bluuebunny/crossref_metadata_2025 huggingface dataset:
Defect Equilibration in Amorphous Silicon Films Submitted to High Intensity Illumination
Authors: Godet C. , Cabarrocas P. Roca i
Published: April 2011

In plasma-deposited a-Si:H films, the increase of the metastable defect density produced by high-intensity illumination usually follows a stretched-exponential time-dependence, with a characteristic time τSE and a steady-state value Nss. For a wide range of deposition conditions, we have observed that both parameters depend on the material properties. The strong correlation between Nss and the monohydride [SiH]2000 density, reported previously, has been interpreted as due to the trapping of metastable H atoms at specific sites.

In this study of the kinetics of defect equilibration under high-intensity illumination, we find two groups of a-Si:H films with fast and slow kinetics, respectively. These two groups display a very different dependence of the defect creation rate as a function of the optical gap. For the fast kinetics films, we emphasize the critical influence of the Urbach energy Eu deduced from the exponential optical absorption edge (1/τSE increases as a function of Eu). The slow kinetics films are characterized by a high nanovoid density evidenced by their SiHx infrared signature at 2090 cm-1. The results are discussed in relation to the medium-range H motion.
Partial Depletion Region Collapse and its Impact on Transient Capacitance Measurements
Authors: Lips Klaus , Unold Thomas , Xu Yueqin , Crandall Richard S.
Published: April 2011

We investigate capacitance transients under various experimental conditions on a number of different amorphous silicon Schottky barrier device structures. The samples differ mainly in their back contact configuration, which is non-ohmic for one type of sample and ohmic for the second type of samples. Anomalous transients can be observed for all samples regardless of the back contact if the depletion region is only partially collapsed by partial voltage pulsing. We find that samples without an ohmic back contact show a slowly rising capacitance during the filling pulse. These samples show anomalous capacitance transients for short filling pulses.
Determination of the Density of States in a-SiC:H from Transient Photoconductivity
Authors: Brüggemann R. , Maint C. , Rösch M. , Webb D. P.
Published: April 2011

In order to fill the gap of little knowledge about their details, the density of states distributions (DOS) in the upper half of the band gap were determined for a series of wellcharacterised amorphous hydrogenated silicon carbide samples with Tauc gaps between 1.78 and 1.94 eV. A DOS spectroscopic technique, based on the Fourier transform of time-sampled transient photocurrents, allowed the DOS determination on an absolute scale for a wide energy range. The DOS increases in the band tail region with carbon content. It exhibits a minimum at about 0.5 eV which is followed by a defect structure at deeper energies, the density of which also increases with C-content. We find a decreasing time-dependent drift mobility for larger C-content consistent with the lower transit time-determined drift mobility in time-of-flight.
Comparison of Experiment and Theory of the Photoconductivity of a-Si:H up to a Generation Rate of 1028cm−3s−1
Authors: Stradins P. , Fritzschei H. , Tzanetakis P. , Kopidakis N.
Published: April 2011

We have studied the dependence of the photoconductivity σp on photocarrier generation rate G in intrinsic a-Si:H at 300K between G=1012cm−3s−1 and 1028cm−3s−1. Below a certain value Go, we find σo =AGγ with γ=0.9±0.05 and the values of A vary considerably with defect concentration Nd which signifies monomolecular recombination through defects. Above Go the recombination is bimolecular, γ=0.5±0.02 and A=(6±3)×10−15 Ω−1cm1/2s1/2 is indpendent of Nd. The transition value Go is about 3×1020cm−3s−1 for high quality annealed a-Si:H and increases with Nd. A simulation of σp(G) assuming conduction in and recombination from extended states fits our experiments within a capture coefficient Ct=(6±2)×10−9cm3s−1 of carriers to their opposite tail states. Our Ct is close to the value (5±2)×10−9cm3s−1 obtained from optical measurements but higher than (0.5±0.1)×10−9cm3s−1 determined from photoelectric studies. Below T=150K our model calculations overestimate σp because the tunneling transitions, becoming important for recombination and conduction, are neglected.
Monte Carlo Simulation of Transient Currents in a-Si:H
Authors: Chen Wen Chao , hamel Louis-André
Published: April 2011

Multi-trapping transient currents through pure exponential band tails are calculated by Monte Carlo simulations of unprecedented accuracy. The time and energy dependent carrier distributions, the current and the charge signals are obtained. The transit time tT and the dispersion parameters α1, and α2, before and after the transit time, are extracted from the simulated currents. Results are presented for the expected temperature dependence of α1 and α2 and of the drift mobility μD for electrons and holes in a-Si:H. At low temperature, α1 = α2 = T/To is found, but above T ≈ 0.6To, α1, bends downwards to saturate at 1 at high temperature while α2 bends upwards, clearly improving the agreement with the experimental data. The temperature dependence of the drift mobility μD is well reproduced for holes with a microscopic mobility of μo = 0.5 cm2V−1s−1. For electrons, the agreement is also excellent but the surprisingly low value of μo = 4 cm2V−1s−1 is found.
Study of Recombination Processes in a-Si:H by the Temperature Dependence of the two Carriers Phototransport Properties
Authors: Lubianiker Y. , Naidis R. , Balberg I. , Fonseca L. , Weisz S. Z.
Published: April 2011

We have studied films of undoped hydrogenated amorphous silicon by measuring their phototransport properties as a function of temperature. The samples were prepared by decomposition of silane using either the rf glow discharge or the hot-wire techniques. Both materials exhibit similar temperature dependences of the phototransport properties. The main difference is that the thermal quenching effects in the hot-wire material occur at a lower temperature. The results are consistent with the “standard” recombination model, to which recombination through the bandtails is added. The differences in the thermal quenching effects are attributed to the higher density of conduction bandtail states in the hot-wire material, and to differences in the position of the Fermi level with respect to the dangling bond states.
Transport Properties of Compensated μc-Si:H
Authors: Wyrsch N. , Goerlitzer M. , Beck N. , Meier J. , Shah A.
Published: April 2011

Electron and hole transport in completely microcrystalline silicon (μc-Si) p-i-n cells and in intrinsic or near intrinsic μc-Si layers have been investigated, for the first time, by time of flight (TOF) at temperatures between 100 and 400 K.At room temperature, both electron and hole drift mobilities were found to be between 0.2 and 1 cm2 V-ls-1. No trace of anomalous dispersive transport was observed, neither for electrons nor for holes, down to 100 K. A decrease of the drift mobility was observed when the temperature was raised from room temperature to 400 K as usually observed in crystalline semiconductors. However, these experimental values of the drift mobilities appear more puzzling than helpful for the comprehension of this “new” photovoltaic material.
Optoelectronic Properties of Thin Amorphous and Micro-Crystalline p-Type Films Developed for Amorphous Silicon-Based Solar Cells
Authors: Winz K. , Rech B. , Eickhoff T. H. , Beneking C. , Fortmann C. M. , Hapke P. , Wagner H.
Published: April 2011

VIIF-PECVD at 110 MI-z was used to deposit micro-crystalline p-layers on glass substrates for detailed analysis and onto ZnO coated substrates for incorporation into p-i-n solar cell structures. Solar cell and film analysis confirmed that the films incorporated into the solar cells contained significant crystalline silicon volume fractions despite being only 30 nm thick. The p-i-n solar cells employing a micro-crystalline silicon p-layer deposited on ZnO coated substrates had series resistances, fill factors and Voc similar to those of the reference solar cells deposited onto SnO2 coated substrates and having optimized amorphous silicon-carbon p-layers. The short circuit current of the micro-crystalline p-layer case was 10 percent lower than that of the reference cell indicating that further optimization is required.
Surface Roughness of Silicon-Nitride Gate Insulators Deposited in a 40-MHZ Glow Discharge
Authors: Meiling H. , Grotenhuis E. Ten , Weg W. F. Van Der , Hautala J. J. , Westendorp J. F. M.
Published: April 2011

The surface morphology of 40-MHz PECVD SiNx films is investigated. We report on the correlation between the deposition conditions, bulk properties, and surface roughness of these TFT insulators. The roughness is measured with atomic-force microscopy, AFM. A link will be presented between the AFM properties and the effects of hydrogen dilution during deposition: gas composition and rf-power-density (P) dependences will be discussed. An increase of the surface roughness to 3.7 nm is observed upon H2 dilution and P increase, ascribed to enhanced ion bombardment of the surface during growth.
Band-Structure Engineering in Novel Optoelectronic Devices
Authors: Shen H. , Dutta M.
Published: April 2011

In this paper we show that unconventionally strained semiconductor heterostructures with unusual band structure exhibit novel and desirable electronic and optical properties not seen in the conventional strained materials. In addition to improving the performance of existing components, unconventional strain may be used to achieve greater functionality in novel optoelectronic devices. We give as examples three such devices that we have conceived and demonstrated, in the two areas of strain, lattice mismatch induced and thermal expansion coefficient mismatch induced. The higher performance and functionality in these devices demonstrate that strain engineered heterostructures are a very promising area for device research and development.
Dry Etching of SiC for Advanced Device Applications
Authors: Flemish J. R. , Xie K. , Mclane G. F.
Published: April 2011

In this paper we review and compare most of the published results on dry etching of silicon carbide using various techniques. The vast majority of reports have used RIE methods due to the wide availability of such reactors. Recently, alternative methods of magnetron enhanced RIE (MIE) and electron cyclotron resonance (ECR) plasmas have been demonstrated. MIE has resulted in extremely high etch rates and ECR etching has resulted in smooth, residue-free surfaces with an ability to control the etched profiles.
Studies of Degradation in Nichia AlGaN/InGaN/GaN Blue Light Emitting Diodes Under Close to Normal Operating Conditions
Authors: Osiński M. , Barton D. L. , Helms C. J. , Perlin P. , Berg N. H. , Sartori P. , Phillips B. S.
Published: April 2011

The reliability of devices fabricated in GaN and related alloys, especially under high current densities as would be found in lasers, has yet to be fully characterized. Our previous work [1] investigated the degradation of GaN-based blue light emitting diodes (LEDs) under high pulsed current stress. This work indicated a possible correlation between the high crystal defect density and failures caused by metal migration along these defect tubes. To assess the impact of this data on devices under more normal conditions, several LEDs from both older and more recent production lots were placed in a controlled temperature and current environment for several thousand hours. The test started with a constant 20 mA current for the first 1000 hours and continued for another 1650 hours at various currents up to 70 mA, all at a temperature of 23 °C. During this test, one of the older generation LED's output degraded by more than 50%. Subsequent failure analysis showed that this was caused by a crack which isolated part of the active region from the p-contact. The remaining LEDs were returned to life testing where the temperature was subsequently increased by 5 °C after each 500 hours of testing. The output from one of the newer LEDs dreiven at 70 mA degraded to 55% of its original value after 3600 hours and a second newer LED degraded by a similar amount after 4400 hours. The first failure, LED #16, did not exhibit a significant change in its I-V characteristics indicating that a change in the package transparency was a likely cause for the observed degradation. The second failure, LED #17, did show a noticeable change in its I-V characteristics. This device was subsequently returned to life testing where the degradation process will be monitored for further changes.
Ion Implantation For High Performance Ill-V Jfets And Hfets
Authors: Zolper J. C. , Baca A. G. , Sherwin M. E. , Klem J. F.
Published: April 2011

Ion implantation has been an enabling technology for the realization of many high performance electronic devices in III-V semiconductor materials. We report on advances in ion implantation processing technology for application to GaAs JFETs, AlGaAs/GaAs HFETs, and InGaP or InA1P-barrier HFETs. In particular, the GaAs JFET has required the development of shallow p-type implants using Zn or Cd with junction depths down to 35 nm after the activation anneal. Implant activation and ionization issues for AlGaAs will be reported along with those for InGaP and InAlP. A comprehensive treatment of Si-implant doping of AlGaAs is given based on the donor ionization energies and conduction band density-of-states dependence on Al-composition. Si and Si+P implants in InGaP are shown to achieve higher electron concentrations than for similar implants in AlGaAs due to the absence of the deep donor (DX) level. An optimized P co-implantation scheme in InGaP is shown to increase the implanted donor saturation level by 65%.
Cl2-Based ECR Etching of InGaP, AlInP and AIGaP
Authors: Hong J. , Lee J. W. , Pearton S. J. , Santana C. , Abernathy C. R. , Hobson W. S. , Ren F.
Published: April 2011

High microwave power (1000W) Electron Cyclotron Resonance (ECR) Cl2/Ar plasma produce etch rates for In0.5Ga0.5P, Al0.5In0.5P and Al0.5Ga0.5P of ˜1um/min. at low pressure (1.5mTorr), moderate rf power levels (150W) and room temperature. Addition of Cl2 into Ar makes much smoother etched surface morphology as well as increasing the etch rate. All parameters, including microwave power, chamber pressure and rf power increase the etch rate of these alloys. Especially, there is at least a minimum rf power in order to get much higher etch rate with increasing microwave power. AlGaP in Cl2/Ar discharges has lower etch rates than InGaP or AlInP, which is similar to the results based on CH4/H2/Ar plasma chemistries. The Cl2/Ar chemistry enables smooth, high-rate etching without the need for polymer addition and thus simplifies the processing.
Plasma Chemistries for Dry Etching GaN, AIN, InGaN and InAIN
Authors: Pearton S. J. , Vartuli C. B. , Lee J. W. , Donovan S. M. , MacKenzie J. D. , Abernathy C. R. , Shul R. J. , McLane G. F. , Ren F.
Published: April 2011

Etch rates up to 7,000Å/min. for GaN are obtained in Cl2/H2/Ar or BCl3/Ar ECR discharges at 1–3mTorr and moderate dc biases. Typical rates with HI/H2 are about a factor of three lower under the same conditions, while CH4/H2 produces maximum rates of only ˜2000Å/min. The role of additives such as SF6, N2, H2 or Ar to the basic chlorine, bromine, iodine or methane-hydrogen plasma chemistries are discussed. Their effect can be either chemical ( in forming volatile products with N) or physical ( in breaking bonds or enhancing desorption of the etch products). The nitrides differ from conventional III-V's in that bondbreaking to allow formation of the etch products is a critical factor. Threshold ion energies for the onset of etching of GaN, InGaN and InAlN are ≥75eV.
Movpe of Inp and Gaas Based Optoelectronic Materials in a Multiwafer Production Reactor Using Tba and Tbp Exclusively
Authors: Schmitz D. , Lengeling G. , Beccard R. , Jürgensen H.
Published: April 2011

In this paper a study of the growth of GaAs and InP based materials using the alternative precursors TBAs and TBP is presented. For this purpose mass production multiple wafer reactors were employed. Both long-wavelength materials such as GaInAsP on IWP and short wavelegth like GaInP and AIGaInP on GaAs are investigated. The results demonstrate that ther is no loss of material quality when using these novel precursors. In all cases growth temperatures and V/III ratios could be significantly lowered.
The Growth and Doping of Al(As)Sb by Metal-Organic Chemical Vapor Deposition
Authors: Biefeld R. M. , Allerman A. A. , Kurtz S. R.
Published: April 2011

AlSb and AlAsxSb1−x epitaxial films grown by metal-organic chemical vapor deposition were successfully doped p- or n-type using diethylzinc or tetraethyltin, respectively. AlSb films were grown at 500°C and 76 torr using trimethylamine or ethyldimethylamine alane and triethylantimony. We examined the growth of AlAsSb using temperatures of 500 to 600 ° C, pressures of 65 to 630 torr, V/Ill ratios of 1–17, and growth rates of 0.3 to 2.7 μm/hour in a horizontal quartz reactor. SIMS showed C and 0 levels below 2 × 1018 cm−3 and 6×1018 cm−3 respectively for undoped AlSb. Similar levels of O were found in AlAs0.16Sb0.84 films but C levels were an order of magnitude less in undoped and Sn-doped AlAs0.16 Sb0.84 films. Hall measurements of AlAs0.16Sb0.84 showed hole concentrations between l×1017 cm−3 to 5×1018 cm−3 for Zn-doped material and electron concentrations in the low to mid 1018 cm−3 for Sndoped material. We have grown pseudomorphic InAs/InAsSb quantum well active regions on AlAsSb cladding layers. Photoluminescence of these layers has been observed up to 300 K.
W, WSix and Ti/Al Low Resistance Ohmic Contacts to InGaN, InN and InAlN
Authors: Vartuli C.B. , Pearton S.J. , Abernathy C.R. , MacKenzie J.D. , Shul R.J. , Zolper J.C. , Lovejoy M.L. , Baca A.G. , Hagerott-Crawford M.
Published: April 2011

W, WSi0.44 and Ti/Al contacts were examined on n+ In0.65Ga0.35N, InN and In0.75Al0.25N. W was found to produce low specific contact resistance (Qc ˜ 10−7 Ω cm2) ohmic contacts to InGaN, with significant reaction between metal and semiconductor at 900 °C mainly due to out diffusion of In and N. WSix showed an as-deposited Qc of 4×10−7 Ω cm2 but this degraded significantly with subsequent annealing. Ti/Al contacts were stable to Ω 600 °C (Qc, ˜ 4×10−7 Ω cm2 at ≤600 °C). The surfaces of these contacts remain smooth to 800 °C for W and WSix and 650 °C for Ti/Al. InN contacted with W and Ti/Al produced ohmic contacts with Qc ˜ 10−7 Ω cm2 and for WSix Qc ˜ Ω cm2.All remained smooth to ˜ 600 °C, but exhibited significant interdiffusion of In, N, W and Ti respectively at higher temperatures. The contact resistances for all three metallization schemes were ≥ 10−4 Ω.cm2 on InAIN, and degrades with subsequent annealing. The Ti/Al was found to react with the InA1N above 400 °C, causing the contact resistance to increase rapidly. W and WSix proved to be more stable with Qc ˜ 10−2 and 10−3 Ω cm2 up to 650 °C and 700 °C respectively.
A Defect Map for Degradation of Ingaasp/Inp Long Wavelength Laser Diodes
Authors: Chu S.N.G. , Nakahara S.
Published: April 2011

We summarize the characteristic defect structures associated with gradual-degradation, rapiddegradation, catastrophic (mirror-facet) optical damage (COD), electric static discharge (ESD) and electric overstress (EOS) damages to provide a defect-map for device failure mode analysis. The generation mechanisms of these lattice defects are discussed which pinpoint the weak links in the device structures.
The 4f Intrashell Transitions of Ytterbium in Indium Phosphide
Authors: Maat-Gersdorf Ingrid De , Gregorkiewicz T. , Ammerlaan C. A. J. , Christianen P. C. M. , Maan J. C.
Published: April 2011

Zeeman measurements in magnetic fields up to 16 T have been performed on the no-phonon lines labelled #3, #4, and #8 of the spectrum of ytterbium impurities in indium phosphide. A strong polarization effect and changes in intensities were observed. An energy level diagram is presented that satisfactorily explains the magnetic field effect and the relative intensities of the photoluminescence lines and is consistent with experiments described in the literature.
Optical Anisotropy of Er Centers in GaAs:Er,O
Authors: Hogg R. A. , Takahei K. , Taguchi A. , Horikoshi Y.
Published: April 2011

For GaAs:Er,O the anisotropic photoluminescence (PL) properties of the Er-20 center and its preferential alignment within the GaAs matrix have been revealed by the polarization dependence of host-excited PL when detecting emission polarized along certain crystallographic directions. In the present paper, a polarized intra-4f-shell photoluminescence excitation (PLE) spectroscopic study of Er centers incorporated in GaAs is reported. This technique is not only sensitive to those centers which luminesce under host-excitation, but also to other Er centers incorporated in the host, thus allowing the polarized PL properties of most Er centers to be studied. A comparison of the polarization characterisitcs of host-excited PL and direct intra-4f-shell PLE, due to the difference in the excitation mechanisms, is made and the information which may be gained from such measurements is discussed. For the Er-20 center, we confirm the optical anisotropy and preferential alignment of the center previously observed in host-excited PL. Incorporation mechanisms for the Er-20 center which could result in the observed polarization dependence are discussed.
Incorporation, Excitation and De-Excitation of Erbium in Crystal Silicon
Authors: De Dood M. J. A. , Kik P. G. , Shin J. H. , Polman A.
Published: April 2011

Temperature quenching of the 1.54 μm photoluminescence intensity and lifetime of Er in crystal Si was investigated between 12 K and 150 K. A p-type Czochralski-grown Si (100) wafer was doped with Er to a peak concentration of 5×1018 cm−3 using 1.5 MeV ion implantation. The Er doped layer was co-implanted with N to a peak concentration of 6×1019 N cm−3 The sample was annealed at 490 °C for 2 hours and at 600 °C for 1 hour. The 1.54 μm photoluminescence intensity shows a weak temperature quenching between 12 and 75 K, characterised by an activation energy of 1–10 meV. For temperatures above 75 K, a strong intensity quenching with an activation energy of 210 ± 10 meV is observed. The luminescence lifetime decreases from 420 μs at 12 K to 1 μs at 170 K, and shows strong quenching behaviour above 75 K, characterised by an activation energy of 135 ± 5 meV. The results are interpreted in terms of an impurity Auger energy transfer model. The lifetime quenching is attributed to a phonon assisted backtransfer process which becomes dominant at high temperatures. Intensity quenching is attributed to both the backtransfer process and a carrier de-trapping process which reduces the Er excitation rate. Spectral response measurements on Er implanted solar cells confirm the presence of a backtransfer process at room temperature.
Photoluminescence Kinetics Model of P-Type GaAs:Nd
Authors: Saha U. K. , Lozykowski H. J.
Published: April 2011

In this work we have developed a model for the kinetics of the energy transfer from the host lattice to the core states of rare earth (RE) centers. We have derived a set of kinetics differential equations of RE luminescence in p-type semiconductor. Numerically computed rise and decay time of RE luminescence as a function of excitation power shows good agreement with the experimental data obtained for p-type GaAs:Nd.
Erbium Doped Silicon for Light Emitting Devices
Authors: Michel J. , Zheng B. , Palm J. , Ouellette E. , Gan F. , Kimerling L. C.
Published: April 2011

We report on the excitation and de-excitation processes of erbium implanted in silicon and the integration of Si:Er light emitting devices (LED) with standard CMOS technology. We find two deexcitation processes, an Auger process below 100 K and a phonon mediated energy backtransfer above 100 K. We present the first optical voice link with a silicon LED as the emitter. Optical transmission system performance with our LED is possible below 200 K.
1.54 μm Photoluminescence and Electroluminescence in Erbium Implanted 6H SiC
Authors: Yoganathan M. , Choyke W. J. , Devaty R. P. , Pensl G. , Edmond J. A.
Published: April 2011

Photoluminescence in the neighborhood of 1.54μm due to the 4I13/2 → 4l15/2 transitions is observed from 2 K up to 520 K in erbium implanted 6H SiC. The integrated 1.54 μm photoluminescence (PL) intensity is almost constant from 2 K up to about 400 K, with slight sample to sample variation. The shallow nitrogen donors play an important role in the excitation of the Er3+ centers. 1.54 μm electroluminescence (EL) is observed in erbium implanted 6H SiC p-n junctions under forward bias conditions. The EL spectrum is identical to the PL spectrum.
Neodymium-doped GaAs Light-emitting Diodes
Authors: Chang S. J.
Published: April 2011

Nd-doped semiconductor light-emitting diodes were fabricated by implanting Nd ions into a GaAs epi-layer. The fabricated GaAs:Nd diodes show good current-voltage characteristics with a typical reverse breakdown voltage between 8 and 12 V By injecting minority carriers into the diodes, Nd3+ related emissions were observed, at 77 K, in the 0.92, 1.11, and 1.3 μm regions. These electroluminescence signals correspond to the transitions from Nd3+4F3/2 state to the Nd3+4I9/2, 4I1/2, and 4I13/2 states, respectively. The measured external quantum efficiency of the GaAs:Nd diodes at 77 K, was 5 × 10−7.
Er-Doping of Gan and Related Alloys
Authors: Pearton S. J. , Abernathy C. R. , MacKenzie J. D. , Schwartz R. N. , Wilson R. G. , Zavada J. M. , Shul R. J.
Published: April 2011

Er incorporation into GaN, AIN, MAIN and InGaN can be achieved using either direct ion implantation or by doping during Metal Organic Molecular Beam Epitaxy using metalorganic or elemental sources. When co-implanted with 0 and annealed between 600–800°C, strong luminescence at 1.54pm from optically excited Er3+ is detected in both binary nitrides and there was no measurable diffusion of Er in any of the materials. The low vapor pressures of the gaseous source compounds (erbium 2, 2, 2, 6-tetramethyl-3, 5-heptanedionate for Er + O; erbium bistrimethylsilylamide for Er) makes transport difficult unless high bubbler temperatures are used. Er concentrations up to ∼3×1021cm−3 in AIN have been obtained using a solid Er source. Microdisk laser structures with Er-doped active layers have been fabricated using a novel KOH selective wet etch and Cl2/CH4/H2/Ar dry etching.
Photoluminescence of Erbium-Diffused Silicon
Authors: Horiguchi H. , Kinone T. , Saito R. , Kimura T. , Ikoma T.
Published: April 2011

Erbium films are evaporated on crystalline silicon substrates and are thermally diffused into silicon in an Ar+02 or H2 flow. Very sharp Er3+-related luminescence peaks are observed around 1.54 μ m.The main peak as well as the fine structures of the luminescence spectra depend on the annealing atmosphere, suggesting different luminescence centers. The full width at half maximum (FWHM) of the main peaks is ≤ 0.5nm at 20K. Thermal diffusion with Al films on top of the Er films is found to increase the intensity of the Er3+-related peaks greatly. The temperature dependence between 20 K and room temperature is relatively small, and a strong luminescence is obtained at room temperature.
About the Electrical and Structural Properties of Erbium Thermally Diffused in Single Crystal Silicon
Authors: Binetti S. , Acciarri M. , Gelmi I. , Pizzini S.
Published: April 2011

Having preliminary confirmed the possibility of erbium doping by thermal diffusion, we have used this process to introduce erbium into a silicon substrate from metallic erbium or erbium oxide sources. Diffusion experiments were carried out at 1050, 1200 and 1250°C. The Er:Si diffused samples were investigated using four probe resistivity and thermopower techniques for the measure of the concentration and type of carriers, SIMS and Auger spectroscopy for chemical analysis of the diffused layers and photoluminescence (PL) measurements at temperatures ranging from 2 to 298 K for the detection of optical activity. None of the samples prepared presented measurable PL at 2 K, except for one single sample on top of which was deposited an erbium doped silica glass. The electrical properties, instead, were deeply influenced by doping, indicating the formation of both donor and acceptors.
Approaches to High Temperature Contacts to Silicon Carbide
Authors: Delucca J. M. , Mohney S. E.
Published: April 2011

Metallurgical reactions between contacts and SiC can alter the electrical characteristics of the contacts, either beneficially or detrimentally. Simultaneously, consumption of the underlying SiC epilayer takes place. During prolonged operation at elevated temperature, contacts that are not in thermodynamic equilibrium with SiC may continue to react with it. For this reason, interest in thermally stable carbide and silicide contacts to SiC has been growing. To select appropriate carbides or silicides for further study, however, knowledge of the transition metal-silicon-carbon (TM-Si-C) phase equilibria is required. A significant body of literature on the TM-Si-C systems exists and should therefore be examined in the context of electronic applications. In this paper, phase equilibria for representative TM-Si-C systems are presented, trends in these systems with respect to temperature and position of the metal in the periodic table are discussed, and attractive carbide and silicide contacts and processing schemes for thermally stable contacts are highlighted.
Characterization of Zirconium - Diamond Interfaces
Authors: Baumann P. K. , Bozeman S. P. , Ward B. L. , Nemanich R. J.
Published: April 2011

Thin Zr films were deposited on natural single crystal diamond (100) substrates by ebeam evaporation in ultra-high vacuum (UHV). Before metal deposition the surfaces were cleaned by UHV anneals at either 500°C or 1150°C. Following either one of these treatments a positive electron affinity was determined by means of UV photoemission spectroscopy (UPS). Depositing 2Å of Zr induced a NEA on both surfaces. Field emission current - voltage measurements resulted in a threshold field (for a current of 0.1 µA) of 79 V/µm for positive electron affinity diamond surfaces and values as low as 20 V/µm for Zr on diamond.
Photocurrent Sensitivities, Surface Color, and Auger Spectroscopy of Silicon Carbide (siC) by Photoelectro-Chemical (Pec) Etching
Authors: Collins D. M. , Harris G. L. , Chen Naiqun
Published: April 2011

This novel technique involves the ultraviolet (UV) lamp-assisted photoelectrochemical etching of n-type 3C- and 6H-SiC for device processing. In order for this method to be effective, the UV light must be able to enhance the production of holes in the SiC during the etching process thus providing larger currents with light from the photocurrents generated than those currents with no light. Otherwise dark methods would be used as in the case of p-type 3C-SiC.

Experiments have shown that the I/V characteristics of the SiC-electrolyte interface reveal a minimum etch voltage of 3 V and 4 V for n- and p-type 3C-SiC, respectively. Hence, it is possible for etch-stops to occur. From Auger spectroscopy, an oxide formation is present on n-type 3C-SiC where after etching a yellowish layer corresponds to a low silicon to carbon (Si/C) ratio with large photocurrents and a white layer corresponds to a high Si/C ratio with small photocurrents. P-type 3C-SiC shows a grayish or silver layer with a high Si/C ratio and a green layer with a low Si/C ratio. Additionally, n-type 6H-SiC shows a brown or blue layer with a minimum etch voltage of 3 V.

The colors of the etched regions of SiC represent layers that have some degree of porousity formed by the electrochemical process. As a result, the photo-excitation allows control of the porousity and changes the electrical properties of SiC. The nature of these porous layers with its increased resistivity can lead to the formation of devices.
Ion Beam Synthesis By Tungsten Implantation Into 6h-Silicon Carbide At Elevated Temperatures
Authors: Weishart Hannes , Matz W. , Skorupa W.
Published: April 2011

We studied high dose implantation of tungsten into 6H-silicon carbide in order to synthesize an electrically conductive layer. Implantation was performed at 200 keV with a dose of 1×1017 W+cm−2 at temperatures of 90°C and 500°C. The samples were subsequently annealed either at 950°C or 1100°C. The influence of implantation and annealing temperatures on the reaction of W with SiC was investigated. Rutherford backscattering spectrometry (RBS), x-ray diffiraction (XRD) and Auger electron spectroscopy (AES) contributed to study the structure and composition of the implanted layer as well as the chemical state of the elements. The implantation temperature influences the depth distribution of C, Si and W as well as the damage production in SiC. The W depth profile exhibits a bimodal distribution for high temperature implantation and a customary gaussian distribution for room temperature implantation. Formation of tungsten carbide and silicide was observed in each sample already in the as-implanted state. Implantation at 90°C and annealing at 950°C lead to crystallization of W2C; tungsten silicide, however, remains amorphous. After implantation at 500°C and subsequent annealing at 11007deg;C crystalline W5Si3 forms, while tungsten carbide is amorphous.
Gallium Nitride Thick Films Grown by Hydride Vapor Phase Epitaxy
Authors: Molnar R. J. , Maki P. , Aggarwal R. , Liau Z. L. , Brown E. R. , Melngailis I. , Götz W. , Romano L. T. , Johnson N. M.
Published: April 2011

Gallium nitride (GaN) thick films (to 150 μm) have been deposited by hydride vapor phase epitaxy (HVPE). These films are unintentionally doped n-type (n = 1–2 × 1017 cm−3 at 300 K) and exhibit structural and electronic properties which are comparable with the best reported for GaN films grown by organometallic vapor phase epitaxy. Additionally, these properties are found to be uniform over 2-in diameter films grown on sapphire substrates. The use of either a GaCl or ZnO surface pretreatment has been found to substantially enhance the nucleation density, resulting in improved surface morphology and film properties, even though it appears that the ZnO film is thermochemically desorbed early on in the growth. Dislocation densities as low as ˜5×107 cm−2 have been attained for films 40 μtm thick. Homoepitaxial overgrowths both by electron-cyclotron-resonance plasma enhanced molecular beam epitaxy and OMVPE proceed in a straightforward manner, essentially replicating the defect structure of the HVPE GaN film.
High Resolution X-Ray Diffraction Analysis Of Gallium Nitride Grown On Sapphire By Halide Vapor Phase Epitaxy
Authors: Matyi R. J. , Zhi D. , Perkins N. R. , Horton M. N. , Kuech T. F.
Published: April 2011

We report a structural analysis of GaN layers with thicknesses ranging from 10 μm to 250 μm which have been grown on sapphire substrates by halide vapor phase epitaxy (HVPE). The effect of growth rate during HVPE growth has also been examined. The growth was performed using GaCl and ammonia as reactants; growth rates in excess of 90 μm/hr have been achieved. The structural characteristics of these layers have been performed wit'i high resolution x-ray diffractometry. Longitudinal scans parallel to the GaN [0002] direction, transverse scans perpendicular to the [0002], and reciprocal space maps of the total diffracted intensity have been obtained from a variety of GaN layers. The transverse scans typically show broad rocking curves with peak breadths of several hundreds of arcseconds. In contrast, the longitudinal scans (or “θ/2θ scans”) which are sensitive only to strains in the GaN layers (and not their mosaic distributions) showed peak widths that were at least an order of magnitude smaller and in some cases were as narrow as 16 arcseconds. These results suggest that the defect structure of the GaN layers grown by HVPE is dominated by a dislocation-induced mosaic distribution, with the effects of strain in these materials being negligible in comparison.
Growth and Characterization of AllnGaN/InGaN Heterostructures
Authors: Roberts J. C. , Mcintosh F. G. , Aumer M. , Joshkin V. , Boutros K. S. , Piner E. L. , He Y. W. , El-Masry N. A. , Bedair S. M.
Published: April 2011

The emission wavelength of the InxGa1−xN ternary system can span from the near ultraviolet through red regions of the visible spectrum. High quality double heterostructures with these InxGa1−xN active layers are essential in the development of efficient optoelectronic devices such as high performance light emitting diodes and laser diodes. We will report on the MOCVD growth and characterization of thick and thin InGaN films. Thick InxGa1−xN films with values of x up to 0.40 have been deposited and their photoluminescence (PL) spectra measured. AlGaN/InGaN/AlGaN double heterostructures (DHs) have been grown that exhibit PL emission in the violet, blue, green and yellow spectral regions, depending on the growth conditions of the thin InGaN active layer. Preliminary results of an AllnGaN/InGaN/AllnGaN DH, with the potential of realizing a near-lattice matched structure, will also be presented.
Particle-Assisted Oriented Deposition of Diamond Thin Films
Authors: Lee Dong-Gu , Singh Rajiv K.
Published: April 2011

We have developed a method for <111> oriented diamond film synthesis using micron-sized diamond particles. Different size of diamond powders were electrophoretically seeded on silicon substrates using diamond suspensions in organic solvents (acetone, methanol, and ethanol). Diamond suspension in acetone was found to be the best for obtaining uniform diamond seeding by electrophoresis. The thickness of diamond seeded films was changed by varying the applied voltage to observe the effect on the orientation of diamond particles. Then diamond films were deposited by the hot filament chemical vapor deposition (HFCVD) process. A preferred orientation with <111> direction normal to the substrate was obtained for monolayer coatings. The surface morphology, crystal orientation, and quality of diamond films were investigated using scanning electron microscopy, x-ray diffractometry, and Raman spectroscopy.
The Influence of Hydrogen Plasma Passivation on Electrical and Optical Properties of Aigan Samples Grown on Sapphire
Authors: Polyakov A. Y. , Shin M. , Pearton S. J. , Skowronski M. , Greve D. W. , Freitas J. A.
Published: April 2011

Hydrogen plasma passivation effects are studied for undoped AlGaN layers grown by MOCVD. Hydrogen treatment at 200°C for lh led to a substantial decrease in carrier concentration accompanied by an increase in electron mobility. The magnitude of the near-band edge absorption tails also dramatically decreased after hydrogen passivation. The effect is explained by pairing of negatively charged hydrogen acceptors with positively charged native donors commonly believed to be related to nitrogen vacancies. The bond strength in such hydrogen complexes increases as the composition of AlGaN moves towards AIN, as revealed by results of post hydrogenation annealing.
Theoretical Study of Hydrogen in Cubic Gan
Authors: Estreicher Stefan K. , Maric Djordje M.
Published: April 2011

Preliminary results of theoretical studies of hydrogen and hydrogen-related defects in cubic GaN are reported. Our calculations contrast with those of other authors in that the host crystal is represented by molecular clusters rather than periodic supercells, and that they are obtained using an all-electron methodology rather than the single effectiveparticle approach of density-functional theory. Our results confirm some predictions of other authors but conflict with others.
Diffusion of Hydrogen in 6H Silicon Carbide
Authors: Linnarsson M. K. , Doyle J. P. , Svensson B. G.
Published: April 2011

6H polytype silicon carbide (SiC) samples of n-type have been implanted with 50 keV H+ ions and subsequently annealed at temperatures between 200 °C and 1150 °C. Using depth profiling by secondary ion mass spectrometry motion of hydrogen is observed in the implanted region for temperatures above 700 °C. A diffusion coefficient of ∼10−14 cm2/s is extracted at 800°C with an approximate activation energy of ∼3.5 eV. Hydrogen displays strong interaction with the implantation-induced defects and stable hydrogen-defect complexes are formed. These complexes anneal out at temperatures in excess of 900°C and are tentatively identified as Carbon-Hydrogen centers at a Si vacancy.
Fabrication of Highly Oriented, Smooth Diamond Films on Silicon for Electronic Devices
Authors: Wolter S. D. , Borst T. H. , Gluche P. , Ebert W. , Vescan A. , Kohn E.
Published: April 2011

A new bias-enhanced nucleation method based on an AC-bias step to form highly oriented diamond (HOD) nuclei on silicon substrates is presented. The uniformity of the nucleated film and the bias time strongly depended on the substrate temperature and the substrate holder. In our case the shortest bias time and highest nucleation densities were achieved at ∼ 850°C while using a graphite susceptor. Following this nucleation enhancement step the diamond films were grown out using conditions employing an α-parameter slightly greater than 2. This ultimately leads to extremely smooth and well-faceted (100) textured HOD films which could be used as substrates for the fabrication of electronic devices.

Schottky diodes with high rectification ratios and high breakdown voltages have been fabricated for the first time via selective growth of the active boron doped diamond layers on these HOD films. Results of the growth procedure and diode performance will be given.
Photoluminescence Properties of CVD Diamond Excited by Ultra-Violet Synchrotron Radiation
Authors: Won Jaihyung , Hatta Akimitsu , Ito Toshimichi , Sasaki Takatomo , Hiraki Akio
Published: April 2011

Photoluminescence (PL) properties of microwave-assisted chemical-vapor- deposition (CVD) diamond have been studied using ultraviolet synchrotron radiation. The defect-related 5RL PL feature, which was not detected in cathodoluminescence (CL), was observed for both undoped and boron-doped (200ppm) CVD diamond. The defect formation in the thin near- surface layer is discussed in relation to dependence of PL spectra on incident photon energy. In the case of boron-doped diamond, the boron-related peak was detected at 2.3eV while the band-A feature was not observed at 2.9eV. PL excitation (PLE) spectra associated with these emissions are also discussed in relation to absorption coefficients at energies above the band gap.
Surface Chemical Effects on the Optical Properties of Thin Nanocrystalline Diamond Films
Authors: Khomich A. V. , Polyakov V. I. , Perov P. I. , Varnin V. P. , Teremetskaya I. G. , Balakirev V. G. , Obraztsova E. D.
Published: April 2011

The effect of annealing in air on internal structure and optical properties of hot filament CVD nanocrystalline diamond films was investigated. Oxidation of the films lead to selective removal of intercrystallite layers with formation of highly porous structure with characteristic dimensions of several nanometers. Dramatic changes in optical transmission and Raman spectra were also observed. The origin of the two Raman spectrum maxima at 1140 and 500 cm−1 is discussed. Hydrogen absorption and desorption processes in porous diamond were studied.
Thermomodulated Reflectivity Spectra of Gan/Sapphire Epilayer
Authors: Li Y. , Lu Y. , Shen H. , Wraback M. , Schurman M. , Koszi L. , Stall R. A.
Published: April 2011

Thermomodulation spectra from the metalorganic chemical vapor deposition (MOCVD) grown GaN have been measured in the temperature range 20 K - 310 K. A theoretical model is established to explain the modulation spectrum by considering the modulation of epilayer thickness and dielectric constant. By performing the lineshape analysis, the bandgap energy and broadening parameter were determined in the temperature range. The nonlinear temperature coefficient (Varshni coefficient) of energy gap is measured to be 5.9×10−4 eV/K. The temperature dependence of broadening parameter is also measured for the first time.
Optical Characterization of GaN Films Grown on (0001) Sapphire Substrate
Authors: Yang K. , Zhang R. , Zheng Y. D. , Qin L. H. , Shen B. , Shi H. T. , Huang Z. C. , Chen J. C.
Published: April 2011

The optical properties of single crystal hexagonal GaN films grown on (0001) sapphire substrate by metalorganic chemical vapor deposition were investigated. The energy gap of hexagonal GaN was determined as 3.39 and 3.400 eV by optical transmission and photoreflectance, respectively. The refractive index of GaN as a function of photon energy was drawn from the transmission spectrum. Furthermore, Raman scattering spectra were employed to study the phonon modes of the GaN film. The properties of LO phononplasmon coupled modes were further studied, and the carrier concentration and damping constant were determined by line-shape fitting of the coupled modes.
Field Emission and Band Bending Considerations From High-Quality NEA Diamond
Authors: Bandis C. , Pate B. B. , Phillips W. , Plano M. A. , Moyer M. D. , Moreno M. A.
Published: April 2011

The near band gap photoelectric emission and field emission properties of diamond are investigated. Our results find three characteristic photoelectric yield spectra which have been observed from both polycrystalline CVD diamond films and single crystal diamond. The categories correspond to differences in bulk doping/surface preparation and illustrate the importance of band bending at the surface. Field emission experiments also find that the same three categories have distinct field emission properties. Our field emission observations are discussed in terms of electron transport properties from the bulk to the surface.
Characterization of 4H-SiC MOS Capacitors by a Fast-Ramp Response Technique
Authors: Sudarshan T. S. , Madangarli V. P. , Gradinaru G. , Tin C. C. , Hu R. , Isaacs-Smith T.
Published: April 2011

The current vs voltage characteristics of 4H-SiC MOS capacitors under deep depletion are obtained by a fast ramp response technique so as to obtain the maximum field that can be applied to the MOS structure without the failure of either the semiconductor or the oxide layer. The experiments on n-type 4H SiC wafers having a 5 μm thick epilayer of 1015 – 1016 cm−3 doping concentration and an oxide layer 1200Å – 1500Å thick, indicate the significant influence of the oxide quality and defects in the semiconductor on the nature of the current response during accumulation and deep depletion measurements. The effect of the conductivity of the oxide layer is reflected clearly in the current response, even though classical C-V measurements do not indicate any abnormality. Apart from obtaining the maximum breakdown fields of the semiconductor and the oxide, the fast-ramp response technique provides useful information about the generation processes associated with defects in the MOS structure.
Polysilicon Thin Film Transistors with Cobalt amd Nickel Silicide Source and Drain Contacts
Authors: Sarcona G. T. , Hatalis M. K.
Published: April 2011

Polysilicon n-type thin film transistors have been fabricated with self-aligned cobalt and nickel silicide contacts to the source and drain regions. The sheet resistance of the source and drain without silicide is above 200 Ω/‪. The cobalt and nickel silicide films have sheet resistance below 30 Ω/‪. The contact resistance of the silicided devices is also much lower. The reduced extrinsic resistance is shown to improve the current in the “on” state, without increasing the leakage current. This study includes examination of cobalt and nickel silicidation on thin polysilicon films at temperatures compatible with polysilicon TFT-LCD processes.