Monocrystalline Film Research Articles

Neutron detection at jet using artificial diamond detectors

Artificial diamond neutron detectors recently proved to be promising devices to measure the neutron production on large experimental fusion machines. Diamond detectors are very promising detectors to be used in fusion environment due to their radiation hardness, low sensitivity to gamma rays, fast response and high energy resolution. High quality “electronic grade” diamond films are produced through microwave chemical vapour deposition (CVD) technique. Two CVD diamond detectors have been installed and operated at joint European torus (JET), Culham Science Centre, UK. One of these detectors was a polycrystalline CVD diamond film; about 12 mm 2 area and 30 μm thickness while the second was a monocrystalline film of about 5 mm 2 area and 20 μm thick. Both diamonds were covered with 2 μm of lithium fluoride (LiF) 95% enriched in 6Li. The LiF layer works as a neutron-to-charged particle converter so these detectors can measure thermalized neutrons. Their output signals were compared to JET total neutron yield monitors (KN1 diagnostic) realized with a set of uranium fission chambers. Despite their small active volumes the diamond detectors were able to measure total neutron yields with good reliability and stability during the recent JET experimental campaign of 2006.

Investigation of the formation of nanostructures on silicon thin films by excimer laser irradiation

We present a theoretical study and experimental results on the formation of conical nano-tips on silicon thin films as a result of single-pulse excimer laser irradiation. The fabricated structures have heights of about 1 µm and apical radii of curvature of several tens of nanometers. An individual cone is formed when a mono-crystalline silicon film on an insulator substrate is irradiated in air environment with a single 25ns pulse from a KrF excimer laser, homogenized and shaped to a circular spot with diameter of several micrometers. Atomic force microscopy was used to study these structures. A simplified analytical model for the formation of these structures is proposed. We also present computer simulations of heat transfer in Si films that results from irradiation with a single laser pulse, shaped to a circular spot.

Growth of thin Fe(0 0 1) films for terahertz emission experiments

The electrical and magnetic properties of thin iron (Fe) films have sparked significant scientific interest. Our interest, however, is in the fundamental interactions between light and matter. We have discovered a novel application for thin Fe films. These films are sources of terahertz (THz) radiation when stimulated by an incident laser pulse. After intense femtosecond pulse excitation by a Ti:sapphire laser, these films emit picosecond, broadband THz frequencies. The terahertz emission provides a direct measure of the induced ultrafast change in magnetization within the Fe film. The THz generation experiments and the growth of appropriate thin Fe films for these experiments are discussed. Several criteria are used to select the substrate and film growth conditions, including that the substrate must permit the epitaxial growth of a continuous, monocrystalline or single crystal film, yet must also be transparent to the emitted THz radiation. An Fe(0 0 1) film grown on the (0 0 1) surface of a magnesium oxide (MgO) substrate makes an ideal sample. The Fe films are grown by physical vapor deposition (PVD) in an ultrahigh vacuum (UHV) system. Low energy electron diffraction (LEED) and Auger electron spectroscopy (AES) are used to characterize the Fe(0 0 1) films. Two substrate surface preparation methods are investigated. Fe(0 0 1) films grown on MgO(0 0 1) substrates that are used as-received and films grown on MgO(0 0 1) substrates that have been UV/ozone-cleaned ex vacuo and annealed in vacuo produce the same results in the THz generation experiments. Either substrate preparation method permits the growth of samples suitable for the THz emission experiments.

Comparison of Photovoltaic Module Performance Measurements

Computer simulation tools used to predict the energy production of photovoltaic systems are needed in order to make informed economic decisions. These tools require input parameters that characterize module performance under various operational and environmental conditions. Depending upon the complexity of the simulation model, the required input parameters can vary from the limited information found on labels affixed to photovoltaic modules to an extensive set of parameters. The required input parameters are normally obtained indoors using a solar simulator or flash tester, or measured outdoors under natural sunlight. This paper compares measured performance parameters for three photovoltaic modules tested outdoors at the National Institute of Standards and Technology (NIST) and Sandia National Laboratories (SNL). Two of the three modules were custom fabricated using monocrystalline and silicon film cells. The third, a commercially available module, utilized triple-junction amorphous silicon cells. The resulting data allow a comparison to be made between performance parameters measured at two laboratories with differing geographical locations and apparatus. This paper describes the apparatus used to collect the experimental data, test procedures utilized, and resulting performance parameters for each of the three modules. Using a computer simulation model, the impact that differences in measured parameters have on predicted energy production is quantified. Data presented for each module includes power output at standard rating conditions and the influence of incident angle, air mass, and module temperature on each module’s electrical performance. Measurements from the two laboratories are in excellent agreement. The power at standard rating conditions is within 1% for all three modules. Although the magnitude of the individual temperature coefficients varied as much as 17% between the two laboratories, the impact on predicted performance at various temperature levels was minimal, less than 2%. The influence of air mass on the performance of the three modules measured at the laboratories was in excellent agreement. The largest difference in measured results between the two laboratories was noted in the response of the modules to incident angles that exceed 75deg.

Grazing incidence neutron diffraction from ferromagnetic films in multi-domain state

Bragg diffraction at grazing incidence of neutrons from a magnetic film decomposed into a set of ferromagnetic domains is considered within the frame of the distorted wave Born approximation. It is shown that the diffracted intensity measured as a function of angles of incidence and exit in the direction normal to the surface can provide information on the lateral distribution of domain magnetization. Theoretical results are illustrated by measurements of a mono-crystalline film of iron.

Growth of silicon thin film by LPE on porous silicon bilayers

The fabrication of solar cells based on the transfer of a thin silicon film on a foreign substrate is an attractive way to realise cheap and efficient photovoltaic devices. The aim of this work is to realise a thin mono-crystalline silicon film on a double porous silicon layer in order to detach and transfer it on mullite. The first step is the fabrication of a double porous silicon layer by electrochemical anodisation using two different current densities. The low current leads to a low porosity layer and during annealing, the recrystallisation of this layer allows epitaxial growth. The second current leads to a high porosity which permits the transfer on to a low cost substrate. Liquid Phase Epitaxy (LPE) performed with indium (or In+Ga) in the temperature range of 950–1050°C leads to almost homogeneous layers. Growth rate is about 0.35 μm min−1. Crystallinity of the grown epilayer is similar on porous silicon and on single crystal silicon. In this paper, we focus on the realisation of porous silicon sacrificial layer and subsequent LPE growth.

Monocrystalline YBa2Cu3O7−x thin films on vicinal SrTiO3 (001) substrates

The correlation between the vicinal properties of SrTiO3 (001) substrates and the twinning in YBa2Cu3O7−x thin films grown by pulsed-laser deposition is studied using x-ray diffraction with reciprocal space mapping. The vicinal properties, i.e., angle and in-plane orientation, play a significant role in the anisotropic strain starting at the interface between substrate surface and film, and affect the twin behavior of YBa2Cu3O7−x. On substrates having an [110] in-plane orientation of the step edges, a completely preferred twin pair is observed if the vicinal angle is increased to 0.60°. Whereas on substrates having their step edges oriented along one of the crystallographic axis, the films exhibit a detwinning as the vicinal angle increases. For α=1.10° a maximum detwinned, i.e., monocrystalline film is obtained. At this angle, the diffusion length of YBa2Cu3O7−x during the growth matches the terrace length of SrTiO3. Up to this specific angle, the films are grown perpendicular to the optical instead of the crystallographic surface.

Short-Term Characterization of Building Integrated Photovoltaic Panels*

Building integrated photovoltaics, the integration of photovoltaic cells into one or more exterior building surfaces, represents a small but growing part of today’s $2 billion dollar photovoltaic industry. A barrier to the widespread use of building integrated photovoltaics (BIPV) is the lack of validated predictive simulation tools needed to make informed economic decisions. The National Institute of Standards and Technology (NIST) has undertaken a multi-year project to compare the measured performance of BIPV panels to the predictions of photovoltaic simulation tools. The existing simulation models require input parameters that characterize the electrical performance of BIPV panels subjected to various meteorological conditions. This paper describes the experimental apparatus and test procedures used to capture the required parameters. Results are presented for custom fabricated mono-crystalline, polycrystalline, and silicon film BIPV panels and a commercially available triple junction amorphous silicon panel.

Why Can Smart Cut® Change the Future of Microelectronics?

Deposition techniques like chemical vapor deposition (CVD) offer to the semiconductor industry the initial flexibility to deposit thin films of key materials on many kinds of substrates. The homoepitaxy or hetroepitaxy techniques using CVD or molecular beam epitaxy (MBE) add the flexibility to get a pure monocrystalline thin film but with a major limitation: the starting substrate has to be monocrystalline. The missing technology has always been the one which allows the growth of a thin monocrystalline film on any kind of substrate. Hydrogen induced splitting (known today as Smart Cut®), discovered at the LETI laboratory in 1991, provides a unique opportunity to get crystalline layers on any kind of substrate. Therefore, a new tool is offered to the semiconductor industry, for new material developments and new structures. This technique is in use in production today on a first application: silicon-on-insulator (SOI) wafers which consist of a monocrystalline film of silicon on a thin amorphous silicon dioxide layer, on top of a silicon wafer. We will discuss the SOI application of the Smart Cut® technology and present other recently demonstrated breakthroughs in new material development, including SiC, compound semiconductor or 3D structures.

WHY CAN SMART CUT® CHANGE THE FUTURE OF MICROELECTRONICS?

Deposition techniques like chemical vapor deposition (CVD) offer to the semiconductor industry the initial flexibility to deposit thin films of key materials on many kinds of substrates. The homoepitaxy or hetroepitaxy techniques using CVD or molecular beam epitaxy (MBE) add the flexibility to get a pure monocrystalline thin film but with a major limitation: the starting substrate has to be monocrystalline. The missing technology has always been the one which allows the growth of a thin monocrystalline film on any kind of substrate. Hydrogen induced splitting (known today as Smart Cut®), discovered at the LETI laboratory in 1991, provides a unique opportunity to get crystalline layers on any kind of substrate. Therefore, a new tool is offered to the semiconductor industry, for new material developments and new structures. This technique is in use in production today on a first application: silicon-on-insulator (SOI) wafers which consist of a monocrystalline film of silicon on a thin amorphous silicon dioxide layer, on top of a silicon wafer. We will discuss the SOI application of the Smart Cut® technology and present other recently demonstrated breakthroughs in new material development, including SiC, compound semiconductor or 3D structures.

Biaxially aligned (013) films on vicinal (011)

Epitaxial (013) films have been grown by pulsed laser deposition onto exact and vicinal (011) substrates. X-ray diffraction measurements showed that the films contained two mirror-related orientations when grown on exact (011) surfaces, but that a strong preference for only one of the two (013) orientations developed when the substrate surface was tilted by about toward the direction. The inclination removed the two-fold symmetry of the surface to induce this preference, resulting in a film with (013) film (011) substrate and [100] film [100] substrate. Films with a single (013) orientation may offer some distinct practical advantages over other monocrystalline film orientations.

Preparation of Thin Films of some Rem Oxides and study of Their Structure, Optical, and electrical properties

ABSTRACTBy ion bombardment of yttrium and europium hot-pressed oxide targets, their amorphous polycrystalline and monocrystalline films have been obtained on the monocrystalline substrates of (111) molybdenum and (1012). (0001) sapphire. The growth direction of the monocrystalline films with respect to the material and orientation of the substrates corresponds to (011). (211) planes for Y2O3 and (011) Eu2O3.It is determined that the structural imperfection of the grown films does not influence either the square root dependence of the absorption coefficient on decreasing photon energy, the value of their specific electric resistance, or the character of its temperature dependence. The values of the forbidden zone width as well as the energy of the investigated oxide conductivity activation are calculated on the basis of experimental results.It is shown that the light absorption in the Y2O3, Eu2O3 films is mediated by the direct allowed transitions of electrons from the valence band to the conduction band whose extrema are at the same point in k-space. The conductivity of the metal-dielectric-metal structure based on a monocrystalline film of yttrium oxide is mediated by the Frenkel-Poole mechanism.

Selected-area liquid-phase epitaxy of iron garnet films applying local ion implantation of the substrate

Selected-area liquid-phase epitaxy of garnet films has been achieved through local substrate damage caused by ion implantation before film deposition. Thus, patterning with a geometrical resolution of a few microns of some micron-thick epitaxial garnet films is possible. Film patterns are defined by ‘‘perfect’’ epitaxial film regions grown on unimplanted substrate areas and defective film regions where the substrate has been implanted before film deposition. The films produced consist either of imperfect monocrystalline film areas, film areas resulting from island growth, or of substrate areas without overgrowth. Application of the method to the growth of epitaxial (Gd,Bi)3(Fe, Ga,Al)5 O12 films permits local magnetic switching of the magnetization direction confined to ‘‘perfect’’ film regions without switching of the adjacent imperfect film area.

Study of the peculiarities of film growth from molecular beams by the method of simulation

The factors are studied that cause a decrease in the temperature of epitaxial film growth during the deposition from an ionized molecular beam. A simulation technique allows for a local increase of the substrate temperature on the site of atom attachment, its decrease by heat removal, and influence on the frequency of diffused junctions of adatoms along the substrate. Silicon condensation illustrates the local heating of the substrate by about 500 K with a cooling time of ≈ 10−4 s, which provides the formation of a monocrystalline film. The influence is investigated of supersaturation on the growth rate of a film and its perfection and a possible decrease of the activation energy of the surface diffusion of adatoms and their incorporation into the crystal is estimated. [Russian Text Ignored].

Stabilization of the low-temperature phase near the layered crystal surface

The temperature dependence of the integrated band intensities in the ε''(ω) and (-1/ε(ω)) spectra of a TlGaSe2 single crystal was investigated. The above spectra were calculated from IR-reflection ones. A two-stage increase of integrated intensities τω of bands, appearing at the phase transition (PT) in the ferroelectric phase, was observed. The beginning of the first stage corresponds to the temperature Tc1, which is 10-20 K higher than Tc determined in other works. The beginning of the second stage corresponds to the temperature near Tc. Since IR-reflection spectra are formed in the surface layer of thickness λ/n(λ) (λ is the wavelength, n(λ) is the refractive index), the observed dependence τω (T) might be explained by successive passing of two PT's; the first one takes place at T=Tc1 in a surface layer of thickness d < λ/n (λ). The second one occurs in bulk at T=Tc. In a thin monocrystalline film (d ≃ 1 μ) a monotonous increase of Iω (T) was observed, i.e.there, as it was expected, only one PT at T=Tc1 takes place. The fact that the surface has an influence on the temperature of the surface layer PT was confirmed by investigations of reflection spectra from the surfaces oriented differently with respect to the axis [image omitted].

Amorphization of Pd-Si at 300K

Abstract Silicon was implanted at 300 K in a Pd monocrystalline film up to a dose of 1.7 × 1017 at.cm−2. In situ channeling analyses were performed after various implantations with 380 keV 4He++ ions delivered by the implanter itself. Amorphization occurred (and the corresponding kinetics was studied) inside the Si implantation profile. The near-surface layer was only slightly disordered by the Si nuclear stopping-induced displacements. The Si atoms clearly stabilize the amorphous state.

Analysis of silicon crystal growth using low pressure chemical vapour deposition

The growth kinetics of silicon films deposited under low pressure condidtions (Si-SiH 4 system) have been investigated by using an experimental reactor. Depending on the growth conditions, polycrystalline are monocrystalline films were obtained with different deposition kinetics. With the help of an ultra high vaccum chamber — equipped with surface analysis facilities — which was directly connected to the reactor chamber, a detailed assessment of the growth interface has been made. As shown by in situ ellipsometry, heating the substrate at a temperature higher than 900°C under an hydrogen flow induced a thermal etching of silicon which could be counterbalanced by a low silicon partial pressure. The stable state of growth polycrystalline or monocrystalline film was also assessed by ellipsometry and additional information concerning the crystallinity or the crystal surface coverage of adsorbed molecules (mainly hydrogen) was obtained by using RHEED and AES techniques.

Investigation of interfacial reactions in monocrystalline and polycrystalline thin film couples of gold and silver by Auger depth profiling, transmission electron microscopy and measurement of contact resistance

Interfacial reactions in monocrystalline and polycrystalline thin film couples of gold and silver were investigated by Auger depth profiling (ADP), transmission electron microscopy (TEM) and measurement of the contact resistance at temperatures ranging from 25 to 418°C in order to determine the effect of grain boundaries on concomitant kinetic processes. Results from both ADP and measurement of the contact resistance indicate that interfacial reactions are controlled by bulk interdiffusion, characterized by a mean activation energy of 1.45±0.10 eV, in monocrystalline couples and by grain boundary diffusion, characterized by an activation energy of 0.50±0.02 eV, in polycrystalline couples. Results from TEM reveal the formation of an interfacial network of dislocations in monocrystalline couples and the expansion of this network during subsequent interdiffusion. It is concluded that characterization of both chemical composition and microstructure, combined with measurement of concomitant electrical properties, provides a reliable description of degradation processes in thin film couples.

Thickness dependence of photoconductivity in tellurium

Photoconductive infrared response has been investigated in bulk monocrystalline and thin film polycrystalline undoped tellurium samples at 77K at wavelengths between about 1 and 4.5μm. Thickness dependence of the response has been specifically investigated and found to be consistent with the calculated results.

Electrical forming action in Te-Se-Cd structures

Improved techniques have been developed for the fabrication of rectifying Te-Se-Cd sandwich structures, where the selenium is present as a thin monocrystalline film. The electrical forming action, which has been used for many years to improve the performance of selenium rectifiers, has been investigated in these simple structures. Analysis of capacitance-voltage characteristics indicates that the electrical forming process is a progressive reduction in the concentration of acceptors in the selenium within a region of about half a micrometer from the junction. Scanning-electron microscopy has failed to reveal CdSe at the Cd-Se interface after electrical forming, although this compound is found after thermal forming. The studies indicate that, contrary to previously held views, CdSe is not necessary for the rectification and that the device involves essentially a Schottky junction rather than a heterojunction of n-CdSe and p-Se.