bluuebunny/crossref_metadata_2025 huggingface dataset:
Detonation Chemistry Of Glycidyl Azide Polymer
Authors: Ling Ping , Sakata Jill , Wight Charles A.
Published: April 2011

The initial step of chemical reaction initiated by laser-generated shock waves has been observed in glycidyl azide polymer (GAP) in condensed phase. Shocks are generated by pulsed laser vaporization of thin aluminum films and launched into adjacent films of GAP at 77 K. Comparison of FIIR spectra obtained before and after shock passage shows that initial reaction involves elimination of molecular nitrogen from the azide functional groups of the polymer. The shock arrival time has been measured by a velocity interferometer as a function of thickness of GAP and laser fluence. The shock pressure has been calculated by using a universal liquid state Hugoniot. A simple model is proposed to calculate shock velocity and pressure as a function of laser fluence. The results are in agreement with experimental data.
Synthesis of High Density Insensitive Energetic Tetraazapentalene Derivatives
Authors: Trudell M. L. , Subramanian G. , Eck G. , Boyer J. H.
Published: April 2011

An improved nitration procedure has been developed for the synthesis of y-Tacot (3). The synthesis of y-DBBD (8) has been completed in three steps from 3 in 37% yield. y-DBBD (8) was found to be thermally stable up to 274 °C (decomposed) and insensitive to impact (hammer blow). Nitration of z-BDDB (6) and y-DBBD (8) gave carbonyl derivatives resulting from in situ hydroysis/oxidation of the corresponding tetranitro derivatives z-TBBD (7) and y-TBBD (9), respectively.
Dynamic Chemical Processes of Detonations: Underwater Explosion and Combustion Processes With the use of Water as an Oxidant
Authors: Slutsky V. G. , Tsyganov S. A. , Severin E. S.
Published: April 2011

The possibility of producing underwater unconfined explosions with the use of propylcarborane as a fuel and water as an oxidant was demonstrated experimentally. The specific TNT equivalent of the energy release in the explosion reaction between propylcarborane and water was found to be 1.5 times higher than conventional explosives. A possibility of organizing the combustion of initially unmixed propylcarborane and water was experimentally proven as well
Computational Determination of Heats of Formation of Energetic Compounds
Authors: Politzer Peter , Murray Jane S. , Grice M. Edward
Published: April 2011

A recently-developed density functional procedure for computing gas phase heats of formation is briefly described and results for several categories of energetic compounds are summarized and discussed. Liquid and solid phase values can be obtained by combining the gas phase data with heats of vaporization and sublimation estimated by means of other relationships. Some observed functional group effects upon heats of formation are noted.
Monte Carlo Simulations of Crystalline TATB
Authors: Sewell Thomas D.
Published: April 2011

We are performing constant-NPT Monte Carlo calculations of the physical properties of crystalline TATB. Our approach is to employ an atomistic model in which the individual molecules are treated as semi-rigid entities. Each molecule is allowed to undergo rigid translations and rotations, and in some cases limited intramolecular flexibility is conferred on the molecules via exocyclic torsions. Additionally, the size and shape of the simulation box is allowed to vary. Our immediate interest is in computing the density, lattice energy, lattice constants, and other structural parameters as a function of temperature. Preliminary results indicate that simulations involving only two molecules suffice for calculations of the energy and density, but that more molecules are required to compute the lattice constants. Intramolecular flexibility is important, particularly at higher temperatures.
Investigation of a-Si:H p-i-n Solar Cell Degradation
Authors: Smole Franc , Groznik Aleč , Topič Marko , Popović Pavle , Furlan Jože
Published: April 2011

Based on measured characteristics of degraded p-i-n structures, simulations of degraded structures were performed using our numerical simulator ASPIN in order to fit and explain pronounced hump-shaped voltage-dependent internal collection efficiency (ICE) characteristics under weak short-wavelength illumination. Agreement with measured hump-shaped ICE characteristics was obtained only if in addition to the introduction of light-induced dangling bond defect states, their capture cross-sections were also increased, in particular capture crosssection for the charged defect states. This causes a change in occupancy of defect states at the p-i interface and front part of the i-layer under forward bias. Consequently, it increases the electric field in the front part of the cell, which results in recovery of the ICE.
The Study of Space Charge Effects by Spectral Response, Steady State Charge Collection and Transient Photocurrents in Thick a-Si:H Pin-Diodes
Authors: Zollondz J.-H. , Brüggemann R. , Reynolds S. , Main C. , Gao W. , Bauer G. H.
Published: April 2011

Charge collection, transient photocurrents and collection efficiency under additional bias illumination were used to characterize 3–4 micron thick a-Si:H pin-diodes. The wavelength dependent decrease or increase in the spectral response, depending on the bias flux and absorption depth, is related to the distribution of the electric field, recombination and majority carrier diffusion. At higher photon flux an overshoot in the transient photocurrent after switch-on of steady illumination indicates the time scale for the changes in internal variables. Collection efficiencies under large bias monochromatic photon flux well in excess of the maximum value of 100 % for probe beam generated carriers are observed with a large amplification ratio. These efficiencies sensitively depend both on the applied voltage and the defect density. Numerical modelling reveals the influence of internal variables on the transient and steady state photocurrents under the different illumination conditions.
Light-Induced Effects on Fluorinated Amorphous and Microcrystalline Silicon Films
Authors: Choi Hong-Seok , Jang Keun-Ho , Yoo Jhun-Suk , Han Min-Koo
Published: April 2011

The fluorinated amorphous and microcrystalline silicon (a,μc-Si:H;F) films have been prepared by rf plasma enhanced chemical vapor deposition (PECVD) with SiH 4 and SiF 4 gas mixtures. The stretching Si-O (1085 cm-1) and SiH2 (2100 cm-1) bands estimated from infrared (IR) spectroscope data have related to the evolution of crystallinity and the optical band gap was shifted by introducing Si-O bonds. The sub-band gap absorption coefficient in a,μc-Si:H;F films was about one order lower than that in hydrogenated amorphous silicon film (a-Si:H). The subband gap absorption in a-Si:H;F film was comparable to that in tic-Si:H;F films. The lightinduced degradation of a,μc-Si:H;F films were also suppressed.
Improvement in a-Si:H Properties by Inert Gas Plasma Treatment
Authors: Maruyama E. , Hishikawa Y. , Tanaka M. , Kiyama S. , Tsuda S.
Published: April 2011

The modification of surface reactions with an inert gas plasma treatment method has been investigated for the first time in order to improve the properties of a-Si:H for solar cells. The deposition of a thin a-Si:H layer and exposure to inert gas plasma such as He, Ar or Xe were repeated by using RF plasma CVD at a substrate temperature of 200 °C. It has been found that the hydrogen content (CH) can be controlled in a wide range from about 18 atomic% to about 35 atomic%, although it is a hydrogen-free process. Experimental results show that the change in CH of a-Si:H films is mainly determined by the decrease in CH of the treated a-Si:H surface and the increase in CH of the a-Si:H deposited on the treated surface. Furthermore, the plasma treatment probably promotes the surface reaction, which reduces SiH2ISiH and CH. Consequently, wide-gap (1.64 eV by ( a h ν )1/3 versus h ν plots, 1.75 - 1.85 eV by Tauc's plot) a-Si:H films with high stabilized photoconductivity (> 10-5 Ω-1cm-1 under AM-1, 100 mW/cm2 irradiation) have been obtained by the inert gas plasma treatment method.
Pulsed Esr Study of Light-Induced Metastable Defects in 17O and 13C Incorporated a-Si:H
Authors: Yamasaki S. , Umeda T. , Isoya J. , Matsuda A. , Tanaka K.
Published: April 2011

Hydrogenated amorphous silicon (a-Si:H) samples containing 17O (3 x 1019 cm-3, nuclear spin, I, = 5/2) and 13C (3 - 4 x 1017cm-3, I = 1/2) isotope impurities were used in the detailed pulsed electron spin resonance (ESR) and pulsed electron-nuclear double resonance (ENDOR) measurements to obtain information on the role of O and C impurities in lightinduced metastable dangling bonds in a-Si:H. No hyperfine structure related to 17O and 13C atoms was observed in echo detected ESR, electron spin echo envelope modulation (ESEEM) of pulsed ESR as well as pulsed ENDOR (Davies and Mims sequences), which suggests that O and C impurities are not directly involved in the formation of light-induced dangling bonds.
Ion Energy Distributions in Silane-Hydrogen Plasmas
Authors: Hamers E. A. G. , Van Sark W. G. J. H. M. , Bezemer J. , Van Der Weg W. F. , Goedheer W. J.
Published: April 2011

For the first time ion energy distributions (IED) of different ions from silane-hydrogen (SiH4-H2 ) RF plasmas are presented, i.e. the distributions of SiH3+, SiH2+ and SiH2+. The energy distributions of SiH3+ and SiH3+ ions show peaks, which are caused by a charge exchange process in the sheath. A method is presented by which the net charge density in the sheath is determined from the plasma potential and the energy positions of the charge exchange peaks. Knowing the net charge density in the sheath and the plasma potential, the sheath thickness can be determined and an estimation of the absolute ion fluxes can be made. The flux of ions can, at maximum, account for 10% of the observed deposition rate.
Hydrogen Distribution in High Stability A-Si:H Prepared by the Hot Wire Technique
Authors: Stephen J. Todd , Han Daxing , Mahan A. Harv , Wu Yue
Published: April 2011

In this work the microstructures of 2–3 hydrogen at.% hot-wire CVD a-Si:H films were characterized by 1H nuclear magnetic resonance (NMR). Significant differences were found between the hydrogen distribution in these samples and that in conventional plasma-enhanced CVD samples. Among other things, the broad resonance line in the hot-wire a-Si:H is 50 kHz wide, which is much broader than that observed 25–35 kHz in PECVD a-Si:H films. Moreover, a 0.5 kHz resonance absorption hole width due to intrinsic dipolar interactions is obtained using the hole-burning technique. Surprisingly, approximately 90 percent of the hydrogen atoms give rise to the 50 kHz line and only a very small percentage of the hydrogen atoms give rise to the much narrower resonance line.
Spectroscopic Evidence for Near-Neighbor Bonded H(D) in A-Si:N:H(D) Thin Films
Authors: Lucovsky G. , Santos-Filho P. , Banerjee A. , Jing Z.
Published: April 2011

Increases in the frequency of the silicon monohydride (Si-H) bond-stretching vibration in hydrogenated silicon nitrides, over and above what can be attributed to chemical induction effects, are shown to be generated by a repulsive interaction between the H-atom of the Si-H group, and a near-neighbor SiN-H group. This interaction increases the effective bond-stretching force constant of the H-atom of the Si-H group. This effect has been verified by ab-initio quantum chemistry calculations that have been used to calculate the energy of the H-atom of the Si-H group as a function of the relative separation between near-neighbor Si-H and SiN-H groups. Decreases in the bond-stretching frequencies of SiN-H groups in heavily hydrogenated nitrides are attributed to H-bonding effects associated with near-neighbor pairs of SiN-H groups.
Hydrogen Energetics and Transport Kinetics in Amorphous Silicon Hydride
Authors: Franz A. J. , Gland J. L.
Published: April 2011

To understand the electrical properties and behavior of amorphous silicon, it is imperative to understand the behavior of hydrogen in the amorphous silicon lattice. Although considerable effort has been extended to study hydrogen trapping in a-Si:H, the energetics and populations of the traps remain unresolved. We have developed a reaction diffusion model which includes multiple bulk trapping mechanisms, bulk transport, and realistic surface processes. The model results are compared with existing hydrogen temperature programmed evolution data, isothermal hydrogen evolution experiments, and thermal quenching experiments. We find consistently good fits for all three types of experiments with a shallow trap depth of 1.5 eV and deep trap depth of 1.8–1.9 eV below the mobility level, with 20–30% of hydrogen present in the deep trap. The difference of 0.3–0.4 eV between the two trap depths is similar to the defect formation activation energy and suggests a defect formation mechanism which involves movement of hydrogen from a deep to a shallow trap.
Optically Detected Magnetic Resonance Studies of Undoped a-Si:H
Authors: Schultz N. , Vardeny Z. V. , Taylor P. C.
Published: April 2011

Photogenerated carrier dynamics in undoped a-Si:H have been studied by photoinduced absorption (PA), photoluminescence (PL) and their respective optically detected magnetic resonances: PADMiR and PLDMR. We have detected for the first time the “g = 4” resonance in PADMR, in addition to the previously measured narrow and broad resonances at g≈2. We compare the PADMR and PLDMR resonances over a broad spectral range of detection energies and conclude from the similarities that they share a common underlying mechanism. The PADMIR spectra of the narrow and the broad resonances at g≈2, measured in the spectral range of 0.7 to 1.7 eV, suggest that a correlation exists between the two resonances and PA.
Kinetics of Both Defects and Electron and Hole Diffusion Lengths During Light-Soaking in a-Si:H Films
Authors: Abramov A. S. , Kosarev A. I. , Cabarrocas P. Roca i , Vinogradov A. J.
Published: April 2011

Concomitant studies of kinetics of defects ND(t), photoconductivity σph(t), electron and hole diffision lengths Le(t), Lh(t) during light soaking have been carried out. The data have been fitted by stretched exponential expressions and characteristic parameters of kinetics have been determined. Correlation between the kinetics is discussed. In contrast to Nd(t), σph(t) and Le(t), the hole diffusion length Lh(t) was observed to remain constant during initial time (˜ 103s) and then decreased with characteri stic time ˜ 104s.
Thermopower and Conductivity Activation Energies in Hydrogenated Amorphous Silicon
Authors: Dyalsingh H. M. , Kakalios J.
Published: April 2011

The long range fluctuation model has been widely used to account for the difference in activation energies seen experimentally in dark conductivity and thermopower measurements in hydrogenated amorphous silicon. We report on a test of this model using measurements of the conductivity and thermoelectric effects carried out in both open and short circuit configurations. While the thermopower activation energy is less than that of the dark conductivity, the short circuit Seebeck conductivity is found to be nearly identical to the dark conductivity in both activation energy and magnitude, consistent with the long range fluctuation model.
Temperature Dependence of Minority Carrier Lifetimes in a-Si:H
Authors: Cornish J. C. L. , Subaer  , Jennings P. , Hefter G. T.
Published: April 2011

Changes in minority carrier lifetimes in a-Si:H, p-i-n photovoltaic cells due to light soaking have been investigated using the open circuit voltage decay (OCVD) method over the temperature range 223 K to 296 K.

Using light from a Xenon flash lamp for excitation produced unexpected results: in the light soaked material, band-to-band transitions were evident at a higher temperature than for the asdeposited samples and became increasingly pronounced as the temperature was reduced. Results obtained using red light at 670 nm from a pulsed diode laser to produce relatively uniform- illumination throughout the thickness of the film, however, produced results very similar to those obtained for as-deposited films.

Plots of the reciprocal of the trap activation time versus 1000/T for the results for both xenon lamp and laser excitation can be fitted by straight lines. Two distinct sets of lines with activation energies in the ranges 0.07 to 0.20 eV and 0.38 to 0.51 eV are obtained with the activation energy and the exponential prefactors exhibiting a Meyer-Neldel relationship.
Technological Development for Commercialization of Amorphous Silicon Based Multijunction Modules
Authors: Yang Liyou , Bennett M. , Chen L. , Jansen K. , Kessler J. , Li Y. , Newton J. , Rajan K. , Willing F. , Arya R. , Carlson D.
Published: April 2011

Some of the significant steps in technological development for large-scale commercialization of amorphous silicon (a-Si:H) based multijunction photovoltaic modules are presented. These developments are establishing a high quality baseline process for manufacturing large-area ( ˜ 8 ft2) a-Si:H/a-SiGe:H tandem junction modules with improved stabilized conversion efficiency, throughput, yield, and reduced materials usage.
Inhibition of Metal Induced Crystallization in the System Ag/ZnO/a-Si:H
Authors: Edelman F. , Brener R. , Cytermann C. , Weil R. , Beneking C. , Beyer W.
Published: April 2011

A systematic investigation has been made on the barrier properties of ZnO layer between ndoped a-Si:H and Ag metallization films in the structures (001)Si/SiO2/Ag/ZnO/a-Si:H:P and (001)Si/SiO2/a-Si:H:P/ZnO/Ag. Plasma assisted CVD deposition was used to produce a-Si:H (2500Å thick) highly P-doped films over thermally oxidized Si-wafers at 190 and 270°C. Transparent conductive ZnO:A1 layers, 1000Å and lμm thickness, and Ag films (1000Å thick) were deposited by sputtering. The polycrystalline ZnO layers were textured along the <0001> axis in the as-deposited state. The structures were annealed in vacuum in the temperature range from 300 to 700°C for 1/4 to 16h. X-ray diffraction and transmission electron microscopy studies demonstrated the a-Si:H:P stability against crystallization under ZnO buffer protection up to 700°C (when free a-Si crystallizes itself). The (111) peak position of the Ag reflection was used to show that while the Ag was always strained, the strain was partially relaxed when in contact with the 0. 1 μm ZnO film, it developed additional strain when in contact with the I μm ZnO film.
Amorphous Silicon Films from Dichlorosilane and SiH4 for Solar Cells
Authors: Payne A. M. , Wagner S.
Published: April 2011

We have deposited amorphous silicon films from mixtures of dichlorosilane (SiH2C12, DCS), and silane (SiH4) and made the first p-i-n solar cells using i-layers of this material. We measured optical and electronic transport properties of the DCS-derived films and relate them to the solar cell performance. The DCS cells are compared to standard cells made with SilH4.
A Simple Optical Properties Modeling of Microcrystalline Silicon by the Effective Medium Approximation Method
Authors: Cho Woo Yeong , Cho Hyun-Mo , Lim Koeng Su
Published: April 2011

The optical properties of microcrystalline silicon (μc-Si) were estimated using the EMA (Effective Medium Approximation) method. This modeling was based on two-phase mixture, amorphous silicon (a-Si) and crystalline silicon (c-Si) with volume fractions of fa and fc respectively. From this modeling, it could be possible to understand that μc-Si has lower light absorption characteristics than a-Si over all solar spectrum by considering hydrogen involvement in embedded a-Si part of μc-Si and crystalline volume fraction. Also, it is proposed that p-type μc-Si is superior to n-type μc-Si because of its high optical gap of Eo4 and its low absorption coefficient spectrum shape.
Intrinsic N-Type Modulation Doping in Inp-Based Heterostructures
Authors: Chen W.M. , Buyanova I.A. , Buyanov A. , Bi W.G. , Tu C.W.
Published: April 2011

We propose and demonstrate a new doping approach, i.e. intrinsic doping, for n-type modulation doping in InP-based heterostructures. Instead of the conventional method of n-type doping by shallow donor impurities, grown-in intrinsic defects are utilized to provide the required doping without external doping sources. The success of this approach is clearly demonstrated by our results from InGaAs/InP heterostructures, where the required n-type doping in the InP barriers is provided by Pin antisites, preferably introduced during off-stoichiometric growth of InP at low temperatures (LT-InP) by gas source molecular beam epitaxy. A twodimensional electron gas (2DEG) is shown to be formed near the InGaAs/InP heterointerface as a result of electron transfer from the LT-InP to the InGaAs active layer, from studies of Shubnikov-de Haas oscillations and photoluminescence. The concentration of the 2DEG is determined to be as high as 1.15×1012 cm−2, where two subbands of the 2DEG are readily occupied.
Complementary Hfet Technology for Low-Power Mixed-Mode Applications
Authors: Baca A. G. , Sherwin M. E. , Zolper J. C. , Dubbert D. F. , Hietala V. M. , Shul R. J. , Sloan L. R. , Hafich M. J.
Published: April 2011

Development of a complementary heterostructure field effect transistor (CHFET) technology for low-power, mixed-mode digital-microwave applications is presented. An earlier digital CHFET technology with independently optimizable transistors which operated with 319 ps loaded gate delays at 8.9 fJ is reviewed. Then work demonstrating the applicability of the digital nJFET device as a low-power microwave transistor in a hybrid microwave amplifier without any modification to the digital process is presented. A narrow band amplifier with a 0.7 × 100 μm nJFET as the active element was designed, constructed, and tested. At 1 mW operating power, the amplifier showed 9.7 dB of gain at 2.15 GHz and a minimum noise figure of 2.5 dB. In addition, next generation CHFET transistors with sub 0.5 μm gate lengths were developed. Cutoff frequencies, ftof 49 GHz and 11.5 GHz were achieved for n- and p-channel FETs with 0.3 and 0.4 μm gates, respectively. These FETs will enable both digital and microwave circuits with enhanced performance.
Investigation of Deep-Level Defects in 10 Mev Electrons Irradiated Si-Gaas
Authors: Wu Fengmei , Zhao Zhouying , Li Haifeng
Published: April 2011

The deep-level defects in 10 MeV electron irradiated undoped semi-insulating (SI) LEC GaAs were investigated. The results show that the density of EL2 (Ec-0.83eV) and EL12 (Ec-0.69eV) defects increases and the density of EL6 (Ec-0.39eV) and EL3 (Ec-0.58eV) defects decreases in irradiated SI-GaAs at higher fluence levels. At lower fluences, we observe decrease in density of EL2 and EL12 defects, however, the density of the EL6 and EL3 defects is increased. It could be related mainly to the dissociation of the EL2 and EL12 defects. The influence of 10 MeV electrons irradiation on the resistivity will also be discussed.
High Quality In1-x(Gax)AsyP1-y/InP Compressive Strained Quantum Well Structures Grown by LP-MOCVD
Authors: Zhu J. T. , Clawson A. R. , Yu P. K. L.
Published: April 2011

We report the results of the growth of InAsyP1−y /InP and In0.86Ga0.14AS0.51P0.49/ In0.86Ga0.14As0.33P0.67 compressive strained multiple quantum wells (CSMQW) structures grown by low pressure metalorganic chemical vapor deposition (LP-MOCVD). Our studies showed high quality 1.06 μm InAs0.21P0.79/InP CSMQW structure with 6 periods can be obtained when the growth temperature is around 650°C and the pressure in the reactor is about 20 Torr. When the well thickness and composition are tuned for wavelength around 1.30 μm, the quality of this structure degrades. By employing 1.1 μm wavelength, lattice-matched InGaAsP as the barrier layers and setting the growth temperature at 600 °C, high quality 1.30 μm wavelength In0.86Ga0.14AS0.51P0.49/ In0.86Ga0.14As0.33P0.67 CSMQW materials with 10 periods can also be obtained. The materials were characterized with high resolution x-ray rocking curves, room and low temperature photoluminescence (PL). The 15K full-width-at-half-maximums (FWHM) of the PL peaks for 1.06 μm InAs0.21P0.79/InP and 1.30 μm In0.86Ga0.14AS0.51P0.49/ In0.86Ga0.14As0.33P0.67 CSMQW structures are 5.6 meV and 4.97 meV, respectively, which are among the smallest FWHMs reported up to date for these kinds of MOCVD growth materials. Buried heterostructure lasers at 1.3 μm wavelength have been obtained with the CSMQWs as the active layer.
Luminescence Decay of the 1.54 μm Emission from Erbium in Silicon
Authors: Hartung J. , Evans J. H. , Dawson P. , Sciioles A. P. , Taskin T. , Huda M. Q. , Jeynes C. , Peaker A. R.
Published: April 2011

Photoluminescence of silicon implanted with erbium and oxygen was measured in the time domain focussing on the temperature and excitation density dependence of the intra-4f-shell emission from Er3+. The decay of this luminescence is similar for the different optically active crystal field split Er-centres. At low temperatures the luminescence transients consist of a fast initial non-exponential component followed by slower exponential behaviour. An increase in excitation density results in a higher proportion of the luminescence decaying with the faster decay time. Our results indicate a relation of the fast component to nonradiative processes. Auger recombination is proposed as a possible mechanism.
Defect Engineering in SI:ER Technology
Authors: Sobolev N. A. , Alexandrov O. V. , Bresler M. S. , Emtsev V. V. , Gusev O. B. , Poloskin D. S. , Shek E. I.
Published: April 2011

Recent results contributing to our understanding of mechanisms of defect formation and excitation of Er luminescence in Si:Er system are presented. An essential role of non-equilibrium intrinsic point defects in Er-related defects formation for both implanted and in-diffused Si:Er structures is demonstrated.

The data of electroluminescence (EL) measurements evidence that the Er3+ excitation occurs via capture of free excitons on neutral Er-related donor centers with subsequent Augerrecombination of bound excitons.
To Probe the Absorption Edge of Porous Silicon by Erbium
Authors: Zhao Xinwei , Komuro Shuji , Maruyama Shinya , Isshiki Hideo , Aoyagi Yoshinobu , Sugano Takuo
Published: April 2011

Intra-4f-transitions from erbium atoms are proposed as a probe to determine absorption edges of the hosts. This idea was firstly applied on erbium-doped porous silicon materials. Intense and sharp 1.54 μm luminescence from erbium triply ionized ions as well as visible emissions from porous silicon were observed up to room temperature. Photoluminescence excitation spectroscopy investigations of the samples indicate identical absorption edges for both the 1.54 μm and the visible emissions. No 1.54 μm luminescence can be observed by directly exciting the erbium triply ionized ions. This fact suggests that the erbium ions are excited by energy transfer process from the excited carriers in the hosts. From this result, we can propose that erbium could behave as a good probe to determine the absorption edge or the bandgap of the host material even it is not luminescent.
Growth Conditions of Erbium-Oxygen-Doped Silicon Grown by MBE
Authors: Stimmer J. , Reittinger A. , Abstreiter G. , Holzbrecher H. , Buchal Ch.
Published: April 2011

We report on a systematic study of the growth parameters of erbium-oxygen-doped silicon grown by molecular beam epitaxy. The surface quality of the grown layers was measured in situ by RHEED. The samples were characterized by photoluminescence measurements and SIMS. An Er-O-doped Si light emitting diode grown with the optimized parameters is presented.
Exafs and X-ray Ctr Scattering Characterization of Er Doped in InP by Omvpe
Authors: Tabuchi M. , Kawamura D. , Fujita K. , Matsubara N. , Yamada N. , Ofuchi H. , Ichiki S. , Fujiwara Y. , Takeda Y.
Published: April 2011

Er-doped semiconductors are considered to be important for optical communication systems since one of the prominent luminescent peaks of Er is in the minimum absorption region of silica based fiber and wavelength of the luminescence is insensitive to the ambient temperature. In this work, OMVPE grown InP samples uniformly and δ-doped with Er were investigated by EXAFS and X-ray CTR measurements. The EXAFS measurement revealed that the uniformly doped Er atoms in InP grown at 580°C formed NaCl-structure ErP, and at 530°C occupied the In-sites. The X-ray CTR measurement revealed that the δ-doped Er atoms in InP at 530'C formed NaCl-structure ErP. In the sample, the total number of Er was analyzed to be about 0.171ML(monolayer), and the FWHM of Er distribution was about 5ML. By comparing the results of PL measurement with those of the EXAFS and the X-ray CTR measurements, it was suggested that the Er atoms on In-sites show high efficiency of luminescence and the Er atoms in the NaCl-structure ErP low efficiency.
Activation of Yb Luminescence in GaAs by Group VI Elements Codoping
Authors: Konnov V. M. , Larikova T. V. , Loyko N. N. , Dravin V. A. , Ushakov V. V. , Gippius A. A.
Published: April 2011

Yb in GaAs is generally believed to be optically inactive due to very low fraction of Yb in substitutional position. In the present work it is demonstrated that Yb can be rendered optically active in GaAs if it is incorporated in three-component complexes (Yb+O+S/Se/Te).
Segregation and Trapping of Erbium in Silicon at a Crystal-Amorphous or Crystal-Vacuum Interface
Authors: Polman A. , Serna R. , Custer J. S. , Lohmeier M.
Published: April 2011

The incorporation of erbium in silicon is studied during solid phase epitaxy (SPE) of Erimplanted amorphous Si on crystalline Si, and during Si molecular beam epitaxy (MBE). Segregation and trapping of Er is observed on Si(100), both during SPE and MBE. The trapping during SPE shows a discontinuous dependence on Er concentration, attributed to the effect of defect trap sites in the amorphous Si near the interface. Trapping during MBE is described by a continuous kinetic growth model. Above a critical Er density (which is lower for MBE than for SPE), growth instabilities occur, attributed to the formation of silicide precipitates. No segregation occurs during MBE on Si(111), attributed to the epitaxial growth of silicide precipitates.
Excitation and Recombination Processes in rare Earth Doped II–VI Semiconductors
Authors: Godlewski M.
Published: April 2011

Rare Earth (RE) doped II–VI semiconductors are currently used for production of thin film light emitting electroluminescence devices. The excitation and recombination processes in RE activated wide band gap II–VI semiconductors (ZnS, ZnSe, SrS and CaS) are reviewed. Mechanisms relevant for obtaining bright photoluminescence (energy transfer processes, RE ionisation and exciton binding), electroluminescence (impact excitation and impact ionisation) and cathodoluminescence are described based on the recent experimental results. Efficiency of the light emission from RE doped II–VI materials is limited by several processes of nonradiative recombination. The Auger-type energy transfer processes and electric field- or thermally-activated processes responsible for 4f-4f nonradiative recombination of RE ions are discussed.
Ion Beam Epitaxy of in-situ Er-O Co-Doped Silicon Films
Authors: Matsuoka Morito , Tohno Shun-Ichi
Published: April 2011

Erbium-doped silicon films are grown by ion beam epitaxy (IBE) using an electric-mirror sputtering-type metal ion source in ultrahigh vacuum. In-situ erbium doping with concentrations ranging from 1×1016 to 6×1020 cm−3 is achieved by sputtering the erbium metal pellet with ions extracted from the silicon metal ion source. The oxygen concentration in the films is also controlled in-situ over the range from below 1×1018 to 2×1020 cm−3 by using argon gases containing 1 ppb to 100 ppm of oxygen impurities. The erbium incorporation probability drastically increases (by two or more orders of magnitude) when oxygen is contained in the argon gas during film growth. Erbium is selectively oxidized in the Si host. Erbium segregation and precipitation formation are well suppressed by the oxidation. Sharp and well-split photoluminescence is clearly observed in as-deposited films grown typically at 480°C with oxygen co-doping.
Electroluminescence of Erbium in Oxygen Doped Silicon
Authors: Lombardo S. , Campisano S. U. , Van Den Hoven G. N. , Polman A.
Published: April 2011

It is demonstrated room-temperature electroluminescence at 1.54 μm in erbiumimplanted oxygen doped silicon (27 at. 0), due to intra-4f transitions of the Er3+. The luminescence is electrically stimulated by biasing metal-(Si:O,Er)-p+ silicon diodes. The 30 nm thick Si:O,Er films are amorphous layers deposited onto silicon substrates by chemical vapour deposition of SiH4 and N20, doped by ion implantation with Er to a concentration up to ≈ 1.5 at.%, and annealed in a rapid thermal annealing furnace. The most intense electroluminescence is obtained in samples annealed at 400°C in reverse bias under breakdown condition and it is attributed to impact excitation of erbium by hot carriers injected from the Si into the Si:O,Er layer. The electrical characteristics of the diode are studied in detail and related to the electroluminescence characteristics. A lower limit for the impact excitation cross-section of ≈6×10−16 cm2 is obtained.
Photothermally Assisted Dry Etching Of GaN
Authors: Leonard R. T. , Bedair S. M.
Published: April 2011

Photoassisted dry etching of GaN in HC1 by 193 nm ArF excimer laser is developed as apotential alternative process to eliminate the ion damage and surface roughness which occur inetching techniques that involve an energetic ion beam impinging the surface. A directed stream ofHC1 etchant with background pressure of ∼ 5 × 10−4 Torr, sample surface temperature between 200 to 400°C, and laser fluence of 10 to 20 mJ/ pulse combine to produce etching. The photoassistedetching reaction under these process conditions is thermal in nature, with activation energy near 1.2kcal/ mol. Increases in laser fluence results in increase of etch rate, but the surface also becomesrougher. Distinct etch features can be produced with smooth surfaces at expense of etch rate.
Beta Silicon Carbide Pn Junction Diodes
Authors: Coleman J. C. , Harris G. L. , Poker D. B.
Published: April 2011

Beta silicon carbide (3C-SiC) diodes have been fabricated using ion implantation as the selective doping technique. Previous work on 3C-SiC diodes have exhibited properties such as low reverse breakdown voltages and high ideality factors. Also, 6H and 4H SiC diodes have been reported. This paper studies a different procedure to produce better 3C-SiC diodes for use in the electronics industry. Current versus voltage, capacitance versus voltage and temperature versus voltage tests were conducted on the devices.

Isolation between devices is a prominent concern when building integrated circuits. Proton bombardment is the preferred planar process for forming isolation regions in gallium arsenide (GaAs) due to the lack of a stable native oxide. Hydrogen and boron in GaAs have exhibited good electrical isolation between devices. This paper investigates using proton bombardment to form isolation regions in 3C-SiC. Cubic SiC samples are implanted with a variety of implant doses, ranging from 1 × 1014 to 1 × 1015 ions / cm2 , and implant energies ranging from 150 to 300 keV. Hall measurement tests were performed to study the characteristics of the implanted material.
TEM and PL characterisation of MBE-grown epitaxial GaN/GaAs
Authors: Xin Yan , Brown P. D. , Boothroyd C. B. , Preston A. R. , Humphreys C. J. , Cheng T. S. , Foxon C. T. , Andrianov A. V. , Orton J. W.
Published: April 2011

MBE-grown epitaxial GaN deposited at 700°C on {001}, {111}A and B GaAs has been characterised using the combined techniques of transmission electron microscopy (TEM) and photoluminescence (PL). On both { 111 } A and 111 B GaAs substrates, single crystal wurtzite GaN was formed, but with very high densities of threading defects. Best epitaxy occurred on 111B GaAs in accordance with PL measurements. An amorphous phase was identified at the GaN/{ 111 }A GaAs interface and the GaN epilayer evolved in this instance with the same Nterminated growth surface as for the case of growth on 111 B GaAs, as determined by convergent beam electron diffraction (CBED). Growth on {001} GaAs produced highly faulted columnar grains of zincblende GaN. Conversely, growth on {001} GaAs under an additional arsenic flux at 700°C resulted in the deposition of single crystal zincblende GaN with a high density of stacking faults and microtwins. Thus, the microstructure of epitaxial GaN depends very much on the detailed growth conditions and substrate orientations used.
Improved Aluminum Nitride Thin Films Grown By Mocvd From Tritertiarybutylaluminum And Ammonia
Authors: Metzger T. , Born E. , Stimmer R. , Rieger W. , Dimitrov R. , Lentz D. , Angerer H. , Ambacher O. , Stutzmann M.
Published: April 2011

AIN thin films were grown on c-plane sapphire by metalorganic chemical vapor deposition from tritertiarybutylaluminum and ammonia at 1050°C. These films exhibit a full width at half maximum of the 002 X-ray rocking curve below 200 arcsec indicating high epitaxial quality. By measuring asymmetric reflections, a structural disorder of the lattice mainly due to edge dislocations can be observed. For further investigations, atomic force microscopy and photothermal deflection spectroscopy were performed. In order to study the effect of increasing AIN layer thickness on the optical and structural properties of GaN in an AIN/GaN heterostructure, AIN thin films with increasing thickness ranging from 0.02 to 0.36 μm were used as sublayers for the deposition of 0.75 μm thick GaN layers. Photoluminescence, micro- Raman and X-ray diffraction measurements confirm the relaxation of biaxial compressive stress in the GaN layers due to different thermal expansion coefficients by increasing AIN layer thickness. The pressure dependence of the band gap shift was determined as 24 meV/GPa for biaxial compressive stress. Our results indicate that the growth of AIN with metal organic chemical vapor deposition from tritertiarybutylaluminum and ammonia is a promising method for obtaining high quality epitaxial films.
Properties Of Homoepitaxially Mbe-Grown Gan
Authors: Suski T. , Krueger J. , Kisielowski C. , Phatak P. , Leung M. S. H. , Liliental-Weber Z. , Gassmann A. , Newman N. , Rubin M. D. , Weber E. R. , Grzegory I. , Jun J. , Bockowski M. , Porowski S. , Helava H. I.
Published: April 2011

Bulk single crystals of GaN were used for epitaxial growth of GaN films by molecular beam epitaxy. Low temperature photoluminescence yields much higher intensity emission in the near bandedge region for epitaxial films with respect to the situation in bulk crystals. Character of this luminescence changes also. Dominant band-to-band transitions in the bulk crystals are exchanged by bound exciton and/or donor-acceptor pair transitions observed in the epitaxial layers. We will compare the obtained results with the available data on the homoepitaxial samples grown by metalorganic chemical vapor deposition method and discuss the importance of establishing the basic information on energetic positions of excitonic transitions in stress free samples.
Origin of High-Conductivity Layer Near the Surface in As-Grown Diamond Films
Authors: Yamanaka Sadanori , Hayashi Kazushi , Okushi Hideyo , Kajimura Koji
Published: April 2011

In order to clarify the origin of p-type high-conductivity layers (HCL) near the surfaces of as-grown diamond films prepared by chemical vapor deposition, we have investigated the properties of Schottky junctions fabricated from HCL. The Schottky junctions between Al and HCL of undoped homoepitaxial films with step-flow growth showed high-rectification properties. The forward current-voltage characteristics of the junctions in the temperature range between 83 K and 400 K are found to be described by the thermionic-field emission theory. Analysis indicates that thin enough depletion layer is formed at the junction by a high concentration (∼1018/cm3) of acceptors existing in HCL due to hydrogenation. The origin of HCL is the acceptors related to incorporated hydrogen near the surface.
High Quality P-Type Gan Films Grown By Plasma-Assistedmolecular Beam Epitaxy
Authors: Myoung J. M. , Kim C. , Shim K. H. , Gluschenkov O. , Kim K. , Yoo M. C.
Published: April 2011

p-type GaN films were grown on a (0001) sapphire substrate by the plasma-assisted molecular beam epitaxy. A low-contamination, high-power efficiency inductively coupled radio frequency plasma source was used, which was developed at the University of Illinois. Using an MBE system equipped with this plasma source, high-quality p-type GaN films were grown without post-growth treatment. X-ray rocking curve measurements for (0002) diffraction showed a full width at half maximum of less than 7 arcmin. The highest room-temperature hole concentration obtained was 1.4× 1020 cm−3, and for the same sample, the mobility was 2.5 cm2/Vs It is believed that the Mott-Anderson transition occurred in this sample resulting in a metallictype conductivity in the impurity subband. Low-temperature photoluminescence had a blue emission band and no deep-level transitions, indicating the high quality of the grown films. Uniformity of the Mg doping was confirmed by secondary ion mass spectrometry.
Laser Wavelength Dependent Properties of BN Thin Films Deposited by Laser Ablation
Authors: Suda Y. , Nakazono T. , Ebihara K. , Baba K.
Published: April 2011

Boron Nitride (BN) thin films are deposited on heated (650 °C ) silicon (100) substrates using Nd:YAG (532 nm) and KrF excimer (248 nm) laser ablation. The laser beam is focused on the hBN targets. The films are grown using a laser repetition rate of 10 Hz atenergy density 3.8 J/cm2. Argon gas is mixed with the reactant nitrogen gas and the total gas pressure in the chamber during deposition is 20 Pa. Auger Electron Spectroscopy shows that the N/B composition ratio depends on the mixture ratio of nitrogen and the relativeemission intensity of B + (345.1 nm). The surface morphology of the films prepared by the 532 nm laser is rough with large particulates, whereas much smoother surfaces with fewer and smaller particulates are obtained with the 248 nm laser. Fourier Transform IR measurement shows that the cBN phase in the films is enhanced by applying the negative RF self-bias voltage ( ˜ 200 V) on the substrate electrode.
Preparation and Characterization of Wurtzitic Gan Single Crystals in Nano and Micro Scale
Authors: Yu San , Li Hongdong , Yang Haibin , Li Dongmei , Sun Haiping , Zou Guangtian
Published: April 2011

Gallium nitride and its alloys are the most promising materials for short wave light emitters. If high quality GaN single crystals can be prepared, the GaN base light emitters should be fabricated directly on the lattice-matched GaN substrate.

In this work, GaN crystals in nano and micro scale with definite faces have been prepared by dc arc discharge using gallium and N2+NH3 as starting materials. Transmission electron microscope, selected area diffraction, x-ray microanalysis of energy dispersive spectroscopy, and x-ray diffraction investigation of the as grown GaN crystals show that the well faceted crystals are single crystalline GaN in wurtzite structure having lattice constants a0=3.18Å and c0=5.18Å. The crystal size of stoichoimetric GaN in wurtzite structure depends on the partial pressure of nitrogen in the plasma. The maximum crystal size in this work is about several micrometers.
Growth and Characterization of Polycrystalline Diamond Thin Films on Porous Silicon by Hot Filament Chemical Vapor Deposition
Authors: Mirzakuchaki S. , Charlson E. J. , Charlson E. M. , Stacy T. , Shahedipour F. , White H. W.
Published: April 2011

Hot filament chemical vapor deposition (HFCVD) was utilized to grow high quality diamond film on porous silicon (PS) substrates to a thickness of 5–6 μm. Boron-doped silicon substrates of <100> orientation and resistivity of 5–15 ohm-cm were anodized by the electrochemical process to form PS. A slurry of diamond paste (1/4 micron average grain size) was rubbed on the samples for a few seconds before introduction into the chamber. Diamond film growth on the PS has the advantages of shorter incubation time and higher nucleation density as evident from scanning electron microscopy (SEM). The results of X-ray diffraction confirm the growth of predominatly (111) oriented high quality diamond film. Electrical properties were also studied by sputtering circular gold contacts on top of diamond film and measuring current-voltage (I-V) characteristics.
Reconstruction of Nonpolar Gan Surfaces
Authors: Elsner J. , Haugk M. , Frauenheim Th.
Published: April 2011

A density-functional theory based nonorthogonal tight-binding scheme is used to investigate the nonpolar surfaces of GaN in the wurtzite and zinc-blende phases. In III-V semiconductors the nonpolar surfaces mainly reconstruct by a bond-length conserving rotation of the surface atoms. In contrast to that for all nonpolar GaN surfaces this bond-length is shortened by ≈3 − 4%. We furthermore find the rotation angle to be significantly smaller than could be expected from results for GaAs and GaP.
A New, Nearly Single-Domain Surface Structure of Homoepitaxial Diamondr (001) Films
Authors: Kuang Yalei , Lee Naesung , Badzian Andrzej , Badzian Teresa , Tsong Tien T.
Published: April 2011

Boron-doped homoepitaxial diamond films were grown on natural diamond (001) substrates using microwave-assisted plasma chemical vapor deposition techniques. The surface structures were investigated using scanning tunneling microscopy (STM). This showed a dimertype 2×1 reconstruction structure with single-layer steps where dimer rows on the upper terrace are normal to or parallel to the step edges. We found that dimer rows parallel to the step edges are much longer than those normal to the step edges. The nearly single-domain surface structure observed by STM is in agreement with the low-energy electron diffraction (LEED) patterns from these surfaces. The high atomic resolution STM image showed that the local 1×1 configurations exist.
Theory of Defects, Doping, Surfaces and Interfaces in Wide Gap Nitrides
Authors: Bernholc J. , Boguslawski P. , Briggs E. L. , Nardelli M. Buongiorno , Chen B. , Rapcewicz K. , Zhang Z.
Published: April 2011

The results of extensive theoretical studies of group IV impurities and surface and interface properties of nitrides are presented and compared with available experimental data. Among the impurities, we have considered substitutional C, Si, and Ge. CN is a very shallow acceptor, and thus a promising p-type dopant. Both Si and Ge are excellent donors in GaN. However, in AlGaN alloys the DX configurations are stable for a sufficiently high Al content, which quenches the doping efficiency. At high concentrations, it is energetically favorable for group IV impurities to form nearest-neighbor Xcation-XN pairs. Turning to surfaces, AIN is known to exhibit NEA. We find that the NEA property depends sensitively on surface reconstruction and termination. At interfaces, the strain effects on the band offsets range from 20% to 40%, depending on the substrate. The AIN/GaN/InN interfaces are all of type I, while the A10.5Ga0.5 N/A1N zinc-blende (001) interface may be of type II. Further, the calculated bulk polarizations in wurtzite AIN and GaN are -1.2 and -0.45 μC/cm2, respectively, and the interface contribution to the polarization in the GaN/AlN wurtzite multi-quantum-well is small.