bluuebunny/crossref_metadata_2025 huggingface dataset:
The Significance of Charged Defects in Understanding the Light-Induced Degradation of Hydrogenated Amorphous Silicon-Germanium Alloys
Authors: Chen Chih-Chiang , Zhong Fan , David Cohen J.
Published: April 2011

We have characterized the defect state structure in a series of device quality glow discharge intrinsic, n-type doped, and p-type doped a-Si,Ge:H alloys with Ge content ranging from 20 at.% to 35 at.%. Our experimental methods include capacitance profiling, transient junction photocurrent and photocapacitance measurements. These methods have allowed us to identify one type of thermally induced defect transition plus two types of optical transitions from deep defects. Our results indicate that these transitions must involve at least two distinct defect sub-bands. Comparison of the magnitudes of these sub-bandsfor the intrinsic, n-type, and p-type alloys has allowed us to confirm that one of the optical transition belongs to D+ defect sub-band. All the optically and thermally induced bands of defect transitions are present with similar magnitudes for the most intrinsic a-Si,Ge:H alloys, which implies that charged defects play a significant role in glow discharge a-Si,Ge:H alloys. We then examined the changes in these defect densities, along with the changes in the hole mobility-lifetime products, that result from prolonged light exposure. By comparing the annealed state and light soaked state of each sample, we have been able to correlate the relative changes of the identified defect sub-band with the measured hole mobility-lifetime products. These data indicate that charged defects probably play a dominant role in determining the degradation of these a-Si,Ge:H alloys in device applications.
Ion Bombardment in Silane VHF Deposition Plasmas
Authors: Hamers E. A. G. , Bezemer J. , Meiling H. , Van Sark W.G.J.H.M. , Van Der Weg W. F.
Published: April 2011

The measurement of mass resolved ion energy distributions at the grounded substrate in an RF glow discharge allows to determine the ion flux and the ion energy flux towards the surface of a growing hydrogenated amorphous silicon (a-Si:H) layer. This provides the means to study the influence of ions on the structural properties of a-Si:H. Here we focus on the α-γ’ transition as occurs in silane-hydrogen plasmas at an RF frequency of 50 MHz and a substrate temperature of 250 °C. The structural properties of the layers appear to depend on the kinetic energy of the arriving ions. This is supported by measurements of ion fluxes under other deposition conditions and by characterization of the corresponding layers. The influence of ions on the growth is discussed in terms of their flux, and the amount of delivered kinetic and potential energy to the growing film. The measurements suggest that a threshold energy of about 5 eV per deposited atom is needed for the construction of a dense amorphous silicon network.
Hydrogen Incorporation During Deposition of a-Si:H From an Intense Source of SiH3
Authors: Van De Sanden M. C. M. , Severens R. J. , Kessels W. M. M. , Van De Pas F. , Van Ijzendoorn L. , Schram D. C.
Published: April 2011

The incorporation of hydrogen during the fast deposition of a-Si:H from an expanding thermal arc is investigated by means of isotope labeling of the precursor gases silane and hydrogen. It is found that hydrogen in a-Si.H originates dominantly from the silyl radical. A small fraction of the hydrogen in a-Si:H is due to exchange reaction of atomic hydrogen in the plasma with hydrogen chemisorbed on the surface during growth.
Observation of Improved Structural Ordering in Low H Content, Hot wire Deposited a-Si:H
Authors: Mahan A. H. , Williamson D. L. , Furtak T. E.
Published: April 2011

We present the results of X-ray diffraction measurements on a series of device quality hot wire (HW) deposited a-Si:H films in which we vary only the substrate temperature of the growing film, which decreases the bonded film H content in a systematic fashion. By increasing the substrate temperature to ∼375°C, where we deposit our low H content (CH) HW films which exhibit a reduced Staebler-Wronski effect, the width of the first peak in the X-ray diffraction pattern narrows noticeably. We interpret this narrowing to be the first indication of improved medium range ordering in our low CH, device quality HW a-Si:H. We note in addition that measurements of the bond angle deviation, obtained from Raman measurements of the half width of the Si-Si TO phonon mode on the same samples, do not show this same evidence of improved ordering as the substrate temperature is increased. We discuss these differences in the context of sample annealing experiments designed to effuse H from the region of the sample probed by the surface sensitive Raman technique, while leaving the bulk of the material, which is sampled by the X-ray beam, largely unaffected.
An Amorphous Silicon Alloy Triple-Junction Solar Cell with 14.6% Initial and 13.0% Stable Efficiencies
Authors: Yang J. , Banerjee A. , Guha S.
Published: April 2011

An initial conversion efficiency of 14.6% has been achieved using amorphous silicon-based alloy in a spectrum splitting triple-junction structure. After 1000 hours of indoor one-sun light soaking at 50 °C, the stabilized efficiency is 13.0%. Both efficiencies are the highest reported to date for amorphous silicon alloy solar cells and have been independently confirmed by the National Renewable Energy Laboratory. The device was deposited onto a stainless steel substrate coated with textured silver/zinc oxide back reflector. The bottom and middle cells use amorphous silicon-germanium alloys, employing high hydrogen dilution in the gas mixture and bandgap profiling in the cell design. The top cell uses amorphous silicon alloy with high hydrogen dilution. Key factors leading to the achievement include a) improvement of the bottom cell that exhibits an AM1.5 efficiency of 10.4% and quantum efficiency of 45% at 850 nm; b) improvement of the tunnel junctions between the component cells by incorporating a novel multilayered structure with microcrystalline p and n layers; and c) improvement of transparent conductive oxide for enhancing the short wavelength response of the top cell.
Persistent Photoconductivity, the Staebler-Wronski Effect, and Long-Range Disorder in a-Si:H
Authors: Quicker D. , West P. W. , Kakalios J.
Published: April 2011

We report measurements of the conductivity, thermopower, and conductance fluctuations before and after light exposure for a-Si:H samples that show either persistent photoconductivity (PPC) or a Staebler-Wronski effect. Both the conductivity and thermopower are changed by light exposure, but no change is observed in the difference between the conductivity and thermopower activation energies for any of the samples studied here. This suggests that the long-range disorder is unaffected by light exposure. For some samples, the magnitude or statistical properties of the conductance fluctuations are affected by light exposure. We compare these results to previous studies of the Staebler-Wronski effect and discuss their implications for models of the light-induced changes and the 1/f noise in a-Si:H.
More Insights into Band Gap Graded a-SiGe:H Solar Cells by Experimental and Simulated Data
Authors: Zimmer J. , Stiebig H. , Fölsch J. , Finger F. , Eickhoff Th. , Wagner H.
Published: April 2011

An experimental and numerical study of a-SiGe:H based solar cells with band gap graded i-layer in the shape of a ‘V’ is presented. The variation of the location of the band gap minimum has strong influence on the solar cell performance. Comparisons of experimental and simulated data of the dark IV-behavior, IV-curves under illumination and the quantum efficiency allow insights into the transport and recombination behavior within the solar cell. The simulations reveal that the position as well as the charge state of the defects determine the device characteristics.
The Effects of Hydrogen Dilution on VOC in a-Si:H Pin Solar Cells
Authors: Wang Qi , Crandall Richard S. , Han Daxing
Published: April 2011

We study the effects of hydrogen dilution on the open circuit voltage of a-Si:H pin solar cells fabricated by rf glow discharge growth. We keep the p and n layers the same and only vary the i layer properties. A normal a-Si:H i layer, an H-diluted i layer, and a thin H-diluted layer inserted between p and normal i layer are selected for this study. We measure the JV characteristics and the internal electric field distribution using a transient-null-current technique both in annealed and light soaked states. We find that hydrogen dilution does stabilize the Voc either in a bulk H-diluted i layer or in a thin layer between p and normal i layer after 100 hours AMI sun light soaking. From dark IV measurement, both H-diluted cells show little change in current at voltage near Voc before and after light soaking; while the normal a-Si:H cell does show a noticeable change. Also the internal field measurements find a stronger electric field starting from p and i interface for both H-diluted cells compared to the normal a-Si:H cell. Furthermore, there are no measurable changes in the field profiles after 100 hour AMI light-soaking for both H-diluted and normal a-Si cells. All these suggest that hydrogen dilution increases the field strength near p and i interface, which is the key that leads to a more stable Voc of H-diluted cells.
Photogeneration and Carrier Transport in Amorphous Silicon/Crystalline Silicon Devices
Authors: Jagannathan B. , Anderson W. A.
Published: April 2011

Hydrogenated amorphous silicon (a-Si:H)/ crystalline silicon (c-Si) type heterodiodes in solar cell structures have been studied by rf glow discharge, dc magnetron sputtering, and a remote plasma deposition of a-Si:H onto p type c-Si. Carrier transport and photogeneration in such structures have been investigated by current-voltage-temperature, thermally stimulated capacitance (TSCAP), and spectral response experiments. Dark carrier conduction is found to be a combination of tunneling and interface recombination, but is dominated by either one depending on the deposition/sputtering conditions. The conditions investigated include energy of the plasma species, type of plasma cleaning, and substrate preparation techniques. For each of the conditions, the trap type, energy and concentration have been identified by TSCAP. Solar cells fabricated by the optimized fabrication scheme routinely yield 10.5% efficient devices having a short circuit current density (Jsc) of 30 mA/cm2, a open circuit voltage of 0.55 volts and a fill factor (FF) of 0.64, without an AR coating, over 0.3 cm2 area.
Amorphous-Silicon Thin-Film Transistors Matched to Ultra-Large Panels
Authors: Matsumura Masakiyo , Saitoh Akihiko
Published: April 2011

Time-delay problems will become extremely severe in active-matrix-addressed ultra-large liquid-crystal display-panels. The problem caused by large crossover capacitance can be solved by moving the signal bus-line to the facing glass plate. The problem caused by large gate capacitance can be solved only by reducing the TFT channel much shorter than the conventional value. This requirement can be satisfied by a novel vertical TFT fabricated by using a selective excimer-laser crystallization method. Switching characteristics have been evaluated for the prototype devices, and good on-characteristics have been confirmed for the O.5μm-long gate device. Improved device structures are also presented.
Amorphous Silicon Photodiode-Thin Film Transistor Image Sensor with Diode on Top Structure
Authors: Powell M J , Glasse C , French I D , Franklin A R , Hughes J R , Curran J E
Published: April 2011

We have developed a new amorphous silicon image sensor technology using a matrix array of amorphous silicon thin film transistors and photodiodes, where the amorphous silicon nip photodiode is fabricated on top of a thick insulating layer, on top of the thin film transistor array. We call this ‘diode on top’ technology or DOTTY. The active diode area can be as high as 93%, compared to 50% for our conventional photodiode-TFT technology. This leads to a higher signal to noise performance, which is important for medical X-ray applications.
Charge Collection I.N A Se Photoconductor on a Thin Film Transistor Array during X-Ray Imaging
Authors: Brauers A. , Conrads N. , Frings G. , Schffibel U. , Powell M. J. , Glasse C.
Published: April 2011

This paper deals with performance aspects of a selenium photoconductor on a thin film transistor array when used in x-ray imaging, e.g. for medical applications. We present the effects of doping structures within the Se on the spatial resolution, temporal response and dark current characteristics. Measurements were done on a 1922 pixel array with 200 μm pitch and a collecting electrode covering 50 % of the pixel area. Without additional measures the detector has a prohibitively slow response. With properly chosen doping structures the lateral conductivity can be engineered in a manner that the speed of the Se-TFT detector is increased to a level acceptable for video rate imaging. There is also a critical relationship between doping structures in the photoconductor and the spatial resolution of the detector. An idea of how these doping structures work in terms of resolution and speed of the detector is presented, together with proposals for an optimized doping scheme.
Improved Concept for Nipiin and PIIIN Color Sensitive Two-Terminal Devices with High Linearity
Authors: Knipp D. , Stiebig H. , Fölsch J. , Carius R. , Wagner H.
Published: April 2011

The detection of the fundamental components of the visible light (blue, green, red) is achieved with two terminal photo diodes based on amorphous silicon. By changing the bias voltage the preferential carrier collection region is shifted which leads to a color sensitivity. In order to obtain a high dynamic range, independent voltage controlled spectral response curves as well as a linear response of the photocurrent on the incident light intensity the μτ-product and the bandgap in the device have to be specially designed to deconvolute the optical signal and generate an RGB-signal. Since the light intensity can strongly influence the spectral sensitivity by recharging of defect states, an optimized design of the multi-layer structure is necessary. Therefore, an improved concept for the design of nipiin- and piiin-detectors is presented which results in a good suppression of these non-linearities. Our concept is based on a decreasing bandgap profile from the front to the back contact and an increasing μτ-product of the individual i-layers in direction of the p-layer.
Rugged Thin Film Diode Liquid Crystal Switches Based on Amorphous Sinx:H
Authors: Mc Garvey B , Clegg J B , Deane S C , Sandoe J N , Shannon J M
Published: April 2011

Amorphous SiNx:H thin film diodes (TFDs) can be used for pixel addressing in active matrix liquid crystal displays. They depend on the application of high electric fields to switch from the ‘off to the ‘on’ states. They prove to be remarkably rugged and can be made with high yield and tolerance. An important feature that contributes to this ruggedness is the ability of these switches to generate defect states at a rate dependent on current density. Current induced defect states trap electrons and cause a reduction in field at the cathode contact, which in turn causes a reduction in current density. Therefore, current will be transferred from regions of high current to regions of low current in the device, making the current flow more uniform. TFDs with thin regions will become effectively thicker during current stressing. In order to check this hypothesis, thin film diodes with nonuniform thickness a-SiNx:H layers were current stressed, and the I-V characteristics compared with those calculated using a defect generation model. The experimental data agreed well with our theoretical model.
Spectroscopic Identification of the Acceptor-Hydrogen Complex in Mg-Doped GaN Grown by MOCVD
Authors: Götz W. , McCluskey M. D. , Johnson N. M. , Bour D. P. , Haller E. E.
Published: April 2011

Mg-doped GaN films grown by metalorganic chemical vapor deposition were characterized by variable-temperature Hall-effect measurements and Fourier-transform infrared absorption spectroscopy. As-grown, thermally activated, and deuterated Mg-doped GaN samples were investigated. The existence of Mg-H complexes in GaN is demonstrated with the observation of a local vibrational mode (LVM) at 3125 cm-1 (8 K). At 300 K this absorption line shifts to 3122 cm-1. The intensity of the LVM line is strongest in absorption spectra of as-grown GaN. Mg which is semi-insulating. Upon thermal activation, the intensity of the LVM line significantly decreases and an acceptor concentration of 2×1019cm-3 is derived from the Hall-effect data. After deuteration at 600°C the resistivity of the Mg-doped GaN increased by four orders of magnitude. A LVM line at 2321 cm-1 (8 K) appears in the absorption spectra which is consistent with the isotopie shift of the vibrational frequency when D is substituted for H.
Incorporation and Optical Activation of Er in Group III-N Materials Grown by Metalorganic Molecular Beam Epitaxy
Authors: Mackenzie J. D. , Abernathy C. R. , Pearton S. J. , Donovan S. M. , Hömmerich U. , Thaik M. , Wu X. , Ren F. , Wilsons R. G. , Zavada J. M.
Published: April 2011

Metalorganic molecular beam epitaxy has been utilized to incorporate Er into AlGaN materials during growth utilizing elemental and metalorganic sources. Room temperature 1.54 μm photoluminescence was observed from AlN:Er and GaN:Er. Photoluminescence from AlN:Er doped during growth using the elemental source was several times more intense than that observed from implanted material. For the first time, strong room temperature 1.54 μm PL was observed in GaN:Er grown on Si. Temperature-dependent photoluminescence experiments indicated the 1.54 μm intensities were reduced to 60% and 40% for AlN:Er and GaN:Er, respectively, between 15 K and 300 K. The low volatility of Er(III) tris (2,2,6,6 - tetramethyl heptanedionate) and temperature limitations imposed by transport considerations limited maximum doping levels to ∼1017 cm-3 indicating that this precursor is unsuitable for UHV.
Site-Selective Photoluminescence Excitation and Photoluminescence Spectroscopy of Er-Implanted Wurtzite GaN
Authors: Kim S. , Rhee S. J. , Turnbull D. A. , Li X. , Coleman J. J. , Bishop S. G.
Published: April 2011

Site-selective photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopy have been carried out at 6K on the ∼1540 nm 4I15/2 → 4I15/2 emissions of Er3+ in Er-implanted GaN. The PLE spectra exhibit several broad, below-gap, defect- or impurity-related absorption bands which excite three distinct site-selective Er + PL spectra. The near-band edge spectral position and lineshape of the PLE spectrum of one of the site-selective PL bands suggest that this Er site forms a trap level within the band gap and an exciton bound at this trap is involved in the excitation mechanism. In addition, high resolution PLE spectra obtained with a tunable laser in the 810 nm spectral range reveal a set of sharp PLE peaks due to the 4I15/2 → 4I9/2 internal Er+ ƒ-band absorption superimposed on the broad defect PLE band. The site-selective PL spectrum excited by the sharp line ∼810 nm Er+ intra-ƒ shell PLE bands is characteristic of a fourth distinct Er+ site. The simple structure of the site-selective PL and PLE spectra associated with direct intra-ƒ shell absorption suggests that the optically active Er site responsible for these spectra is of high symmetry in wurtzite GaN and that it could be attributed to a single Er atom on a Ga site.
GaN Crystals Grown from a Liquid Phase at Reduced Pressure
Authors: Ivantsov V. A. , Sukhoveev V. A. , Dmitriev V. A.
Published: April 2011

Gallium nitride crystals were grown from a Ga-based melt at an ambient gas pressure not exceeding 2 atm. Growth temperature was about 1000°C. The crystals were 2H-GaN and had a (0001) plane orientation. Crystal size varied from 0.05×0.05×0.01 mm3 to 2×2×0.05 mm3. Lateral growth rate of the crystals ranged from 0.05 to 1 mm/hr. Normal growth rate was about 0.01 mm/hr. Depending on growth conditions, the crystals have a platelet or dendrite shape. Crystals were characterized by optical and electron microscopy, Auger electron spectroscopy, x-ray differential diffraction, photoluminescence and optical absorption. Lattice parameters and band gap value of the grown crystals were determined at 300 K.
Excitons Bound to Stacking Faults in Wurtzite GaN
Authors: Rebane Y. T. , Shreter Y. G. , Albrecht M.
Published: April 2011

A model of the exciton bound to stacking faults (SF) in GaN is suggested. It is shown that SFs are potential wells (depth ∼ 120 meV) for electrons and potential barriers (∼ 60 meV) for holes. The binding energy of the exciton at stacking faults is estimated as 30 − 60 meV. The 364 nm line in GaN photoluminescence is attributed to excitons at stacking faults.
High-Pressure Raman Scattering of Biaxially Strained GaN on GaAs
Authors: Siegle H. , Goñi A. R. , Thomsen C. , Ulrich C. , Syassen K. , Schöttker K. , As D. J. , Schikora D.
Published: April 2011

We present results of high-pressure Raman-scattering experiments on bulk GaN and GaN grown on GaAs. We determined the Grüneisen parameters of both the cubic TO and LO phonon modes and the hexagonal A1, E1 and E2 modes. Our measurements reveal that the Grüneisen parameters for the GaAs substrate are about 30% smaller than those of bulk GaAs. This is a consequence of the lower compressibility of GaN compared to GaAs, which results in a pressure-induced biaxial strain on the substrate. From the pressure behavior of the GaAs modes and by comparing with our results for bulk GaN we obtained information about the biaxial strain in the GaN epitaxial layer.
Measurement of InxGa1-xN and AlxGa1-xN Compositions by RBS and SIMS
Authors: Gao Y. , Kirchhoff J. , Mitha S. , Erickson J. W. , Huang C. , Clark-Phelps R.
Published: April 2011

Secondary ion mass spectrometry (SIMS) and Rutherford Backscattering Spectrometry (RBS) techniques were used to determine InxGa1-xN and AlxGa1-xN compositions. While RBS is generally considered a quantitative technique for compositional analysis, SIMS has not been. We have applied a new analytical technique, which reduces the matrix effect in SIMS analysis, to accurately determine stoichiometry. The composition of InxGa1-xN (AlxGa1-xN) in the multiple layers and quantum well of the LED can be measured by SIMS, but is inaccessible to RBS.
Luminescence Related to Stacking Faults in Heterepitaxially Grown Wurtzite GaN
Authors: Albrecht M. , Christiansen S. , Salviati G. , Zanotti-Fregonara C. , Rebane Y. T. , Shreter Y. G. , Mayer M. , Pelzmann A. , Kamp M. , Ebeling K. J. , Bremser M. D. , Davis R. F. , Strunk H. P.
Published: April 2011

We correlate structure analyzed by transmission electron microscopy with photo- and cathodoluminescence studies of GaN/Al2O3(0001) and GaN/SiC(0001) and show that an additional UV line at 364nm/3.4eV can be connected to the occurrence of stacking faults. We explain the occurrence of this line by a model that is based on the concept of excitons bound to stacking faults that form a quantum well of cubic material in the wurtzite lattice of the layer material. The model is in reasonable agreement with the experimental observations.
Impurity Contamination of GaN Epitaxial Films From the Sapphire, SiC and ZnO Substrates
Authors: Popovici Galina , Kim Wook , Botchkarev Andrei , Tang Haipeng , Solomon James , Morkoç Hadis
Published: April 2011

Likely contamination of GaN films by impurities emanating from Al2O3, SiC and ZnO substrates during growth has been studied by secondary ion mass spectrometry analysis. The highly defective interfacial region allows impurities to incorporate more readily as comparedjo the equilibrium solubility in a perfect crystal at a given temperature as evidenced by increased impurity levels in that region as detected by SIMS. The SIMS measurements in GaN layers grown on SiC and sapphire showed large amounts of Si and O, respectively, within a region wider than the highly disordered interfacial region pointing to the possibility of impurity diffusion at growth temperatures. The qualitative trend observed is fairly clear and significant. These observations underscores the necessity for developing GaN and/or AlN substrates.
Development of GaN and InGaN Gratings by Dry Etching
Authors: Lee J. W. , Hong J. , Mackenzie J. D. , Abernathy C. R. , Pearton S. J. , Ren F. , Sciortino P. F.
Published: April 2011

Sub-micron periodic gratings with pitch ∼3,000Å were formed in GaN and InGaN using holographic lithography and room temperature ECR BCl3/N2 dry etching at moderate microwave (500W) and rf (100W) powers. The process produces uniform gratings without the need for elevated sample temperatures during the etch step.
ICP Dry Etching of III-V Nitrides
Authors: Vartuli C. B. , Lee J. W. , MacKenzie J. D. , Donovan S. M. , Abernathy C. R. , Pearton S. J. , Shul R. J. , Constantine C. , Barrati C. , Katz A. , Poyakov A. Y. , Shin M. , Skowronski M.
Published: April 2011

Inductively coupled plasma etching of GaN, AlN, InN, InGaN and InAlN was investigated in CH4/H2/Ar plasmas as a function of dc bias, and ICP power. The etch rates were generally quite low, as is common for III-nitrides in CH4 based chemistries. The etch rates increased with increasing dc bias. At low rf power (150W), the etch rates increased with increasing ICP power, while at 350W rf power, a peak was found between 500 and 750 W ICP power. The etched surfaces were found to be smooth, while selectivities of etch were ≤ 6 for InN over GaN, AlN, InGaN and InAlN under all conditions.
Recovery of Structural Defects in GaN After Heavy Ion Implantation
Authors: Running C. , Dalmer M. , Deicher M. , Restle M. , Bremser M. D. , Davis R. F. , Hofsäss H.
Published: April 2011

Single crystalline GaN-layers were implanted with radioactive 111In ions. The lattice location of the ions and the recovery of the implantation induced damage was studied using the emission channeling technique and perturbed-γγ-angular-correlation spectroscopy as a function of the annealing temperature. We find the majority of indium atoms on substitutional sites even directly after room temperature implantation, but within a heavily disturbed surrounding. During isochronal annealing treatments in vacuum, a gradual recovery of the implantation damage takes place between 873 K and 1173 K. After 1173 K annealing about 50 % of the In atoms occupy substitutional lattice sites with defect free surroundings.
Temperature Behavior of Pt/Au Ohmic Contacts to p-GaN
Authors: King D. J. , Zhang L. , Ramer J. C. , Hersee S. D. , Lester L. F.
Published: April 2011

Ohmic contacts to Mg-doped p-GaN grown by MOCVD [1] are studied using a circular transmission line model (TLM) to avoid the need for isolation. For samples which use a p-dopant activation anneal before metallization, no appreciable difference in the specific contact resistance, rc, as a function of different capping options is observed. However, a lower rc is obtained when no pre-metallization anneal is employed, and the post-metallization anneal simultaneously activates the p-dopant and anneals the contact. This trend is shown for Pt/Au, Pt, Pd/Pt/Au, and Ni/Au contacts to p-GaN. The rc 's for these metal contacts are in the range of 1.4–7.6 × 10-3 ohm-cm2 at room temperature at a bias of 10mA. No particular metallization formula clearly yields a consistently superior contact. Instead, the temperature of the contact has the strongest influence.

Detailed studies of the electrical properties of the Pt/Au contacts reveal that the I-V linearity improves significantly with increasing temperature. At room temperature, a slightly rectified I-V characteristic curve is obtained, while at 200°C and above, the I-V curve is linear. For all the p-GaN samples, it is also found that the sheet resistance decreases by an order of magnitude with increasing temperature from 25°C to 350°C. The specific contact resistance is also found to decrease by nearly an order of magnitude for a temperature increase of the same range. A minimum rc of 4.2 × 10-4 ohm-cm2 was obtained at a temperature of 350°C for a Pt/Au contact. This result is the lowest reported rc for ohmic contacts to p-GaN.
Optimization of III-N Based Devices Grown by RF Atomic Nitrogen Plasma Using In-Situ Cathodoluminescence
Authors: Van Hove J. M. , Chow P. P. , Klaassen J. J. , Hickman R. , Wowchak A. M. , Croswell D. R. , Polley C.
Published: April 2011

In-situ cathodoluminescence (CL) is presented as a technique to optimize GaN, and AlGaN films deposited by MBE using an RF plasma as a source of reactive nitrogen. Excitation of the MBE grown nitride films is conveniently achieved in the preparation chamber using an Auger electron gun. The photoemission is monitored through a side port and dispersed with a 1/8 m monochromator with a typical resolution of 3 nm. The in-situ CL spectra of AlGaN and GaN films provides quick determination of both material composition, doping, and quality from the position and width of the band edge emission. The use of CL for the assessment of material composition in the growth of nitride materials is extremely beneficial since the complementary technique of RHEED oscillations is not routinely observed for these systems. The determination of material quality using CL has been used to optimize growth conditions for GaN PIN junction photovoltaic detectors on (0001) sapphire. Detectors having peak responsivity of 0.175 AAV at the GaN band edge of 365 nm and a UV to visible rejection ratio of greater than 105 have been fabricated. The high rejection ratio is accredited to the reduction of the yellow defect levels in the MBE grown material. Material optimization using in-situ CL for growth of AlGaN MODFETs having drain currents of 425 ma/mm and gm of 66 mS/mm is discussed.
Reliable, Reproducible and Efficient MOCVD of III-Nitrides in Production Scale Reactors
Authors: Wachtendorf B. , Beccard R. , Schmitz D. , Jürgensen H. , Schön O. , Heuken M. , Woelk E.
Published: April 2011

In this paper we present a class of MOCVD reactors with loading capacities up to seven 2″ wafers, designed for the mass production of LED structures.

Our processes yield device quality GaN with excellent PL uniformities better than 1 nm across a 2″ wafer and thickness uniformities typically better than 2%.

We also present full 2″ wafer mapping data, High Resolution Photoluminescence Wafer Scanning and sheet resistivity mapping, revealing the excellent composition uniformity of the nitride compounds InGaN and AlGaN. As well we will show sheet resistivity uniformity for Si-doped GaN and Mg-doped GaN.
Pyrolytic Preparation of Gallium Nitride From [Ga(NEt2)3]2 and its Ammonolysis Compound
Authors: Koyama Seiichi , Sugahara Yoshiyuki , Kuroda Kazuyuki
Published: April 2011

Gallium nitride (GaN) was prepared by the pyrolytic conversion of both [Ga(NEt2)3]2 and its ammonolysis product at 600 °C for 4 h under Ar. The pyrolyzed residues were analyzed by X-ray powder diffraction and scanning electron microscopy, and the pyrolysis processes of the precursors under He were investigated by thermogravimetry-mass spectrometry. The XRD pattern of the pyrolyzed residue of [Ga(NEt2)3]2 showed well-resolved peaks due to a mixture of cubic and hexagonal close-packed layers of GaN. The broad XRD pattern of the pyrolyzed residue of the ammonolysis product was also attributed to the mixture of cubic and hexagonal close-packed layers of GaN. For the pyrolysis of [Ga(NEt2)3]2, the evolution of hydrocarbons was extensively observed at relatively high temperature, but a large amount of carbon (11 mass%) was still detected in the pyrolyzed residue. On the other hand, the amount of carbon was only 1.1 mass% in the pyrolyzed residue of the ammonolysis product. The pyrolysis results of the ammonolysis product under Ar were very similar to those of [Ga(NEt2)3]2 under NH3.
Effect of C and Ge Concentration On The Thermal Stability of RTCVD Grown Si1-x-yGexCy Alloys
Authors: Warren Patricia , Retzmanick Stephane , Gotza Martin , Begems Marc
Published: April 2011

Si / Si1-x-yGexCy / Si heterostructures containing up to 17 at.% Ge and 1.9 at.% C were grown on (001) silicon by low pressure Rapid Thermal Chemical Vapor Deposition, using a mixture of silane, germane and methylsilane, diluted in hydrogen. The samples were then annealed in a Rapid Thermal Processing furnace, under an atmospheric pressure of nitrogen, at temperatures ranging from 900 to 1130 °C.

The samples were characterized using infrared spectroscopy and x-ray diffraction. SIMS profiling and TEM observation were performed on some of the samples.

Substitutional C gradually disappeared, either precipitating out to form cubic silicon carbide (β-SiC), or simply vanishing into interstitial positions. In any case, the in-plane lattice constant remained constant after annealing, indicating that there was no mechanical strain relaxation by formation of misfit dislocations. The perpendicular lattice constant increased due to the decrease in substitutional C concentration, as well as it decreased due to the germanium out-diffusion. This variation of the strain during annealing was modeled, and allowed the determination of the kinetics of the substitutional carbon disappearance. The same behavior was observed for all samples. Indeed, the Cs disappearance rate was always increased for samples with higher initial Ge and C concentrations. The kinetics of this precipitation was found in very good agreement with previous published results.
The Growth of β-SiC on Si and Poly-Si on β-SiC by Rapid Thermal Chemical Vapor Deposition
Authors: Liu C. W. , Sturm J. C.
Published: April 2011

The growth properties of β-SiC on (100) Si grown by rapid thermal chemical vapor deposition, using a single precursor (methylsilane) without an initial surface carbonization step, were investigated. An optimun growth temperature at 800°C was found to grow single crystalline SiC. The single crystalline SiC films were used to be the buffer layers for the growth of subsequent poly Si films. For the poly Si grown at low temperature (625°C), the (110) Si diffraction was found to be the dominant peak in the X-ray diffraction spectra at the initial growth stage, while the poly Si grown on oxide was dominated by (111) texture. A small average misfit (4 %) between (110) Si planes and (100) SiC planes was proposed to explain this effect. To apply the Si/SiC/Si multilayers, SiC/Si heterojunction bipolar transistors (HBT's) were fabricated and compared to Si bipolar junction transistors.
Rapid Thermal Processing: When Will it Replace Batch Processing?
Authors: Pas M. F. , Pas S. D.
Published: April 2011

Rapid Thermal Processing (RTP) is currently well established at the < 0.5 μm nodes for implant anneal and suicide formation/anneal in logic applications. Rapid Thermal Chemical Vapor Deposition (RTCVD) is being evaluated to deposit thin nitride for the DRAM storage node dielectric. A combination RTP/RTCVD has been evaluated in the form of a cluster tool to evaluate 60 Å gate oxides. These applications of RTP are considered to be process enabling because of either improved temperature ramp control or ambient control which are not available in batch processing. However, even with these specialized applications, rapid thermal processing comprises less than 20% of the front end thermal processes in a typical 0.35 μm fab. Process and equipment issues with rapid thermal processing remain which must be overcome if it is to replace batch processing at the 0.25 μm node. Process issues which are especially critical for RTCVD processing require improved temperature measurement, high growth/deposition rate, and an efficient method of cleaning the process chamber. Equipment issues are reliability and throughput which directly affect the tool cost of ownership. In this paper, each of these issues will be addressed and compared to batch processing using a generic logic process flow.
The Performance of The Fast Ramp Vertical Furnace
Authors: Torres Kenneth , Lam Denny , Weaver Robert , Solomon Gary
Published: April 2011

This paper summarizes a Joint Development Project between SEMITOOL, member company and SEMATECH to demonstrate and develop the fast ramp vertical furnace. The goal of this project was to deliver a production vertical furnace capable of heating and cooling a batch of 50 wafers at average ramp rates of 75 and 50 °C/min, respectively. The furnace did meet these goals. This paper will outline the distinctive and enabling design features of the furnace, such as the use of model predictive control techniques to stabilize the wafer temperatures within 2 to 5 minutes of reaching the nominal target temperature. The test results of a ten run passive data collection for a 145 ohm/sq boron S/D anneal and a 65 angstrom gate oxidation process will be discussed. The boron S/D anneal PDC results exceeded the 3 sigma standard deviation for all points goal of 5.0%. The gate oxidation PDC gave a mean of 65 angstroms and met its 3 sigma standard deviation for all points goal of 4.5%. Using an unyielded model (defect density=0) the cost of ownership is estimated to be $3.02/wafer for a 50 wafer load and as low as $1.68 for a 200 wafers load for a gate oxide process. The fast ramp vertical furnace is designed to meet 0.25 and 0.18 micron technology needs, improve cycle time, and give the customer the flexibility of using different wafer batch sizes within a 25” flat temperature zone (where the ramp rates are adjusted according to the wafer pitch).
Formation of Titanium Silicide on Ion-Implanted Silicon
Authors: Gilboa Y.E , Eizenberg M.
Published: April 2011

The formation of TiSi2 was compared over samples implanted with arsenic and BF2 at different doses and annealed at different temperatures and lengths of time in a rapid thermal process. Measurements were done to determine the composition and thickness of the suicide formed. The composition was determined from Auger electron spectroscopy, Rutherford backscattering spectroscopy, and transmission electron microscopy. The phase formation of the suicide was characterized by X-ray diffraction. Dopant redistribution was studied using secondary ion mass spectroscopy. Comparing the results of the different implant doses we found that the amount of suicide formed over heavily doped Si at formation temperatures of 600°C to 650°C was reduced compared to undoped Si. At formation temperatures above 750°C the implanted dose and species did not significantly affect the amount of suicide formation. Above 750°C the TiSi2 structure was found to be the C54 phase. Arsenic was found to diffuse into the Ti suicide layer in a diffusion controlled process. Boron was found to accumulate at the Ti suicide interfaces both with the substrate and with the surface TixOyNz layer.
Problems with The Concept of Thermal Budget: Experimental Demonstrations
Authors: Ditchfield R. , Seebauer E. G.
Published: April 2011

Up to now, kinetic effects in rapid thermal processing (RTP) have been assessed using the concept of thermal budget, with the idea that thermal budget minimization should minimize dopant diffusion and interface degradation. This work highlights shortcomings with that principle. Experiments comparing directly the rate of Si chemical vapor deposition with that of dopant diffusion show how thermal budget minimization can actually worsen diffusion problems rather than mitigate them. We present a straightforward framework for improving the results through comparison of activation energies of the desired and undesired phenomena. This framework explains the experimental results and provides strong kinetic arguments for continued development of rapid isothermal processing and small batch fast ramp methods.
Deep Diffusions and Soi Layers Produced by Rapid Thermal Processing for Smart Power Applications
Authors: Dilhac J-M. , Cornibert L. , Ganibal C.
Published: April 2011

Power devices often contain very deep boron diffusions extending through the thickness of the wafer to create junction isolation. In this paper we first report our investigations to replace the standard solid-state deep diffusion, with Temperature-Gradient Zone Melting (TGZM). During TGZM, a molten silicon/aluminium solution moves through a Si wafer in minutes, leaving a highly Al doped trail behind it. The liquid phase diffusion is driven by the vertical thermal gradient created in the wafer by a properly designed RTP.

On the other hand, for the purpose of high voltage (> 400V) smart power applications, substrates with localised and thick SOI layers are needed. We also present a method for recrystallization of thick poly silicon films by Lateral Epitaxial Growth over Oxide (LEGO), using a similarly designed RTP.

The two processes, that is LEGO and TGZM, use a Rapid Thermal Processor and are compatible. The RTP is specially designed to create a thermal gradient perpendicular to the wafer surface.
Near and SUB-keV Boron Implantation and Rapid Thermal Annealing: a Sims and Tem Study
Authors: Lcurrent M. , Foad M. A. , England J. G. , Lopes D. , Jones C. , Su D.
Published: April 2011

Atomic profiles (SIMS) and cross-section TEM images of selectively etched, annealed profiles were studied for Boron energies from 20 da eV (200 eV) to 10 keV and RTP anneals at 900, 975 and 1050 C Consistent variations of dopant depth was obtained over this process range. TEM images showed evidence of lateral dopant variation near the edges of poly-Si gate structures, perhaps an effect of lateral straggling and reflection of ions from the poly mask.
Enabling Thermal Processing of High and Low Dielectric Constant Materials
Authors: Thakur R. P. S. , DeBoer S. J. , Singh R.
Published: April 2011

The focus of ULSI electronics is shifting rapidly towards the development and integration of various low and high dielectric constant materials. Memory manufacturers are driving the quest for integration-friendly, high dielectric constant materials, while the logic makers are seeking materials with the lowest possible dielectric constant to use as interlayer dielectrics for their multilayer backend needs. Both of these categories of materials need the highest possible level of reliability, integrability, and manufacturability in the current and upcoming real world. Strong development emphasis in improving the structural aspects of these materials is needed more now than ever before both in university laboratories and industrial R&D. An intense focus on these materials demands immediate, improved, and innovative process solutions. One key process area is the thermal engineering and processing of these materials and hence is the focus of this paper.

In this paper, we present recent results from both university and industry process development work. We compare and contrast the thermal process requirements of some enabling materials with dielectric constants ranging from 2 to more than 100. The examples in our study encompass materials such as Teflon™, PLZT, cell nitride, and tantalum pentoxide. The enhancements in the structural and electrical performance of these materials as a function of thermal cycles used either for deposition or annealing is demonstrated through various examples.
Nitric Oxide Rapid Thermal Nitridation of Thin Gate Oxides
Authors: Kuehne J. , Hattangady S. , Piccirillo J. , Xing G. C. , Miner G. E. , Lopes D.
Published: April 2011

Nitric oxide rapid thermal nitridation of thin gate oxides was investigated. Oxides from 25 to 55 Å were grown in O2 and subsequently nitrided in a nitric oxide (NO) ambient using an Applied Materials RTP Centura chamber. Nitrogen incorporation and film thickness growth during NO nitridation were evaluated. Peak nitrogen incorporation was most strongly influenced by temperature and time, with moderate influence by initial oxide thickness, and no significant influence due to NO flow rate. Peak nitrogen concentrations ranged from 1 to 9 atomic percent as characterized by Secondary Ion Mass Spectrometry (SIMS) analysis. Oxide growth during nitridation ranged from 2 Å to 11 Å with no degradation in uniformity. These data were used in the design of two 40 Å oxynitride processes incorporating 2 and 4 peak atomic percent nitrogen. High quality MOS capacitors were demonstrated with these dielectrics. Performance was compared against a baseline furnace process as well as non-nitrided RTO. Throughout this work, the chamber integrity was monitored using visual inspection, minority carrier lifetime (MCLT) and surface photovoltage (SPV). No contamination, corrosion or other degradation of the process chamber was observed in over 6 months' operation with over 700 NO processes completed. The controllability, uniformity and high nitrogen incorporation of rapid thermal NO nitridation make it an attractive process for deep sub-micron gate insulators.
A Generalized Model of Beryllium Diffusion in InGaASs Epitaxial Structures Under Point Defect Nonequilibrium Conditions
Authors: Gautier S. , Koumetz S. , Marcon J. , Ketata K. , Ketata M. , Gautier B.
Published: April 2011

Beryllium diffusion during post-growth annealing is investigated in InGaAs epitaxial layers. Indeed, this undesirable diffusion may occur during thermal treatments of InGaAs/lnP Heterojunction Bipolar Transistors (HBT's), which can generate a limitation of frequency performances of these devices. Epitaxial structures have then been grown, one set by Chemical Beam Epitaxy (CBE), and another one by Gas Source Molecular Beam Epitaxy (GSMBE). The post-growth Rapid Thermal Annealing (RTA) was then performed, and Secondary Ion Mass Spectrometry (SIMS) has been used to characterize the Be depht profiles.

In parallel with our experimental study, we propose two models of Be diffusion in InGaAs in the case of point defect nonequilibrium. First, a Kick-out Diffusion model considering neutral Be interstitial species and charged point defects has been studied. Then, a Generalized Substitutional-Interstitial Diffusion model based on simultaneous diffusion by Dissociative and Kick-out mechanisms is proposed. Good agreements between experimental depth profiles and simulated curves have been obtained.
Grain Enhancement of Thin Silicon Layers Using Optical Processing
Authors: Sopori B. L. , Alleman Jeff , Chen W. , Tan T. Y. , Ravindra N. M.
Published: April 2011

We describe a new technique for producing large-grain, poly-Si thin films on low-cost glass substrates for solar cell applications. A layer of fine-grain poly-Si is deposited on metal-coated substrate followed by a grain enhancement using optical/thermal annealing at low temperatures (∼ 500 °C). The results show that in thin-layer silicon, less than 3 microns, grains can be formed in a short time (few minutes) with grain sizes larger than the film thickness. The possible mechanisms involved in this process are also presented.
Temperature Estimation and Precision Control of RTP Systems by Multi-Zone Lamp Interference and Wafer Emissivity Compensation I: Model Identification
Authors: Belikov Sergey , Kamali Jalil , Lee Yong Jin , Moslehi Mehrdad
Published: April 2011

RTP temperature measurement using conventional pyrometric technique has serious limitations such as uncertainty of emissivity, lamp interference, and window/chamber heating effect. In this paper, we propose to compensate for these effects using a real-time computational algorithm based on physical model of pyrometric detectors and wafer temperature dynamics. We consider an RTP system for processing 200 mm wafers with five circular zones of heating lamps and ten pyrometric sensors, five of which measure the radiation from five optically isolated dummy lamps and the rest measure the radiation of the wafer back side at different radial positions. Thermocouple measurements are also used to identify the model parameters. Part I of the paper is concerned with modeling and parameter identification.