bluuebunny/crossref_metadata_2025 huggingface dataset:
Fast Changes in a-Si:H Solar Cells After Severe Light-Soaking
Authors: Roedern Bolko Von
Published: March 2011

The fast changes observed in the stabilized state of a-Si:H solar cells and modules at temperatures below 70°C are inconsistent with the commonly accepted picture of “defect annealing.” The fast changes observed in the stabilized state, for example when the temperature is altered, are explained in terms of converting the charge state of the dangling bond defects that are already present in the material. It is suggested that the slow degradation of solar cells arises from the creation of new defects and can be described by fitting stretched exponential curves to the solar cell performance data.
Temperature Dependence of Metastable Defect Creation in a-SiNx:H
Authors: Hamed A. , Fritzsche H. , Köhler S.
Published: March 2011

Light exposure of multilayers consisting of alternating 2.5 nm thick a-Si:H and about 40 nm thick a-SiNx:H produces a large metastable excess dark conductance. This appears to be due to metastable defects in a-SiNx:H produced by hopping injection of photocarriers from the a-Si:H. They anneal at an equilibration temperature TE∼460°K. These metastable defects are created with the same efficiency between 4K and 300K. The efficiency rapidly falls above 350K. The metastable defects have the same anneal temperature regardless of creation temperature. The mechanism of defect creation will be compared with that in a-Si:H.
Amorphous Silicon Analogue Memory Elements
Authors: Rose M. J. , Hajto J. , LeComber P. G. , Snell A. J. , Owen A. E. , Osborne J. S.
Published: March 2011

Both Cr/p+/V and Cr/p+/Cr devices exhibit fast electrically programmable memory switching with a programmable voltage range, ΔVS, which depends only on the choice of the top metal. Despite a difference in ΔVS, both types of device have very similar electrical properties, but show one major difference in room temperature I-V characteristics, where under certain conditions, discontinuities are observed.
Density of States Spectroscopy in p-Type a-Si:H and a-SiC:H
Authors: Crandall Richard S. , Salamon Stanley J. , Xu Yueqin
Published: March 2011

We derive a closed form expression for differential junction capacitance applicable when the density of states (DOS) varies exponentially with energy. Using this expression, we analyze p/n junction capacitance measurements that probe the DOS in boron doped hydrogenated amorphous silicon and silicon carbide alloy. In both materials we find that the p-layer DOS is described by an exponential increase with energy above the Fermi level.
An Investigation of Spin and Charge States Associated with Metastable Defects in N-Type Hydrogenated Amorphous Silicon
Authors: Rasmussen R. J. , Cohen J. D. , Essick J. M.
Published: March 2011

Depletion-width-modulated (DWM) ESR spectroscopy and junction capacitance techniques were employed to investigate deep-defect states in various metastable states of 10 and 80 Vppm PH3-doped a-Si:H. From the joint application of these methods, we enumerate the change in total spin and charge associated with emission of carriers from states within the mobility gap resulting from a modulated bias voltage. We conclude that the magnitude of the modulated spin-to-charge ratio is nearly unity, consistent with earlier similar investigations of n-type a-Si:H, where the D-/D0 transition was shown to dominate. Furthermore, we present results of a previously unreported “quadrature” DWM-ESR signal of large magnitude under a wide range of experimental conditions. Similar related effects are also reported from spin- and capacitance-transient studies. These results clearly demonstrate that the changes in spin significandy lag corresponding changes in charge.
Effects of Temperature and Charge Depletion on the Spin Density in Hydrogenated Amorphous Silicon
Authors: Lee J.-K. , Schiff E. A.
Published: March 2011

The dependence of the spin density upon temperature and charge depletion is calculated based on the standard defect model in a-Si:H of a D-center with positive, neutral, and negative charge states. The results are compared with recent measurements of depletion width modulated spin densities and temperature-dependent spin densities. It is shown that the initial charge density assumed for the defect system substantially affects conclusions regarding electronic correlation energies drawn from the measurements.
Surface Processes Limiting the High Rate Deposition of High Electronic Quality a-Si
Authors: Veprek S. , Anibacher O. , Riickschloβ M.
Published: March 2011

Amorphous silicon of a high electronic quality with Odatk 10-10, σPh ≈ 1·10-4 (Ωcm)-3 and density of gap states of about 0.3 to 2.1016 eV-1cm-3 is deposited at rates up to 17 Å/sec. The rate limiting steps are identified and their control via the plasma parameters is explained. This allows one to establish the fundamental scaling parameters for large-area high-rate deposition of a-Si. Long term stability of the films in terms of postoxidation and photode-gradation is briefly addressed.
Hydrogen Dilution effects on Amorphous Hydrogenated Silicon (a-Si:H) Prepared by Glow Discharge Near Room Temperature
Authors: Cheung Man Ken , Petrich Mark A.
Published: March 2011

We report here the first phase of our attempt to deposit “device-quality” a-Si:H films by glow discharge near room temperature (50 °C). We have found that, at a low rf power density (40 mW/cm2) and high hydrogen/silane ratios (≥ 2), film quality is not uniquely determined by the substrate temperature, Ts. The microstructure of our low hydrogen content films as revealed by infrared (IR) and nuclear magnetic resonance (NMR) spectroscopies is similar to that of “device-quality” films deposited at standard Ts. The next phase of our work is to ascertain whether or not similar IR and NMR characteristics between our low Ts films and the standard Ts films imply also similar opto-electronic properties.
Optical Properties of Random Multilayers of Amorphous A-Si:H/A-Si3N4+x:H and the Classical Localization
Authors: Nitta Shoji , Ogawa Kohji , Furukawa Takehiro , Itoh Takashi , Nonomura Shuichi
Published: March 2011

In the optical reflectance spectrum of the random multilayers of a-Si:H/a-Si3N4+x:H, it is observed an anomalous peak which is explained by the classical localization of light propagation. The following two subjects are discussed in this report; (a). The Kramers-Kronig transformation is done including the anomalous disorder-related reflectance peak. Extra absorption coefficients Δα are obtained by this analysis. Energy dependence of the localization length 1(hv) of light propagation are obtained by 1(hv)=1/Δα(hv). (b). The other is the experiment on scaling where the ratio of the disorder and the average layer thickness is kept constant but the size of each layer is changed in each experiment
Surface Absorption Below the Band Gap in a-Si:H Using Photoluminescence Absorption Spectroscopy
Authors: Gu S. Q. , Nitta S. , Taylor P. C.
Published: March 2011

Photoluminescence absorption spectroscopy or PLAS has been used to measure the below gap absorption in a-Si:H at 77 K. As the absorption probed by this technique is composed of contributions from the bulk and the surfaces of the a-Si:H, we have developed an improved sample structure to separate these two contributions. Two kinds of interface have been investigated: a-Si1−xNx:H/a-Si:H and a-Si1−xOx:H/a-si:H. For the studies ofa-Si1−xNx:H/a-Si:H.x, two samples have been employed. The first sample consisted of an a-Si1−xNx:H/a-Si:H/a-Si:H/a-Si1−xNx:H/NiCr layered structure; the second one had a similar structure except that the a-Si:H layer was interrupted periodically by two thin (100 A°) a-Si1−xNx:H layers to increase the contribution of the interface absorption. A shoulder of the absorption around 1.2 eV for the second sample, which was not found in the first one, is probably due to the interfaces between a-Si:H and a-Si1−xNx:H. All samples were light-soaked using an Ar+ laser (5145 A°). The increases in the absorption measured by PLAS at 77 K are essentially the same as the results of PDS at 300 K, which suggests that the interfaces do not contribute to the light-induced absorption.
Fundamental Consideration on Carrier Transport in Amorphous Silicon Superlattices
Authors: Jiang Y. L. , Hwang H. L.
Published: March 2011

Basic consideration of parameters including electron de Broglie wavelength, resonant tunneling time (τr) and inelastic scattering tunneling (τi) were studied to identify the intrinsic tunneling properties of amorphous double—barrier (DB) structure. The order of magnitude of τr/τi. of amorphous DB structure is about 5 to 12 which is far beyond that of crystalline case which is 1 to 2. The transmissivity versus applied voltage or versus electron energy were calculated to identify the influence of barrier height, barrier thickness and electron effective mass. The influence of carrier distribution will also be discussed.
Reducing the Saturated Defect Density- in a-Sl:H by Post-Growth Anneals
Authors: Yoon J. H. , Xu X. , Kotharay M. , Wagner S.
Published: March 2011

The saturated light-induced defect density Nsat in a-Si:H was studied as a function of deposition temperature and of pre-light-soaking anneals. The deposition temperature and annealing affect the microstructure, which we characterize by the Si-H and Si-H2 infrared absorption intensities. We find correlations between Nsat and the initial defect density, the Urbach energy, the hydrogen concentration and the fraction of H in SiH4 groups. Annealing before light-soaking can reduce the saturated defect density substantially.
Assessment of Weak Si-Si Bond Breaking Mechanisms of the Staebler-Wronski Effect
Authors: Biswas R. , Kwon I. , Soukoulis C. M.
Published: March 2011

The mechanisms of the Staebler-Wronski effect are investigated by examining the stability of computer-generated amorphous hydrogenated silicon networks with a molecular dynamics approach. Models with both monohydride and dihydride species are examined. A new Si-H interatomic potential is utilized for the simulations. A localized excitation is used to model the non-radiative transfer of photo-excited carrier energy to the lattice. The a-Si:H model with only monohydride species is stable to bond-breaking excitations. The a-Si:H model with both monohydride and dihydride species is less stable and exhibits, after local excitations, higher energy dangling bond states that can however be easily annealed away.
Mechanism of Ion Transport in Cooled and Supercooled Water at High Pressure
Authors: Nakahara M. , Takisawa N. , Osugi J.
Published: March 2011

As predicted by the Hubbard-Onsager continuum dielectric friction theory for ionic mobility in solution, the observed pressure coefficient of the difference ζ between the observed ionic drag coefficient and the Stokes law friction (4πηR), is negative for the small ion Li+ even at low temperatures where the water structure is highly developed. For the large ion Cs+, however, it is positive at any temperature in contrast to the theoretical prediction, its magnitude being larger at lower temperatures and pressures. The anomaly is shown also by the medium-sized ion K+ below room temperature. The passing-through-cavities (PTC) mechanism has been proposed to explain the limitations of the continuum theory.
Liquid State Thermodynamics: Application to Highly Compressed Solids
Authors: Jones Randall S. , Ashcroft N. W.
Published: March 2011

Thermodynamic properties of materials above a few hundred KBars can normally be obtained only by dynamic techniques which have the associated difficulty (from the theoretical point of view) that the high pressure states are usually also at quite high temperatures. Thus, it is important to obtain accurate estimates of the thermal contribution to the thermodynamic functions. Within the pair potential model of solids, these thermal contributions may be determined by a self-consistent phonon approximation, but this is generally a very complicated calculation. Numerous approximate methods have thus been developed to estimate the thermal contribution to the thermodynamic functions [1].
Thermodynamic Properties of the Alkali Metals at High Pressures and High Temperatures
Authors: Boehler Reinhard
Published: March 2011

The melting temperatures of Li, Na, K, Rb, and Cs versus pressure were measured to 32 kbar in a piston cylinder apparatus with hydrostatic pressure medium and in situ pressure measurements. The accuracies in pressure and temperature are ± 0.4 % and ± 0.25° C, respectively. Substantial deviation from measurements using solid, non-hydrostatic pressure media is observed. The adiabat, (δT/δP)s,was measured to 32 kbar and 400°C by adiabatic compression. Ln (δT/δP)s is a linear function of volume with good consistency in the slopes. (δT/δP)s changes insignificantly at the liquid-solid phase transitions. The Grüneisen parameters, calculated from γ = Bs/T (δT/δP)s, decreases with pressure and temperature. Bs is the adiabatic bulk modulus. The γ-volume curves show strong curvature and γ tends to become volume independent at compressions of about 30 %. γ increases by several percent at the liquid-solid transition.
Condie Process
Authors: Ritter N. , Avitzur B.
Published: March 2011

The process of conventional hydrostatic extrusion limits the length of the billet that can be extruded to a length somewhat shorter than that of the chamber. Production units are also limited to pressures of about 8,000 Kg/cm2. Thus the reduction that can be affected in one pass of hydrostatic extrusion of mildly tough materials like low carbon steels or copper is limited to no more than 75% R.A., if the extrusion is performed at room temperature. For subsequent passes, each previous extrudate must be cut to suitable length so it will fit again into the chamber.

The Condie process (Austen, U.S. Pat. #3,999,415) provides the means to perform extrusion through several dies, one die at a time, in one loading of the chamber. In the present model, only two dies are loaded into the chamber together with the billet. A short length is first extruded through the first die, while the second die is kept free to move idly with the extrudate. Then extrusion through the first die ceases and the billet is forced to extrude through the second die. As the second die approaches the first die and the intermediate diameter section shortens, the extrusion stops. Thus, one cycle of a finite length is completed. But, the accumulated reduction from billet to extrudate is large, similar to the reduction obtainable by a single die from a chamber of twice as high a pressure.
High Pressure Method for Identification of Crystal Elastic Imperfections - Generation of Defects in Silicon Single Crystals Under Pressure
Authors: Jung J. , Lefeld-Sosnowska M.
Published: March 2011

New method for identification of the kind of elastic stress-free crystal imperfections which are not visible by standard X-ray and electron microscopy methods was presented. The method is based on the high pressure annealing creating large stresses at defect sites,followed by X-ray topography. This method was applied in structural defects studies of high quality silicon single crystals and allowed to determine the composition and structure of precipitates in silicon.
Investigation of Carbon Vapor Pressure at Very High Temperatures and Pressures with the Aid of Laser Heating
Authors: Scheindlin M.A.
Published: March 2011

For several decades the behavior of carbon and carbonaceous materials has been observed with unvarying interest. Well known are two polymorphous modifications of carbon, namely, graphite and diamond, each possessing unique physicochemical properties which make them attractive for extensive utilization in numerous industries.

The history of carbon studies at high temperatures and pressures produced quite a few examples of ingenious experimental techniques and experimenter's skill, however, many of those studies only resulted in the emergence of new, hard-to-solve problems. This is precisely the case with the melting and vaporization of graphite.
Equation of State for Fluid and Solid Hydrogen-Isotopes H2, D2, and T2
Authors: Shimizu Hiroyasu
Published: March 2011

The calculations of the P-V isotherms of fluid hydrogen isotopes H2 , D2 , and T2 up to their freezing pressures at 200, 300 and 500 K have been performed for 4 kinds of intermolecular potentials by using the modified hard-sphere variational perturbation theory with a quantum correction. By comparing the results with the 300 K experimental equation of state, it has turned out that the agreement is good for the potentials of Silvera-Goldman and Nellis et al. except near the freezing point of H2 . The quantum pressures were estimated, and their dependences on volume, molecular mass, and temperature are discussed quantitatively. We discuss the discrepancy of the P-V isotherms between experiments by Brillouin scattering and theoretical results for H2 near the freezing point, including the recent solid isotherms to higher pressures.
Experimental Measurements of the Solubility of Hydrocarbons in Compressed Natural Gas Under Pressure (10 – 100 MPa) and Temperature (50 – 150°C).
Authors: Nogaret E. , Tufeu R. , Le Neindre B.
Published: March 2011

An apparatus to measure phase equilibria under pressure is described. The composition of the gas phase was determined using a high pressure, high temperature sampling cell. We have found that compressed natural gas is a very good solvent of hydrocarbons. A possible application of this study is the understanding of processes which lead to migration of oil and the location of oil and gas fields.
Surface Segregation of Boron During Si-MBE Growth
Authors: Sardela M. R. , Ni W. -X. , Ekberg J. O. , Sundgren J. -E. , Hansson G. V.
Published: March 2011

Boron doping, using an elemental boron source during molecular beam epitaxial growth of silicon, has been studied. The boron flux was provided by a high temperature source heated by radiation and electron bombardment. The maximum boron deposition rate used was 1×1012 cm−2 s−1 at an estimated B temperature of 1950 °C. For growth at a substrate temperature of 650 °C, there is very little surface segregation when the doping level is in the range 1×1016-1×1019 cm−3. For very high boron to silicon flux ratio (>7×10−3) there is a strong surface segregation that results in surface accumulation of boron. This initially leads to a 2×2 reconstruction of the Si (100) surface, and further surface segregation during growth results in roughening of the surface due to the creation of (311)-facets. In a separate set of experiments, the surface segregation was studied using in situ Auger electron spectroscopy of predeposited layers of boron that were gradually covered by Si capping layers. Strong and surface coverage dependent surface segregation was observed both in the case of Si (100) and (111) substrates.
Boron Doping in Si-MBE
Authors: Eberl K. , Iyer S. S. , Delage S. L. , Ek B. A. , Cotte J. M.
Published: March 2011

We have investigated p-type doping of Si and SiGc layers in M BE by using two different boron sources. One is a SiB alloy which is prepared in situ by melting elemental boron into Si. Typical B concentrations in the source material are a few percent. Doping levels within 1×1018 cm−3 and 5.5×1019 cm−3 can be adjusted within the temperature range of 350°C to 850°C. No indication of segregation or memory effects is found. The activation is between 90 and 100%. The second p-type doping source investigated is a diborane (B2H6) gas source. Diborane provides doping capability in the range between 1016. to 1020. The incorporation efficiency at 550°C is about 2×10'3. It depends on the diborane exposure and the substrate temperature. The activation at 550°C is above 90%. For lower growth temperatures the activation is considerably reduced. The problem of memory effects is discussed.
Comparison of Growth and Strain Relaxation of Si/Ge Superlattices Under Compressive and Tensile Strain Field
Authors: Wegscheider Werner , Eberl Karl , Abstreiter Gerhard , Cerva Hans , Oppolzer Helmut
Published: March 2011

Optimization of growth parameters of short period Si/Ge superlattices (SLs) has been achieved via in situ low-energy electron diffraction (LEED) and Auger electron spectroscopy (AES) measurements during homo- and heteroepitaxy on Si (001) and Ge (001) substrates. Transmission electron microscopy (TEM) reveals that pseudomorphic SimGe12-m (m = 9 and 3 for growth on Si and Ge, respectively) SLs with extended planar layering can be prepared almost defect-free by a modified molecular beam epitaxy (MBE) technique. Whereas the SLs on Ge can be deposited at a constant substrate temperature, high-quality growth on Si demands for temperature variations of more than 100°C within one superlattice period. Strain relaxation of these SLs with increasing number of periods has been directly compared by means of TEM. For the compressively strained structures grown on Si we found misfit dislocations of the type 60° (a/2)<110>. Under opposite strain conditions i.e. for growth on Ge, strain relief occurs only by microtwin formation through successive glide of 90° (a/6)<211> Shockley partial dislocations. This is consistent with a calculation of the activation energy for both cases based on a homogeneous dislocation nucleation model.
Structural Characterization of P-I-N Diode Superlattice Structures Grown on <100>, <110>, and <111> Orientation Si Substrates
Authors: Adams P. M. , Bowman R. C. , Arbet-Engols V. , Wang K. L. , Ahn C. C.
Published: March 2011

P-I-N diodes whose intrinsic region consists of strained layer superlattices (SLS), separated by 40 nm Si spacers, have been grown by MBE on Si substrates with <100>, <110>, and <111> orientations. These structures have been characterized by x-ray diffraction (XRD) and cross-sectional transmission electron microscopy (XTEM). The dual periodicities in these structures produced unique XRD effects and the quality was highly dependent on substrate orientation. The <100> sample was in general free of defects, whereas the <110> and <111> specimens contained significant numbers of twins and dislocations.
Dislocation Glide Velocity in N- and P-Doped Si1−xGex Layers on Si (001)
Authors: Gibbings C. J. , Tuppen C. G. , Higgs V.
Published: March 2011

Misfit dislocation glide velocities in Si.94Ge.06 layers doped to 2.1018cm−2 with boron were measured over the temperature range 500 – 600°C and found to be up to two times slower than that of undoped material. Arsenic doped Si.932Ge.0ee layers on silicon were also studied, and the glide velocity was found to be enhanced by a factor of 80 at the lowest temperature (500°C) and highest doping level (9.1018cm−2) consistent with a decrease in the activation energy for glide from approximately 2eV to 1.3eV as the doping level was increased.
Interface Structure of Ge/Si Superlattices Determined by X-Ray Absorption Fine Structure
Authors: Aebi P. , Tyliszczak T. , Hitchcock A. P. , Baribeau J. -M. , Lockwood D. J. , Jackman T. E.
Published: March 2011

We illustrate the usefulness of the Extended X-ray Absorption Fine Structure (EXAFS) technique to determine the amount of interface mixing and strain condition in the study of (SimGen)p short-period superlattices. It is found that for n < 4, the number of Ge and Si nearest neighbours to Ge atoms is consistent with ∼25% interfacial mixing and that the Ge-Ge bond length corresponds to that of coherently strained Ge. The Si-Ge bond length is shorter, close to that of a strained Si0.25Ge0.75 alloy. For n > 4, the Ge-Ge bond length and the number of Si-Ge nearest neighbours increase significantly consistent with partial relaxation and interdiffusion. Raman scattering spectroscopy and x-ray reflectometry measurements are also presented and are consistent with the conclusions of the EXAFS analysis.
Si-Based Photonic Devices by MBE
Authors: Houghton D. C. , Noël J. -P. , Rowell N. L.
Published: March 2011

The prospect of efficient electroluminescence and photodetection in Si-based heterostructures has stimulated considerable interest in recent years. Si-based optoelectronic devices would allow monolithic integration of mature Si technology with optical signal processing. However, Si and epitaxial Si1−xGex/Si (100) alloys are indirect semiconductors and band structure perturbations are necessary to enhance luminescence efficiencies to practical levels. In this review we consider the relative success of the various approaches used to obtain efficient luminescence from Si based heterostructures after first considering the optical properties of Si grown by MBE and doped by several techniques. Exciton binding centers such as isoelectronic defect complexes, zone folding in atomic layer superlattices, e.g. SimGen, and rare earth doping, e.g. Er in Si and Si1−xGex alloys are discussed. The internal quantum efficiencies for the above processes will be compared in both electroluminescence and photoluminescence together with the prospects for room temperature light emission. The twin requirements of band structure engineering and superlative crystal quality extend the challenge to the materials scientist / crystal grower further into the nanoscopic regime. It is a formidable task involving the controlled removal of non-radiative point defects and complexes, controlled introduction of radiative centers, and simultaneous maintenance of coherent interfaces without misfit dislocation injection. Recent progress in our study of intense photoluminescence (wavelength range 1.2 -1.7 μm) from random Si1−xGex alloys (0.53 > × > 0.06) grown by MBE, a 1.5 μm Si0.82Ge0.18/Si LED and a novel Si1−xGex/Si optoelectronic switch will be highlighted.
Integration of Si-MBE and Device Processing
Authors: Gravesteijn D. J. , Van De Walle G. F. A. , Pruijmboom A. , Van Gorkum A. A.
Published: March 2011

A review is given of the requirements on MBE-grown layers as far as processing is concerned. Aspects that are considered are: defect density, particulates, background doping and metallic contamination. The stability of the grown layers against thermal anneals is considered. It is shown that normal thermal diffusion in HBT structures is not important, other effects, like transient diffusion following ion implantation, have drastic effects on the grown profiles. As an example the processing of mesa-isolated heterojunction bipolar transistors is treated. It is shown that all-Si transistors can be grown with ideal Gummel plots. The Gummel plots of SiGe HBTs show small non-idealities. The current gain enhancement of the HBTs with respect to the all-Si transistors is shown to be as large as 200 times. Due to transient diffusion, parasitic barriers are formed, that have a detrimental effect on the AC and DC performance.
Characterization and Optical Studies of Short-Period SimGen Superlattices
Authors: Presting H. , Kibbel H. , Kasper E. , Grimmeiss H. G. , Nagesh V. G.
Published: March 2011

Short-period SimGen (m monolayer (ML) Si, n ML Ge. n+m<∼40ML∼5.5nm) strained layer superlattices (SLS) are grown on <100> silicon by low temperature molecular beam epitaxy. Various characterization tools such as X-ray diffraction, transmission electron microscopy, Rutherford backscattering, Raman spectroscopy and photocapacitance measurements are used to analyze the growth quality, stram distribution, periodicity, interface sharpness and optical properties of the SLS. Recent photoluminescence experiments give hints of a direct bandgap transition from a 10 ML Si6Ge4 SLS in the near infrared spectral region. I-U and C-U measurements on mesa diodes (Am=2 10−4 cm2) are performed at various temperatures down to T=35K. Photocapacitance measurements show a Wannier-Stark localization of the superlattice states in a p+-n doped Si4Ge4 SLS diode, for the first time observed in type II superlattices. The observed transitions are believed to be defect or impurity related and are discussed in terms of a Wannier-Stark ladder behaviour.
Single and Symmetric Double Two-Dimensional Hole Gases at Si/SiGe Heterojunctions Grown by Rapid Thermal Chemical Vapor Deposition
Authors: Venkataraman V. , Sturm J. C.
Published: March 2011

Two dimensional hole gases have been investigated in Si/SiGe modulation doped heterostructures grown by RT-CVD for the first time. Single, both normal and inverted, and double heterostructures were studied. The results suggest that any asymmetry due to dopant segregation or autodoping between the normal and inverted structures occurs on a scale of less than 1 nm.
Resonant Tunneling of Holes in Si/Si1−xGex, Quantum Well Structures
Authors: Schuberth G. , Abstreiter G. , Gornlk E. , Schäffler F. , Luy J. -F.
Published: March 2011

EXTENDED ABSTRACT: We investigated resonant tunneling of holes in Si/Si1−xGex double barrier resonant tunneling (DBRT) diodes grown by MBE [1]. The aim of this study was an unambiguous identification of the quantum states involved In the two dominating resonances (Fig. 1), which have been observed by several groups [2],[3], [4]. For this purpose we calculated the transmission probabilities as a function of the well width by means of a transfer matrix method in a one-particle model [5]. The respective effective masses of heavy-holes (hh) and light-holes (lh) in the strained SiGe layers were calculated following Refs. (6) and [7], with appropriate strain corrections added according to Ref. (8); hh/lh mixing [9] was Introduced a posteriori. The calculated resonance positions are in reasonable agreement with experiments (Fig. 2), if the resonance at lower energy is attributed to a hh channel in the well, and the second resonance to a lh channel. Since only hh states are occupied in the emitter cladding layer at the temperatures (≈1.5K) studied, hh/lh coverslon due to the loss in rotational symmetry is involved in the second resonance.
SiGe Heterojunction Bipolar Transistors
Authors: Arienzo Maurizio , Comfort James H. , Crabbé Emmanuel F. , Marame David L. , Iyer Subramanian S. , Meyerson Bernard S. , Patton Gary L. , Stork Johannes M. C. , Sun Yuan-Chen
Published: March 2011

Strained layer growth of SiGe on Si by either Molecular Beam Epitaxy (MBE) or various methods of Chemical Vapor Deposition (CVD), including Limited Reaction Processing (LRP) and Ultra High Vacuum CVD (UHV/CVD) have been used to realize narrow bandgap base double heterojunction bipolar transistors (HBTs). This review paper will focus on the fabrication of high performance transistors, and on the material and process challenges facing the implementation of SiGe HBT technology. In particular, the use of SiGe alloys for bandgap engineering of bipolar devices and the development of self-aligned, epitaxial base bipolar device structures will be discussed, including the most recent accomplishment of 75 GHz ƒr heterojunction bipolar transistors, and the record sub-25 ps EC L ring oscillator delay. The design flexibility and trade-offs offered by SiGe heterojunction technology, like junction field/capacitance control, liquid nitrogen operation and complementary processes, arc also reviewed, to assess the leverage of a SiGe base bipolar technology in high speed circuits.
Charge Control in SiGe Quantum-Well MOSFETs and MODFETs
Authors: Hofmann Karl R.
Published: March 2011

A one-dimensional charge control model based on the self-consistent numerical solution of the Schroedinger and Poisson equation has been developed for n- and p-channel quantum-well (QW) MOSFETs and MODFETs in the strained-layer SiGe heterostructure material system. Results are presented for prototype QW n-channel MODFET and MOSFET structures experimentally demonstrated in the literature. Side channel formation limits the maximum usable QW channel densities and voltage swings. The optimization of the charge control characteristics of the p-channel QW-MOSFET is achieved by maximizing the Ge content of the QW SiGe layer and minimizing the Si spacer thickness to the oxide. Channel densities on the order of 1×1013cm22 are feasible.
Silicon-Based Long Wavelength Infrared Detectors Fabricated by Molecular Beam Epitaxy
Authors: Lin T. L. , Jones E. W. , George T. , Ksendzov A. , Huberman M. L.
Published: March 2011

SiGe/Si heterojunction internal photoemission (HIP) long wavelength infrared (LWIR) detectors have been fabricated by molecular beam epitaxial (MBE) growth of p+ SiGe layers on p-type Si substrates. The SiGe/Si HIP detector offers a tailorable spectral response in the long wavelength infrared regime by varying the SiGe/Si heterojunction barrier. Degenerately doped p+ SiGe layers were grown by MBE using either HBO2 or elemental boron as the dopant source. Improved crystalline quality and lower growth temperatures were achieved for boron-doped SiGe layers as compared with the HBO2-doped layers. The dark current density of the boron-doped HIP detectors was found to be thermionic emission limited and was drastically reduced as compared with that of HBO2-doped HIP detectors. The heterojunction barrier was determined to be 0.066 eV from activation energy analysis of the HIP detectors, corresponding to a 18 μm cutoff wavelength. Photoresponse of the detectors at wavelengths ranging from 2 to 12 μm has been characterized with corresponding quantum efficiencies of 5 – 0.1%.
Optical Properties and Internal Photoemission in Epitaxial Composites of CoSi2 Particles in Silicon
Authors: Jimenez J. R. , Schowalter L. J. , Fathauer R. W.
Published: March 2011

An analysis of optical absorption and internal photoemission in epitaxial CoSi2 particles buried in silicon is carried out. The optical absorption is dominated by the well-known surface plasma resonance, and calculations of the surface plasma frequencies, using the previously measured dielectric constant of CoSi2, agree well with experiment. A model for the photoemission yield is presented which includes the effects of the surface plasmon excitation and decay. The model can reproduce the observed features of the yield in photoresponse experiments. A model for the replenishment of photoemitted carriers is also presented, in which the metal particles acquire a small steady-state charge under illumination.
Carbonization Dynamics of Silicon Surfaces By Hydrocarbon Gas Molecular Beams
Authors: Yoshinobu Tatsuo , Fuyuki Takashi , Matsunami Hiroyuki
Published: March 2011

Carbonization dynamics of Si surfaces using a hydrocarbon gas molecular beam was investigated. In case of carbonizing atomically clean Si surfaces with C2H2, single crystalline 3C-SiC layers were obtained only In the narrow range of a substrate temperature near 780 °C. Control of surface reaction by a cap of very thin surface oxide layer and gradual increase of substrate temperature during carbonization were found to be effective in forming single crystalline 3C-SiC layers reproducibly.
Dopant Enhanced Low-Temperature Epitaxial Growth by Rapid Thermal Processing Chemical Vapor Deposition
Authors: Hsieh T. Y. , Jung K. H. , Kwong D. L.
Published: March 2011

We have demonstrated, for the first time, that the epitaxial growth temperature can be lowered by dopant incorporation using rapid thermal processing chemical vapor deposition (RTPCVD). Heavily arsenic-doped epitaxial layers with very abrupt dopant transition profiles and relative uniform carrier distribution have been achieved at 800°C. The defect formation is closely related to dopant concentration; the defect density as a function of carrier concentration shows a sharp transition at about 3×1018 cm−3.
Observation of Intersubband Absorption in Boron δ-Doped Si Layers
Authors: Park J. S. , Karunasiri R. P. G. , Wang K. L. , Mii Y. J. , Murray J.
Published: March 2011

Strong hole intersubband infrared absorption in δ-doped Si multiple quantum wells is observed. The structures consist of 10 periods of boron doped Si quantum wells and undoped Si barriers. Near 100 % infrared absorption is measured by FTIR spectrometer using waveguide structures. Absorption peaks ranging between 3–7 μm are measured, and these peaks can be tuned by varying the doping concentration in the δ-doped layer. Polarization dependence has been verified to agree with the intersubband selection rule. The estimated peak energy positions using a self-consistency calculation are considerably lower than experimental values, probably due to a large exchange energy of many body effects. This observation suggests multiple quantum well IR detectors using Si- technology.
Applications of In Situ Ellipsometry in RTP Temperature Measurement and Process Control
Authors: Massoud Hisham Z. , Sampson Ronald K. , Conrad Kevin A. , Hu Yao-Zhi , Irene Eugene A.
Published: March 2011

The applications of in situ automated ellipsometry in the measurement and control of temperature in rapid-thermal processing (RTP) equipment are investigated. This technique relies on the accurate measurement of the index of refraction of a wafer using ellipsometry and the strong temperature dependence of the index of refraction to determine the wafer temperature. In principle, this technique is not limited to silicon wafer processing and could be applied to any surface whose index of refraction has a strong and well known temperature dependence. This technique is non-invasive, non-contact, fast, accurate, compatible with ultraclean processing, and lends itself to monitoring the dynamic heating and cooling cycles encountered in rapid-thermal processing.
Characterization of Preclean Induced Surface Damage by Rapid Thermal Processing
Authors: Hsieh T. Y. , Jung K. H. , Kwong D. L. , Koschmieder T. H. , Thompson J. C.
Published: March 2011

In-situ precleaning of the substrate surface plays a critical role in Si epitaxial growth. We have demonstrated that the preclean process can cause considerable surface damage, which strongly depends on process parameters such as system base pressure and temperature. Nomarski optical microscopy, SEM, and optical reflectance were used to characterize the surface morphology. Optical reflectance was more sensitive to surface damage but was also strongly dependent on substrate dopant redistribution after high temperature processing.
The Gettering and Electrical Activity of Ni, Au, and Cu in Epitaxial Si/Si(2%Ge)/Si during RTA
Authors: Zhou Tian-Qun , Buczkowski Andrzej , Radzimski Zbigniew , Rozgonyi George A.
Published: March 2011

A study of gettering and electrical activity of metallic impurities Ni, Au and Cu has been carried out on epitaxial Si/Si(2%Ge)/Si wafers containing interfacial misfit dislocations. The impurities were intentionally introduced from a backside deposited thin metal followed by rapid thermal annealing (RTA). Transmission Electron Microscopy (TEM) results indicate that the impurities were gettered along the misfit dislocations in near-surface regions either as Au precipitate colonies, or as NiSi2 and CuSi silicide precipitates. Data from Scanning Electron Microscopy (SEM) in the Electron Beam Induced Current (EBIC) mode revealed that these precipitates dominate the recombination properties of the initially inactive misfit dislocation.
The Effects of Plasma Immersion Ion Implantation on Thermal Hillock Formation
Authors: Pico Carey A. , Tao Jiang , Cheung Nathan
Published: March 2011

The effect of shallow (< 500 Å) implanted ions on the formation of thermal hillocks in thin (5000 Å) patterned Al9 9w%Si1w%, films was studied. The ions were implanted by plasma immersion ion implantation (PIII) and the gases (N2, O2, and Ar) used in the implantation ranged from completely inert to highly reactive with Al. The voltages used to accelerate the ionized molecules were 2.5 kV to 30 kV. This corresponds to implant depths of 50 Å to 400 Å. The nominal doses were adjusted to achieve a ∼20% dopant concentration over the fullwidth- at-half-maximum of the calculated implant profile. Following implant, the samples were sintered at 450°C for 30 minutes and inspected for thermal hillock formation by scanning electron microscopy. We find that PIII is effective in suppressing thermal hillock formation for implant depths greater than 60 Å.
The Kinetics of Electromigration Damage in Copper Films Studied by Isothermal Resistance Change Analysis
Authors: Park C. W. , Vook R. W.
Published: March 2011

Electromigration damage is one of the primary causes of the failure of interconnects in VLSI circuits. In this work, the response of Cu films to electromigration stress has been studied by an isothermal electrical resistance method. Accurate temperature measurement and control of Cu stripes stressed at elevated temperatures and high current densities were accomplished by use of a thin film thermistor. The activation energy and current density exponent were measured for vacuum evaporated Cu films and the values that were obtained are 0.79±0.02eV and 3.6±0.2, respectively. Scanning electron micrographs of stripes that underwent electromigration damage showed many voids in the cathode region, hillocks in the anode region, and both voids and hillocks in the rest of the stripe. The activation energies of two aluminum stripes were also measured by the same method. An average value of 0.54±0.02eV was obtained.
Void Growth as a Function of Residual Stress Level in Thin, Narrow Aluminum Lines
Authors: Korhonen M. A. , Børgesen P. , Paszkiet C. A. , Lee J. K. , Li Che-Yu
Published: March 2011

High tensile stresses develop in passivated aluminum line metallizations on silicon substrates after excursion to elevated temperatures. The principal mechanisms to relax these stresses at room temperature are plastic deformation and grain boundary void growth. It is shown that stress relaxation and void growth are intimately connected.
Silicon Carbide Whisker Reinforced Aluminum with Improved Temperature Resistance Due to the Use of a Phosphate Binder
Authors: Chiou Jeng-Maw , Chung D.D.L.
Published: March 2011

Silicon carbide whisker reinforced aluminum with improved temperature resistance, increased tensile strength and decreased coefficient of thermal expansion was obtained by using a phosphate binder instead of a commonly used silica binder for preparing the SiC whisker preform, to which liquid aluminum was infiltrated in order to form the composite. The composite is attractive for applications as a heat sink with a low coefficient of thermal expansion.
On The Electronic Contribution to Elastic Constants of Ultrathin Films of P-Type Si
Authors: Ghatak Kamaxhya P , De Badal
Published: March 2011

In this paper we have formulated the electronic contribution to the elastic constants in ultrathin films of p-Si by considering the influences of heavy, light and split-off holes respectively. We have suggested an experimental method of determining the same in degenerate materials having arbitrary dispersion laws. The elastic constants increase with increasing hole concentration in an oscillatory way and decrease with increasing film thickness. The theoretical formulation is in agreement with the suggested experimental method of determining second and third order elastic constants.
Microstructure and Mechanical Behavior of Magnetron Sputtered Al-Cu Films
Authors: Lin Tsann , Raman V.
Published: March 2011

We have investigated the microstructure, electrical resistivity and mechanical behavior of DC magnetron sputtered A1-4wt%Cu films. The substrate temperatures were varied systematically from room temperature to 500 °C. Scanning and transmission electron microscopy of the sputtered films show that the top surface of the films sputtered at low temperatures (< 200 °C) exhibits a pure Al-like fine grain morphology. In contrast, sputter deposition at higher temperatures (> 300 °C) produces films that are characterized at the top surface by a distribution of θ’-A12Cu precipitates with a platelet morphology. The mechanical behavior of the sputtered films were investigated by performing indentation tests using a depth-sensing technique.
Mechanical Behavior of Benzocyclobutene Films on Silicon Substrates
Authors: Townsend P. H. , Stokich T. M. , Huber B. S.
Published: March 2011

The evolution of the stress in coatings derived from divinylsiloxane bisbenzocyclobutene, mixed stereo and positional isomers of 1,3-bis(2-bicyclo[4.2.0]octa-1,3,5-trien-3-ylethenyl)-1,1,3,3-tetramethyl disiloxane (CAS 117732-87-3), has been measured on silicon substrates with an optically levered beam during thermal cycles. The stress at room temperature in gelled coatings varies between ca. 15 MPa and 45 MPa depending on the cure schedule. The progression of the polymer's glass transition temperature is correlated with the evolution of the structural state observed with FTIR. A method is presented for predictably controlling substrate curvature during multilayer processing.
Microhardness of Thin SIO2 Films On Silicon.
Authors: Yost B. , Li Che-Yu , Bergman-Reuter Bette , Sullivan Tim
Published: March 2011

Hardness properties of CVD SiO2, films deposited on silicon substrates are investigated by microindentation techniques. It is found that the hardness of these films is sensitive to the thermal histories and doping and is less influenced by the residual stress levels.
Preparation of TI-Ba-Ca-Cu Superconducting Oxide Films by Spray Pyrolysis Technique
Authors: Koo H.S. , Kuo T.L. , Kuo D.H. , Lin R.J. , Lee W.H. , Wu P.T.
Published: March 2011

Superconducting TI-Ba-Ca-Cu-O(TBCCO) films with zero resistance temperatures above 100K have been prepared on (001)MgO single-crystal substrates by the combination techniques of spray pyrolysis and Tl-diffusion. The as-sprayed Ba-Ca-Cu-O films and the sintered TBCCO superconducting bulks were wrapped in Au foil and heated in oxygen at temperatures ranging from 890 to 920°C and cooled to room temperature by furnace cooling. Highly c-axis oriented superconducting films were obtained and their average thicknesses were about 5-10 μm. The characteristics of TBCCO films by X-ray diffraction, scanning electron microscopy and electrical property are discussed.
Stress and Resistivity in Reactively Sputtered Amorphous Metallic Ta-Si-N Films
Authors: Kwok C.-K. , Kolawa E. , Nicolet M-A. , Lee Ray C.
Published: March 2011

We have measured the stress and the electrical resistivity of Ta-Si-N films deposited in an rf magnetron system by reactive sputtering of Ta5 Si3 target in an Ar-N2 mixture. The stress was determined by measuring the curvature of thin Si substrates with a stylus instrument. The atomic composition was established from backscattering spectra. The resistivity was derived from four-point probe measurements. The stress, the resistivity, and the atomic composition were studied as a function of various processing parameters (total pressure, gas composition). The stress is always compressive and can be changed from 0.38 - 1.48 GPa by such means. The resistivity is principally a function of the nitrogen composition and rises as the nitrogen amount increases. The results are compared with those reported for other amorphous metallic alloys.
Strains and Relaxations Near metal Alumlnide/Semiconductor Interfaces
Authors: Gerberich W.W. , Angelo J.E. , Keller R.R. , Wowchak A.M. , Cohen P.I.
Published: March 2011

Mechanisms and phenomena of strain relaxation at bi-material interfaces have been studied for over half a century. The details, however, and limiting kinetics, thermodynamics and mechanics are still being sorted out - particularly for large misfit systems. Three techniques are required to accurately portray strain distributions during and after epitaxial growth: RHEED, TEM and SACP. Reflection high energy electron diffraction (RHEED) is used to measure the lattice parameter during growth. Both transmission electron microscopy (TEM) and selected area electron channeling pattern (SACP) analysis are necessary to identify the defects and the strain distribution. These techniques have been applied to NiAl and FeAl grown by MBE on GaAs with a thin AlAs buffer layer. It is shown that both island and layer by layer growth can occur with the corresponding defects being remarkably similar in character. From a combined Moiré, HREM and computer simulation, the dislocation character is assessed. Both <100> dislocations from half-loops or island edges may occur providing only partial relaxation of the film-substrate systems. The impact of the remaining elastic strain distribution on kinetic measurements of dislocation velocities is discussed.