bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of TCO/a-Si:C:H Interface Defect States on p-i-n a-Si:H Solar Cell Performance
Authors: Smole Franc , Topič Marko
Published: April 2011

To explain realistic circumstances with regard to energy band profiles at the TCO/a-Si:C:H heterojunction, the ASPIN computer simulation has been used. Numerical calculations indicate that the increased interface defect densities result in a steep potential drop inside the interface region, while the rest of the work function difference extends into the p-layer. The detrimental effect of a-Si:C:H partial oxidation has been simulated by additionally increased density of states at a-Si:C:H surface, and its influence on the potential barrier has been analyzed. The impact of both TCO/a-Si:C:H interface states and a-Si:C:H surface states on the photoelectric properties of p-i-n a-Si:H solar cell is discussed, and a possible improvement of Voc is envisaged.
VHF Coaxial Helix Plasma Source for a-Si:H
Authors: Stephan U. , Kuske J. , Schade K.
Published: April 2011

Coaxial helical resonators are used in the field of high frequency engineering for narrow band selection of signals from about 10 MHz to 500 MHz (VHF and low UHF range) [1, 2]. Their favorable geometric construction suggests their utilization as plasma source for etching and deposition of a-Si:H at frequencies between 30 and 200 MHz - an additional, but still unusual application.

The resonator consists of a cylindric outer conductor, which is closed on one side by a bottom plate, and a rotationally symmetrical inner conductor of spiral form (helix) Measuring γ/4. One end of the helix is grounded to the bottom plate (short circuit), the other end is open (open circuit). Power supply is feasible either galvanically by connecting to the helix or inductively by means of a coupling coil. Applying a suitable coupling factor allows operation at resonance without matchbox. The plasma is generated within the resonator and above its open end, which can be adjusted to special conditions of application with the aid of several grids. In contrast to the source commonly used, the coaxial helix plasma source has proved advantageous with regard to simple design, easy mounting, Minimal outer electrical equipment, no dependence of generated plasma on substrate measures, good breakdown and discharge behavior, low supply voltage (some tens of volts), high power density, and, due to a discharge occurring without filament, also to life durability and no thermally generated particle emission. The application of very high frequencies leads to a low ion bombardment intensity of a-Si:H, and thus additional magnetic fields are not necessary.
A Large Area, High-Resolution a-Si:H Array for X-Ray Imaging
Authors: Antonuk L.E. , El-Mohri Y. , Huang W. , Siewerdsen J. , Yorkston J. , Street R.A.
Published: April 2011

The development of a large area, high-resolution, a-Si:H x-ray imager is reported. The array has 1536×1920 pixels, a pixel pitch of 127μm, and an area of 19.5×24.4 cm2. Tne array is tailored to the high frame rate and high spatial resolution requirements of diagnostic x-ray imaging. The design of this array is presented and examples of x-ray images are illustrated. Initial Measurements of the sensor capacitance and pixel time constant properties are in good agreement with theoretical expectations. These results indicate that high-resolution arrays of this construction are capable of providing fluoroscopic images at rates of at least 30 frames per second.
Technology and Performance of TFA (

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SIC-Sensors
Authors: Fischer H. , Schulte J. , Rieve P. , Böhm M.
Published: April 2011

A TFA image sensor consists of an amorphous silicon based multilayer structure on top of a crystalline ASIC. The Multilayer acts as the optical detector, whereas the ASIC performs analog or digital signal processing for each individual pixel. Depending on the operation Mode, the dynamic range of the detector exceeds the performance of conventional CCDs by far. Pixel electronics which is adapted to the requirements of the detector can thereby maximize the dynamic range of the complete sensor array. Crosstalk among adjacent pixels can be eliminated by technological or electronic Means.
“Thick” a-Si:H P-i-n diodes, produced by the VHF-GD process: spectral response for visible/infrared light and current transients
Authors: Chabloz P. , Keppner H. , Fischer D. , Wyrsch N. , Shah A.
Published: April 2011

With the possibility to deposit thick amorphous silicon layers, applications like particle- or X-ray detectors can be envisaged. The present paper describes new results obtained with a series of thick p-i-n diodes produced by VHF-GD (Very High Frequency Glow-Discharge). The goal is to obtain the maximum output signal for given detection conditions (reverse voltage, generation rate,…). The problem of the collection of the electrons and holes is discussed in this paper, in relation with the distribution of the electric field. As is well known, trapped charges screen the inner part of the intrinsic layer of the detector. Due to this effect, even under strong reverse bias-voltage, a complete depletion of the whole intrinsic layer can in general not be obtained for thick diodes; however, even if the diode is not completely depleted, the signal increases with increasing diode thickness until a maximum is reached for the signal, and then it decreases again. Finally, different rise-times of the transient current (current after a jump in bias voltage is applied) have been Measured. Differing between one diode and the other, the rise-time of the transient current was found to vary between 0.1 seconds and 1 hour; a clear dependence on the deposition conditions is observed. Long rise-times are major difficulty to be removed, because most of the applications like imaging require short response time of the detector.
Improvement of film Quality of A-Si:H Deposited by Photo-CVD using SiH2Cl2
Authors: Oshima T. , Yamaguchi K. , Yamada A. , Konagai M. , Takahashi K.
Published: April 2011

Hydrogenated Amorphous silicon films (a-Si:H) were prepared by mercury sensitized photo-CVD using SiH4 and SiH2Cl2 gas mixture. The effects of chlorine (Cl) on the electrical, optical and structural properties of the a-Si:H films were investigated. It was found that a small addition of SiH2Cl2 to the deposition system increases the photo-sensitivity, decreases the defect density, and reduces the light induced degradation of a-Si:H films. At a large addition of SiH2Cl2, however, the CI incorporation into the films was observed, resulting in the deterioration of the film properties. The electrical and optical properties were successfully improved by the H2 dilution when the films were deposited with a large addition of SiH2Cl2.
The Evolution of Chem-Mechanical Planarization: From Aberrant to Prosaic
Authors: Renteln Peter , Coniff John
Published: April 2011

Chem-Mechanical Planarization (CMP) is a rapidly growing technology in the semiconductor fabrication repertoire. Initially offering an answer to the need for truly global planarization brought about by optical steppers' ever decreasing Depth of Focus (DOF), CMP may come to stay more for its impressive ability to actually decrease defect density, as well as potentially reduce the contact resistance of Tungsten plugs. But even the use of CMP at this post-etchback step first requires a manufacturable oxide planarization CMP technology, the single most difficult challenge of all the different CMP applications. In this presentation, We will describe various remaining mysteries of some of the more fundamental questions involving the process in addition to some present manufacturing issues.
Consumables for the Chemical Mechanical Polishing (Cmp) of Dielectrics and Conductors
Authors: Jairath Rahul , Desai Mukesh , Stell Matt , Tolles Robert , Scherber-Brewer Debra
Published: April 2011

Chemical mechanical polishing (CMP) is rapidly becoming the process of choice for planarizing dielectrics in very large scale integrated circuits. In addition, it is being used at an increasing rate in the removal of metals in order to define conducting levels. In the case of dielectric CMP, planarization ability is dictated by the mechanical aspects of polishing such as pad rigidity, polishing pressure and speed of the polishing platen, while inherent removal rate of the dielectric material is generally a function of the polishing chemistry. Polishing rate of both, dielectric and metallic films can be significantly increased by changing the nature of the dispersed abrasive in the slurry and that of the dispersing agent. However, such changes have profound implications to the surface quality, planarity, and cleaning of the polished surface. In addition, the polishing pad plays an important role in manufacturability of metal CMP processes. This work reviews the chemistry of polishing slurries containing silica, ceria and alumina abrasives for dielectric and metal CMP. Also, the contribution of the polishing pad to CMP processes is explained. The need for balancing the chemical and mechanical aspects of polishing in order to achieve overall planarization and pattern definition is demonstrated.
Surface Layer Formation During the Chemical Mechanical Polishing of Copper Thin Films
Authors: Steigerwald J.M. , Murarka S.P. , Duquette D.J. , Gutmann R.J.
Published: April 2011

Three chemical processes that occur during the chemical mechanical polishing (CMP) of copper are described in terms of their effect on surface planarity, polish rate, and corrosion resistance of the polished copper. These processes are surface layer formation, dissolution of mechanically abraded copper, and chemical acceleration of the polish rate. The role of these processes is demonstrated with two slurry formulations used in the CMP of copper at Rensselaer.
The Surface Damage in SiO2 Caused by Chemical Mechanical Polishing on Ic-60 Pads
Authors: Murarka Shyam , Ko Sen-Hou , Tomozawa Minoru , Ding Pei-Jun , Lanford William A.
Published: April 2011

Chemical Mechanical polishing (CMP) is a useful technique for achieving global planarization in the ICs. The CMP of oxide has been used and studied for decades. Only recently the technique has been employed for planarizing the interlayer dielectric (ILD) on the silicon devices circuits. The effect of such polishing on the performance of the ILD has been the concern. This paper examines the attempts on defining the damage caused by CMP and its effect on the electrical properties after polished SiO2 wafers. In this investigation the PECVD and thermal oxide films were polished in the colloidal silica slurry on IC 60 pad. The polished oxide were then studied using I-V and nuclear reaction technique. The results show a surface damage which extends to about 800 Å in the polished oxide. The changes occurring in the concentration of hydrogenous species at the surface of SiO2 as determined by nuclear reaction technique will also be presented. It is shown that due to CMP as-deposited CVD SiO2 films loose water from surface regions whereas well annealed or dry oxides gain water at the surface. The results will be discussed and mechanisms will be presented to explain electrical results.
Growth Kinetics and Materials Properties of Cu5Si
Authors: Hymes S. , Murarka S.P. , Ding PJ. , Wang W. , Lanford W.A.
Published: April 2011

Thin copper films have been passivated by exposure to a dilute silane mixture (2% SiH4/Ar) at temperatures in the range of 225 - 375 °C. Previous XRD characterization indicates the surface layer to be Cu5Si[l]. Subsequently, the growth kinetics were examined by sheet resistance (Rs), RBS and step height measurements. Two distinct growth regimes are observed. The flow rate and time dependencies of the low temperature growth indicate parabolic solid state diffusion limited growth. The corresponding activation energy is 0.7 eV. A mass transport limitation is evidenced at higher temperatures. In addition, the biaxial stress and adhesion responses have been observed using the substrate curvature technique and scotch tape peel tests, respectively. A biaxial modulus (Eb) of 2.9x1011 Pa and coefficient of thermal expansion (CTE) of 8.6xl0-6 /°C have been determined from stress temperature cycling on Si and a-quartz substrates.
Room Temperature Oxidation of Silicon Catalyzed by Cu3Si
Authors: Liu C. S. , Chen L. J.
Published: April 2011

The dependence of room temperature oxidation of silicon catalyzed by Cu3Si on silicide thickness, silicide grain size and the substrate orientation has been investigated by transmission electron microscopy and x—ray diffractometry.

The extent of oxidation was found to depend critically on the thickness of starting Cu3Si film. The oxidation was found to be more restricted on (lll)Si than that of (001)Si samples. The thickness of SiO2 layer was found to decrease with the average grain size of the starting Cu3Si layer. HRTEM revealed that the oxidation is initiated at the grain boundaries. Oxide film as thick as 4.5 μm was grown at room temperature over a period of two weeks in (001) samples. The growth of thick oxide film was achieved by minimizing the grain size of Cu3Si through a reaction between Cu and an intermediate amorphous silicon layer at 200 °C.
Interconnection Technology for Modern Logic Devices; an Exercise in System Engineering to Assure Manufacturability
Authors: Siegle William T.
Published: April 2011

The history of the semiconductor IC has often been dominated by the issues associated with transistor engineering. In recent years however, it has become clear that successful mastery of advanced logic devices depends not only on transistor engineering, but also on the ability to engineer and manufacture multiple level metallization systems to form the interconnect structure of modern and dense logic ICs.
The Stability of Reactively Sputtered WNx Thin Films on III-V Semiconductors
Authors: Pang Zhengda , Boumerzoug Mohamed , Mascher Peter , Simmons John G.
Published: April 2011

WNX thin films were deposited at room temperature on (100) n-type GaAs substrates by rf reactive sputtering of a high purity W target in Ar/N2 gas mixtures. Deposition parameters such as the rf power, the ratio of gas flows, and the total pressure can be optimized for the preparation of uniform and low resistivity WNX thin films. The W:N ratio in the as-deposited WNX films was determined using Auger spectroscopy and the morphology was examined by scanning electron microscopy (SEM).

The WNx/GaAs samples were subjected to rapid thermal annealing in an N2 atmosphere at temperatures between 400°C and 800°C. The thermal stability of these structures was examined using electrical measurements and Auger profiling . The results are correlated with the properties of as-deposited films and the influence of various processing parameters will be discussed.
The Effects of Interfacial Reactions in the Formation of Ohmic Contacts to GaAs
Authors: Fischer Verlyn , Viljoen P.E. , Ristolainen E. , Holloway P.H. , Lampert W.V. , Haas T.W. , Woodall J.M.
Published: April 2011

The effect of heat treatments between 400°C and 500°C on electrical contacts of In, Ga, Pb, and AU to n- or p-GaAs, and Ni to n-GaAs have been studied using current-voltage (I-V), Auger electron spectroscopy and scanning electron microscopy. Ohmic contacts were formed between In and GaAs upon heating due to formation of an InGaAs surface layer with low interfacial transport barriers. The contacts between Ga or Pb and n- and p-GaAs remained rectifying due to a lack of interfacial reaction. Films of Au reacted with both n-and p-type GaAs resulting in rectangular "pits". This led to ohmic contacts only on n-type substrates due to segregation of the Si dopants to the surface of the decomposed GaAs "pits". Dopant segregation did not occur when Au reacted with p-GaAs or Ni reacted with n-GaAs, thus these contacts remained rectifying at lower doping densities (4 x 1017 cm-3).
Buried Schottky Contacts in Patterned Cobalt Silicide Layers in Silicon Using Wafer Bonding
Authors: ThungströM GöRan , FröJdh Christer , Petersson C. Sture
Published: April 2011

We have fabricated buried cobaltdisilicide schottky contacts in silicon using wafer bonding with a patterned metal layer. The schottky contacts show good rectifying behaviour with ideality factors of 1.02-1.09 and low reverse leakage currents.
Stress-Voiding and Electromigration in Multilevel Interconnect Metallizations
Authors: Korhonen M.A. , Brown D.D. , Li C.-Y. , Rathore H.S.
Published: April 2011

Stress-voiding or stress migration (SM), and electromigration (EM) are urgent problems in ULSI microcircuits with features in the submicron range. Severe stress-voiding arises in multilevel metallizations because of the high constraint offered by the refractory metal layers, the ceramic insulation, and the rigid contact and via structures which prevent plastic relaxation of the thermally induced stresses. Also, W-plugs and/or refractory barrier layers block entirely the EM flux, resulting in an enhanced probability of EM damage. We review the physical bases of a recently introduced unified SM and EM model [1,2]. We apply the model to an interconnect line confined by vias at both ends and derive equations which explicitly show the effects of external conditions and microstructural parameters on the evolution of SM and EM damage. Particularly we analyze the effects of Cu depletion on void growth rate at vias. We also show how the shifts in the line resistance are related to void growth. Finally we demonstrate that the model predictions compare well with the recently published experimental EM data.
Surface Spectroscopic Studies of the Deposition Mechanisms of TinX Films from Organometallic Precursors
Authors: Chen P. J. , Truong C. M. , Corneille J. S. , Oh W. S. , Goodman D. W.
Published: April 2011

The adsorption and thermal behavior of tetrakis-(dimethylamido)-titaniurn (TDMAT), Ti[NMe2]4, were investigated by surface spectroscopic techniques in the temperature range 100-1100K. A metallic Ti substrate readily dissociates TDMAT even below 300 K, producing a carbon-rich interface. When the substrate is exposed to a continuous flux of TDMAT at growth temperatures (550-700K), deposition of carbon-rich TiCxNy films readily occurs with a high precursor reactive sticking coefficient. With the addition of sufficient NH3 flux, we demonstrate the existence of a direct surface-reaction-driven deposition mechanism which involves reaction(s) between adsorbed TDMAT and NHX species on the film surface and thus leads to growth of substantially cleaner TiNx films. This growth mechanism dominates at low pressures (≤10-4Torr) where gas-phase reaction between the precursor gases becomes insignificant.
Electronic Structure of Rare-Earth Pnictides for Metallization of Semiconductors
Authors: Petukhov A. G. , Lambrecht W. R. L. , Segall B.
Published: April 2011

The results of first-principles calculations of the electronic band structures, equilibrium lattice constants, cohesive energies, bulk moduli, and magnetic moments are presented for the rare-earth pnictides with the rocksalt structure and chemical formula RX, where R = Gd, Er and X = N, P, As. Some of these materials are semimetals and are suitable for metallization of III-V semiconductors. The results for the lattice constants are in good agreement with experimental data. For ErAs, which is closely lattice-matched to GaAs, the calculated magnetic exchange splittings, electron and hole concentrations, Fermi surface cross-sectional areas and cyclotron masses are found to be in satisfactory agreement with the available experimental data.
Electron and Photon Irradiation Effects in Metal/Amorphous Chalcogenide Bilayers
Authors: Ploessl Andreas , Dhanjal B.J. , Fitzgerald A.G. , Gibson R.A.G. , Gillies A.D.
Published: April 2011

Thin film bilayers of metal and amorphous chalcogenides have been prepared by evaporation. The metals were silver and zinc, while the chalcogenides were P2Se3 and arsenic sulphides, mainly As2S3. The metals dissolved into the chalcogenide films when illuminated with ultraviolet light or when irradiated with an electron beam. The changes in composition and chemical bonding which were caused by this irradiation, were investigated by x-ray photoelectron spectroscopy. The concomitant structural changes have been investigated by electron diffraction.

After the metal and chalcogenide had intermixed, either due to photon or electron irradiation, the layers became sensitive to an electron beam; this sensitivity depended on the composition of the chalcogenide. Energy-dispersive x-ray microanalysis showed that the electron beam rapidly, but reversibly, depleted the irradiated areas of the dissolved metal. Very fine patterns, of better than half-micron resolution, could be written. By exposing a pure arsenic sulphide film through a shadow mask to ultraviolet light, zinc could be deposited selectively to form fine patterns. Plasma processing developed either kind of pattern reliably, thus rendering the material a dry inorganic resist for photo- and electron-beam-lithography with potential benefits in particular for GaAs.
Designing and Building Reliability Into VLSI Interconnect Systems
Authors: Graas Carole D. , Hong Qi-Zhong , L Ting Larry
Published: April 2011

The optimization of electromigration (EM) and stress-induced voiding (SV) properties of advanced interconnects impacts many critical system design parameters. In particular, the choice of materials and manufacturing processes must be carefully planned during the early phases of product development. In layered metallizations, both the barrier and capping layers design can affect electromigration resistance and stress-relaxation behavior, while electrical performance often constitutes a trade-off. This is shown specifically in a study of titanium diffusion into Al-Cu from TiN barrier layers, and in initial stress-relaxation tests characterizing the effect of Ti addition in the capping layer. The development of advanced characterization techniques supports the trial-and-error experimental optimization process, but models predicting EM and SV reliability are needed and should include complex sets of microstructural and design parameters.
Interfacial Reactions Between Sputtered Cr-Sio2 Cermet Thin Film and Polyimide.
Authors: Yamazaki Tetsuya , Watanabe Takayoshi , Ogata Kiyoshi , Narizuka Yasunori , Inoue. Takashi
Published: April 2011

Interfacial chemical bonding states between polyimides (PI) and sputter coated Cr-SiO2 thin film have been investigated mainly by XPS to obtain a reliability basis for thin film resistor application of Cr-SiO2.We tried to leave different level of etch residue by applying two etchants of different etching power, then analyzed the etched surfaces by XPS, TEM and EXAFS. It proved that at first Cr in the sputtered Cr-SiO2 reacts with oxygen atoms which were introduced during O2 plasma treatment of the PI surface and also with original carbonyl oxygen of the PI to offer Cr-O-C bond at the Cr-SiO2/PI interface. This was concluded from the attenuation of Cls peak intensity corresponding to the carbonyl group. Then after thermal annealing, Cr extracted most of the interface oxygen to give a Cr2O3 layer of a discrete thickness. These phenomena were supported by TEM and SR-EXAFS as well.
Electronic Process of Joining Metal and Ceramic by “Surface Activated Bonding”
Authors: Ohuchi Fumio S. , Hu Xiao , Suga Tadatomo
Published: April 2011

Residual thermal stresses due to thermal expansion mismatch at dissimilar material interfaces can cause serious problems in the current bonding technology, yet this is an unavoidable consequence as long as the interfaces are fabricated at elevated temperatures. An innovative solution to this problem is that the materials be bonded without applying heat, i.e., bonding at room temperature. A new technique to join two dissimilar materials, “Surface Activated Bonding (SAB)”, has been recently developed. The basic concept underlying this technique is that two atomically clean solid surfaces under contact develop a strong adhesive force. We have recently demonstrated that this method works on various materials systems, including Al2O3, A1N, SiC and Si3N4, on which polycrystalline aluminum is bonded at room temperature. In this paper, we will describe: What is “Surface Activated Bonding”? What are the electronic and chemical driving factors for bonding? Complementary experimental and theoretical studies in elucidating the fundamental aspects of the SAB will be described.
A Multilayer Interconnect Process for 0.5um Logic Technology
Authors: Kim Donghyun , Oh H.S. , Lee K.Y. , Kim Y.S. , Kim B.S. , Kim B.G.
Published: April 2011

A submicron triple metal process for 0.5um logic CMOS is described, focusing on key process steps such as the dielectric planarization and metallization. The main emphasis has been placed on development of arcomplicated planarization process utilizing SOG (Spin on Glass) etchback. In this paper, we report process data of triple metal technology which uses aluminum alloy for interconnects and P-TEOS (Plasma Tetra Ethyl Ortho Silicate) with siloxane SOG and etchback process for planarization.
Diamond Field-Effect Transistors
Authors: Dreifus David L. , Tessmer Alison J. , Holmes Joseph S. , Kao Chien-Teh , Malta Dean M. , Plano Linda S. , Stoner Brian R.
Published: April 2011

Metal-oxide-semiconductor field-effect transistors (FETs) have been fabricated using B-doped diamond thin films deposited on polycrystalline, (100) highly-oriented, and single crystal diamond insulating substrates. Diamond films were grown using a microwave plasma chemical vapor deposition technique. Various electrical and materials characterization techniques were employed to confirm that the films exhibited properties suitable for FET fabrication. Devices with gate lengths and widths of 2 μm and 314 μm respectively, were processed using standard photolithography. Silicon dioxide was used as the gate dielectric. Current-voltage characteristics of these devices have been measured during variable temperature cycling in air. Devices fabricated on the randomly oriented polycrystalline diamond substrates have been operated to 285°C. Field-effect transistors fabricated using the highly-oriented diamond substrates have been characterized to 400°C. Single crystal diamond devices exhibited saturation and pinch-off of the channel current at temperatures up to 500°C. These devices have been biased in amplifier circuit configurations that have been characterized from 20 Hz to 1 MHz. Single crystal FETs exhibited voltage gain over an extended temperature range. Transconductances as large as 1.7 mS/mm have been observed. The electronic properties, fabrication technologies, and performance of devices fabricated on the three diamond substrate materials will be discussed and compared.
Excimer Laser Planarization of Diamond Films
Authors: Lee Dong-Gu , Harkness S. D. , Singh Rajiv K.
Published: April 2011

The planarization of rough polycrystalline diamond films synthesized by DC arc discharge plasma jet CVD was attempted using KrF excimer laser pulses. The effects of laser incidence angle and reaction gases (ozone and oxygen) on etching rate were studied. The temperature change of diamond and graphite with different laser fluences was calculated by computer simulation to explain the etching behavior of diamond films. The calculated threshold energy density for etching of pure crystalline diamond was about 1.7 J/cm2. However, the threshold energy density was affected by the angle of laser incidence. Preferential etching of a particular crystallographic plane was observed through scanning electron microscopy. The etching rate of diamond with ozone was lower than that with oxygen. Also, the etching rate of diamond films at normal laser incidence was lower than that of films tilted at 45° for laser fluences above 2.3 J/cm2. When the angle of incidence was 80° to the diamond surface normal, the peak-to-valley surface roughness was significantly reduced, from 30 μm to 0.5μm.
Electronic and Optoelectronic Devices Based on GaN-AIGaN Heterostructures
Authors: Asif Khan M. , Kuznia J. N. , Krishnankutty S. , Skogman R. A. , Olson D. T. , Schaff W. J. , Burm J. W. , Shur M. S. , George T.
Published: April 2011

Availability of optoelectronic components operating in the U V-Visible part of the spectrum opens several exciting and important system applications. Solid state ultraviolet and blue-green lasers can increase the optical data storage density of CDROM/WORM and magneto-optical disks by a factor of four. They are also ideally suited for environmental pollutant identification and monitoring. On the other hand, solid state ultraviolet detectors that do not respond to visible or IR radiation are highly desirable for various commercial systems. These include medical imaging, industrial boiler systems, fire/flame safeguard systems around oil and gas installations and several military applications. A key requirement for these ultraviolet laser and sensor devices is the availability of a semiconductor material system with high quality controlled doping and fabrication technology.

AlxGa1−xN and InxGa1−xN for which the direct bandgap can be tailored from the visible to the deep UV is such a material system. Ours and several other research groups (nationally and internationally) have been developing AlxGa1−xN materials and processing technologies over the past several years. Recently, by employing innovative approaches, significant advances have been made in heteroepitaxy of AlxGa1−xN on sapphire substrates. Also, controlled n and p-type doping has been achieved. Several high performance devices that form the basis of exciting future research have been demonstrated. These include high responsivity visible blind ultraviolet sensors, basic transistor structures and high power blue light emitting diodes. These pave the way for future research leading to exciting products such as blue-green lasers and UV-imaging arrays. The demonstrated transistor structures are foundation for building AlxGa1−xN -GaN based high power, high frequency and high temperature electronic components. In this paper, we will summarize some of our recent work and reflect on the potential and the issues in AlxGa1−xN-InxGa1−xN based device development.
Amortization and Recrystallization of 6H-SiC by ion Beam Irradiation
Authors: Heera V. , Kögler R. , Skorupa W. , Stoemenos J.
Published: April 2011

The evolution of the damage in the near surface region of single crystalline 6H-SiC generated by 200 keV Ge+ ion implantation at room temperature (RT) was investigated by Rutherford backscattering spectroscopy/chanelling (RBS/C). The threshold dose for amorphization was found to be about 3 · 1014 cm-2, Amorphous surface layers produced with Ge+ ion doses above the threshold were partly annealed by 300 keV Si+ ion beam induced epitaxial crystallization (IBIEC) at a relatively low temperature of 480°C For comparison, temperatures of at least 1450°C are necessary to recrystallize amorphous SiC layers without assisting ion irradiation. The structure and quality of both the amorphous and recrystallized layers were characterized by cross-section transmission electron microscopy (XTEM). Density changes of SiC due to amorphization were measured by step height measurements.
UV-Sensitive Metal-Semiconductor Photodiodes on 6H-SIC.
Authors: Fröjdh Christer , Thungström Göran , Nilsson Hans-Erik , Sture Petersson C.
Published: April 2011

Schottky diodes on Silicon Carbide (SiC) are of interest for many applications because of the relatively simple fabrication process. In this work we have fabricated Schottky diodes by evaporation of Ti on 6H-SiC and measured their electrical and optical properties. Most of the diodes show good rectifying behaviour with low reverse current and an ideality factor below 1.20. The photoresponse of the diodes has been measured in the range 200 – 400 nm. The peak sensitivity was found to be at 270 nm.
Metallization of GaN Thin Films Prepared by Ion Beam Assisted Molecular Beam Epitaxy
Authors: Chan J. S. , Fu T. C. , Cheung N. W. , Newman N. , Liu X. , Ross J. T. , Rubin M. D. , Chu P.
Published: April 2011

Gallium nitride has generated much interest due to its ability to emit light in the blue to UV range [1]. We have investigated the ohmic contact properties of various metals evaporated onto highly auto-doped n-type GaN thin films which were grown on basal sapphire substrates by ion-assisted molecular beam epitaxy (IAMBE). Electrical measurements of transmission line structures with the metals In, InSn and AuGeNi revealed a wide range of contact resistivity (10∼2 to 10-6 Ω-cm2) which changed with annealing.
Solid-Phase Reaction of Tungsten Thin Films with Polycrystalline Diamond
Authors: Bachli A. , Chen J. S. , Ruiz R. P. , Nicolet M-A.
Published: April 2011

The thermally induced solid-phase reaction of 135 nm thick sputter-deposited W films with polycrystalline CVD-grown diamond substrates is investigated. The samples are annealed in vacuum (5×10/-7 torr) at temperatures between 700 °C and 1100 °C for 1 hour and examined by 2 MeV 4He++ backscattering spectrometry, x-ray diffraction, and scanning electron microscopy.

The as-deposited W films contain roughly 5 at.% oxygen. After annealing the samples at 800 °C this oxygen concentration falls below the detection limit of less than 1 %. Incipient W2C phase formation occurs during annealing at 900 °C. The final state, the WC phase, is reached after annealing at 1100 °C.
Deposition of Epitaxially Oriented Films of Cubic SiC on Silicon by Laser Ablation of Elemental Targets.
Authors: Rimai L. , Ager R. , Weber W. H. , Hangas J. , Poindexter B. D.
Published: April 2011

Silicon carbide films are grown epitaxially on crystalline silicon substrates heated above 1000 °C, by laser ablation of pure carbon targets to thicknesses between 300 and 400 nm. These films grow on top of the silicon substrate from the carbon in the ablation plume and from the silicon of the substrate. By using a method of alternate ablation of a pure carbon and a pure silicon target, similar epitaxial films can be grown to thicknesses in excess of 1 μm with part of the silicon being supplied by the ablation plume of the silicon target.
Stacking Fault Energy Calculations in 6H- and 15R-SiC
Authors: Chien F. R. , Nutt S. R. , Yoo W. S.
Published: April 2011

As-grown SiC single crystals and as-deposited SiC epilayers often exhibit stacking faults. The most probable fault configurations that occur in 6H- or 15R-SiC crystals are deduced from calculations of the stacking fault energies using a modified Ising model with the Ising parameters taken from earlier ab initio calculations. In this study, experimental TEM observations reveal stacking fault configurations in 6H- and 15R-SiC, and the observed configurations are compared with calculated stacking fault energies.
XPS and Sims Studies of CVD-GROWN Cubic SiC Films on Si(100)
Authors: Wee A. T. S. , Feng Z. C. , Hng H. H. , Tan K. L. , Tin C. C. , Hu R. , Coston R.
Published: April 2011

A series of CVD-grown 3C-SiC/Si(100) films of different growth times, and hence film thicknesses, are studied by X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS). XPS showed that the surfaces of the samples consist of Si oxides (SiO2 and SiOx where x < 2) and unreacted C.H. Unreacted elemental Si is also present and its amount decreases with increasing growth time. This surface overlayer is further investigated by changing the photoelectron take-off angle and from chemical etching studies. Compositional variations of the SiC films are also studied using SIMS.
Reactive Magnetron Sputtering of Silicon in AR + CH4: Identity and Energy of the Slc Growth Species
Authors: Fitzner M. P. , Abelson J. R.
Published: April 2011

Double-modulation mass spectrometry is used to analyze the identity and energy distribution of the particle flux during low-temperature growth of Si1−xCx by reactive magnetron sputtering of a silicon target in 3 mTorr argon and 0 – 0.35 mTorr methane. The ion fluxes, methane consumption, film deposition rate, and film composition are determined as a function of the methane partial pressure at fixed target current. Argon, silicon, carbon and hydrocarbon ions are detected at the substrate position. The argon and hydrocarbon ions have a narrow energy distribution consistent with the plasma potential. The silicon and carbon ions have a broad energy spread, consistent with that of sputtered neutrals which are post-ionized by the plasma. The film composition (C/Si) varies in the same manner as the arrival ratio of (C+/Si+) ions, but does not correlate well with the arrival ratio of (ΣCHX+/Si+) ions or the methane consumption rate. We conclude that the main source of carbon in Si1−xCx films is the sputtering of C atoms from the Si target surface.
Surface Fermi Level Position of Diamond Treated with Plasma
Authors: Sugino Takashi , Sakamoto Yoshifumi , Furukawa Atsuhiko , shirafuji Junji
Published: April 2011

The surface Fermi level position of undoped epitaxial diamond layers is estimated from contact potential difference between Au reference and diamond measured by Kelvin probe method. The surface Fermi level position of the as-grown layer is located at the energy of 0.75 eV above the valence band edge. O2 plasma treatment leads to an upward shift of the surface Fermi level position to an energy of 1.89 eV from the valence band edge. The surface Fermi level is located at an energy of 0.97 eV above the valence band edge after H2 plasma treatment. Reversible change in the surface Fermi level position is found between O2 and H2plasma treatments. A change in the band bending is observed at the surface of polycrystalline diamond films treated with various ways by X-ray photoclcctron spectroscopy (XPS) analysis. A variation in the current-voltage characteristics of epitaxial and polycrystalline diamonds treated with O2 and H2 plasmas can be qualitatively explained in terms of a change in the band bending due to the shift of the surface Fermi level position.
GaN On 6H-SiC – Structural And Optical Properties
Authors: Wetzel C. , Volm D. , Meyer B. K. , Pressel K. , Nilsson S. , Mokhov E. N. , Baranov P. G.
Published: April 2011

Recent progress in the growth of high quality 6H-SiC single crystals has led to an ideal substrate material for GaN epitaxial films. Nearly matching lattice constants of wurzite GaN to 6H-SiC in the hexagonal plane can reduce strain effects at the interface. We employed the sublimation sandwich method to grow single crystal layers at reasonable growth rates with free carrier concentrations of 2×1017 cm-3. Very sharp x-ray diffraction peaks of the GaN (0002) plane are obtained indicating the high quality of this system (Δ(2θ) < 0.1 degrees). These findings are directly reflected in the optical properties. The photoluminescence is dominated by a single sharp exciton line, impurity related donor acceptor transitions are seen with very weak intensities. However, at lower energies the internal luminescence transitions of the 3d transition metal ions Fe and V are observable. The incorporation of Fe is confirmed by electron paramagnetic resonance.
Growth and Characterization of GaN on Si(111)
Authors: Ohtani A. , Stevens K. S. , Beresford R.
Published: April 2011

Wurtzite GaN films on AlN buffer layers were grown on Si (111) by electron cyclotron resonance microwave plasma assisted MBE (ECR-MBE). High resolution x-ray diffraction studies indicate that the mosaic disorder decreases with increasing growth temperature. The grain size is related to the growth temperature. The best (0002) diffraction peak full width at half maximum was 22 min. for a film 1.7 μm thick. Prominent exciton luminescence is observed at 3.46 eV at 10 K.

The plasma I-V characteristics were measured with a Langmuir probe near the growth position. The nitrogen ion density has been extracted from the data, and is a strong function of the N2 flow rate, the microwave power and the aperture size of the ECR source. The crystal quality of AlN is strongly affected by the plasma conditions.
Effect of Aluminum Nitride Buffer Layer Temperature on Gallium Nitride Grown by OMVPE
Authors: Rowland L. B. , Doverspike K. , Gaskill D. K. , Freitas J. A.
Published: April 2011

Gallium nitride layers were grown by organometallic vapor phase epitaxy on AlN buffer layers deposited in the range of 450–650°C. The GaN growth conditions were kept constant so that changes in film properties were due only to changes in the buffer layer growth temperature. A monotonie improvement in relative crystallinity as measured by double-crystal X-ray diffraction corresponded with a decrease in buffer layer growth temperature. Improvements in GaN electron transport at 300 and 77 K were also observed with decreasing AlN buffer layer temperature. Photoluminescence spectra for the lowest temperatures studied were dominated by sharp excitonic emission, with some broadening of the exciton linewidth observed as the buffer layer growth temperature was increased. The full width at half maximum of the excitonic emission was 2.7 meV for GaN grown on a 450°C buffer layer. These results indicate that minimizing AlN buffer layer temperature results in improvements in GaN film quality.
Electron Spin Resonance Studies of Donors in Bulk and thin Film β3-SiC
Authors: Carlos W. E. , Freitas J. A. , Pazik J. C. , Ivanova L. M. , Altaiskit YU.M. , Zuev V. L.
Published: April 2011

We have investigated the electron spin resonance of donors in bulk and thin film β-SiC at T = 10K to 40K. In both, two donor spectra are resolved; a three line spectrum associated with nitrogen on the carbon site and a broader line of unidentified origin. The observable hyperfine splitting decreases with increasing temperature due to a small valley-orbit splitting, in qualitative agreement with photoluminescence results. The lineshape has a significant lorentzian character even at the lowest temperatures, indicating exchange interactions with residual conduction electrons, possibly from a shallower donor. We find a lower concentration of both donors in the bulk material and a different temperature dependence of the lineshape for the two samples.
Infrared Luminescence from MOCVD Gan
Authors: Leksono M. W. , Oiu C. H. , Melton W. , Pankove J. I.
Published: April 2011

An infrared emission peak at 1.25 eV is observed from a GaN film which exhibits strong yellow luminescence peaking at 2.15 eV. It is most efficient at a temperature of 160 K. The full width at half maximum (FWHM) of the IR peak is 0.17±0.01 eV, which is about 1/3 that of the yellow peak.
Tunable Second-Harmonic Studies of Gan Films Near the Fundamental Bandedge
Authors: Miragliotta Joseph , Bryden Wayne A. , Kistenmacher Thomas J. , Wickenden Dennis K.
Published: April 2011

Tunable second-harmonic (SH) transmission measurements were performed on a series of GaN films epitaxially deposited onto (OOOl)-oriented sapphire. Analysis of the nonlinear response showed an increase in the second-order nonlinear susceptibility (χ(2)ijk) when the photon energy of the SH field was tuned above the absorption edge in each respective film. Specifically, the magnitude of the χ(2)zxx element in χ(2)ijk reached a maximum of 0.5 × 10-7 e.s.u. just above the the fundamental bandgap with a dispersion similar to the predicted nonlinear response in wide-bandgap cubic zincblende II-VI semiconductors such as ZnSe.
Perturbed -Angular -Correlation Spectroscopy on Indium- and Cadmium- Complexes in Silicon Carbide
Authors: Meier J. , Forkel-Wirth D. , Licht T. , Reislöhner U. , Uhrmacher M. , Witthuhn W. , Collaboration Isolde
Published: April 2011

Complex formation at indium and cadmium impurities implanted into samples of 3C-, 4H-and 6H- SiC was investigated by means of Perturbed Angular Correlation (PAC)-Spectroscopy. After annealing at 1600 K up to five different configurations characterized by their specific electric field gradients (EFG(i)) were observed in 6H- SiC, only four complexes in 4H- SiC; in the 3C- modification no complex was observed. All EFG's are axially symmetric and are oriented along the c- axis of the crystal. In a highly nitrogen doped 6H- SiC epi- layer an new EFG was observed. It is tentatively assigned to a close indium- nitrogen pair.
Surface Studies Relevant to the Initial Stages of Diamond Nucleation
Authors: Lannon J. M. , Gold J. S. , Stinespring C. D.
Published: April 2011

Studies of diamond heteroepitaxy on silicon indicate that C-C surface species act as nucleation precursors. We have investigated the conversion of the Si(100) 2×1 surface to SiC using C2H4 to obtain an understanding of how C-C species may be formed and to determine the effect of an O-adlayer on enhancing or selecting the reaction channel which leads to these species. Under appropriate conditions, the interaction between C2H4 and the clean silicon surface yields both SiC and C-C species. The presence of an O-adlayer significantly reduces the activity of silicon and enhances the formation of sp2 and sp3 C-C species. These results provide key insights into diamond nucleation conditions in conventional growth processes.
Energies and Atomic Structures of Grain Boundaries in Diamond: Comparison With Grain Boundaries in Silicon
Authors: Kohyama M. , Ichinose H. , Ishida Y. , Nakanose M.
Published: April 2011

Fairly different features of grain boundaries in diamond from those in Si were experimentally observed in diamond thin films. As the first step in order to understand the fundamental properties of grain boundaries in diamond, the energy and atomic structure of the {122} σ=9 tilt boundary have been calculated for the first time by using the tight-binding electronic theory. The results have been compared with the calculations of the same boundary and the {111} σ=3 boundary in Si. It has been shown that the σ=9 boundary in diamond has a very large interfacial energy caused by the large bond rigidity as compared with the boundaries in Si and the {111}σ=3 boundary in diamond. This point should be related to the observation that the {122}σ =9 boundary is rarely found in diamond thin films.
Fast Recombination of Excess Carrier in 6H-SiC
Authors: Tomashiunas R. , Vanagas E. , Petrauskas M. , Zhindulis A. , Willander M. , Wahab Q. , Bergner H.
Published: April 2011

Fast carrier recombination phenomena in 6H-SiC has been investigated. Evaluation of carrier recombination in nitrogen doped n-type 6H-SiC grown by the Lely method have been carried out using picosecond photoconductivity, time-resolved photoluminescence and dynamic gratings (DG) techniques. From photoluminescence measurements the hole capture by neutral (nitrogen) donors is discussed. The hole capture times and capture cross sections 820 ps, 2.32 ns and 1.5–10-15cm2, 1.2–10-15cm2, respectively, by each of the inequivalent donor were evaluated. From the photoconductivity measurements the electron lifetimes ∼ 1.5 μs at 300 K and (3.5÷6.5)μs at 125 K were obtained. The ambipolar diffusion coefficient 1.4 cm2.s-1 obtained from dynamic gratings measurements is in good coincidence with the calculated values.
X-Ray Topographic Studies of Defects in PVT 6H-SiC Substrates and Epitaxial 6H-SiC Thin Films
Authors: Wang S. , Dudley M. , Carter C. H. , Kong H. S.
Published: April 2011

Synchrotron white beam X-ray topography has been used to characterize defect structures in (0001) 6H-SiC substrates grown by the sublimation physical vapor transport (PVT) technique as well as in 6H-SiC epitaxial thin films grown on these substrates. Defects revealed in 6H-SiC substrates include super screw dislocations and basal plane dislocations. It has been found that back-reflection topographs are particularly suitable for imaging such super screw dislocations as well as basal plane dislocations whenever transmission topography is not applicable. Epitaxial 6H-SiC thin films grown on such (0001) substrates (tilted a few degrees towards the a-axis) were also examined by using surface sensitive grazing Bragg-Laue topography. It has been shown that super screw dislocations were replicated in the epitaxial thin films but no basal plane dislocations were revealed in the thin films. Results from various topographic techniques are discussed.