bluuebunny/crossref_metadata_2025 huggingface dataset:
Photoquenching Of Persistent Photoconductivity In N-Type GaN
Authors: Hirsch Michèle T. , Seiferta O. , Kirfel O. , Parisia J. , Wolk J. A. , Walukiewicz W. , Haller E. E. , Ambacher O. , Stutzmann M.
Published: April 2011

We report on the observation of optical quenching of persistent photoconductivity (PPC) in unintentionally doped n-type GaN films. The PPC is induced by subbandgap illumination between room temperature and 77K. The corresponding decay, which.is thermally activated, is substantially increased upon low energy illumination, e.g. illumination by wavelengths between 1O50nm and 700nm. We measure the saturation conductivity under simultaneous illumination with excitation and quenching light and find that some wavelengths can induce both excitation and quenching of photoconductivity. Additionally, we present a preliminary investigation of the spectral dependence of the quenching effect. A simulation indicates only a weak spectral dependence of the quenching cross-sections in the wavelength range from 470nm–1050nm.
Radiative And Nonradiative Relaxation Of Excitons In GaN
Authors: Göldner A. , Eckey L. , Hoffmann A. , Broser I. , Alemu A. , Gil B. , Ruffenach-Clur S. , Aulombard R. L. , Briot O.
Published: April 2011

We report on investigations of the excitonic quantum efficiency in GaN epilayers as function of buffer layer thickness, buffer layer material, sample thickness and residual oxygen content. These values are compared to that of GaN bulk material. The quantum efficiency of the free excitons rises with increasing buffer layer thickness, increasing sample thickness and decreasing residual oxygen content. The influence of oxygen on the quantum efficiency is stronger than that of the buffer layer thickness. Additionally, the homoepitaxial growth of GaN shows higher quantum efficiencies than the growth with an AIN buffer layer. In general, the observed quantum efficiencies in GaN epilayers are below 20% indicating the strong impact of nonradiative relaxation and recombination processes in the excitonic range. Only, GaN bulk material shows quantum efficiencies of 25 % for the free A-exciton XA and of 50 % for the donor-bound exciton complex D0,X).
Near Band Gap Photoluminescence Broadening In n-Gan Films
Authors: Iliopoulos E. , Doppalapudi D. , Ng H. M. , Moustakas T. D.
Published: April 2011

This paper addresses the broadening mechanism of the near band gap photoluminescence in GaN films doped n-type with silicon. The films were produced by plasma assisted MBE and their carrier concentration was varied systematically from 1015 to 1020 cm−3. The photoluminescence was excited with a 10 mW He-Cd laser at 77K. At low carrier conentration ( < 1017 cm−3 ) the photoluminescence peak has FWHM of about 18 meV, while at high carrier concentration (>1018 cm−3 ) the FWHM increase monotonically with the carrier concentration up to about 120 meV. The broadening of the line at high carrier concentration is attributed to impurity band broadening and tailing of the density of states. The data were quantitatively analyzed, as a function of carrier concentration and compensation ratio, using the impurity band broadening model of Morgan [1] and the agreement between model and experimental data supports the model's validity and suggest a potential method of determining the compensation in degenerate semiconductors.
Photoluminescence Characterization of p-type GaN:Mg
Authors: Corlatan Dorina , Krüger Joachim , Kisielowski Christian , Klockenbrink Ralf , Kim Yihwan , Sudhir G. S. , Peyrot Yann , Rubin Michael , Weber Eicke R.
Published: April 2011

We report on results of low-temperature photoluminescence measurements performed on GaN films, grown by molecular beam epitaxy (MBE) on sapphire substrates. The GaN films are either Mg doped (p-type) or consist of a Mg-doped layer on top of a Si doped GaN layer (n-type). In the p-doped samples, the sharpness of the donor-acceptor-pair transition is striking, three phonon replicas are clearly resolved. A transition band occurs around 3.4 eV, which becomes dominant for samples with an np-layer structure. The position and the composition of the near band edge transitions are influenced by the growth of the buffer layers. Depending on the growth conditions a transition at 3.51 eV can be observed.
The Effect of Low Temperature GaAs Nucleation on the Growth of GaN on Silicon (001) During MOVPE Process
Authors: Zheng L. X. , Liang J. W. , Yang H. , Li J. B. , Wang Y. T. , Xu D. P. , Li X. F. , Duan L. H. , Hu X. W.
Published: April 2011

High quality cubic GaN was grown on Silicon (001) by metalorganic vapor phase epitaxy (MOVPE) using a GaAs nucleation layer grown at low temperature. The influence of various nucleation conditions on the GaN epilayers' quality was investigated. We found that the GaAs nucleation layer grown by atomic layer epitaxy (ALE) could improve the quality of GaN films by depressing the formation of mixed phase. Photoluminescence (PL) and X-ray diffraction were used to characterize the properties of GaN epilayers. High quality GaN epilayers with PL full width at half maximum (FWHM) of 130meV at room temperature and X-ray FWHM of 70 arc-min were obtained by using 10–20nm GaAs nucleation layer grown by ALE.
Photoluminescence Excitation Study of Lo-Phonon Assisted Excitonic Transitions in Gan
Authors: Hwang S. J. , Cho Y. H. , Song J. J. , Shan W. , Chang Y. C.
Published: April 2011

We report the results of a photoluminescence excitation (PLE) study on excitonic transitions in GaN. PLE measurements were carried out as a function of temperature to investigate exciton formation, thermalization, and annihilation processes in GaN. The PLE spectra detected at free-exciton resonance were found to exhibit a large number of oscillatory emission structures with an energy spacing of LO-phonon (92 meV), and such emission persisted up to 400K. The observation suggests that a phonon-assisted indirect exciton formation process, which simultaneously generates a free-exciton and an LO-phonon, is very significant and efficient in GaN, and the lifetime of the free-exciton is longer than the relaxation time of LO-phonon emission but much shorter than that of acoustic-phonon emission. The appearance of the broad spectral features at the PLE spectrum detected at free-exciton resonance, similar to those measured at the boundexciton resonance, is attributed to the higher order transition processes which involve acousticphonon scattering and thermal repopulation of free-excitons. In addition, we observed up to the 12th LO-phonon emission in PLE spectrum around 120 K, indicating the existence of the excitons with a large kinetic energy in GaN.
Carbon And Hydrogen Induced Yellow Luminescence In Gallium Nitride Grown By Halide Vapor Phase Epitaxy
Authors: Zhang R. , Kuech T. F.
Published: April 2011

Yellow luminescence (YL) from GaN was systematically investigated through the intentional introduction of carbon, from propane, and excess H2 during growth by the halide vapor phase epitaxy technique. All GaN films were studied by photoluminescence, X-ray diffraction and Hall measurements. The unintentionally doped GaN showed undetectable or very weak YL signal, while both C-doping and H2 addition resulted in a significant enhancement of YL. The blue- and red-shift of the YL band of the C-doped and ‘H2-grown’ GaN with the increasing temperature indicated that different mechanisms existed in these two cases. The temperature dependence of the integrated intensity of the YL band of both groups implicated that shallow donors, not ‘shallow’ acceptors participated the YL transition and that there were more than one radiative recombination channel within the YL band.
Temperature Dependence Of The Fundamental Band Gap In Hexagonal GaN
Authors: Herr H. , Alex V. , Weber J.
Published: April 2011

Photoluminescence spectra of hexagonal GaN were measured in the temperature range T= 2 – 1200 K. We identify the Free Exciton (FX) as the dominant recombination process in our high quality samples for temperatures above 200 K. From the line shape fit of the FX we determine the excitonic band gap shift with temperature. An analysis according to the empirical Varshni equation gives Eg (T)-Eg(0 K) = (-α T2)/(T + β), with α = (7.3 ± 0.3)·10−4 eV/K and β = (594 ± 54) K. We have detected significant differences in the band gap energy at low and higher temperatures for GaN layers grown on different substrate materials. Heating GaN above 1200 K leads to irreversible changes in the near band gap photoluminescence spectra.
Structural And Electronic Properties of GaN/AL Interfaces
Authors: Picozzi S. , Continenza A. , Massidda S. , Freeman A. J.
Published: April 2011

The structural and electronic properties of the GaN/Al interface are determined from first principles local density full potential linearized augmented plane wave (FLAPW) calculations. The charge distribution of the gap states as a function of the distance from the interface shows that the gap states induced into the semiconductor by the presence of Al are strongly localized in the junction region. Furthermore, we find that Al does not provide good ohmic contacts on thecleannitrides considered, in contrast with experimental results on chemically treated GaN, but in agreement with recent measurements on the clean surface[1]. We also study some auxiliary systems (all grown on a GaN substrate), i.e. the Al/AlN interface, the GaN/AlN heterojunction and the GaN/Al with an AlN intralayer (GaN-AlN/Al). The transitivity rule for the GaN/Al, AlN/Al and GaN/AlN interfaces is fairly well satisfied and small differences must be ascribed to differences in the interface morphology. Finally, we find that the AIN intralayer does not significantly affect thep-type Schottky barrier height of the GaN/Al interface.
The Velocity-Field Characteristic Of Indium Nitride
Authors: O'Leary S. K. , Foutz B. E. , Shur M. S. , Eastman L. F. , Bhapkar U. V.
Published: April 2011

We determine the velocity-field characteristic of wurtzite indium nitride using an ensemble Monte Carlo approach. It is found that indium nitride exhibits an extremely high room temperature peak drift velocity, 4.2 × 107 cm/s, at a doping concentration of 1 × 1017 cm−3. This exceeds that of gallium nitride, 2.9 × 107 cm/s, by approximately 40 %. For our nominal parameter selections, the saturation drift velocity of indium nitride is found to be 1.8 × 107 cm/s. The device performance of this material, as characterized by the cut-off frequency, is found to superior to that of gallium nitride, gallium arsenide, and silicon.
AB-Initio Calculations Of Second Order Optical Response Functions In Wurtzite GAN and ALN, And Their Short Period Superlattices
Authors: Rashkeev Sergey N. , Lambrecht Walter R. L. , Segall B.
Published: April 2011

Second harmonic generation coefficients were calculated from first-principles for wurtzite GaN, AlN and the (0001) superlattices (SL) (GaN)n,(AlN)n for n = 2, 4. The effects of the LDA gap underestimate are discussed. The SLs are found to have a strongly reduced static SHG response. The frequency dependent SHG coefficients are found to be sensitive to the SL band structure and to differ significantly form a superposition of the bulk components, indicating a strong intermixing of the bands.
Thermal Expansion Of GaN And Ain
Authors: Wang Kai , Reeber Robert R.
Published: April 2011

The temperature dependence of the thermal expansion and the bulk modulus are critical for predicting the residual stress distribution in epitaxial films and provides information relevant for interatomic potentials and equations of state. The thermal expansions of aluminum nitride (AIN) and gallium nitride (GaN) are calculated with two models that employ the limited elastic and lattice parameter data. These semiempirical models allow prediction of the thermal expansions to higher temperatures. Calculated results are compared with experimental data.
Simulation of Vacancy Pairs in GaN Using Tight-Binding Molecular Dynamics
Authors: Boucher Derrick E. , Gál Zoltán A. , DeLeo Gary G. , Fowler W. Beall
Published: April 2011

The electronic structure, geometry and energetics of Ga vacancy pairs and N vacancy pairs in both wurtzite and zincblende GaN are investigated via molecular dynamics (MD) simulations using an empirical tight-binding (TB) model with total energy capabilities and supercells containing up to 216 atoms. Our calculations suggest that, by pairing, N vacancies, which in isolation act as shallow donors, can lower their collective formation energy by about 5 eV. In doing so, however, these N vacancies lose their shallow-donor character as the lattice relaxes in response to this aggregation. Contrasting with the N vacancies, the Ga vacancies are found to retain their isolated shallow acceptor behavior and do not gain significant energy upon aggregation. The possible implications for larger aggregate defects are discussed.
Hydrogen Passivation Of Er-Doped AIN
Authors: Pearton S. J. , Abernathy C. R. , MacKenzie J. D. , Hömmerich U. , Zavada J. M. , Rent F. , Wilson R. G. , Schwartz R. N.
Published: April 2011

AIN(Er) doped with Er during Metal Organic Molecular Beam Epitaxy has been plasma hydrogenated in-situ at 200–250°C using an Electron Cyclotron Resonance source. By isotopic substitution of 2H for 1H, we have found from Secondary Ion Mass Spectrometry profiling that a 30 min hydrogenation treatment can incorporate ˜2×1019cm−3 deuterium atoms to depths ≥1μm. The intensity of the 1.54μm Er3+ luminescence is increased by a factor of ˜5 by the 200°C hydrogenation, and this effect is thermally stable to 300°C, indicating a binding energy of >1.5eV for hydrogen at defects in the AIN. These defects would normally either be recombination centers or provide an alternative de-excitation path for the Er. We have previously found that AIN provides the best resistance to thermal quenching of Er luminescence of any semiconductor due to its wide bandgap. Together, these results suggest that AIN(Er) may be a promising material for optical control of devices such as light-triggered SiC or GaN thyristors for power switching applications, where a fiber-transmitted signal from temperaturetolerant material is necessary in controlling power distribution grids. Hydrogen does not leave the AIN until ˜800°C and presumably forms an intermediate state such as H2 or larger clusters prior to evolution from the surface, and again this stability is among the best for any semiconductor.
Residual Oxygen Determination In Silicon Epilayer, Comparison With Ftir Measurements
Authors: Degas F. , Blondiaux G. , Pichaud B.
Published: April 2011

For power devices the use of silicon epilayer on CZ substrate is a solution to make devices with a low oxygen concentration in the active zone. Oxygen is probably one of the most important residual impurities in silicon samples. Usualy the determination of the interstitial oxygen is done by Fourier Transform Infra Red spectroscopy (FTIR). In this work we have determined oxygen by Charged Particle Activation Analysis (CPAA). The main difference between these two techniques is that CPAA gives the total oxygen concentration whereas FTIR gives interstitial oxygen.

We have determined the oxygen in 200μm thick silicon epilayer and studied its behavior during thermal treatments. Oxygen concentration is found in the range of 1015/cm3 just after the epitaxial process. After thermal treatment the concentration in the epilayer rose to several 1016/cm3 to 1017/cm3, depending on the treatment. A comparison with FTIR experiment is done and the amount of oxygen precipitate is determined.
In-Situ Monitoring Of Etch By-Products During Reactive Ion Beam Etching Of Gaas In Chlorine/Argon
Authors: Lee J. W. , Pearton S. J. , Abernathy C. R. , Vawter G. A. , Shul R. J. , Bridges M. M. , Willison C. G.
Published: April 2011

Mass spectrometry of the plasma effluent during Reactive Ion Beam Etching (RIBE) of GaAs using an Inductively Coupled Plasma (ICP) source and a Cl2/Ar gas chemistry shows that AsCl3, AsCl2 and AsCl are all detected as etch products for As, while GaCl2 is the main signal detected for the Ga products. The variation in selective ion currents for the various etch products has been examined as a function of chuck temperature (30–100°C), percentage Cl2 in the gas flow, beam current (60–180 mA) and beam voltage (200–800 V). The results are consistent with AsCl3 and GaCl3 being the main etch product species under our conditions, with fragmentation being responsible for the observed mass spectra.
Understanding The Role Of Defects In Limiting The Minority Carrier Lifetime In Sic
Authors: Doolittle W. A. , Rohatgi A. , Ahrenkiel R. , Levi D. , Augustine G. , Hopkins R. H.
Published: April 2011

Deep level Transient Spectroscopy (DLTS), Electron Beam Induced Current (EBIC), EBIC Diffusion Length Mapping (EBIC-DLM) and contactless Photoconductive Decay (PCD) were used to characterize both bulk substrates and epitaxially grown Silicon Carbide films. Traps as deep as 0.93 eV were observed via DLTS. These traps may play a role in the persistent photoconductivity effect. EBIC reveals the electrical activity of the well known triangular defects. However, only some of these defects display electrical activity consistent with that of 3C-SiC inclusions, others do not. Additionally, not all defects identified in the EBIC images are observable in the topographic SEM image, possibly indicating a new, yet unidentified defect. EBIC revealed the electrical activity of defects including micro-pipes, dislocations (or possibly growth step edge decoration), surface polish damage, and bulk defects. Diffusion length maps of SiC indicate wide variations in diffusion length on both microscopic and macroscopic scales. EBIC-DLMindicatedepitaxial 4H SiC resulted in diffusion lengths from 0.1 to 3 μm, while bulk values were less than 0.07 μm. PCD measurements indicate tens of nanosecond to microsecond variations in lifetime. Lifetime verses injection level variations are observed and explained on the basis of trap energy. The injection level dependence of lifetime was observed at various nitrogen doping concentrations. Finally, electron beam annealing is found to dramatically improve the minority carrier lifetime in epitaxial SiC.
Theoretical Model And Computer Simulation Results Of Enhanced Diffusion Of High-Temperature Implanted Aluminum In Silicon Carbide
Authors: Gadiyak G. V.
Published: April 2011

Wide applications of silicon carbide (SiC) films in microelectronics devices make especially important predictions of the doping profiles during and/or after thermal treatment. A macroscopic kinetic model of enhanced diffusion of aluminum in SiC films during ion bombardment at high temperatures has been considered. The set of equations describing the kinetic model takes into account generation Vc and Csi vacancies during bombardment, migration of mobile species (Al) toward the surface and reactions of Al atoms with Vc and Vsi vacancies, as well as Al evolution from the film. The calculations were carried out for the flux of Al ions with energy 40 keV and current density 20 μA/cm2 to a dose 2 1016 cm−2 at 1800° C. The calculations have shown that the Al content in SiC at these condition does not exceed 40%. The calculation profile of Al is in a good agreement with experimental data [1].
Pld Epitaxial Tin Contacts To 6H-Sic And Gan
Authors: Talyansky V. , Vispute R. D. , Andronescu S. N. , Iliadis A. A. , Jones K. A. , Choopun S. , Dowries M. J. , Sharma R. P. , Venkatesan T. , Li Y. X. , Salamanca-Riba L. G , Wood M. C. , Lareau R. A.
Published: April 2011

We have investigated the influence of TiN growth temperature on the contact resistance in TiN/SiC and TiN/GaN heterostructures. Epitaxial TiN layers grown at temperatures above 600°C formed low resistance contacts to n-type 6H-SiC and GaN of 1.1× 10−3 Ωcm2 and 7.9 ×10−5 Ωcm2, respectively. Structural and electrical characterization of TiN thin films is discussed.
Wet Chemical Etching Survey Of III-Nitrides
Authors: Cho Hyun , Hays D. C. , Vartuli C. B. , Pearton S. J. , Abemathy C. R. , MacKenzie J. D. , Ren F. , Zolper J. C.
Published: April 2011

Wet chemical etching of GaN, InN, AIN, InAlN and InGaN was investigated in various acid and base solutions at temperatures up to 75°C. Only KOH-based solutions were found to etch AIN and InAlN. No etchants were found for the other nitrides, emphasizing their extreme lack of chemical reactivity. The native oxide on most of the nitrides could be removed in potassium tetraborate at 75°C, or HCl/H2O at 25°C.
Applications Of High Power Electronic Switches In The Electric Power Utility Industry And The Needs For High Power Switching Devices
Authors: Heydt G. T. , Skromme B. J.
Published: April 2011

This paper is a review of the main issues relating to power electronic devices as used (or proposed) for the electric power engineering area. Several applications are described. Costs of the devices are discussed. The future of the area is conjectured in terms of the needed breakthroughs in power electronic devices.
Bulk Growth Of Silicon Carbide Crystals: Analysis Of Growth Rate And Crystal Quality
Authors: Hofmann D. , Eckstein R. , Kadinski L. , Kölbl M. , Müller M. , Müller St. G. , Schmitt E. , Weber A. , Winnacker A.
Published: April 2011

The process conditions during SiC bulk crystal growth by physical vapor transport (PVT) are studied both theoretically and experimentally focussing on the magnitude of achievable growth rates V and possible correlations with defect formation. An increase of micropipe density with crystallization rate is observed. Growth parameters determining V are identified allowing a general non-dimensional representation of the dependencies of growth rate from kinetics, mass transport and heat transfer. It can be shown that at conventional process conditions of SiC growth by sublimation in graphite environment (5 mbar ≤p≤ 100 mbar, 2400K ≤T≤ 2600K) growth is limited by diffusion and kinetics for very short crystal lengths L and by heat transfer for geometries L> 1 mm. Including possible destabilizing effects due to constitutional supercooling an augmentation of V without deteriorating crystal quality should be conducted by stochiometry control for supression of graphitization and control of the thermal field tailoring the axial heat transfer with process time. Finally SiC growth from the liquid phase is introduced to promise a growth technique for specific SiC material as, in contrast to PVT growth, the closing of micropipes is demonstrated to be feasible.
Uniformity, High Temperature Performance And Reliability Of X-Band Nitride Power Hemts Fabricated From 2-Inch Epitaxy
Authors: Hickman R. , Hove J. M. Van , Chow P. P. , Klaassen J. J. , Wowchack A. M. , Polley C. J.
Published: April 2011

X-band performance, high temperature DC operation, and uniformity have been evaluated for 1 μm gate AlGaN/GaN HEMTs grown by RF atomic nitrogen plasma MBE. Deposition and fabrication were performed on 2-inch (0001) saphirre substrates to determine process uniformity. HEMTs with 300 μm total gate width and dual gate finger geometry have been fabricated with 650–700 cm2/V s mobility. Maximum frequency cut-offs on the order of of 8–10 were achieved. DC performance at room temperature was >500 mA/mm, and external transconductance was >70mS/mn. The transistors operated at test temperatures of 425°C.
Novel Fabrication of C-Doped Base InGaAs/InP DHBT Structures For High Speed Circuit Applications
Authors: Kopf R.F. , Hamm R.A. , Malik R.J. , Ryan R.W. , Burm J. , Tate A. , Chen Y-K. , Georgiou G. , Lang D.V. , Geva M. , Ren F.
Published: April 2011

We have fabricated InGaAs/InP based DHBTs for high speed circuit applications. A process involving both wet chemical and ECR plasma etching was developed. Carbon was employed as the p-type dopant of the base layer for excellent device stability. Both the emitter-base and base-collector regions were graded using quaternary InGaAsP alloys. The extrinsic emitter-base junction is buried for junction passivation to improve device reliability. The use of an InP collector structure with the graded region results in high breakdown voltages of 8V to IOV, with no current blocking. The entire structure is encapsulated with spin-on-glass. These devices show no degradation in DC characteristics after operation at an emitter current density of 90kA/cm2 and a collector bias, VCE, of 2V at room temperature for over 500 hours. Typical common emitter current gain was 50. An ft of 80 and fmax of 155 GHz were achieved for 2 × 4 μm2 emitter size devices.
Wide Bandgap Semiconductor Power Devices
Authors: Chow T. P. , Ramungul N. , Ghezzo M.
Published: April 2011

The present status of high-voltage power semiconductor switching devices is reviewed. The choice and design of device structures are presented. The simulated performance of the key devices in 4H-SiC is described. The progress in high-voltage power device experimental demonstration is described. The material and process technology issues that need to be addressed for device commercialization are discussed.
Atomic-Scale Analysis of the Reactivity of Radicals from Silane/Hydrogen Plasmas with Silicon Surfaces
Authors: Ramalingam Shyam , Maroudas Dimitrios , Aydil Eray S.
Published: April 2011

A systematic atomic-scale analysis is presented of the interactions of chemically reactive radicals originating in silane/hydrogen discharges with surfaces of hydrogenated amorphous silicon (a-Si:H) films. The hydrogen concentration on the surface is identified as the major factor that controls both the reactivity of the radicals and the surface reaction mechanism; other important factors include the location of impingement of the radical on the surface and the molecular orientation of the radical with respect to the surface. SiH is found to react with a-Si:H surfaces independent of location of impingement and radical orientation; the reaction mechanism, however, depends strongly on the hydrogen coverage of the surface and impingement location. Our results are in excellent agreement with experimental data for the reaction probability of SiH with a-Si:H film surfaces.
Ion Beam Deposition of Epitaxial Silicon Films
Authors: Khan H. R. , Frey H.
Published: April 2011

Silicon films of thicknesses (100 – 800 nm) are deposited on Si[111] substrate at 490°C using Si+ ions of energies (20 – 70 eV) from Silane plasma. The structure of the films depends on the energy of Si+ ions and the film grows epitaxially for ion energy <20 eV. Si films are analyzed by X-ray diffraction technique.
Novel Multilayer Process for CuInSe2 Thin Film Formation by Rapid Thermal Processing
Authors: Chang Chih-hung , Stanbery Billy , Morrone Augusto , Davydov Albert , Anderson Tim
Published: April 2011

CuInSe2 thin films have been synthesized from binary precursors by Rapid Thermal Processing (RTP) at a set-point temperature of 290°C for 70 s. With appropriate processing conditions no detrimental Cu2-xSe phase was detected in the CIS films. The novel binary precursor approach consisted of a bilayer structure of In-Se and Cu-Se compounds. This bilayer structure was deposited by migration enhanced physical vapor deposition at a low temperature (200°C) and the influence of deposition parameters on the precursor film composition was determined. The bilayer structure was then processed by RTP and characterized for constitution by X-ray diffraction and for composition by Wavelength Dispersive X-ray Spectroscopy.
Effects of Back Contact Treatments on Junction Photoluminescence in CdTe/CdS Solar Cells
Authors: Levi D. H. , Woods L. M. , Albin D. S. , Gessert T. A. , Niles D. W. , Swartzlander A. , Rose D. H. , Ahrenkiel R. K. , Sheldon P.
Published: April 2011

Device performance in CdTe/CdS solar cells is critically linked to the quality of the back contact. In this paper we report on a phenomenon wherein application of the back contact significantly alters the electro-optical properties of the absorber near the junction. We have studied the photoluminescence (PL) spectrum of the near-junction CdTe region in CdTe/CdS solar cells before and after contact application. It is found that the elemental Tellurium layer formed on the CdTe surface by the standard nitric-phosphoric etch process results in a dramatic qualitative change in the junction PL spectrum. Prior to NP etch, the spectrum has two peaks at energies of 1.50 eV and 1.45 eV, corresponding to recombination in bulk CdTe, and in a CdTeS alloy with 9% sulfur content, respectively. After NP etch, the relative intensity of the low-energy peak is reduced, and the peak shifts towards higher energy. These changes are consistent with a model of increased band-bending at the grain boundaries near the CdTe/CdS heterojunction.
Detailed Kinetics Modeling of Indium Phosphide Films in Mocvd Reactors
Authors: Masi Maurizio , Cavallotti Carlo , Radaelli Guido , Carrà S.
Published: April 2011

The deposition kinetics of InP in MOCVD reactors is presented. The proposed chemical mechanism involves both gas phase and surface reactions. The fundamental hypothesis adopted in deriving the mechanism was a dual site dissociative adsorption of the precursors on the growing surface. In any case, all the rate constants either were taken from the literature or estimated through thermochemical methods. In addition, the deposition reactor was simulated by means of a monodimensional model that accounts for the main reactor features through the boundary layer theory.
Composition and Structure of Vicinal Ge(100) Surfaces Exposed to Tertiarybutylarsine
Authors: Gan Shupan , Li Lian , Han Byung-Kwon , Hicks Robert F.
Published: April 2011

Germanium (100) substrates, 9° off axis towards the [011] direction, were heated in 2.0 Torr tertiarybutylarsine and 97.0 Torr hydrogen for 30 min at 650°C, then transferred to an ultrahigh vacuum system and annealed at several temperatures between 400 and 700°C. The arsenic coverage remained constant at 1.0 monolayer during heating in vacuum to 400°C. Further heating to 700°C caused the As coverage to gradually fall to zero. A mixed domain (l×2)+(2×l) dimer-terminated surface was observed by scanning tunneling microscopy after annealing at 400 to 510°C. Between 510 and 580°C, a single domain (l×2) reconstruction was recorded that contained equally spaced terraces separated by steps four atomic layers in height. Above 600°C, a (2×l) Ge(100) surface was produced that contained uniform terraces separated by steps two atomic layers in height.
Nucleation Studies Of Zns And ZnO Growth By Chemical Bath Deposition (CBD) On The Surface Of Glass And Tin Oxide Coated Glass
Authors: Mcaleese John , O'Briena Paul
Published: April 2011

We have studied the initial stages of nucleation and growth of ZnS and ZnO on glass and tin oxide coated glass in chemical baths containing thiourea as a source of sulfide ions. The results are used to comment on strategies for the deposition of ZnS and related ternary materials.
Deposition Of Znte Thin Films By Close Spaced Sublimation: Structural And Electrical Studies
Authors: Goyal D. J. , Bilurkar P. G. , Thorat S. K. , Mate N. V.
Published: April 2011

Zinc telluride has the potential of being a low-cost, environmentally stable, lowresistance and easily manufacturable back contact for CdS/CdTe solar cells. Close Spaced Sublimation (CSS) technique is used to deposit thin films of ZnTe. The results are reported in this study.

The effects of substrate temperature and film thickness on the structural properties of the deposited thin films are studied. X-ray diffractograms show that all the films prominently exhibit presence of (111) and (200) orientations. However, the degree of the preferred orientation changes as a function of the film thickness. Increase in film thickness reduces the preferential orientation.

The as deposited ZnTe thin films, being that of p-type semiconductor, are highly resistive. In order to effectively use these as contact to CdS/CdTe solar cells, they are made more conductive by doping copper. The doping is effected by dipping the films in alcoholic solution of copper chloride, followed by air annealing at 200°C. The resistivity of all the doped films drops drastically in the initial 10 minutes of annealing. The extent of doping is controlled by varying the dipping time.

The effects of substrate temperature, film thickness and doping, on the stoichiometry of the films, are studied using Atomic Absorption Spectroscopy (AAS).
Solution-Grown Cds Thin Films For Solar Cells
Authors: Shin Jae Heyg , Hyeun Seung Wook , Shin Sung Ho , Park Jung , Park Kwang Ja
Published: April 2011

Thin films of CdS were prepared from an solution containing Cd(Ac)2, NH4OH, NH4Ac and (NH2)2CS for solar cells. Growth rate of CdS films was increased with increasing temperature of reactive solution and with decreasing concentration of NH4OH. Optical transmittances were more than 60% independent with temperature and concentrations and was changed with thickness of CdS films. Grown films mostly showed the presence of polycrystallines with mixed cubic and hexagonal phases, but showed the hexagonal preferred phases in some growth condition. The resistivities of CdS were decreased by doping boron from 104 to 101 order(Ω - cm) and the critical amount of dopant was 5 × 10− .mol %
The Properties Of a-Si:H/c-Si Heterostructures Prepared By 55 kHz Pecvd For Solar Cell Application
Authors: Budaguan B. G , Aivazov A. A. , Sherchenkov A. A. , Blrjukov A. V , Chernomordic V. D. , Metselaar J. W.
Published: April 2011

In this work a-Si:H/c-Si heterostructures with good electronic properties of a-Si:H were prepared by 55 kHz Plasma Enhanced Chemical Vapor Deposition (PECVD). Currentvoltage and capacitance-voltage characteristics of a-Si:H/c-Si heterostructures were measuredto investigate the influence of low frequency plasma on the growing film and amorphous silicon/crystalline silicon boundary. It was established that the interface state density is low enough for device applications (<2.1010 cm−2). The current voltage measurements suggest that, when forward biased, space-charge-limited current determines the transport mechanism in a- Si:H/c-Si heterostructures, while reverse current is ascribed to the generation current in a-Si:H and c-Si depletion layers.
Low Temperature Growth of Crystalline Silicon Thin Films by ECR Plasma CVD
Authors: Wang Licai , Reehal H S
Published: April 2011

Crystalline silicon films have been deposited on silicon and metal-coated coming 7095 glass substrates at temperatures of 280 ˜ 680°C by electron cyclotron resonance (ECR) plasma assisted chemical vapor deposition (PACVD) using an ultrahigh vacuum chamber and SiH4 as the feedstock. X-ray diffraction (XRD), Raman spectroscopy, Rutherford backscattering (RBS) and secondary ion mass spectrometry (SIMS) have been used to characterize the films. At temperatures of ˜280 °C, the as-grown films are microcrystalline with crystalline fractions between 50–97%. From XRD patterns, randomly oriented crystalline silicon grains were clearly present in the films with the grain sizes estimated to be between 170 – 370Å. As the growth temperature is increased to 470°C, epitaxial growth on silicon is observed at growth rates of 240Å/min without bias or hydrogen plasma treatment before film growth. N-type doping of the layers has been achieved using PH3 as the doping gas and solar cells with ECR grown emitters fabricated on 15μm thick p-type epilayers on p+ substrates.
Impact Excitation And Auger Quenching Processes In Er Doped Light Emitting Si Devices
Authors: Franzo' G. , Priolo F. , Coffa S.
Published: April 2011

A detailed investigation of the Auger non radiative de-excitation processes, which compete with the radiative emission of Er in Si, will be presented. This process, in which the energy released by the Er de-excitation is transferred to free carriers, is demonstrated to be extremely efficient and characterized by an Auger coefficient CA˜4.4×l0−13 cm3/s. This Auger process and an efficient incorporation method have been used to improve the performances of Er implanted light emitting diodes. It will be shown that by exciting Er within the depletion region of reverse biased p+-n+ Si diodes in the breakdown regime, it is possible to avoid Auger quenching and to achieve high efficiency. Moreover, at the switch off of the diode, when the depletion region shrinks, the excited Er ions become suddenly embedded within the neutral heavily doped region. In this region Auger de-excitation with free carriers sets in allowing to modulate the light signal at frequencies as high as a few MHz.
Light-Emitting Si:Er:O Diodes Operating In The Avalanche Regime
Authors: Sobolev N. A. , Emel'yanov A. M. , Gastev S. V. , Khakuashev P. E. , Nikolaev Yu. A. , Trishenkov M. A.
Published: April 2011

Electroluminescence (EL) characteristics of avalanching diodes fabricated by Er and O co-implantation and subsequent annealing have been studied. Distribution of Er3+-related EL at 1.538 μm was found to be uniform over the device area at 300 K. Saturation of the Er-related EL intensity is achieved under the avalanche regime at current density one order of magnitude lower than that under the tunnel regime. An EL decay is less than 10 μs (being time response of our detector) after the diode turned off the avalanche regime.
Electroluminescence Studies Of Si Bulk Materials Using Al-Si Schottky Diodes
Authors: Du Chun-Xia , Ni Wei-Xin , Joelsson Kenneth B. , Shen Guang-Di , Hansson Göran V.
Published: April 2011

Electroluminescence (EL) of Si bulk materials has been studied using lowly doped substrate with two Al-Si Schottky contacts. By applying a forward bias on the structure, the intense light emissions at 1.094 eV due to the TO-phonon assisted recombination was obtained at 40 K while other TA- and 2TO-associated transitions were also observed. The Si-TO EL peak persists up to RT with a radiative decay of ∼ 5 μs. EL emission mechanisms of these Si Schottky diodes are discussed based on temperature dependent- and injection current-dependent EL measurements.
The Oxidation Behavior of Silicon Nanocrystals in the Submonolayer Region
Authors: Diener J. , Ben-Chorin M. , Kovalev D. I. , Polisski G. , Koch F.
Published: April 2011

Fourier transform infrared spectroscopy is used to determine the time evolution of oxygen incorporation onto the surface of silicon nanocrystals. Oxygen concentrations up to one monolayer are investigated. The temporal progress of surface oxidation of Si nanocrystals in porous silicon shows a linear dependence on the square root of the oxidation time. This is similar to the oxidation of bulk Si and mesoporous silicon.
Composition dependence of room temperature 1.54μm Er3+ luminescence from erbium doped silicon:oxygen thin films deposited by electron cyclotron resonance plasma enhanced chemical vapor deposition
Authors: Shin Jung H. , Kim Mun-Jun , Seo Se-Young , Lee Choochon
Published: April 2011

The composition dependence of room temperature 1.54 μ Er3+ photoluminescence of erbium doped silicon:oxygen thin films deposited by electron cyclotron resonance plasma enhanced chemical vapor deposition of SiH4 and O2 with concurrent sputtering of erbium is investigated. The Si:O ratio was varied from 3:1 to 1:2 and the annealing temperature was varied from 500 to 900 °C. The most intense Er3+ luminescence is observed from the sample with Si:O ratio of 1:1.2 after 900 °C anneal and formation of silicon nanoclusters embedded in SiO2 matrix. High active erbium fraction, efficient excitation via carriers, and high luminescence efficiency due to high quality SiO2 matrix are identified as key factors in producing the intense Er3+ luminescence.
Silicon-Based Optoelectronics
Authors: Buchal Ch. , Löken M. , Siegert M.
Published: April 2011

The potential of silicon-based designs for various optoelectronic functions is discussed. Sibased light detectors are the most advanced, especially in the form of metal-Si-metal (MSM) photodetectors. They use Si band to band absorption for visible light and Schottky-barrier emission for the infrared (IR). The different light sources show rapid progress, but still face challenges to reach a quantum efficiency of 10−2. In addition to the intrinsic silicon based designs, some new Si breadboard concepts are shown: especially for waveguides, modulators and all-optical amplifiers, it may be advantageous to add entirely different materials (polymers, glasses, BaTiO3 or Al2O3) onto the Si wafer.
Optical Characterization of As2Te3 Films for for Optical Interconnects
Authors: Globus T. R. , Gaskill D. K. , Groshens T.
Published: April 2011

Absorption coefficient and refractive index measurements of stoichiometric As2Te3 thin films grown on Si and KBr substrates are presented. The films were grown by an organometallic deposition process where the sources for both As and Te react at reduced pressures and temperatures to produce stoichiometric films in the presence of a surface; no growth occurs otherwise. Films were grown at 300 and 373 K and had a thickness range of about 0.2–1.2 μm. The refractive index was sample independent and had strong dispersion near the optical gap, rapidly increasing from the value of 3.8 at 1.5 μm as the wavelength decreases. An interference technique was utilized to measure the absorption of the films since interference effects and substrate absorption bands hindered the application of conventional optical transmission techniques. The optical gaps, obtained from Tauc plots, were in the range 0.83–0.95 and the results confirm that the As2Te3 films behave as noncrystalline semiconductors, being either amorphous or partially crystalline. Amorphous films on Si had absorption in the range of optical transparency comparable to that of the substrate, films on KBr substrates had much higher absorption.
Beyond-The-Roadmap Technology: Silicon Heterojunctions, Optoelectronics, and Quantum Devices
Authors: Seabaugh Alan , Lake Roger , Brar Bobby , Wallacet Robert , Wilk Glen
Published: April 2011

The roadmap for silicon device technology has been drawn, extending to the year 2010, and featuring a CMOS transistor with a gate length of 0.07 μm [1]. Beyond this point, silicon heterojunctions could provide a means to further device scaling. Silicon heterojunctions could also bring new devices to the silicon substrate including light emitters and detectors, and resonant tunneling diodes (RTDs). Today SiGe/Si and SiGeC/Si heterojunctions are receiving the greatest attention, but heterojunctions now being developed to realize silicon RTDs are increasing the heterojunction options for silicon-based quantum-well and optical devices. Here we outline the fundamental device requirements for silicon optical and tunneling devices and describe progress on silicon heterojunction development towards demonstration of silicon-based RTDs. Materials now under study include, ZnS, crystalline oxides and nitrides; new processes could provide methods for forming crystalline materials over amorphous barriers.
Modeling of the Surface Annihilation of Excess Self-Interstitials Generated by Gold Diffusion into Silicon
Authors: Stolwijk N. A. , Lerch W. , Giese A.
Published: April 2011

Based on the kick-out mechanism, we have modeled the time evolution of the Si self-interstitial supersaturation during gold diffusion from evaporated surface layers into silicon substrates. The model comprises a limited annihilation velocity υI of self-interstitials at the Si surface, which accounts for the gradual increase of the Au boundary concentration observed during rapid thermal annealing at higher temperatures and furnace annealing at lower temperatures. Experimental data were fitted by computer simulation of the Au diffusion process. An approximate analytical expression describing the increase of the Au boundary concentration with time is also given. We obtain υI 1.35 × 1011 exp(−3.91 eV/kBT) ms-1 for gold-covered {100}-oriented Si surfaces between 845 °C and 1119 °C.
Gold Diffusion in Silicon During Gettering by an Aluminum Layer
Authors: Joshi Subhash M. , Gösele Ulrich M. , Tan Teh Y.
Published: April 2011

Previous modeling of Al gettering of Au in Si indicated that, for an Al gettering layer placed on one surface of a Si wafer, Au will be gettered from both surface regions of the wafer to progressively greater depths with time. This is because, in Si, Au is a substitutional-interstitial (Aus-Aui) species with its diffusion governed by the kick-out mechanism which is mediated by Si self-inter-stitials (I). During gettering by the Al-Si liquid at one wafer surface, Aus atoms change over to Au atoms to rapidly migrate out of Si into the liquid. The changeover process consumes I. At the two wafer surface regions, the consumed I will be quickly replenished, while in the wafer interior an I undersaturation develops which hinders the Aus-Aui changeover and hence the gettering process. Experimental evidences which confirm the predictions have been obtained. Au was indiffused into a FZ Si wafer at 950°C for 16 hr. After removing the Au source and etching, samples from the in-diffused wafer were annealed at 1000°C without or with an Al layer on one surface. For samples without Al, there is no change in the net Au content, while the U-shaped indiffused profile becomes flatter. For samples with an Al layer, both wafer surface region Au concentrations were significantly decreased in 30 min while the wafer interior Au concentrations decreased only after annealing for longer times. The model predictions, the experimental results, and the implications on Si self-diffusion parameters will be discussed.
Robust Reaction-Transport Models of Movpe Reactors
Authors: Theodoropoulos C. , Moffat H. K. , Mountziaris T. J.
Published: April 2011

A simple gas-phase and surface kinetic model describing the Metalorganic Vapor Phase Epitaxy (MOVPE) of GaAs from trimethyl-gallium (TMG) and arsine has been extracted from reported reaction mechanisms through sensitivity analysis. This model was coupled with fundamental descriptions of the flow, heat and mass transfer in MOVPE reactors. All the uncertainties of the model were lumped into the two rate constants of the surface growth reaction. Finite element simulations of GaAs growth in a rotating-disk MOVPE reactor reported in the literature were used to fit the two unknown rate constants. Without any adjustment, the model could predict observed growth rates at higher susceptor rotational rates. A more serious robustness test was the fully coupled 2-D simulation of GaAs growth in a horizontal MOVPE reactor by using a state-of-the-art code (MPSalsa) developed at Sandia National Laboratories. The model predicted observed growth rates reasonably well in 2-D fully coupled simulations of flow, heat and mass transfer. Further development of the kinetic model by testing different kinetic scenaria in 2- and 3-d simulations and by using data obtained at kinetically-limited growth conditions is planned in order to develop a reactor-independent simulator of the MOVPE of GaAs. Such a model will be essential for the development of a conceptual virtual MOVPE reactor, which can be used for reactor design, optimization and model-based control.
A Theoretical Study on the Fundamental Chemical Reactions in Titanium Plasma-Enhanced CVD
Authors: Tsuda K. , Watanabe K. , Ohshita Y. , Takada T.
Published: April 2011

The important intermediates in the Ti plasma-enhanced CVD using TiCl4/Ar/H2 are investigated by ab initio molecular orbital (MO) calculations. From the experimental point of view, it is pointed out that'TiCls is a key species for the Ti deposition reaction. So, its reactivity with the Si and SiO2 substrates is estimated theoretically from the stabilization energy. The difference of the stabilization energies of TiCl3 between them, which is 12.3kcal/mol in Hartree-Fock level calculations with using the on-top deposition reaction model, indicates a longer existing time by the factor of 102 on SiO2 than on Si. In addition to these calculations, the stabilization energies on the suicide substrates are also calculated and compared with the results on the Si and Si02 substrates. But other reaction paths may have to be considered because the growth rates of Ti thin films onto between Si and SiO2 don't necessarily coincide with the tendency of calculated results.