bluuebunny/crossref_metadata_2025 huggingface dataset:
A Long-Wavelength Infrared Photoluminescence Spectrometer for the Characterization of Semiconductor Materials
Authors: Wright R. P. , Kohn S. E. , Haegel N. M.
Published: April 2011

A new photoluminescence spectrometer has been developed for the characterization of optical emission in the 2.5 to 14.1 micron wavelength range. This instrument provides high sensitivity for the detection of interband and defect luminescence in a variety of infrared detector materials. The spectrometer utilizes a solid state photomultiplier detector and a circular variable filter, which serves as the resolving element. The entire spectrometer is cooled to 5K in order to decrease thermal radiation emission. Band-edge luminescence at 10.1 microns from HgCdTe samples has been readily detected with argon-ion laser excitation powers less than 70 mW/cm2. Representative spectra from HgCdTe and other infrared detector materials are presented.
Photoluminescence and Photomodulation Spectroscopy of CdTe/Cd1−xMnxTe:In Multiple Quantum Wells
Authors: Jiang S. , Zhang L.J. , Zhang J.M. , Shen S.C.
Published: April 2011

The photomodulated reflectivity (PR) spectroscopy of modulation-doped diluted magnetic semiconductor Cd0.72 Mn0.28 Te:In/CdTe multiple quantum wells has been measured at 20 K – 300 K. Several spectral features associated with intersubband transitions have been found. The feature associated with Fermi level is first reported in PR spectra of II–VI heterostructures. In addition, a abnormal transition intensity ratio of 22H to 11H caused by electron filled effect has been reported. The Photoluminescence(PL) spectra of the sample have also been measured at 10 K – 300 K. A strong enhancement of the photoluminescence intensity towards the electron Fermi energy, which is caused by multiple electron-hole scattering processes, is reported. The temperature dependence of the Fermiedge singularity has been measured and discussed. The mechanism of the Fermi-edge singularity can be explained by hole localization.
Toward a Practical Model of a-Si:H Defects in Intensity-Time-Temperature Space
Authors: Caputo D. , Bullock J. , Gleskova H. , Wagner S.
Published: April 2011

In this paper we develop a model of the defect kinetics in hydrogenated Amorphous silicon (a:Si:H) with the goal of predicting the density of defect states g (E) established by any given light intensity I, for arbitrary times t and temperatures T. While we build on widely accepted expressions for the the rates of light-induced and thermal annealing, we examine in more detail the light induced annealing (LIA) term. The model shows that the LIA process can be described with the thermal annealing term if a suitable reduction to the annealing energy is introduced. This reduction depends on the light intensity such as to suggest a relation to the shift of the electron quasi-Fermi level under illumination.
Thermally Stimulated Conductivity in a-Si:H at low Temperatures
Authors: Zhu M. , Von Der Linden M.B. , Van Der Weg W.F.
Published: April 2011

The low temperature thermally stimulated conductivity (TSC) in a-Si:H film has been investigated in the temperature range from 20 to 150 K. Unlike the results of the high temperature TSC, the low temperature peak value and position (Tm) of TSC do not depend on the starting temperature T0 at low temperatures. This new phenomenon can not be explained by TSC theory [1]. Based on the multiple trapping (MT) Model, TSC theory limits its application to the intermediate and high temperature range. In this paper, a model of the hopping conduction with the transport energy Et in the band tail is proposed to understand the behavior of the low temperature TSC in which the thermal emission energy Em does not depend on the starting temperature of TSC.
In-Situ Crystallization and Doping of a-Si film by means of Spin-On-Glass
Authors: Sakoda Tomoyuki , Kim Chang-Dong , Matsumura Masakiyo
Published: April 2011

A novel technique has been proposed for selective and in-situ excimer-laser crystallization and doping to thin poly-Si films. Dopant atoms are supplied, during the Si laser crystallization process, to the Si film on glass from the doped SOG (spin-on-glass) film coated on the top. Conductivity of the processed film was increased to more than 10S/cm from about 10−8S/cm of the starting film. This technique has been applied to the bottom gate Amorphous-Si TFTs with self-aligned poly-Si source and drain. The electron field-effect mobility was 1.0cm2/Vs and the on/off current ratio was more than 106. No parasitic effects were observed, and the hole conduction was effectively suppressed. This in-situ crystallization and doping technique can also be applied to the top gate a-Si TFT process.
The Electronic Structure of a-Si,Ge:H Alloys
Authors: Zhong F. , Cohen J.D. , Yang J. , Guha S.
Published: April 2011

We have carried out a detailed study of the energy distribution of deep defects for high quality glow discharge a-Si,Ge:H alloys using both thermal emission and optical Methods: drive-level capacitance profiling, transient photocapacitance and photocurrent plus modulation photocurrent spectroscopy. Four distinct bands of transitions involving defect states have been identified: two associated with thermal transitions, and the other two related to optical transitions. We have, for the first time, observed a negative signal in the photocapacitance spectra at photon energies near 1.2eV. This striking aspect verifies the presence of a distinct defect band above Ep from which electron thermal emission is greatly suppressed. Our Measurements also disclose a fairly narrow defect band below the Fermi level which contrasts with the defect properties observed in a-Si:H. Time resolved photocapacitance spectra indicate that this defect band exhibits configuration relaxation.
The Mechanism of the Plasma Induced Deposition of a-Ge and μc-Ge from Germane: The limits and Possible Alternatives
Authors: Glatz F. , Konwitschny R. , Vepřek-Heijman M.G.J. , Vepřek S.
Published: April 2011

Time resolved mass spectrometry and the measurement of appearance potentials of various GeH -cationic fragments combined with selfconsistent theoretical modelling have been used to study the mechanism of plasma induced deposition of germanium. It is shown, that the high rate deposition occurs via germylene, GeH as the direct precursor. Digermane May play some role only at low deposition rates. Although we could reproduce the best values of theμτ product reported so far, no further improvement could be achieved.
Minority Carrier Diffusion Lengths And Photoconductivity In a-Si,N:H Deposited By Remote Pecvd
Authors: Williams M.J. , Cho S.M. , He S.S. , Lucovsky G.
Published: April 2011

We have deposited films of a-Si,N:H by remote PECVD from N2 and SiH4 for N-concentrations, [N], to about 12 atomic percent (at. %). Bonded-H concentrations were ∼7–10 at. %, Mostly in Si-H groups. The films with [N] = 9–12 at. % have εθ4 bandgaps of ∼2.0 to 2.2 eV, which makes them potentially useful as wide bandgap photo-active materials in tandem PV cells. Several properties are of special interest for PV applications. First, like many other a-Si:H-based alloys, the photoconductivity relative to a-Si:H is degraded by alloying, but less than for a-Si,C:H alloys with the same bandgaps. Second, the ambipolar diffusion lengths (Ld) obtained with the Steady State Photocarrier Grating (SSPG) technique for films with [N] = 10 at. % and εθ4 = 2.1eV, are comparable to those of a-Si:H. For lightly-nitrided films to [N] ∼5 at. %, Ld first decreases with respect to a-Si:H and then increases as [N] increases from ∼7 at.% to 10–12 at. %. These trends follow the dark conductivity activation energy, Ea, which initially drops due to doping, and then increases into an alloy regime for [N] > 5 at. %. Films with [N1=10 at. % have dark conductivities and Ea's comparable to those of undoped a-Si:H. Third the magnitude of the Staebler-Wronski effect, as monitored by the photo- to dark conductivity ratio after a 1000 Minute lightsoak, was about the same as in a-Si:H. Finally, we contrast the properties of these films prepared from N2 with a-Si,N:H alloys with the same [N] and E04, but prepared from an ammonia N-atom source gas and attribute differences in their photoelectronic behavior such as a significantly enhanced Staebler-Wronski effect.to the presence of Si-NH bonding arrangements in the films grown from NH3.
Boron and Phosphorus Ion Implantation In a-SixC1−x:H Thin Films
Authors: Rizzoli R. , Galloni R. , Summonte C. , Demichelis F. , Pirrp C.F. , Tresso E. , Crovini G. , Rava P. , Zignani F.
Published: April 2011

In this paper we report results on the optoelectronic and structural properties of device-quality a-SixC1−x:H intrinsic films with energy gap of 1.94 eV and Urbach energy of 70 MeV, grown by PECVD of SiH4+CH4 Mixture, which have been doped by means of boron or phosphorus ion implantation. Doping levels varied in the range 1018 to 5×1020 atoms/cm3. The behaviour of electrical characteristics, as well as energy gap and defect density, Measured on samples annealed in the range 150–400°C, showed that the optimum annealing temperature for the recovery of radiation damage is in the range 250–270°C independent of the implanted dose. Our results also show that after ion implantation and annealing, an increase of the SiH bonds concentration is detected, which is associated to a decrease of the contribution of SiH2, SiCH3, and SiCH vibrations in IR spectra.
Excitation Frequency-Dependent Raman Scattering in a-Sic:H Alloys
Authors: Morel G. , Katiyar R.S. , Weisz S.Z. , Balberg I.
Published: April 2011

We have carried out a comprehensive Raman scattering study of a-S1-xCx:H alloys using three laser excitations: 458, 514, and 581 nm. The alloys studied were prepared with and without H2 dilution, had carbon concentrations, x, between 7 and 20 at %, and Taue optical gaps in the range of 1.8 ≤ Eg ≤ 2.2 eV. The results obtained explain the previous conflicting reports in the literature regarding the Si network disorder and indicate that in the Si-rich compositions, chemical clustering takes place with increasing carbon content.
Nitrogen: Not a Dopant in Crystalline Si (C-Si), But an N-Type Dopant in A-Si:H, Why?
Authors: Lucovsky G. , Williams M.J. , He S.S. , Cho S.M. , Jing Z. , Whitten J.L.
Published: April 2011

We have incorporated N-atoms into hydrogenated amorphous silicon in the Si-rich alloy regime to ∼12 at.% N, and have observed a transition from n-type doping to alloying as the concentration of N-atoms is increased above about 5 at.%. By analogy with the local bonding arrangements of P-donors in n-doped a-Si:H, we attribute the doping to four-fold coordinated N-atoms with second neighbor H-atoms as in N+-Si-H linkages. The occurrence of these arrangements is supported by (i) IR studies which indicate a non-statistical association of N and H-atoms bonded to the same Si-atom, and (ii) a chemical bonding model in which the large effective electronegativies of four-fold coordinated N+ atoms and neutral O-atoms promote similar bonding properties with respect to their nearest-neighbor arrangements with Si and H atoms such as N+ (O) -Si-H linkages
Identification and Reduction of P-I Interface Instability and Establishment of 8.5% Stabilized Efficiency for Single Junction a-Si Solar Cells
Authors: Xi Jianping , Liu Tongyu , Iafelice Vincent , Si Kevin , Rampas Frank
Published: April 2011

Our previously reported 7.5% stabilized efficiency single junction a-Si devices had relatively low Voc, around 0.80 volts. Devices with higher Voc tended to exhibit a decrease in Voc upon light soaking. This effect was found to be independent of the properties of the i-layer. Further optimizing the p layer and p-i interface has enabled us to produce single junction devices with a stable Voc of up to 0.86 volts and a 8.5% stabilized device efficiency has been established.
Adjusting the Defect Profile in a-Si:H Solar Cells with Energy Resolved Electron or Laser Beams: Experiment and Modeling
Authors: Vasanth K. , Caputo D. , Wagner S. , Bennett M. , Bae S. , Fonash S.
Published: April 2011

We light-soaked a-Si:H pin solar cells with blue laser light through the front glass substrate or electron irradiated them through the back Al layer. By using short wavelength light and energy resolved electron beams we localize the damage preferentially near the p/i or n/i interface and thus study their effect on cell performance. I-V characteristics and quantum efficiency spectra were measured before and after the damage was introduced. We Modeled the changes in the quantum efficiency using the numerical device Model AMPS. Comparing changes in the measured and modeled quantum efficiencies (QE) we find that cells light-soaked with the blue laser have damage localized near the front of the device, and localized near the back for cells irradiated with electrons. This indicates that quantum efficiency measurements are sensitive to the location Of defects in the i-layer of the solar cell. However after long light-soaking and electron irradiation times the difference between the two types of damage becomes less visible in the QE Measurements.
In Situ Ellipsometric Monitoring of Low Temperature Growth of Poly-Si Films By RF Plasma CVD
Authors: Shirafuji T. , Hayashi Y. , Tachibana K.
Published: April 2011

In situ ellipsometry has been applied for monitoring silicon-thin-film growth on a glass substrate in RF-discharge plasma of SiF4+SiH4 diluted with H2 (80%). Polycrystalline silicon films were obtained at substrate temperature of 300°C and RF power density of 500MW/cm2. Volumetric fraction of c-Si increased from 50 to 80% by increasing the SiF4/ (SiF4+SiH4) flow ratio from 0 to 0.5. The fraction of c-Si also increased to 63% by sequential repetition of deposition with SiH4/H2 and etching with SiF4. The etching rate of a-Si was less than that of c-Si. These results suggest that semi-preferential etching of a-Si enhances the increase of c-Si fraction. A gas-phase reaction simulation has suggested that the dominant deposition precursor is SiH3, and the etchant is F in the present condition.
Silicon Nitride Optimisation for A-Si:H Tfts Used in Projection LC-TVS
Authors: French I. D. , Curling C. J. , Goodyear A.L.
Published: April 2011

Multi-layer devices based on thin films in Large Area Electronics have different intrinsic and extrinsic properties that must be optimised to produce the correct physical shape of the device, in addition to having acceptable electrical characteristics. For instance it is quite easy to produce individual layers optimised for electrical performance that will physically “pull off’ underlying films, or result in poor step coverage. The factors that must be considered include mechanical stress, etching rates and profiles, thickness and stoichiometry uniformity, and thermal budgets, as well as electrical characteristics. This paper gives an example of silicon nitride optimisation for use in a-Si:H TFT projection displays. Three different silicon nitride layers were included to give a storage capacitor, together with controlled etch profiles for step coverage. The layers were optimised with respect to several different parameters in the minimum number of depositions by the use of experimental design techniques.
Effects of N2 Plasma Treatment on SiO2 Gate Insulator in a-Si:H Thin Film Transistor
Authors: Kim Sung Chul , Bae Sung Sig , Oh Eui Yeol , Kim Jeong Hyun , Lee Jong Wan , Kim Cha Yeon , Kim Donggil
Published: April 2011

We fabricated the high performance a-Si:H TFT using the N2 plasma treated APCVD SiO2 as a gate insulator. The effects of N2 plasma treatment on the APCVD SiO2 were investigated by XPS and SIMS Measurements. And the formation of the oxynitride interface layer between a-Si:H and APCVD SiO2 was found in the a-Si:H TFT. From our experimental results, It May be concluded that most nitrogen atoms, which were incorporated by the exposure of SiO2 layer to N2 plasma, exist, not bonded to other atoms, near the surface of the SiO2 layer and during the sequential deposition of a-Si:H on the N2 plasma treated APCVD SiO2 layer Si-N bonds are formed, resulting in the oxynitride layer in the interface region. This explains the high performance a-Si:H TFT with the N2 plasma treated APCVD SiO2 gate insulator.
Stability of a-Si:H TFTs Employing APCVD SiO2 with N2 Plasma Treatment as a Gate Dielectric
Authors: Jun M.C. , Kim Y.S. , Oh E.Y. , Kim D.G. , Han M.K.
Published: April 2011

We have investigated the stability of the hydogenated amorphous silicon thin film transistors (a-Si:H TFTs) employing silicon dioxide (SiO2) with N2 plasma treatment as a gate dielectric, where SiO2 was deposited by atmospheric pressure chemical vapor deposition (APCVD). Their stability was compared with those of a-Si:H TFTs whose gate dielectric was silicon nitride (SiNx) deposited by plasma enhanced chemical vapor deposition (PECVD). Two kinds of stresses, gate bias and light illumination, were applied. The threshold voltage shin (AVu,) and the inverse subthreshold slope shift (ΔVth) were measured as a function of the bias voltage and the light stress time. For the positive bias stress, the ΔVth, of the a-Si:H TFTs with the N2 plasma treated SiO2 dielectric is smaller than that with the PECVD SiNx gate dielectric. For the negative bias stress and light stress, however, the ΔVth of TFT with N2 plasma treated SiO2 dielectric is larger than that with the SiNx dielectric
Density of Deep Bandgap States in Amorphous Silicon From the Temperature Dependence of Thin Film Transistor Current
Authors: Globus T. , Slade H. C. , Shur M. , Hack M.
Published: April 2011

We have measured the current-voltage characteristics of amorphous silicon thin film transistors (a-Si TFTs) over a wide range of temperatures (20 to 160°C) and determined the activation energy of the channel current as a function of gate bias with emphasis on the leakage current and subthreshold regimes. We propose a new method for estimating the density of localized states (DOS) from the dependence of the derivative of activation energy with respect to gate bias. This differential technique does not require knowledge of the flat-band voltage (VFB) and does not incorporate integration over gate bias. Using this Method, we have characterized the density of localized states with energies in the range 0.15–1.2 eV from the bottom of the conduction band and have found a wide peak in the DOS in the range of 0.8–0.95 eV below the conduction band. We have also observed that the DOS peak in the lower half of the bandgap increases in magnitude and shifts towards the conduction band as a result of thermal and bias stress. We also measured an overall increase in the DOS in the upper half of the energy gap and an additional peak, centered at 0.2 eV below the conduction band, which appear due to the applied stress. These results are in qualitative agreement with the defect pool Model [1,2].
Color Document Imaging with Amorphous Silicon Sensor Arrays
Authors: Street R. A. , Wu X. D. , Weisfield R. , Nelson S. , Nylen P.
Published: April 2011

We describe the performance of an amorphous silicon imaging system designed for high speed (>10 frames/sec) scanning of a document. The system comprises a new page-sized sensor array with 1536×1920 pixels, an illumination source, and the readout electronics. With appropriate color filters, one can achieve color imaging of a document without the registration problems associated with linear scanners. We describe the color imaging properties and discuss how the color response, sensitivity and uniformity depend on the properties of the amorphous silicon sensors.
a-Si:H/a-SiC:H Heterostructure for Bias-Controlled Photodetectors
Authors: De Cesare G. , Irrera F. , Lemmi F. , Palma F. , Tucci M.
Published: April 2011

We present a novel family of photodetectors based on hydrogenated amorphous Si/SiC p-i-n-i-p heterostructures. Front p-i-n and rear n-i-p diodes work one as a detector and the other as a load impedance, depending on the polarity of the applied voltage. Due to different absorption at different wavelengths, the devices operate as bias-controlled light detectors in either the blue or the red regions. The energy gap and the thickness of the two intrinsic layers have been optimized to obtain a sharp wavelength selection (centered at 430 and 630 nm) with high rejection-ratios and good quantum efficiencies. The I-V characteristics and the device time response are investigated and simulated by SPICE.
Amorphous Silicon Films from Dichlorosilane and Hydrogen
Authors: Bullock J.N. , Wagner S.
Published: April 2011

We deposited a-Si:H thin-films by PECVD of dichlorosilane (SiH2Cl2) diluted with H2 in a DC-triode glow-discharge reactor. The dilution ratio, given as the ratio of H2 to SiH2Cl2 flows, was varied from 0 to 130 and the pressure was varied from 0.3 to 0.75 Torr as the hydrogen fraction was increased. We report on the properties of the deposition plasma and the resulting films; namely the plasma pressure-voltage characteristics and the films' chemical composition, structure, and optoelectronic properties. For hydrogen dilution ratios greater than 2:1, dense, rigid films are deposited, with optical bandgaps from 1.75 to 1.9 eV. With increasing hydrogen dilution a growth rate of 5 Å/s is maintained while photoconductivities increase and defect densities decrease. The best films are obtained at a dilution ratios of 16:1 to 32:1, where we have obtained a dark conductivity of 10−13 S/cm, a photoconductivity of 2×10−7 S/cm (at G=1020 cm-3 s−1) and a defect density of 1.5×1016 cm−3.
Chemical-Mechanical Polishing of Tungsten with Hologen-Based Slurries
Authors: Yang K. , Gutmann R. J. , Murarka S. P. , Stonebraker E. , Atkins H.
Published: April 2011

Halogen-based slurries have been investigated for chemical-mechanical polishing of tungsten. Among these slurries, Bromine-methanol-water slurry gives the best results. Depending on the polishing parameters and slurry concentration, polishing rate of the slurry for W varies from 100 nm/min to 300 nm/min, while the chemical etch rate of the slurry for W and SiO2is near zero. The W and SiO2films after polishing with the slurry show very smooth surfaces (featureless under a high quality optical microscope). The selectivity of larger than 15 has been achieved between W and PECVD TEOS oxide. Tungsten stud formation through CMP with this slurry has been demonstrated with no significant dishing in the metal.
Plasma Etching of Copper Films Using IR Light Irradiation
Authors: Hosoi N. , Ohshita Y.
Published: April 2011

Copper films are etched at a low temperature of 60 °C using a Cl2 plasma etching method with IR light irradiation. The etch rate is as high as 1 μm/min. The anisotropic Cu line patterns are obtained independent of the Cl2 gas flow rate and the etching pressure conditions. Moreover, there is no corrosion on the etched sample.
Impact of Microstructure of Alternative Al-Si-V-Pd Alloy Films on Interconnect Reliability, Compared to Al-Si-Cu
Authors: Dirks A.G. , Augur R.A. , Kordić S. , Wolters R.A.M.
Published: April 2011

Difficulty during plasma etching and post-etch corrosion are major drawbacks of Al-Si-Cu alloy films, when used for integrated circuit interconnect. Moreover, the relatively large solute mobility of Cu in Al may lead to void formation by precipitate coarsening. As integrated circuit dimensions decrease reliability issues, such as electromigration and mechanical stress voiding, are becoming increasingly important. At present several types of Al alloys are considered as possible alternatives for Al-Si-Cu: Al-Pd, Al-Sc, Al-Pd-Cu, Al-Si-Pd, Al-Si-V, Al-Si-Sc, Al-Si-Pd-Nb, and Al-Si-V-Pd. The latter quaternary alloy has been designed such as to combine the positive aspects of both Pd and V. In comparison with Cu in Al, a) the (low temperature) solid solubility is negligible for Pd and small for V, and b) the mobility is similar for Pd, but very small for V.

With transmission-electron microscopy, passivated Al-Si-Cu alloy films have been studied after thermal stressing at 200 °C: ө-Al2Cu coarsening was observed together with void condensation. Lifetests on unpassivated Al-Si-V-Pd alloys at 180 °C and 2xl06A/cm2 have shown an extremely high resistance to electromigration. Electromigration and microstructural data on these quaternary alloys will be presented. These findings suggest how the microstructure is stabilized by the combined action of the V and Pd solute atoms, a) by nm-scale (A1,V) precipitates within the Al grains and b) by small (Al,Pd) particles at the Al grain boundaries. Furthermore, the key issues in terms of reliability related microstructural phenomena are both solute and solvent mobilities in grain interiors as well as along interfaces and grain boundaries. Arguments will be given showing that at low solute concentrations the metals (V and Pd) each by themselves are not effective enough to influence the solvent motion of aluminium along interfaces and grain boundaries significantly. The combination of the two metals, however, was found to be very effective.
Ohmic Contact Metallization for n-Type GaAs
Authors: Murakami M. , Oku T. , Otsuki A. , Uchibori C. J.
Published: April 2011

The performance of GaAs devices is significantly influenced by the qualities of the substrates, Schottky and Ohmic contact materials. Development of Ohmic contact materials is far behind compared with that of the other materials. Low resistance, alloyed AuGeNi Ohmic contacts have been extensively used in the current manufacturing GaAs devices. However, extension of usage of these devices to Very Large Scale Integration levels requires the contacts with excellent thermal stability, shallow diffusion depth, and smooth contact surface in addition to low contact resistance. In the present paper recent studies for development of Ohmic contacts which improve the poor contact properties of the alloyed Ohmic contacts are reviewed.
Low-Resistivity Non-Alloyed Ohmic Contacts to p- and n-Gaas Using In-Situ Integrated Process
Authors: Hong M. , Vakhshoori D. , Mannaerts J. P. , Kwo J.
Published: April 2011

Very low-resistivity non-alloyed ohmic contacts (Rc) to both p- and n-GaAs were realized using molecular beam epitaxy (MBE) in a vacuum integrated system. Three different metals of Au, Ag, and Nb were in-situ deposited on (1) p+-GaAs which was heavily Be-doped either in a uniform doping or with a 5-doping scheme; and (2) n+-GaAs which was doped in a 5-pair Si δ-doping with a spacer GaAs-Si 2.5 nm thick. In both cases, low Rc values of ≤ (1-5) x 10-7 Ω-cm2 were achieved.
The Ge/Pd/n-GaAs Ohmic Contact Interface Studied by Backside Raman Spectroscopy
Authors: Watté J. , Silverans R.E. , Miinder H. , Palmstrøm C.J. , Florez L.T. , Van Hove M. , Borghs G. , Wuyts K.
Published: April 2011

The Ge/Pd/n-GaAs ohmic contact structure constitutes a near-ideal model system to test the applicability of the different metal/GaAs ohmic contact models. After annealing, an atomically flat interface between the GaAs substrate and a regrown Ge layer is obtained. A main point of discussion is whether the ohmic conduction across this junction either occurs by an enhanced Ge-doping of the GaAs (regrown) substrate surface layers (the doping model), and/or by a degenerate As-doping ot the Ge overlayer (the heterojunction hypothesis). In order to examine the applicability of both models, a Raman study of this system is undertaken. By a backside thinning procedure, a metallization/60 nm GaAs structure is preserved, allowing for a backside optical analysis of the regrown Ge/GaAs interface region.
Effects of Pt and W2N/W Bottom Electrodes on Dielectric Properties of BaTiO3 Thin Films
Authors: Tae Kim Yong , Lee Chang Woo , Lee Jeong-gun
Published: April 2011

Effects of Pt and W2N/W bottom electrodes on dielectric properties of 1000 Å thick BaTiO3 thin film capacitors are studied. The tetragonality of BaTiO3 on W2N/W electrode is better than that of BaTiO3 on Pt electrode and leakage current of W2N/W/BaTiO3/Au capacitor is four orders of magnitude less than that of Pt/BaTiO3/Au capacitor. The excellent properties of W2N/W/BaTiO3/Au capacitor is ascribed to both of the tetragonal structure of WO3 formed at the interface of W/BaTiO3 and the diffusion barrier property of W2N preventing the interfacial reaction among bottom electrodes, BaTiO3, and Si.
Optical Properties of Metal Films and Their Silicides
Authors: Simard-Normandin M. , Naem A. , Saran M.
Published: April 2011

Silicides are used widely in microelectronic fabrication, yet there are very little data available regarding their optical constants at most wavelengths, and specifically at those of interest to G-line and I-line lithography. We have studied extensively the optical properties of Ti, Co, as metal films and as silicide films formed at various temperatures, and of CVD (chemical vapour deposition) W. Using spectroscopic ellipsometry at two angles of incidence, we have calculated the complex index of refraction N = (n, k) of these films every 10nm at 68 wavelengths between 230 and 900nm. These data are necessary to model accurately the reflectivity of wafers to study the effects of various thermal and surface treatments on silicide growth and to set exposure times for lithography. They also allow the use of reflectivity vs X as a non-contact method to map film thicknesses across wafers within the patterned devices themselves.
Non-Destructive Electrical Techniques as Means for Understanding the Basic Mechanisms of Electromigration
Authors: Scorzoni A. , De Munari I. , Stulens H.
Published: April 2011

In this paper results of recently developed high resolution resistometric electromigration techniques will be described, with particular attention to the behaviour of narrow, near-bamboo metal lines. After a discussion on recent theoretical results published in the literature, a diffusion model correlating mechanical stress and electromigration will be adopted to describe experimental results of relative resistance change both during and after electromigration. The good agreement between experimental data and simulations must not hide that something must still be understood about the physical mechanism leading to resistance changes during electromigration experiments.
Reduction of Sn02 by A-Si1-XGeX
Authors: Edelman F. , Brener R. , Cytermann C. , Eizenberg M. , Weil R. , Beyer W.
Published: April 2011

Thin films of amorphous Si1−xGex:H with x=0, 0.3, 0.6, and 1 were deposited by RF glow discharge at 200-250°C on SnO2/glass substrates. The tin dioxide was reduced by heat treatment at the temperature range of 400-600°C resulting in a layered structure of silicon oxide, tin suboxide and ß-Sn which formed at the a-Si1−xGex:H/SnO2 interface. A strong dependence of the extent of the reduction on the Ge content in the a-Si1−xGex:H films was found: at low temperatures (T≤475°C) the Si-rich layers were more reactive, whereas at T≥475°C the Ge-rich films totally reduced the SnO2. The interfacial reduction process was followed by a drop in the transparency and drastic changes in the sheet resistance of the a-Si1−xGex:H/SnO2 contacts.

PACS: 61.43.Dq; 78.66; 82.65.-i; 82.65.Fr; 82.65.Yh
Single Crystal Epitaxial Ge Based Contacts to Gaas, and InGap
Authors: Dubey M. , Jones K.A. , Casas L.M. , Eckart D. , Pfeffer R.L.
Published: April 2011

Nonalloyed, single crystal, oxide free Ge based ohmic contacts are almost atomically abrupt, have a smooth interface, and have the potential to be better understood. Ultra high vacuum electron beam evaporation is used to deposit a single crystal Ge film on GaAs and InGaP substrates. A large grain, highly oriented Au film or a poly crystalline Pd film with more randomly oriented grains was then deposited on the Ge. These films were characterized in the as grown condition by high resolution electron microscopy (HREM), double crystal x-ray diffraction (DXRD), Auger electron spectroscopy (AES), Rutherford back scattering (RBS) and scanning electron microscopy (SEM). The as deposited Ge film grown at 400°C on GaAs and at 350°C on InGaP are epitaxial with a smooth abrupt, oxide free interface. The highly oriented Au film deposited at 100°C had a smooth interface with the Ge with the orientation relationship (100)Au II (100)Ge and [001]Au II [011 ]Ge or [0-1 1 ]Ge.
Kinetics of Copper Grain Growth During Nitridation of Cu-Cr and Cu-Ti Thin Films by In Situ Tem
Authors: Atzmon Z. , Sharma R. , Russell S. W. , Mayer J.W.
Published: April 2011

Co-deposited Cu-Cr and Cu-Ti thin films were heated at various temperatures in an ammonia ambient in an environmental cell placed into the column of a transmission electron microscope (TEM). The reaction dynamics were observed in situ and recorded on a videotape using a TV camera with 1/30 second time resolution. Nitridation of chromium and titanium was accompanied by the nucleation and growth of copper particles starting at 370 and 580°C, respectively. It was found that in the Cu-Ti system at a temperatures regime of 370-400°C the growth rate behaves under a parabolic law; namely, the process is controlled by diffusion of Cu through the nitride matrix. However, for the Cu-Cr system at temperatures of 610-630°C two growth regimes were observed. In the initial growth stages, the surface reaction is rate-limiting, while for longer nitridation times, growth is diffusion-controlled.
Dry Etching of Ta-Si-N Diffusion Barrier Material in Cf4+02 Gas Mixtures
Authors: McLane G.F. , Casas L. , Reid J.S , KoIawa E. , Nicolet M-A.
Published: April 2011

Sputtered Ta36Si14N50 amorphous diffusion barrier layers were reactive ion etched in CF4+02 plasmas. Etch rate varied with gas composition, with 15 percent 02 concentration producing maximum etch rate. Etch rates increased with both pressure and power. Etching proceeded only after an initial delay time which was dependent upon gas composition and applied power. The delay time was probably caused by the presence of a surface native oxide which must first be removed before etching can commence. Auger electron spectroscopy measurements showed the native oxide to be approximately 2 nm thick on as-grown samples, and indicate that near-surface stoichiometry is maintained on etched samples.
Comparison of Growth and Microstructure of Copper Films Deposited From Different Cu(Ii) Precursors
Authors: Goswami J. , Shivashankar S.A. , Raghunathan Lakshmi , Devi Anjana , Ramanathan K.V.
Published: April 2011

High quality copper thin films have been obtained by low pressure thermally-activated chemical vapour deposition from two different Cu(II) metalorganic precursors, (a) bis(dipivaloyl-methanato) Cu (II) or Cu(dpm)2 and (b) bis(t-butylaceto acetato)Cu(II) or Cu(tbaoac)2, the latter synthesised with a view to reducing the deposition temperature. A comparative study of the volatility and thermal stability of the two precursors, as well as of the growth and microstructure of copper films from these two precursors, is presented.While the threshold deposition temperature is significantly lower for Cu(tbaoac)2 compared to Cu(dpm)2, the growth rate is considerably higher with Cu(dpm)2-Films obtained from Cu(tbaoac)2 are denser and of lower resistivity at a given thickness compared to those from Cu(dpm)2, and are also smoother, exhibiting mirror-like reflectivity.
Polyimides and Copolyimides with Low Dielectric Constant, Low Moisture Absorption, and Low Coefficient of Thermal Expansion for use as Interlayer Dielectrics
Authors: Auman Brian C.
Published: April 2011

The mechanical, thermal, electrical and moisture absorption properties of a series of fluorinated, highly rod-like polyimides and copolyimides are reported. Copolymerization with appropriate flexibilizing comonomers resulted in improved elongations versus those of the highly rod-like homopolymers while maintaining, to a large extent,the other desirable properties of the backbone. These materials are considered prime candidates for interlayer dielectric due to their excellent combination of properties.
Transmission Electron Microscopy of Mocvd Titanium Nitride Films
Authors: Itoh Toshio , Konno Toyohiko J. , Sinclair Robert , Raaijmakers Ivo J.M.M. , Roberts Bruce E.
Published: April 2011

The effect of substrate temperature and process pressure on microstructure of MOCVD-TiN films deposited on oxidized Si substrates are studied by transmission electron microscopy (TEM). It is found that microstructure of MOCVD-TiN films distinctly changes with these deposition parameters and that the resistivity of the films is uniquely related to the microstructure. Films with the lowest resistivity (< 500 μohm-cm) show a uniform semi-columnar grain structure. Films with the highest resistivity (> 10,000 μohm-cm) show a uniform equi-axed micrograin structure. The other films exhibit a bi-layer structure: one layer of semi-columnar grains and the other of equiaxed micrograins. The thickness ratio of these layers changes with the deposition conditions and the resistivity is a unique function of the thickness of the semi-columnar grain layer.
Basic Science in Silica Glass Polishing
Authors: Tomozawa Minoru , Yang Kai , Li Hong , Murarka Shyam P.
Published: April 2011

Water entered into oxides when the oxides were indented with diamond in the presence of water or water vapor. Similar water entry is expected during silica glass polishing because of the high stress concentration on the glass surface in contact with small abrasive particles. Both chemical and mechanical properties of silica glasses change with water content. Polishing rate of silica in oil-based slurry with diamond abrasive increased with water content in the silica. Since oil has no chemical reactivity with silica, mechanical property degradation with water incorporation must be responsible for the fast polishing rate of the water-containing samples. A plausible mechanism of the polishing of silica is, therefore, water entry into silica under stress and mechanical removal of the altered layer. In the presence of water this process repeats itself.
High Power and High Frequency Silicon Carbide Devices
Authors: Palmour John W. , Carter C. H. , Weitzel C. E. , Nordquist K. J.
Published: April 2011

The breakdown electric field of 4H-SiC as a function of doping was measured using pn junction rectifiers, with maximum voltages of 1130 V being achieved. 4H-SiC vertical power MOSFET structures have shown specific on-resistances of 33 mΩ-cm2 for devices capable of blocking 150 V. A current density of 100 A/cm2 was achieved at a drain voltage of 3.3 V. Thyristors fabricated in SiC have also shown blocking voltages of 160 V and 100 A/cm2 at 3.0 V. High temperature operation was measured, with the power MOSFETs operating to 300°C, and the thyristors operating to 500°C.

Submicron 6H- and 4H-SiC MESFETs have shown good I-V characteristics to Vd= 40 V, with an Idss of 200–300 mA/mm. The maximum operating frequencies (fmax) achieved for 6H-SiC MESFETs is 13.8 GHz, with small-signal power gains of 9.8 dB and 2.9 dB at 5 GHz and 10 GHz, respectively. 4H-SiC MESFETs have demonstrated an RF output power density of 2.8 W/mm at 1.8 GHz. This is the highest power density ever reported for SiC and is 2–3 times higher than reported for comparable GaAs devices.
Comparison of Microwave ECR and RF Plasmas for Dry Etching of Single Crystal 6H-SiC
Authors: Flemish J. R. , Xie K. , Buchwald W. , Casas L. , Zhao J. H. , McLane G. , Dubey M.
Published: April 2011

Electron cyclotron resonance (ECR) plasma etching of single crystal 6H-SiC has been investigated using a CF4/O2 gas mixture and compared to conventional reactive ion etching (RIE) in a radio frequency (13.56 MHz) reactor. The use of ECR results in higher etch rates, lower levels of bias and smoother etched surfaces than rf-RIE. ECR etch rates exceeding 100 nm/min have been obtained at a substrate bias of-100 V. Etch rate and surface morphology have been studied as a function of pressure, bias and power. Auger electron spectroscopy shows that ECR etching leaves no residues unlike rf-RIE which leaves residues containing Al, F, O and C. The current-voltage and capacitance-voltage measurements of Schottky diodes show that there is far less damage induced by ECR etching compared to rf-RIE.
Characterization of MS, MiS, and Mos Contacts to Type IIB Diamond by Capacitance-Voltage and Current-Volt Age
Authors: Wynands Henry A. , Hartsell M. L. , Fox Bradley A.
Published: April 2011

Three types of electrical contacts on natural type lib single crystal diamonds have been studied by current-voltage (IV) and capacitance-voltage (CV) measurements. Vertical structures were fabricated with the metal-diamond (MS), metal-undoped diamond-doped diamond (MiS), or metal-SiO2-doped diamond (MOS) contacts and ohmic contacts on the opposite face of the diamond. The MS contact was rectifying and both the MiS and MOS were blocking contacts. While very high leakage currents were measured on the MiS structure in forward bias (MO6times the reverse bias), an accumulation region was observed in the MiS CV data. The uncompensated acceptor concentration values calculated from the CV data were in good agreement for different structures fabricated on the same samples and with the secondary ion mass spectroscopy (SIMS) measurements of the bulk boron concentration. Extreme stretch out was observed in the CV of the MiS and MOS due to interface traps. The density of interface traps was estimated to be in the 1012 cm-2 eV-1 range for these structures.
Diamond Growth Rates and Quality: Dependence on Gas Phase Composition
Authors: Cassidy William D. , Evans Edward A. , Wang Yaxin , Angus John C. , Bachmann Peter K. , Hagemann Hans-Jurgen , Leers Dieter , Wiechert Detlef U.
Published: April 2011

Diamond growth rates and quality were studied as a function of source gas composition and correlated with position on the ternary C-H-O diagram. The chemical potentials of carbon and oxygen change dramatically on either side of the H2-CO tie line, leading to large differences in the equilibrium distribution of species. These differences are reflected in the species flux reaching the diamond surface, and hence in the quality and growth rate of the diamond. In situ microbalance measurements in a hot-filament reactor show that the reaction rate is independent of the CO concentration, but decreases with increasing O2. Quality, as measured by Raman spectroscopy, increases as the C/C+O ratio in the source gases is reduced to approach the critical value of 0.5. The stability of the filaments to decarburizing and oxidation are correlated with the carbon and oxygen chemical potentials and hence to the position on the C-H-O diagram. A preliminary ternary diagram for the C-H-F system is presented.
Characterization of a Thick Homoepitaxial CVD Diamond Film
Authors: Plano M. A. , Moyer M. D. , Moreno M. M. , Black D. , Burdette H. , Robins L. , Pan L. S. , Kania D. R. , Banholzer W.
Published: April 2011

A thick homoepitaxial CVD diamond film was grown on a large high temperature, high pressure (HTHP) Ha diamond to study the defects present in the CVD film. The HTHP diamond had dimensions of 6 mm x 6 mm x 0.44 mm. The thickness of the diamond was increased to 0.84 mm by microwave plasma CVD. X-ray topographs were taken before and after growth to compare the defects in CVD diamond to those in the HTHP diamond. Prior to growth the substrate was unstrained and the characteristic microstructure of stacking faults and dislocations was observed. There was also a surface relief, visible optically, on the substrate of lines along the [100] which are probably due to polishing. After deposition of the CVD film, the crystal was strained with the film in tension. The defect structure observed throughout the CVD film followed the surface relief of the substrate. Cathodoluminescence spectra indicate that the film contains nitrogen defect complexes which are not present in the substrate. Cathodoluminescence also indicates that there are more non-radiative recombination centers in the film than in the substrate. Electrical results from transient photoconductivity measurements indicate that while the mobilities of the film and the substrate are comparable, the lifetime is much shorter in the film, possibly reflecting the higher concentration of non-radiative recombination centers.
Cathodoluminescence Spectroscopy of Boron Nitride Films
Authors: Taylor C. A. , Brown S. W. , Subramaniam V. , Kidner S. , Rand S. C. , Clarke R.
Published: April 2011

We report results from cathodoluminescence spectroscopy of boron nitride films grown on Si (100) substrates by ECR ion source assisted magnetron sputtering of a hexagonal BN target. Three main peaks are observed in the near-bandgap region for hexagonal boron nitride films at energies of 4.90 eV, 5.31 eV, and 5.50 eV. In addition, deep-level emission spectra of predominantly cubic boron nitride films are correlated with sample growth conditions. In particular we show that the emission intensity, position, and linewidth are strongly dependent on the substrate bias voltage used during sample growth.
Low Energy Threshold in the Growth of Cubic Boron Nitride Films by ECR Plasma Assisted Magnetron Sputtering
Authors: Taylor C. A. , Kidner S. , Clarke R.
Published: April 2011

We report the growth of cubic boron nitride (cBN) films by magnetron sputtering on Si (100) substrates. The films are grown in the presence of negative substrate bias voltages and a nitrogen plasma produced by an electron cyclotron resonance source. We find evidence for a sharp low-voltage threshold in the substrate bias (-105 V) beyond which the samples are predominantly cBN. The structural quality of the cBN films is optimized in a narrow range of voltages near this threshold. We discuss the important role of energetic ions in the formation of cBN in light of recent theoretical findings.
Nucleation and Step Dynamics in SIC Epitaxial Growth
Authors: Atsunami Hiroyuki , Kimoto Tsunenobu
Published: April 2011

Recent progress in horaoepitaxial growth of 6H-SiC by stop-controlled epitaxy utilizing off-angle substrates is discussed in detail. Features of step-controlled epitaxy and its growth mechanism are described based on experimental results. The growth mode on off-angle substrates is explained by a stagnant layer model. The diffusion length of adatoms on a surface is calculated using a simple surface diffusion model. The critical conditions of two-dimensional nucleation and step-flow growth are predicted based on theoretical calculation and experimental results. Microscopic surface processes such as nucleation and step motion are made clear by observing the grown layer after short-time growth.
Growth of Epitaxial 2H-silicon Carbide by Pulsed Laser Deposition
Authors: Stan Mark A. , Patton Martin O. , Vithana Hemasiri K. M. , Johnson David L. , Warner Joseph D. , Piltch Nancy D. , Yang Jinwei , Pirouz Pirouz
Published: April 2011

Silicon carbide films have been grown on 6H-SiC (0001) and Si (001) wafers by laser ablation using an excimer laser. The films were deposited at heater plate temperatures between 970° C to 1270° C. Film composition, morphology and polytypism were determined by Auger electron spectroscopy, atomic force microscopy and high resolution transmission electron microscopy (TEM). In the course of these experiments growth of 2H-SiC on 6H-SiC was observed at the highest heater plate temperatures. Cross-sectional TEM images clearly show the symmetry of a film grown at 1270° C as c-axis oriented 2H-SiC containing columnar grains with average diameter of 20 nm and length of 100 nm.
Dynamics of the Nitrogen Bound Excitons in 6H and 3C SiC
Authors: Bergman J. P. , Harris C. I. , Kordina O. , Henry A. , Janzén E.
Published: April 2011

We have measured the photoluminescence decay time of the bound excitons at the neutral nitrogen donors in the 6H and 3C polytypes of SiC. At 2K the decay times are 8.0 ns, 1.8 ns and 1.5 ns, for the P, R and S bound excitons in 6H SiC. For the nitrogen exciton in 3C, we find a decay time of 160 ns. These values are faster than previously reported for shallow donors in other indirect bandgap materials such as Si or GaP. Each of the observed decay times is found to be independent of the doping level in the sample, is temperature independent at low temperatures but decrease when the bound excitons are thermally ionised. The decay time related to different donor levels in 6H exhibits a strong dependence on the donor binding energy. We suggest that the dominant mechanism responsible for the observed decay time is a phonon-less Auger process. In high-purity 6H samples we have also measured the free exciton decay time at low temperatures to be 12 ns.