bluuebunny/crossref_metadata_2025 huggingface dataset:
The Properties of GaInAsSb/GaSb Heterostructure Grown by Mocvd and P-GaInAsSb/N-GaSb Photodiodes
Authors: Zhang Baolin , Jin Yixin , Zhou Tianming , Jiang Hong , Ning Yongqiang , Li Shuwei
Published: April 2011

GaInAsSb/GaSb heterostructures have been grown by metalorganic chemical vapor deposition (MOCVD). The optical properties were characterized using low temperature(71K) photoluminescence(PL) and infrared transmission spectroscopy. The FWHM of the typical PL spectrum peaked at 2.3μm is 30meV. Hall measurement results for undoped GaInAsSb layers are presented showing a p-type background and low hole concentration of 6.5 × 1015cm−3. The room temperature performances of the p-GaInAsSb/n-GaSb photodiodes are reported. Its responsivity spectrum is peaked at 2.2 5μm and cuts off at 1.7μm in the short wavelength and at 2.4μm in the long wavelength, respectively. The room temperature detectivity D* is of 1 × 109cm.Hz1/2.W−2
Improvement Of Pecvd-SiNx For Tft Gate Insulator By Controlling Ion Bomberdment Energy
Authors: Kasama Yasuhiko , Ohmi Tadahiro , Fukuda Koich , Fukui Hirobumi , Iwasaki Chisato , Ono Shoich
Published: April 2011

It has been revealed that ion energy and ion flux density play an essentially critical role in SiNx deposition process of PECVD in TFT-LCD production. Ion energy and ion flux density bombarding onto substrate surface are known to be extracted from waveform of RF applied to an electrode. Using this method, authors investigated film quality of SiNx formed in the conventional parallel plate PECVD equipment. When N2+H2 or N2+Ar is employed as a carrier gas in source gas(SiH4+NH3), authors have defined normalized ion flux density as ion flux density divided by deposited SiNx molecule which must be increased to obtain high quality SiNx film while ion energy is suppressed at low level as not giving damages on the film surface. This technique has made it possible to securely form SiNx film (2500 Å) featuring dielectric breakdown field intensity of 8.5MV/cm at 250°C on a glass substrate with Cr gate interconnects of 1000 Å having vertical step structure. One of the important factors to improve film quality of SiNx deposited in PECVD is to increase ion flux density while keeping ion energy low enough to protect growing surface against any damages. Using this technique inverse-staggered TFT-array featuring field effect mobility of 0.96 •/V·s has been demonstrated which gate insulator SiNx, non-doped a-Si:H and a- Si:H(n+) were formed continuously at the same substrate temperature of 2500°C.
Group 13-16 Precursors: What Controls Their Volatility?
Authors: Gillan Edward G. , Bott Simon G. , Barron Andrew R.
Published: April 2011

The volatility of a series of group 13–16 cubane compounds, [(R)ME]4 (M = Al, Ga; E = S, Se, Te) has been investigated by thermogravimetric analysis. The effects of the M4E4 core, the ligand (R), and molecular packing on the relative sublimation temperature and the activation energy of sublimation are discussed. For any given ligand type (e.g., [(tBu)ME] 4) volatility is dependent on the compound's molecular mass. The volatility of a homologous series (e.g., [(R)GaS] 4) is proposed to be dependent on the interlocking of the ligands in the solid state. In contrast, the energy of activation for sublimation (Ea) may be related to the molecular packing of the cubane cores in the solid state.
Kinetics And Morphology Of Homoepitaxial Cvd Growth On Diamond (100) And (111)
Authors: Rawles R. E. , Morris W. G. , D’Evelyn M. P.
Published: April 2011

Growth rates for homoepitaxy of diamond (100) and (111) by hot-filament chemical vapor deposition were measured via in situ Fizeau interferometry and the surface morphologies were subsequently characterized by atomic force microscopy (AFM). (100)-oriented growth from 0.5% CH4 in H2 exhibited pure Arrhenius behavior, with an activation energy of 17±1 kcal/mol, up to a substrate temperature of 1100°C. Addition of oxygen to the feed gas resulted in an increased growth rate below 900°C, a maximum growth rate between 900 and 1000°C, and etching (of diamond) above 1050 - 1100°C. However, the presence of oxygen apparently had less effect on the surface morphology than did the (100)-to-(111) growth rate parameter α, determined directly from the relative growth rates of (100) and (111) substrates mounted side by side. During homoepitaxial growth from 0.5% CH4 in H2 at 875°C of ca. 1-micron-thick films,α = was 2.2 without oxygen and 1.3 for growth with 0.14% O2. The (100) film grown with α = 2.2 was quite smooth, while that with α = 1.3 was covered by numerous hillocks and penetration twins. AFM analysis revealed surprisingly little difference between the (111) films despite the considerable difference in α. Implications of these results for the growth mechanism are discussed.
Nanoscale Modification Of Amorphous Diamond-Like Carbon Film Surfaces
Authors: Mercer T. W. , Dinardo N. J. , Sullivan J. P. , Friedmann T. A. , Siegal M. P. , Martinez-Miranda L. J.
Published: April 2011

Scanning Tunneling and Atomic Force Microscopy (STM, AFM) of amorphous tetrahedral carbon films (a-tC) film surfaces grown by pulsed laser deposition indicate extreme flatness and uniform electronic properties.1 This is consistent with the observed predominance of sp3 (diamond-like) bonding in these materials.2 Potential applications of a-tC films may be enhanced with the ability to modify their surfaces on the nanoscale. Exploiting the metastable nature of the sp3 hybridized state of carbon, the high flux electron beam from an STM tip was used to modify ˜100 nm regions; processing in air or in vacuum produces similar results. STM and AFM maps of the modified regions indicate stable morphologic and electronic structures consistent with a local transformation to sp2 (graphitic) hybridization. Surface potentiometric mapping of these regions indicates a correlation between electron dose and a lowering of the surface potential. In addition, spatially-resolved electron energy loss spectroscopy of the modified areas performed with a Scanning Auger Microscope shows plasmon energy shifts that confirm an elevated sp2 content in the modified regions.3
Growth Of Diamond Films From C-h-o MixturesM
Authors: Ford I. J.
Published: April 2011

A simple model of the competition between the growth of diamond and amorphous, graphitic carbon has been extended to include oxygen within the mixture of gases in a chemical vapour deposition (CVD) process. The model is based on linear rate equations which describe the growth and removal of layers of carbonaceous material on the surface of a substrate placed within the CVD reactor. The main effect of oxygen is to tie up a proportion of the available gas-phase carbon in the form of CO, which reduces the flux of reactive carbonaceous material onto the surface. Hydrogen atoms can remove carbonaceous material from the surface, and in addition can perform the key task of cementing such groups into place on the surface to make diamond. Starting with these simple assumptions, it is possible to account for the shape of the diamond domain in the C-H-O phase diagram, namely the boundaries with the domains of graphitic growth and no-growth.
Raman and FTIR Study of Neutron Irradiated CVD Diamond
Authors: Khasawinah S. , Popovici G. , Prelas M. A. , Mccormick M. , Loyalka S. K. , Manning G. , Farmer J. , White H. W. , Pour F. Shahedi
Published: April 2011

Undoped and 10B doped diamond films were neutron irradiated at a moderately high fluence level (thermal neutron fluence of 1.3 × 1020 n/cm2 and a fast neutron (E> 0.1 MeV) fluence of 1.6 × 1020 n/cm2). The unirradiated, irradiated, irradiated and annealed samples were studied using Fourier Transform Infrared (FTIR) and Raman spectroscopies. A dependence of radiation induced stress on the initial boron concentration was observed. The radiation induced stress was lower for the undoped samples. Correlations between FTIR and Raman data were found. The radiation damage was removed after annealing, as measured by Raman and FTIR spectroscopy.
Preparation of Diamond-Like Carbon by Pulsed Laser Deposition
Authors: Matsui T. , Yudasaka M. , Imai K. , Ohki Y. , Yoshimura S.
Published: April 2011

Diamond-like carbon (DLC) films have been prepared by pulsed laser deposition using graphite and cured phenol resin as targets. By comparison with previous reports, it is found that the lower power density (fluence) of irradiated pulsed laser can form DLC. In case of cured phenol resin used as a target, DLC was formed at almost the same wavelength and fluence region as that with graphite.
Diamond Growth Chemistry During Atmospheric-Pressure Plasma Cvd
Authors: Girshick S. L. , Lindsay J. W.
Published: April 2011

Diamond films were deposited by chemical vapor deposition using a radio- frequency induction plasma operating at 130 torr. Linear growth rates of polycrystalline diamond films ranged from 18 to 37 μm h-1. For a fixed substrate temperature of 1000°C the input methane-hydrogen ratio was varied from 2% to 10%. Over this range the resulting film morpologies changed from faceted ball-like structures to well-faceted diamond, then to non-faceted balls, and for the well- faceted films increases in methane-hydrogen ratio caused the film texture to shift toward the <100> direction. During these experiments gas sampled through an orifice in the center of the substrate was delivered to a gas chromatograph for measurement of stable hydrocarbon species. As the input methane-hydrogen ratio was increased the measured methane-acetylene ratio decreased. The gas chromatograph measurements showed marked differences from measurements made for an RF reactor with somewhat different flow geometry operating at atmospheric pressure.
Nickel catalyzed reconstruction of a diamond (110) surface
Authors: Smith C. , Chu C. J. , Margrave J. L. , Hauge R. H.
Published: April 2011

A polished diamond (110) surface was observed to undergo surface rearrangement above ˜700 °C to a micro faceted diamond surface when in contact with a nickel film and in the presence of hydrogen. Formation of a graphitic layer at the diamond-nickel interface above 700 °C was observed in the absence of hydrogen. The presence of 0.1 Torr of hydrogen was shown to be sufficient to prevent graphite formation at the nickel-diamond interface.
Surface damage effects on secondary electron emission From the negative electron affinity diamond surface
Authors: Malta D. P. , Posthill J. B. , Humphreys T. P. , Mantini M. J. , Markunas R. J.
Published: April 2011

The effects of surface damage on the secondary electron emission characteristics of a natural diamond (100) surface have been investigated using ultraviolet photoelectron spectroscopy and scanning electron microscopy. Surface damage was intentionally induced by abrading the (100) diamond face with diamond paste. Removal of the damage was achieved by a sequence of ion implantation, graphitization, electrochemical etching and oxygen/argon plasma etching. Prior to characterization performed between steps in the sequence, the surface was hydrogenated by exposure to a hydrogen plasma in attempts to create a negative electron affinity surface condition. Upon removal of the surface damage, the secondary electron yield from the negative electron affinity surface was enhanced by a factor of ˜20 over that from the damaged negative electron affinity surface.
A Study of Dopants in Diamond Using Electron Paramagnetic Resonance Spectroscopy
Authors: Zvanut M. E. , Zhang Shigang , Carlos W. E.
Published: April 2011

Chemical incorporation of impurities into diamond films is important for both electronic and optoelectronic applications. The study reveals the effect of incorporated dopants in diamond films using electron paramagnetic resonance (EPR), a non-destructive highly sensitive spectroscopy. Both the stress and damage associated with dopants is assessed using the center line of the EPR spectra. The films studied were grown by chemical vapordeposition and doped with phosphorus by two different methods, fast ion doping and chemical incorporation. The results suggest that damage increases with increased dopant density and saturates with dopant densities about l×1020 cm-3. Although electrical measurements did not reveal n-type conductivity, at low fluences the films grown using fast ion doping exhibited a density of 1017 cm-3 shallow substitutional phosphorus sites. Comparison of different dopants in the films doped by chemical incorporation show that phosphorus produces ten times greater damage than boron. Overall, the study illustrates that EPR may be used as a quick nondestructive characterization tool for diamond films.
The Current And Future Status Of Diamond in Electronics
Authors: Chalker Paul R. , M. Ian , Golder Buckley
Published: April 2011

Both passive and active electronic applications of CVD diamond have been proposed since the earliest stages of its development, largely based on an extrapolation of the superlative properties of single crystal diamond. Consequently, CVD diamond research has striven hard to match up to this expectation and significant advances have been made.

CVD diamond compares favourably with natural or high pressure synthetic single crystal material for passive electronic applications. The development of CVD diamond deposition technology for thermal management has led producers to address issues such as production cost, yield and quality. CVD polycrystalline diamond is becoming a commodity material and commercial applications in thermal management are emerging. Many of these developments are expected to feed into active electronic applications and will act as a springboard for diamond into commercial technology.

The active electronic applications for diamond are more demanding in terms of materials and process technologies. For example, doping, structure delineation and contact schemes have been widely demonstrated and prototype devices are showing potential benefits in sensors, detectors, photonics and cold cathodes. The current and future status of diamond electronics is reviewed.
Homoepitaxial growth of CVD diamond: effect of nitrogen contaminations on growth rates
Authors: Wild C. , Locher R. , Koidl P.
Published: April 2011

Homoepitaxial diamond films were deposited on {100} and {111} oriented substrates using microwave plasma assisted CVD. The growth rate was measured in situ using laser interferometry. Various amounts of 15N2 were admixed to the process gas (0-50 ppm). The growth rate on {100} faces was found to increase significantly (by a factor 1.8) with increasing 15N2 content. In contrast, on { 111 } faces only a minor increase of the growth rate upon nitrogen admixture was observed. These findings are in perfect agreement with the observed influence of nitrogen contaminations on the α-parameter, as derived by the X-ray texture analysis of polycrystalline diamond films [1]
Thermal Decomposition of HMX: Low Temperature Reaction Kinetics and their Use for Assessing Response in Abnormal Thermal Environments and Implications for Long-Term Aging
Authors: Behrens Richard , Bulusu Suryanarayana
Published: April 2011

The thermal decomposition of HMX between 175°C and 200°C has been studied using the simultaneous thermogravimetric modulated beam mass spectrometer (STMBMS) apparatus with a focus on the initial stages of the decomposition. The identity of thermal decomposition products is the same as that measured in previous higher temperature experiments. The initial stages of the decomposition are characterized by an induction period followed by two acceleratory periods. The Arrhenius parameters for the induction and two acceleratory periods are (Log(A)= 18.2 ± 0.8, Ea = 48.2 ± 1.8 kcal/mole), (Log (A) = 17.15 ± 1.5 and Ea = 48.9 ± 3.2 kcal/mole), (Log (A) = 19.1 ± 3.0 and Ea = 52.1 ± 6.3 kcal/mole), respectively. The data can be used to calculate the time and temperature required to decompose a desired fraction of a test sample that is being prepared to test the effect of thermal degradation on its sensitivity or burn rates. It can also be used to estimate the extent of decomposition that may be expected under normal storage conditions for munitions containing HMX. The data, along with previous mechanistic studies conducted at higher temperatures, suggest that the process that controls the early stages of decomposition of HMX in the solid phase is scission of the N-NO2 bond, reaction of the NO2 within a “lattice cage” to form the mononitroso analogue of HMX and decomposition of the mononitroso HMX within the HMX lattice to form gaseous products that are retained in bubbles or diffuse into the surrounding lattice.
NTO Decomposition Studies
Authors: Oxley J. C. , Smith J. L. , Yeager K. E. , Rogers E. , Dong X. X.
Published: April 2011

To examine the thermal decomposition of 5-nitro-2,4-dihydro-3H-1,2,4-triazol-3-one (NTO) in detail, isotopic labeling studies were undertaken. NTO samples labeled with 15N in three different locations [ N(l) and N(2), N(4), and N (6)] were prepared.1 Upon thermolysis, the majority of the NTO condensed-phase product was a brown, insoluble residue, but small quantities of 2,4,-dihydro-3H- 1,2,4-triazol-3-one (TO) and triazole were detected.2 Gases comprised the remainder of the NTO decomposition products. The analysis of these gases is reported herein along with mechanistic implications of these observations.
AnAb Initio Investigation of Crystalline PETN
Authors: Kunz A. Barry
Published: April 2011

Solid energetic substances have long played an important technological role as explosives and also as fuels. Much of the research on the solid phases has been concentrated on ground state properties, and also on the chemistry of the molecules comprising the solid. In addition, significant understanding of the detonation properties has been obtained by semi-empirical continuum mechanical modeling. Traditional solid state studies of this important class of materials have mostly been ignored. This may be due to the apparent success of the semi-empirical models in describing the detonation properties, as well as the practical difficulties in performing band theoretical studies. Recent interest in more fundamental questions relating to the basic properties of these systems as materials, coupled with a desire to probe fundamental questions relating to the initiation and sustaining of the chemical reactions leading to combustion/detonation is generating significant interest in the basic solid state properties of such energetic systems. In particular, recent analysis of detonation by J. J. Gilman emphasizes the need to include excitation of the electronic system in obtaining an understanding. In this manuscript, the basic solid state properties of PETN are considered.
Initiation of Crystalline Explosives by Shock or Impact
Authors: Coffey C. S.
Published: April 2011

The central issue determining initiation response of explosive crystals to shock or impact is the generation of the energy necessary to cause molecular dissociation. This controls the initial rate of release of chemical energy. Here, the energy dissipated in the crystals as they undergo plastic deformation due to shock or impact is taken to be the source of the energy required to achieve initiation. This determines initiation sensitivity to shock or impact. Several problems are discussed including initiation of detonation and the von Neumann pressure spike structure of a detonation wave.
Shock Induced Energetic Phase Transformations
Authors: Bardo Richard D. , Agassi Dan
Published: April 2011

Ultrafine diamond dust and the metastable fullerenes C60 and B24N36 offer new pathways of energy release which are unattainable in conventional energetic materials. Theoretical and experimental studies indicate that the high bare-surface strain energies of these small particles are released in rapid (< 1 μsec) phase changes. For diamond, C60 and B24N36, strain energies of 1000, 1210 and 1245 cal/g, respectively, may be released during transition to graphite, diamond and hexagonal BN under pressures exceeding 100 kbar. It is shown that the behavior of these nanoscale particles under high shocks may be traced to their intrinsic five-fold and icosahedral symmetry, which leads to an incompatibility of global and local driving forces for space filling under high compression. From a correlation function analysis, it is shown that shear can induce long range correlations of fluctuations which arise from geometrical frustration, thereby reducing the activation energy for phase change. For the first time, critical stresses and symmetry rules are determined for such phase changes in aggregates of nanoscale particles.
Laser Interference Structuring of a-Si:H
Authors: Nebel C. E.
Published: April 2011

Laser interference structuring with a pulsed Nd:YAG laser set-up is introduced and typical geometric dimensions and limitations are discussed. Intensity modulated laser beams are used to recrystallize amorphous silicon layers periodically at the intensity maxima. Stripe or tip structures of multi-crystalline (mc) silicon with sub-micrometer dimensions are shown. Structural, electronic and optical properties of the mc-Si structures are discussed. A hybrid thin film p-i-n solar cell architecture is described where the textured TCO is replaced by a flat TCO and a laterally structured boron doped mc-Si window layer. Light trapping, light diffraction and higher internal electric fields are proposed to be the main advantages of such a solar cell.
Efficiency Improvement of a-Si Solar Cells Deposited in a Single Chamber, Large Area, Pecvd Reactor
Authors: Terzini E. , Privato C. , Avagliano S. , Mangiapane P. , Fasolino T.
Published: April 2011

In order to realize large area integrated a-Si modules using a commercial, single chamber, PECVD reactor, an accurate optimization of deposition process for p-i-n solar cell has been performed leading to a 1 cm2 device efficiency value of 10.3 %.

Besides the efficiency improvements achieved by the insertion of a graded layer at p/i interface and by the introduction of SnO2 Asahi type U substrate, an “interface cleaning procedure”, based on NF3 flushing step, was the key for the cells Voc and fill factor increase.

Microcrystalline n+ layer, ZnO/Ag back contact and device thermal annealing gave further contributions to the cell efficiency.

Utilizing this technology, a large area p-i-n modules (900 cm2) with an initial efficiency of 8.5% has been manufactured.
Examination of 1-D Position Sensitive Detector Performance Through Analysis of Front Contact Heterojunction
Authors: Topiˇ M. , Smole F. , Furlan J. , Fortunato E. , Martins R.
Published: April 2011

The influence of different TCOs (SnO2 and ITO) on the photoelectrical properties of 1 -D position sensitive detectors based on p-i-n structures was studied. A strong cross-contamination in the p-layer and contamination in the i-layer reduce the quality of the device. Numerical analysis of TCO/p-i-n structure also revealed a strong increase in defect states at the p-layer surface which can be attributed to the reduction of TCO. ITO seems to be less appropriate for a front TCO, although the spectral response of the p-i-n structure under reverse bias is not significantly affected by the conditions at the TCO/p heterojunction.
Light-Induced Degradation of Amorphous Silicon-Germanium Alloy Solar Cells Deposited at High Rates
Authors: Sugiyama S. , Xu X. , Yang J. , Guha S.
Published: April 2011

We have studied the light-induced degradation of amorphous silicon-germanium (a-SiGe:H) alloy single-junction solar cells with high initial performance deposited at high rates. The intrinsic layers were deposited using microwave (MW) glow-discharge technique at deposition rates between 10 and 40 Å/s. The results show that light-induced degradation of the cells is higher than that of cells deposited at low rates using RF glow-discharge technique, and it does not strongly depend on deposition rates over this range. The total hydrogen content and the ratio of Si-H2, Ge-H, and Ge-H2 to Si-H bonding estimated by infrared (IR) absorption in films are correlated with the cell degradation results. We have also investigated the effect of ionbombardment on film properties. Films with low ion-bombardment are more porous and have higher composition of Si-H2 and Ge-H2 bonding. Appropriate ion-bombardment makes denser structure in a-SiGe:H alloy films deposited at high rates. This improves the cell performance as well.
Analytical model of a-Si/c-Si Hit Solar Cell
Authors: Furlan J. , Popović P. , Smole F. , Topič M.
Published: April 2011

Using suitable simplifying approximations inside the particular regions of a p-i a-Si/n c-Si heterojunction solar cell, the analytical expressions for the solar cell current-voltage characteristics are derived showing clearly the dominating first-order effects on solar cell performance. The derived closed form solutions indicate that in the useful forward voltage range the largest dark current component of this cell is the interface recombination current and that the main contribution to the photocurrent comes from the light generated holes in the c-Si substrate layer. The transfer of holes across the intrinsic layer and over the ΔEv barrier is strongly suppressed resulting in an attenuation of solar cell dark and photocurrent.
Analysis of the Conduction Properties of a-Si:H n+-i-n+ Structures Via Accurate Computer Modelling
Authors: Chatterjee P. , Vanderhaghen R. , Equer B.
Published: April 2011

Analysis of the current density-voltage (J-V) characteristics of sandwich a-Si:H n+-i-n+ structures made of the same materials but with varying thicknesses of the i-layer, has given rise to two somewhat contradictory speculations regarding the density of states (DOS) at the Fermi level of the i-layer. The first of these postulates that the DOS over the first 2000–4000A of the i-a-Si:H layer is larger by a factor of 3–10 than that in the rest of the film With this hypothesis however, the experimentally observed low activation energies (Ea) for thin n+-i-n+ devices remain unexplained. In the other analysis, a consideration of the n+-i space-charge regions enables a fair description of the experimental results assuming that the electron DOS is position independent in the i-layer. In the present report we use accurate computer modelling to calculate and analyse the J-V characteristics of a-Si:H n+-i-n+ structures in the low bias ohmic region as a function of device thickness, ambient temperature and the quality of the i-layer. We find that the n+-i interface is abrupt only for a device with a high dangling bond density. For good quality material however, the depletion width extends right across the i-layer for a thin device and the zone of charge neutrality is never reached, resulting in low values of Ea in the ohmic region. In the latter case Ea increases with i-layer thickness. Analysis by detailed computer modelling confirms that the experimental results may be explained by assuming a density of states independent of the thickness of the i-layer.
Thin p-type Microcrystalline Silicon Film on Various Substrates
Authors: Rath J. K. , Wallinga J. , Schropp R. E. I.
Published: April 2011

Thin(<20nm) p-type microcrystalline silicon f'dms have been deposited by PECVD in an unusual parameter regime, specifically optimized for extremely thin films. High conductivity (>10.2 Scm−1) and low activation energy(<0.08eV) of thin films have been achieved on various metal oxide substrates i.e., Coming 7059 glass, SnO2:F, TiO2 and Ta2O5. Crystallinity was confirmed by Raman spectroscopy and UV reflectance. Deposition of p-μc-Si:H is possible on void rich films (a-SiC:H and low temperature deposited a-Si:H) but not on device quality a-Si:H. Cells made in a superstrate structure using p-μc-Si:H as the window layer directly on top of SnO2:F coated glass yielded 9.63% efficiency, with an improvement in the blue spectral response compared to the cell made with a- SiC:H(B) as window layer. Tandem cells (a-Si:H/a-Si:H) incorporating p-μc-Si:H along with n-μc- Si:H in the tunnel junction yielded 8.8% efficiency.
Low Temperature Hydrogen Induced Amorphous to Crystalline Silicon Phase Transformations
Authors: Fortmann C. M. , Hapke P. , Lambertz A. , Finger F.
Published: April 2011

The low temperature hydrogen induced phase transformations are the basis for the layer-by-layer micro-crystalline silicon growth technique which involves the sequential deposition of thin amorphous silicon layers followed by hydrogen treatment. Very high frequency-PECVD layer-by-layer microcrystalline film growth was studied as a function of frequency. The highest crystalline content films were prepared on glass substrates at 49.7 MHz with deposition cycle times of 12 seconds and hydrogen treatment times of 120 seconds or longer. At lower frequencies, 13.56 and 27 MHz, no micro-crystalline content was observed. At higher frequencies (94.7 MHz) crystalline content was reduced compared to that of the 49.7 MHz case. Crystalline content is not correlated with the hydrogen etch rate as the highest etch rates occurred at 94.7 MHz while etch rates at 49.7 and 27 MHz were lower. It is possible to prepare thin micro-crystalline films using the VHF layer-by-layer growth technique.
Recrystallisation of Preamorphized Silicon Investigated by RBS and PAC
Authors: Rohrlack G. , Freitag K. , Vianden R. , Gwilliam R. , Sealy B. J. , Jafri Z.
Published: April 2011

The technique of preamorphization is a well-known method to avoid channeling tails of implanted dopants when fabricating devices. This is achieved by implanting a nondopant atom to produce the amorphous layer. We studied the recrystallisation of silicon preamorphized by Si, Ge and Sn implants. The recrystallisation was investigated by RBS and the y-y perturbed angular correlation (PAC) technique. RBS provides information about the thickness and the perfection of the recovered layer. Additional experimental data are supplied by the PAC technique, which used the postimplanted radioactive isotope 111Ina s a probe atom. The recovery of the lattice structure in the vicinity of the probe atoms is monitored on a microscopic scale via the electric field gradient produced at the site of the In nucleus by the surrounding lattice defects. The results are discussed and compared to the RBS data.
Modified Triode Plasma Configuration Allowing Precise Control of Ion-Energy for Preparing High Mobility a-Si:H
Authors: Ganguly G. , Ikeda T. , Sakata I. , Matsuda A.
Published: April 2011

We have previously shown that the carrier drift mobility in amorphous silicon can be enhanced by optimizing the ion-bombardment energy during growth on conducting substrates. However, there exists a lack of reproducibility of samples exhibiting high mobility which we attribute to the rf field induced fluctuation of the plasma potential in a conventional (Te ≈ 2eV) silane plasma. Here we introduce an enclosed plasma configuration that allows us to confine the effect of the rf field and therefore obtain a low-electron-temperature (Te ≈ 0.1 eV) silane plasma as determined from Langmuir probe measurements. The measured ion-energy distributions correlate with those for electrons and the mean ion-energy can be controlled by biasing the substrate which allows us to reproducibly fabricate high drift mobility amorphous silicon.
A-Si:H Films Deposited by Dc-Masd Technique at High Substrate Temperature
Authors: Golikova O. A. , Kuznetsov A. N. , Kudojarova V. Kh. , Kazanin M. M. , Ikosarev A.
Published: April 2011

Dc-magnetron assisted silane decomposition technique has been tested for deposition of undoped a-Si:H at substrate temperature Ts=300–400°C. In the optimized conditions device-quality a-Si: H films were deposited independently of Ts. A low hydrogen content CH (up to 2 at.°) and microstructure variations are characteristic of the MASD films.
Saddle-Field Glow-Discharge Deposition of Amorphous Semiconductors
Authors: Gaspari F. , Sidhu L. S. , O'leary S. K. , Zukotynski S.
Published: April 2011

We present a dc saddle-field glow-discharge deposition procedure which combines the positive attributes of the conventional dc and rf glow-discharge techniques. Preliminary mass spectra analyses of both silane and methane glow-discharges demonstrates that ions constitute a significant fraction of the species reaching the film surface. Growth rate analyses suggest that ions play a significant role in the saddle-field glow-discharge deposition of amorphous semiconducting films.
Light-induced Stability of Layered Amorphous Hydrogenated Silicon Grown with Alternating Substrate Temperature
Authors: Yoona Jong-Hwan , Lee Czang-Ho
Published: April 2011

We present the results of studies on the light-induced stability of undoped layered hydrogenated amorphous silicon films grown with alternating substrate temperature between optimal and non optimal temperatures for device-quality films. Compared to the single layer films grown at optimal substrate temperature, the layered films show improved stability in the lightinduced state. Under intense light illumination of 3 W/cm2, the steady-state defect density of the layered film reached a saturation of 2×1016 cm−3, while the single layer film saturates at about 6×1016 cm−3. It is found that in the completely degraded state the photoconductivity in the layered film is also improved by a factor of two compared to the single layer film.
Properties of Substrate-Type a-Sihh Devices Prepared Using ECR Conditions
Authors: Dalal Vikram L. , Kaushal Sanjeev , Girvan Robert , Sipahi Levent , Hariasra Swati
Published: April 2011

We report on the preparation and properties of a-Si:H devices prepared at high temperatures on stainless steel substrates using low pressure ECR plasma deposition techniques. The devices were prepared using either Hydrogen or Helium as the plasma diluent gas. The use of He as the plasma gas led to films having significantly lower H concentration(4–5%) and a lower bandgap than comparable films made using hydrogen dilution. We find that we can make excellent devices, with good fill factors(over 70%) and voltages(over 0.86 V) using either H or He dilution. The use of He led to devices having smaller bandgap, by about 35–40 meV compared to devices made using H dilution. Detailed quantum efficiency measurements show that the hole collection in both types of devices is excellent, and that Urbach energies of tail states in each case is in the range of 43–45 meV.
Inert Gas Dilution and Ion Bombardment Effects in Room Temperature (35°C) Plasma Deposition of a-Si:H
Authors: Srinivasan Easwar , Lloyd Daniel A. , Fang Ming , Parsons Gregory N.
Published: April 2011

Plasma enhanced chemical vapor deposition (PECVD) of a-Si:H with silane or silane and hydrogen at temperatures lower than 200°C commonly results in films with significant dihydride bonding and a high defect density. In this paper, we demonstrate the formation of monohydride dominant a-Si:H films using rf parallel plate PECVD at 35°C at deposition rates greater than 100 Å/min. In the as-deposited state, these films have low dark conductivity (∼10−9 S/cm) and low photoconductivity. Annealing the films at 150°C caused the monohydride dominant films to show photo to dark conductivity ratio near 105. Our results also indicate that an increase in monohydride fraction is not linked with a decrease in deposition rate.
Modulation of Growing Surface with Atomic Hydrogen and Excited Argon to Fabricate Narrow Gap a-Si:H
Authors: Futako W. , Shimizu I. , Fortmann C. M.
Published: April 2011

Hydrogenated amorphous silicon (a-Si:H) with a gaps narrower than 1.7 eV were made by repeating the deposition of a thin layer (1–3 nm thick) and the treatment of growing surface with a mixture of H and Ar*. Crystallization induced by permeation of hydrogen into the subsurface at high substrate temperature (>200C) was efficiently prevented by treating with a mixture of H and Ar*. The activation of growing surface may arise from releasing a part of hydrogen on surface by treating with Ar*. High quality a-Si:H films containing hydrogen of 3 atom % with a gap of 1.6 eV were made by chemical annealing with a mixture of H and Ar*.
In Situ Investigation of the a-Si:H/C-Si Interface
Authors: Feist H. , Swiatkowski C. , Elmiger J. R. , Zipfel M. , Kunst M.
Published: April 2011

The deposition of a-Si:H films on crystalline silicon substrates was monitored in situ by transient photoconductivity measurements in the microwave frequency range. At the start of the deposition a drastic increase of the interface recombination velocity was observed, followed by a rapid decrease. The implications of these results for the structure of the interface are discussed. Changes of the interface after deposition were detected without a change of the temperature, even at 250'C: The long relaxation time of the structure of the interface will be discussed. Ex situ results on the samples produced will be compared to the in situ results in view of the passivation properties of a-Si:H films on c-Si substrates.
Nuclear Magnetic Resonance Studies of Hydrogen in Amorphous Silicon
Authors: Norberg R. E. , Fedders P. A. , Leopold D. J.
Published: April 2011

Proton and deuteron NMR in hydrogenated amorphous silicon yield quantitative measures of species-specific structural configurations and their dynamics. Populations of silicon-bonded and molecular hydrogens correlate with photovoltaic quality, doping, illumination/dark anneal sequences, and with infrared and other characterizations. High quality films contain substantial populations of nanovoid-trapped molecular hydrogen.
1H Nmr in μc-Si:H Deposited With Different Plasma Excitation Frequencies and Silane Concentrations
Authors: Hari P. , Taylor P. C. , Finger F.
Published: April 2011

Six samples of pc-Si:H were prepared by PECVD at 200°C with plasma excitation frequencies ranging from 13 MHz to 95 MHz. Four samples were prepared with gas mixtures of 3% SiH 4 in H2. For these samples the plasma excitation frequencies ranged from 13 MHz to 95 MHz. Two samples at a plasma excitation frequency of 95 MHz were prepared at 5% and 8% SiH4 in H2. All samples were deposited on aluminum foil and etched off using dilute HCI to form powdered samples. These samples were studied by nuclear magnetic resonance (NMR), electron spin resonance (ESR) and infrared (IR) absorption measurements. The broad and narrow components of the free induction decay (FID) in the NMR measurements were compared to the respective components that occur in a-Si:H. The broad components in the various samples of μc-Si:H are similar in width to the broad component in a-Si:H, but the narrow component is narrower by a factor of two as compared to the narrow components in μ-Si:H. The narrow component in pic-Si:H samples exhibits a beat pattern similar to a previously observed Pake doublet. ESR measurements performed between 20 K and 300 K show that the spin densities, which can be attributed to silicon dangling bond states, increase as a function of plasma excitation frequency. The hydrogen content of each μc-Si:H sample was estimated from the NMR measurements, and these estimates are in good arrangement with the hydrogen content estimated from IR measurements.
H2-Dilution vs. Buffer Layers for Increased Voc
Authors: Platz R. , Fischer D. , Hof C. , Dubail S. , Meier J. , Kroll U. , Shah A.
Published: April 2011

Hydrogen dilution and buffer layers, as two ways to obtain higher Voc values in a-Si:H p-i-n solar cells, are directly compared in the present study. Special emphasis is laid on stability against light soaking. H2-dilution in combination with lower substrate temperature yields higher Voc values and better stability as compared to buffer layers. However, light absorption is decreased due to the increased gap in H2-diluted cells. The stability of buffer layer cells can remarkably be ameliorated by boron doping and H2-dilution of the a-SiC:H buffer layer. However, stabilized efficiency is higher for optimized diluted cells than for cells with a buffer layer. An a-Si/a-Si stacked cell with a graded dilution for both cells yielded 10% initial efficiency with 17% relative degradation. Diluted a-Si:H cells at lower temperature become specially interesting in combination with a microcrystalline bottom cell. For such a “micromorph” tandem cell we obtained 11.4% initial efficiency.
New Model for “Stretched Exponential” Relaxation
Authors: Walle Chris G. Van De
Published: April 2011

A new model to explain stretched exponential relaxation in hydrogenated amorphous silicon is presented. The model does not invoke statistical distributions; rather, it is based on a careful treatment of diffusion, including retrapping. Excellent fits to a variety of experimental data are obtained.
Photocreated Defects and Light-Induced ESR in a-Si:H and Related Alloy Films
Authors: Shimizu Tatsuo , Durny Rudolf , Kumeda Minoru
Published: April 2011

Two major problems in the field of a-Si:H and related alloy films such as a-Sil-xNx:H are addressed in this contribution, namely, the photocreation of neutral Si dangling bonds and the origin of the components of the light-induced ESR (LESR). We have proposed a new model for the photocreation of neutral Si dangling bonds in a-Si:H based on the presence of floating bonds. The model can explain the metastabilization of the broken weak bonds without the movement of H atoms. The broad, the narrow, and the dangling bond components of the LESR signal have been attributed to holes captured at negatively charged floating bonds, electrons trapped at antibonding states of weak bonds and photoexcited carriers captured at charged dangling bonds, respectively.
Defect Characterization of High-Rate Deposited Hydrogenated Amorphous Silicon Films
Authors: Chan Florence Y. M. , Lam Y. W. , Chan Y. C. , Lin S. H. , Lin X. Y. , Lau W. S. , Chua S. J.
Published: April 2011

High rate deposition of a-Si:H films has become one of the key techniques for low-cost, large-scale production of thin film devices. Hydrogenated amorphous silicon films were fabricated with a thermocatalytic PCVD method of which the deposition rate was up to 1.5 nm/sec. The Heterojunction Monitored Capacitance method was employed to determine the midgap-state densities in the undoped semiconductor film from high frequency C-V characteristics. Experimental results showed that the thermocatalytic PCVD method is an effective way to produce high-rate deposited a-Si:H films.
Dependence of Light-Induced Esr on NitroGen Content in Amorphous Silicon-Nitrogen Alloys
Authors: Zhang Jinyan , Ohtsuka Toshihiro , Kumeda Minoru , Shimizu Tatsuo
Published: April 2011

The LESR signals are observed for the a-Si1-xNx:H samples over a wide range of nitrogen content at 77K. By decomposing the LESR signals using three components, i.e. the neutral Si dangling bond (Do) component, the broad component with a linewidth of 16 G, and the narrow component with a linewidth of 5 G, we find that the three components are observed only in the Si-rich samples. The density of light-induced Do increases with x, whereas the densities of both the narrow and the broad components increase in the range of x≦0.32 and are almost independent of x for larger x. The g-value of the broad components falls down sharply from 2.01 to 2.006 with an increase in x, while the g-value of the narrow component is unchanged and it is around 2.004. All of the three components can be annihilated by sub-gap illumination. The origins of the broad and the narrow components are discussed.
Recovery Kinetics of Phosphorus Ion-Implanted a-Si:H
Authors: Nakata J. , Wagner S. , Gleskova H. , Stolk P. A. , Poate J. M.
Published: April 2011

Hydrogenated amorphous silicon was implanted with phosphorus ions to a uniform concentration of 3×1020 cm-3 and defect saturation. The implants were annealed isochronally up to 400°C in the dark or under additional illumination. This illumination had no effect on recovery. The Urbach energy remains higher than that of silicon-implants. The midgap defect density anneals to ˜ 1018 cm-3, typical of gas-phase doped samples. The dark conductvity remains lower and its thermal activation energy higher than in gas-phase doped samples. We surmise that the Si-Si network absorbs some of the donor electron-induced defect density by forming strained Si-Si bonds. These strained bonds widen the band tails, and thus reduce the effective electron mobility and pin the Fermi level.
Local Structural Changes Around Charged Dangling Bonds
Authors: Biswas R. , Li Qiming
Published: April 2011

Tight-binding total energy calculations are used to describe the changes in local structure following either electron or hole capture by a neutral dangling bond in computer generated a-Si:H models. After the change in charge state, the structure is allowed to relax by a steepest descent energy minimization procedure. Generally the local bond angles increase (decrease) rapidly by 3- 100 in transitions from the D0 to the D+ (D-) configurations. The displacement of nearest neighbor atoms and nearby H atoms is large (more than 0.2 Å), but displacement of distant atoms is generally much smaller. Calculated optical transition levels have the D- level below D0 and the D+ level above D0. The fast relaxation of the charged defect configurations suggest a smooth energy surface for the relaxation.
Observation of Configurational Switching of Deep Defects in a-Si:H Using Thermal Step Insertion During Capacitance Transient Measurements
Authors: Gardner Adam D. , Cohen J. David
Published: April 2011

In standard, isothermal capacitance transient measurements, configurational changes in defect states are normally very difficult to identify because, depending on the relative rates of thermal emission to the configurational relaxation, charge will be emitted predominantly from only one configuration. We have found, however, that employing a thermal step during the emission phase of the transient enhances the effect of defect relaxation; one can then observe the resultant switch between distinct configurations. We have applied this method quite successfully to lightly doped n-type a-Si:H samples by varying the overall temperature (between 270K and 350K) and the magnitude of the temperature switch (from 20K to 35K). For the smallest temperature steps, the resultant transients suggest two distinct configurations that, we believe, reflect only a fraction of the many latent configurations that account for the full range of relaxation possible.
CPM and PDS - A Critical Interpretation of Experimental Results
Authors: Stiebig Helmut , Siebke Frank , Carius Reinhard
Published: April 2011

CPM and PDS spectra of a-Si:H yield identical shape of the Urbach tail, while the defect absorption measured by PDS differs significantly from CPM. In this work an analysis of CPM and PDS spectra of annealed and degraded films is presented. Numerical simulations of CPM and PDS data, taking into account optical transitions, capture and emission processes as well as the Fermi level, yield information on the energy distribution and the charge state of the defects. The simulations reveal the coexistence of defects in the D−, D+ and D0 states. The defect distribution is dominated by charged states as predicted by the defect-pool model. Good agreement between measured and simulated PDS and CPM spectra can be obtained in the case of a homogeneous defect density. It is shown that differences between CPM and PDS are due to different sensitivities of the techniques to charged and neutral defect states. Microscopic inhomogeneities may cause significant additional differences.