thompson C.V. , de Avillez R.R. , Tu K.N.
Published: March 2011

Cross-sectional transmission and scanning transmission electron microscopy and thermodynamic and kinetic analysis have been used to characterize amorphous and crystalline nickel silicide formation in nickel/amorphous-silicon multilayer thin films. An amorphous-nickelsilicide layer was formed between the nickel and amorphous-silicon layers during deposition. Heating caused crystalline Ni2Si to form at the nickel/amorphous-nickel-silicide interface. The composition of the amorphous-siicide was determined to be approximately 1 Ni atom to 1 Si atom. Thermodynamic analysis indicates that amorphous-nickel-silicide could be in equilibrium with nickel and amorphous-silicon if there were kinetic barriers to the formation of the crystalline silicides. Kinetic analysis indicates that the “nucleation surface energies” of the crystalline silicides, other than Ni3Si, must be 1.6 to 3.0 times larger than that of amorphous-nickel-silicide.
Thermal Equilibrium, Metastable and Irreversible Defects in a-Si:H
Authors: Street R. A , Winer K.
Published: March 2011

Measurements are reported of metastable defect states in undoped a-Si: H, with the aim of understanding the relation between the different types of metastability. The temperature dependence of the thermal equilibrium defect density agrees well with a proposed thermodynamic model and their relaxation time varies with deposition conditions. The rate of light induced defect creation and annealing in samples deposited at low temperature and with a large initial defect density, decreases progressively as the irreversible defects are removed by annealing.
Space Charge Limited Current in A-Si:H Devices Using High Electric Fields
Authors: Van Den Heuvel J. C. , Van Oort R. C. , Bokhorst B. , Geerts M. J.
Published: March 2011

Space Charge Limited Current (SCLC) measurements are used to obtain the density of gap states of intrinsic a-Si:H. If an electron is trapped by a positively charged defect, then the electron can be released by a high electric field which disturbs the SCLC measurement. A correction for this effect, which is called Poole-Frenkel emission, in SCLC measurements is derived and used to analyze current-voltage measurements performed on n-i-n a-Si:H devices. It is shown that the Poole-Frenkel emission is absent, and that this is in accordance with the contemporary models for the gap states in a-Si:H.

We also studied the characteristic temperature which is based on the concept that the distribution of gap states is exponential, and concluded that this distribution is not exponential.
Electronic Structure of Compensated Dopants in Hydrogenated Amorphous Silicon
Authors: Yang L. H. , Fong C. Y.
Published: March 2011

We use first principles pseudopotential method to study the electronic structures of compensated dopants in a realistic model of hydrogenated amorphous silicon. Boron and phosphorus atoms are treated as dopants. Two states in the gap are identified as the boron-phosphorus pair related states. The lower energy state, strongly localized around the boron atom, is obtained when the atom has a hydrogen atom as a nearest neighbor. The local environment does not affect the localization feature of the state. Other environment around the boron atom cause the charge distribution to be more extended in space. The higher energy state having its charge around the phosphorus atom does not show, strong localization at the phosphorus atom.
Properties and Application of Undoped Hydrogenated Microcrystalline Silicon Thin Films
Authors: Kanicki J. , Hasan E. , Kotecki D. F. , Takamori T. , Griffith J. H.
Published: March 2011

Device quality undoped hydrogenated microcrystalline silicon has been prepared by plasma enhanced chemical vapor deposition under different conditions. The dependence of physical, chemical, structural, and electrical properties on the deposition conditions has been investigated. Conductive (conductivity above 10−3Ω−1 cm−1) and resistive (conductivity around 10−9Ω−1cm−1) layers having approximately the same grain size, at a given substrate temperature, have been deposited between 200 and 500°C at two different hydrogen dilutions. Independently of the hydrogen dilution, the average grain sized is dependent on the deposition temperature and the film thickness; and a maximum average grain size of about 40 nm has been achieved for a thick film deposited at 500°C. The density of paramagnetic defects also increases with increasing deposition temperature, which indicates that more dangling bond defects are introduced as the total area of the grain boundaries increases. The etch rate decreases with increasing deposition temperature, and for the films deposited at 250 and 500°C the etch rate has been measured to be 6.6 and 2.7 nm/min, respectively. Thin film transistors incorporating a microcrystalline channel have been fabricated and evaluated. The best device had the following properties: field effect mobility, threshold voltage, and on/off current ratio of about 0.8 cm2/V sec, below 5 V, and around 106, respectively.
Fluorine-Induced Microvoids in Amorphous Silicon
Authors: Langford A. A. , Mahan A. H. , Fleet M. L. , Bender J.
Published: March 2011

The effects of fluorine incorporation on the microstructural and electronic properties of a-Si:H:F with 1–7 at.% F have been systematically studied. Films were prepared by direct photo-CVD of disilane with xenon difluoride as the fluorine source. The fluorine content was measured by infrared spectroscopy, xray photoelectron spectroscopy (XPS) and electron microprobe. Infrared spectra show that as the fluorine content increases, silicon dihydride bonding increases. Density measurements confirm that this is associated with an increase in microvoid content. With the increase in F and SiH2, the photoconductivity decreases over two orders of magnitude. A review of the literature shows that the appearance of SiH2 is a universal result of >1% F incorporation and is not limited to the present study. This suggests that fluorination of amorphous silicon is not beneficial for photovoltaic application.
Substrate Temperature Dependence of the Optical and Electronic Properties of Glow Discharge Produced a-Ge:H
Authors: Li Yuan- Min , Turner Warren A. , Lee Choochon , Paul William
Published: March 2011

Glow discharge a-Ge:H films produced at substrate temperatures (Tδ) between 50°C and 350°C, with and without a top a-Si:H capping layer, have been studied. The uncapped samples produced at Tδ < 250°C suffer severe post-deposition atmospheric contamination, resulting in orders of magnitude of unstable increase in both the photoresponse and dark conductivity. The capped samples, which have very much reduced immediate post-deposition contamination, show only small increases in the efficiency-mobility-lifetime product (ŋμτ) with increasing Tδ. This contrasts with the results of earlier similar studies on uncapped samples, which showed a peak in either the photoconductivity1 or the ratio of photoconductivity to dark conductivity2 for 150°C < Tδ < 2000C. We have also observed a decrease in the bandgap, a narrowing of the band-tails, an increase in the index of refraction, and a reduction of hydrogen content of the films with increasing Tδ.
Carrier Transport Properties of DC Magnetron Reactive Sputtered a-Si:H Films
Authors: Pinarbasi M. , Maley N. , Abelson J. R. , Chu V. , Wagner S.
Published: March 2011

We have prepared device quality hydrogenated amorphous silicon (a-Si:H) films by DC magnetron reactive sputtering in an Ar+H2 atmosphere. The hydrogen content (CH) of these films ranges from ∼10 to ∼28 at.% (determined from IR absorption) and is controlled mainly by the hydrogen partial pressure in the discharge. The electron and hole transport, and the density of defect states show that these films are suitable for solar cell applications. In this report we will emphasize the carrier transport properties of the films. The electron drift mobilities, determined by time-of-flight experiments, are between 0.5 and 2 cm2/V-sec. The minority carrier (hole) mobility-recombination lifetime product, (μτrec)p, has been determined on Schottky barrier structures from a fit of the voltage dependence of the photocurrent to the Hecht expression. This measurement gives results of (μτrec)p ∼ 0.9- 3×10−8 cm2/V. The density of deep-level defect states for these films (10≤CH≤28), measured with CPM, is between ∼1×1015 and ∼1×1016 cm−3. The AM-1 photoconductivity is in the range from 0.8−3.5×10−5 (Ω-cm)−1 and the dark conductivity decreases from ∼1×10−9 to ∼1×10−12 (Ω-cm)−l as the hydrogen content (CH) increases. These results show that device quality a-Si:H films can be grown by the DC magnetron reactive sputtering technique.
Alternative Complex Liquid Crystal Displays
Authors: Raynes E P
Published: March 2011

The first major progress towards complex LCD's has been made using arrays of thin film transistors (TFT's) fabricated using amorphous silicon (a - Si) technology. However, apart from other two and three terminal devices, there are also two new LCD technologies which directly improve the performance of the LCD without the need for extra switching elements. These are the supertwist (or STN) LCD and displays based on ferroelectric liquid crystals (FELC). These two alternative technologies are described and teir performance compared with that of displays fabricated using α - Si TFT's.
Plasma Chemistry in Silane and Silane-Germane Discharge Deposition
Authors: Gallagher A. , Doyle J. , Doughty D.
Published: March 2011

The spatial and energetic characteristics of rf and dc parallel-plate deposition discharges are discussed, along with their implications to plasma chemistry. We discuss the results and interpretation of our recent measurements of silane, disilane, germane, and mixed-gas stochiometry. These yield the initial dissociation branching between even and odd dangling-bond radicals, as well as the relative roles of higher silanes and silyl germanes (produced by the discharge) in the chemistry. Our deposition model and supporting data are discussed, as are various causes of film-quality variations which this suggests.
Properties of High Conductivity Phosphorous Doped Hydrogenated Microcrystalline Silicon and Application in Thin Film Transistor Technology
Authors: Kanicki J. , Hasan E. , Griffith J. , Takamori T. , Tsang J. C.
Published: March 2011

Device quality phosphorous (P) doped hydrogenated microcrystalline silicon (n+μc - Si:H) has been prepared by using the plasma enhanced chemical vapor deposition technique. The dependence of physical, chemical, structural and electrical properties on substrate temperature have been investigated. Conductivities for thick films up to 12 Ω−lcm−1 and 40 Ω−1cm−1 have been achieved for layers deposited at 300°C and 500°C, respectively. For films 50 nm thick deposited at 300°C a conductivity of about 5 Ω−1cm−1 has been obtained. A maximum average grain size around 30 nm was obtained. The etch rates of P-doped microcrystalline silicon have been found to be between 8 and 10 times higher than that of undoped hydrogenated amorphous silicon (a-Si:H) films deposited at the same temperature. Thin film transistors incorporating heavily P-doped amorphous and microcrystalline layer between source/drain metal and the a-Si:H channel have been fabricated. We show that an n+μc - Si:H source/drain contacts in thin film transistors provides very good characteristics, yielding an average effective field effect mobility, threshold voltage, and on/off current ratio of about 0.9cm2V−1 sec−1, below 4 V, and above 107, respectively.
Is B(CH3)3 An Interesting Alternative to B2H6 for a-Si:H p Doping?
Authors: Zongyan Wu , Lloret A. , Siefert J.-M. , Cabarrocas P. Roca i , Equer B.
Published: March 2011

The contamination effects induced by B2H6 and B(CH3)3 in a-Si:H layers are compared, using in-situ Kelvin probe experiments as well as SIMS measurements. It is found that B(CH3)3 induces at least 50 times less contamination, even at 250°C. It is also found that materials containing CH3 radicals have a lower electron affinity.
Temperature Dependence of Structure, Transport and Growth of Microcrystalline Silicon: Does Grain Size Correlate with Transport?
Authors: Tsai C. C. , Anderson G. B. , Wacker B. , Thompson R. , Doland C.
Published: March 2011

The temperature dependence of the growth, structure and transport of plasma-deposited microcrystalline and polycrystalline silicon films have been investigated over the temperature range of 50°C to 350°C. While low substrate temperature yields small grain sizes as expected, high temperature also tends to suppress the grain growth, contrary to the normal behavior observed in thermal CVD (chemical vapor deposition) where crystallinity grows with temperature. In fact, the highest temperature of 350°C corresponds to the lowest degree of crystallinity. Furthermore, it is found that, unlike the polycrystalline Si prepared by thermal CVD, the transport properties of the Si films do not necessarily correlate with the grain size or structural defects. While the largest average grain size of 800–1000 Å was obtained at 200°C, the highest Hall mobility and conductivity were obtained near 250°C, which corresponds to a material with smaller grains and an abundance of voids.
Radiation Effects on the Optical and Transport Properties of Amorphous Silicon
Authors: Payson J. Scott , Li Yang , Woodyard James R.
Published: March 2011

The focus of our work is to investigate the role of defects introduced by particle irradiation on the electrical and optical properties of amorphous silicon based alloys. We have studied photovoltaic cells and intrinsic films and have found that irradiation produces electrical and optically active defects which anneal at temperatures less than 200 degrees Celsius. The defects produce sub-band-gap states with a peak 1.4 eV below the conduction band edge; the structure of the material does not appear to be altered as evidenced by the band-tail states. Significant room temperature annealing effects have been observed following 1.00 MeV proton irradiation of intrinsic films.
Low Temperature Crystallization of Amorphous Silicon Films Using an Excimer Laser
Authors: Ready S. E. , Boyce J. B. , Bachrach R. Z. , Johnson R. I. , Winer K. , Anderson G. , Tsai C. C.
Published: March 2011

In an effort to enhance the electrical properties of silicon thin films, we have performed recrystallization experiments on a variety of amorphous silicon films using an excimer laser. The intense, pulsed UV produced by the laser (308nm, using XeCl gas) is highly absorbed by the amorphous material and thus provides intense localized heating in the near surface region. Two types of starting films were studied: plasma CVD a-Si:H and LPCVD a-Si. The subsequent modification produces crystallites whose structure and electrical characteristics vary due to starting material and laser scan parameters. The treated films have been characterized using Raman, x-ray diffraction, TEM, SIMS and transport measurements. The results indicate that crystallites nucleate in the surface region. The degree of crystallization near the surface increases dramatically as a function of deposited laser energy density and less so as a function of laser shot density. The hall mobility of the highly crystallized samples exhibit an increase of 2 orders of magnitude over the amorphous starting material. In the PECVD material, the rapid diffusion of hydrogen causes voids to be formed at intermediate laser energy densities and removal of film at higher energy densities. The LPCVD material withstands the high laser energies to produce well crystallized films with crystallite sizes greater then 1000Å.
Deposition of a-Si:H Films with a Remote Hydrogen Plasma
Authors: Johnson N. M. , Walker J. , Doland C. M. , Winer K. , Street R. A.
Published: March 2011

Results are presented on the properties of a-Si:H thin films deposited with a remote hydrogen plasma. An essential feature of the reactor design is the use of an alumina (rather than quartz) tube to contain the hydrogen plasma for low oxygen contamination of the films. High doping efficiency is demonstrated for both P-and B-doped amorphous films, and the effects of high silane dilution and deposition temperature are illustrated with P-doped amorphous and microcrystalline silicon films.
Amorphous Silicon-Germanium Alloy Solar Cells with Profiled Band Gaps
Authors: Yang J. , Ross R. , Glatfelter T. , Mohr R. , Guha S.
Published: March 2011

We have studied the spectral dependence of various types of amorphous silicon-germanium (a-Si:Ge) alloy p-i-n solar cells in which the band gap of the intrinsic (i) layer is profiled between 1.4 and 1.7 eV. It is observed that the cell performance depends critically on the shape of the profile, especially for red-light illumination where the device output is found to vary by more than a factor of two. We have correlated the experimental data with optical absorption and dynamic internal collection efficiency (DICE) measurements. We have also fabricated two-cell tandem and three-cell triple devices by incorporating a-Si:Ge alloy with multiple band-gap profiles in the bottom cell and achieved 13.0% and 13.7% conversion efficiencies, respectively. These are the highest efficiency amorphous silicon-based alloy solar cells reported to date.
High Deposition Rate P-I-N Solar Cells Prepared from Disilane Using VHF Discharges
Authors: Chatham H. , Bhat P. K.
Published: March 2011

We report on the influence of the discharge excitation frequency on the material properties of intrinsic a-Si:H films deposited from disilane. A monotonic increase in the deposition rate with increasing frequency is observed in the range 13.56–110 MHz. Comparison of the properties of materials deposited at ˜1.5 nm/s using 13.56 and 110 MHz discharges in disilane indicates that there are some advantages to using 110 MHz. The performance of p-i-n devices fabricated from disilane at ˜2 nm/s at these two frequencies support this conclusion. We have fabricated a device from disilane at 1.8 nm/s using a frequency of 110 MHz with an AMl.5 efficiency of 9.7%.
Substrate Temperature Dependence of the Structural Properties of Glow Discharge Produced a-Ge:H
Authors: Jones Scott J. , Lee Susanne M. , Turner Warren A. , Paul William
Published: March 2011

A series of glow discharge a-Ge:H films has been produced at substrate temperatures, Ts, between 100 and 350°C. The films were structurally characterized using Differential Scanning Calorimetry (DSC), Gas Evolution (GE), Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM). The DSC and GE results are substrate dependent. Two exothermic peaks are seen in DSC spectra for films deposited on aluminum foil while only one peak, identified by Raman measurements as the crystallization peak, is seen for samples deposited on beryllium, NaCl, carbon coated mica, crystalline silicon and 7059 glass. The crystallization peak temperature of films deposited on 7059 glass decreases with increasing Ts until 250°C where it then remains constant up to Ts=350°C. GE results show a relative increase of high temperature evolution with an increase in Ts. A well defined island/tissue structure seen in TEM micrographs of low Ts films disappears at higher Ts values. SEM measurements show columnar structure present only in films produced at Ts≤250°C. All the structural measurements point to a more stable material of higher density for Ts>250°C.
Stability, Performance and Trend Modeling of Amorphous Silicon Photovoltaic Modules
Authors: Mrig L. , Berry W. B.
Published: March 2011

The Solar Energy Research Institute (SERI) has been conducting field tests on amorphous silicon modules and analyzing the results in terms of both stability and performance. Both single p-i-n and tandem modules have been under evaluation for the past few years. This paper presents performance test results for several of these modules. Analytical models for efficiency and fill factor are presented. These models are used to project design lifetime performance. Mean square error curve fitting techniques are used to overcome data scatter. The models bracket best and worst case performance. A phenomena based, double exponential model is included to project end of life performance. This model primarily focuses on degradation due to light induced defects.
Hydrogen-Plasma Reactive Flushing for a-Si:H P-I-N Solar Cell Fabrication
Authors: Tsuo Y. S. , Xu Y. , Crandall Richard S. , Ullal H. S. , Emery K.
Published: March 2011

We have studied the effects of a hydrogen-plasma reactive flush between the pand i-layer depositions in fabricating solar cells of glass/TCO/p(a-SiC:H)-i(a-Si:H)-n(a-Si:H)/metal in a single-chamber, glow-discharge deposition system. Spectral response, photoluminescence, and photovoltaic conversion efficiency measurements show that the hydrogen-plasma reactive flush is effective in reducing the p-i interface recombination of charge carriers and in improving solar cell performance.
Double-Stacked a-Si/a-Si and a-Sic/a-Si Tandem Solar Cells with High Efficiency and High Reliability
Authors: Sakai Hiroshi , Yoshida Takashi , Fujikake Shinji , Ichikawa Yukimi
Published: March 2011

Amorphous silicon (a-Si) based solar cells with a double-stacked tandem structure have been studied with a view to reduce light-induced degradation in photovoltaic performance without lowering the initial conversion efficiency. We have attained a conversion efficiency of 11.3% in a 1cm2 a-Si/a-Si tandem cell and 10.8% in a 1cm2 a-SiC/a-Si tandem cell. Using an a-Si/a-Si tandem cell with an initial efficiency of more than 10%, we have carried out a light soaking test, and found that the degradation in conversion efficiency was about 10% under open-circuit condition after 600 hours exposure.
Band Tailing and Transport in a-SiGe:H-Alloys
Authors: Bauer G. H. , Nebel C. E. , Schubert M. B. , Schumm G.
Published: March 2011

Optical and transport studies of both cb- and vb-tail states in a-Si1−xGex:H such as subband absorption (PDS), instationary photocurrent experiments (TOF, PTS) for electrons and holes, Modulated Photocurrent Spectroscopy (MPS), and Raman scattering have been performed. The main consequences of Ge-alloying into the a-Si:H network are i) an increase in cb-tail state density at the conduction band edge and in the exponential cb- tail even for small x (O<x<0.3), accompanied by ii) a rise in deep cb-tail and midgap states which to some extent can be reduced by appropriate deposition methods; iii) at the valence band side up to x≈0.3 the tail seems not to be affected at all and for 0.3<x<0.9 the vb-tail obviously can be kept similar to that of a-Si:H (Evo≈(50–60) meV). Halfwidths of Raman TO-like modes point to the existence of a rigid Si-network in O<x<0.3 in which Ge is incorporated and to a transition at x>0.35 into a Si-Ge compound structure with maximum disorder at x≈0.5.
Hole properties of a-Si:H and a-Si,Ge:H,F alloys
Authors: Chu V. , Liu J. Z. , Conde J. P. , Wagner S.
Published: March 2011

We present a study of the temperature and intensity dependence of the (μτ)p for Schottky barriers on an a-Si:H and a 1.3eV aSi,Ge:H,F alloy. Measured values for the activation energy of (μτ)p, , and the generation rate exponent of the (μτ)p, φ, show good agreement with calculated values. We also relate the (μτ)p with the mid-gap defect density, Na.
Effects of Hydrogen Radicals on the Composition and Hydrogen Bonding of Amorphous Silicon-Germanium Thin Films
Authors: Albright D. E. , Fortmann C. M. , Russell T. W. F.
Published: March 2011

A reaction engineering model of the mercury sensitized photochemical vapor deposition of amorphous silicon-germanium thin films is used in conjunction with experimental results to describe the role of hydrogen radical reactions in determining film composition, hydrogen bonding and microcrystallinity. Selective removal of silicon from the film by hydrogen radicals is shown to increase with decreasing temperature, raising the germanium content of films in hydrogen diluted depositions below 2 torr. Etching of a-Ge:H by hydrogen radicals is determined to be nearly two orders of magnitude slower than that of a-Si:H. Hydrogen radicals are also shown to promote microcrystallinity by selectively removing amorphous phase silicon and bonded hydrogen.
Physical Properties of Annealed a-CSiGe:H Alloys
Authors: Demichelis F. , Kaniadakis G. , Pirri C. F. , Tagliaferro A. , Tresso E.
Published: March 2011

The optoelectronic properties of the new semiconducting alloy a-CSiGe:H have been studied with particular regard to the dependence upon deposition and annealing temperature. Infrared and electrical results are interpreted in terms of hydrogen bonding.
Effect of Low-Level Boron Doping on Transport Properties of a-Si:H and a-SiGe:H Alloys
Authors: Yang Liyou , Catalano A. , Arya R. R. , Bennett M. S. , Balberg I.
Published: March 2011

Large simultaneous changes in ambipolar diffusion length and d.c. photoconductivity are observed with boron doping below 5ppm. We show that the observation can be explained successfully with a model for the doping effect, which is also consistent with earlier studies. The μτ products for both carriers as a function of doping are determined. The light intensity dependence of diffusion length and photoconductivity is also discussed.
Dispersive Hydrogen Motion and Creation of Light-Induced Defects in Hydrogenated Amorphous Silicon
Authors: Jackson W. B.
Published: March 2011

This paper investigates the application of the dispersive hydrogen diffusion defect kinetic equation for the generation of light-induced defects. Self-limited monomolecular carrier defect generation by dispersive motion can explain the observed t1/3 and the G0.6 dependence where t is the illumination time and G is the illumination intensity as well as the equilibrium defect density as a function of temperature. However, the temperature dependence of the creation rate and compatibility with current degradation experiments remain unresolved problems.
Defect Relaxation in Disordered Materials: Stretched Exponentials, Meyer-Neldel Rule, and Staebler-Wronski Effect
Authors: Crandall Richard S.
Published: March 2011

Using an exponential distribution of activation barriers, annealing data for metastable effects in hydrogenated amorphous silicon, a-Si:H, are quantitatively explained. This includes the stretched exponential time dependence of annealing and a Meyer-Neldel rule for the annealing time constant. An exponential distribution of annealing energies arises because defects are frozen in during growth at high temperature. Mechanisms that lead to an exponential distribution of annealing energies are weak bond-breaking and charge trapping.
Stability Studies on A-Si:H Films
Authors: Dalal Vikram L. , Fuleihan Camille
Published: March 2011

We report on kinetics of photo-induced degradation in a-Si:H films and devices. We find that in device-quality films, the degradation kinetics do not follow either the time or the intensity behavior predicted by the bondbreaking model. Instead, there is a strong tendency towards saturation, as predicted by Redfield's equilibration model. We also find that increased SiH2 bonding in the film leads to increased degradation. The initial degradation kinetics follow the intensity behavior predicted by the trap-todangling bond conversion model of Adler. Trace levels of impurities such as O and P significantly increase the initial degradation, also in accord with the predictions of the trap conversion model.
Imaging Transfer Devices Operated by PSD Mode a-Si P-I-N Junctions
Authors: Yamaguchi M. , Murakami S. , Todo S. , Tawada Y.
Published: March 2011

Two types of position sensitive device (PSD) using a-Si:H thin films have been developed. One has been produced by large area plasma CVD, with usual metal deposition techniques. The other is the application of a linear image sensor as a one dimensional position sensor. There are some advantages and disadvantages in these two types of position sensitive device. Resolution of the linear image sensor is limited by the size of the elements and the pitch; in contrast, uniformity of the electrodes on the p-i-n diode and thickness of the a-Si thin film are the key factors for the resolution of one and two dimensional analogue PSDs.

The analogue PSD is applicable to a digitizer which takes the role of a man-machine (computer) interface. The large area two dimensional digitizer was fabricated using the same technique as large area solar cell production, and was shown to be useful as a drawing tool on a CRT or other display devices with the aid of a micro-computer.