Showing papers in "Journal of Vacuum Science & Technology B in 2013"

Synthesis, properties, and applications of silicon nanocrystals

Abstract: Silicon nanocrystals have been widely investigated for several years because of their many interesting properties and their potential use in several applications This field has grown enormously after the observation of quantum confinement in porous silicon and remains an area of great interest for different reasons Most importantly, silicon is already widely used in the semiconductor industry, is nontoxic at least in its bulk form, is the second most earth-abundant element in the crust, and is relatively cheap to process A large number of groups have investigated silicon in the form of nanocrystals, and the authors intend to provide a comprehensive review of their contribution to the field The author has decided to address first the synthesis and properties of silicon nanocrystals Several different techniques, such as nucleation in substoichiometric thin films or gas-phase nucleation and growth in silane-containing nonthermal plasmas, have been proposed for the controlled synthesis of silicon nanoparticles The author outlines the strengths and weaknesses of each approach and identify the research groups that have advanced each particular synthesis technique The understanding of the properties of silicon nanocrystals has evolved as new synthetic approaches were developed, and for that reason the material properties are discussed together with its production approach The use of silicon nanocrystals for the development of novel electronic devices, light emitting devices, photovoltaic cells, and for biorelated applications will be discussed Waste heat recovery and energy storage applications are also discussed

New method for determining flat-band voltage in high mobility semiconductors

Abstract: The method that is commonly used for determining the flat-band voltage (VFB) and the flat-band capacitance (CFB) of metal oxide semiconductor (MOS) capacitors depends on many parameters and can only be used in the case of low interface trap density (Dit) when the capacitance–voltage measurements are carried out at high frequencies. This paper demonstrates a new and simple method for determining VFB and CFB. The method is based on the point of inflection in the capacitance–voltage curve. This method does not require the knowledge of material or experimental parameters and can be used on high Dit and high border trap density MOS structures at all frequencies.

Large-area fabrication of high aspect ratio tantalum photonic crystals for high-temperature selective emitters

Abstract: The authors present highly selective emitters based on two-dimensional tantalum (Ta) photonic crystals, fabricated on 2 in. polycrystalline Ta substrates, for high-temperature applications, e.g., thermophotovoltaic energy conversion. In this study, a fabrication route facilitating large-area photonic crystal fabrication with high fabrication uniformity and accuracy, based on interference lithography and reactive ion etching is discussed. A deep reactive ion etch process for Ta was developed using an SF6/C4F8 based Bosch process, which enabled us to achieve ∼8.5 μm deep cavities with an aspect ratio of ∼8, with very steep and smooth sidewalls. The thermal emitters fabricated by this method show excellent spectral selectivity, enhancement of the emissivity below cut-off approaching unity, and a sharp cut-off between the high emissivity region and the low emissivity region, while maintaining the low intrinsic emissivity of bare Ta above the cut-off wavelength. The experimental results show excellent agreemen...

Low-temperature plasmas in carbon nanostructure synthesis

Abstract: Plasma-based techniques offer many unique possibilities for the synthesis of various nanostructures both on the surface and in the plasma bulk. In contrast to the conventional chemical vapor deposition and some other techniques, plasma-based processes ensure high level of controllability, good quality of the produced nanomaterials, and reduced environmental risk. In this work, the authors briefly review the unique features of the plasma-enhanced chemical vapor deposition approaches, namely, the techniques based on inductively coupled, microwave, and arc discharges. Specifically, the authors consider the plasmas with the ion/electron density ranging from 1010 to 1014 cm−3, electron energy in the discharge up to ∼10 eV, and the operating pressure ranging from 1 to 104 Pa (up to 105 Pa for the atmospheric-pressure arc discharges). The operating frequencies of the discharges considered range from 460 kHz for the inductively coupled plasmas, and up to 2.45 GHz for the microwave plasmas. The features of the direct-current arc discharges are also examined. The authors also discuss the principles of operation of these systems, as well as the effects of the key plasma parameters on the conditions of nucleation and growth of the carbon nanostructures, mainly carbon nanotubes and graphene. Advantages and disadvantages of these plasma systems are considered. Future trends in the development of these plasma-based systems are also discussed.

Cross point arrays of 8 nm × 8 nm memristive devices fabricated with nanoimprint lithography

Abstract: Building arrays of memristive devices with sub-10 nm lateral dimensions is critical for high packing density, low power consumption, and better uniformity in device performance. Here, the authors demonstrate arrays of 8 × 8 nm2 cross point memristive devices using wet chemical etching and nanoimprint lithography. The devices exhibited nonvolatile bipolar switching with extreme low programming current of 600 pA. The devices also exhibited fast switching speed and improved uniformity and promising endurance and data retention. This work opens the opportunities for memristive devices in the next generation ultrahigh-density data storage and low-power high-speed unconventional computing.

Ultraclean freestanding graphene by platinum-metal catalysis

Abstract: While freestanding clean graphene is essential for various applications, existing technologies for removing the polymer layer after transfer of graphene to the desired substrate still leave significant contaminations behind. The authors discovered a method for preparing ultraclean freestanding graphene utilizing the catalytic properties of platinum metals. Complete catalytic removal of polymer residues requires annealing in air at a temperature between 175 and 350 °C. Low-energy electron holography investigations prove that this method results in ultraclean freestanding graphene.

Development of AlGaN-based graded-index-separate-confinement- heterostructure deep UV emitters by molecular beam epitaxy

Abstract: The authors report on the growth, structure, and emission properties of AlGaN double heterostructures having a graded-index-separate-confinement-heterostructure design. These devices were grown on the Si-face of 6H-SiC substrates by plasma-assisted molecular-beam epitaxy. The active region of the device consists of 75-nm thick Al0.72Ga0.28N film, confined by two 50-nm thick compositionally graded AlxGa1−xN films (x = 1–0.8 and x = 0.8–1) and two AlN cladding layers. X-ray diffraction and transmission electron microscopy provide evidence that the compositionally graded AlGaN layer may also be serving as a strain transition buffer, by blocking threading defects in the vicinity of the AlN/AlGaN heterointerface. Polarization dependent photoluminescence studies indicate that the emission from these structures at 257 nm is transverse magnetic polarized. Simulation studies indicate that the vertical confinement of the optical mode in these structures is 32.5% and simulations of the band structure indicate the formation of a p-n junction resulting from polarization-induced doping. Electron-beam pumping of these structures provides evidence of the onset of stimulated emission at room temperature.

Improved approach to Fowler–Nordheim plot analysis

Abstract: This article introduces an improved approach to Fowler–Nordheim (FN) plot analysis, based on a new type of intercept correction factor. This factor is more cleanly defined than the factor previously used. General enabling theory is given that applies to any type of FN plot of data that can be fitted using a FN-type equation. Practical use is limited to emission situations where slope correction factors can be reliably predicted. By making a series of well-defined assumptions and approximations, it is shown how the general formulas reduce to provide an improved theory of orthodox FN-plot data analysis. This applies to situations where the circuit current is fully controlled by the emitter characteristics, and tunneling can be treated as taking place through a Schottky–Nordheim (SN) barrier. For orthodox emission, good working formulas make numerical evaluation of the slope correction factor and the new intercept correction factor quick and straightforward. A numerical illustration, using simulated emission data, shows how to use this improved approach to derive values for parameters in the full FN-type equation for the SN barrier. Good self-consistency is demonstrated. The general enabling formulas also pave the way for research aimed at developing analogous data-analysis procedures for nonorthodox emission situations.

Structural, morphological, and band alignment properties of GaAs/Ge/GaAs heterostructures on (100), (110), and (111)A GaAs substrates

Abstract: Structural, morphological, and band offset properties of GaAs/Ge/GaAs heterostructures grown in situ on (100), (110), and (111)A GaAs substrates using two separate molecular beam epitaxy chambers, connected via vacuum transfer chamber, were investigated. Reflection high energy electron diffraction (RHEED) studies in all cases exhibited a streaky reconstructed surface pattern for Ge. Sharp RHEED patterns from the surface of GaAs on epitaxial Ge/(111)A GaAs and Ge/(110)GaAs demonstrated a superior interface quality than on Ge/(100)GaAs. Atomic force microscopy reveals smooth and uniform morphology with surface roughness of Ge about 0.2–0.3 nm. High-resolution triple axis x-ray rocking curves demonstrate a high-quality Ge epitaxial layer as well as GaAs/Ge/GaAs heterostructures by observing Pendellosung oscillations. Valence band offset, ΔEv, have been derived from x-ray photoelectron spectroscopy (XPS) data on GaAs/Ge/GaAs interfaces for three crystallographic orientations. The ΔEv values for epitaxial GaAs...

Preparation of a clean Ge(001) surface using oxygen plasma cleaning

Abstract: The authors demonstrate a method to obtain a clean and smooth Ge (001) surface using oxygen plasma cleaning without sputtering or Ge regrowth. The preparation of the germanium surface consists of four cycles of ex situ wet etching using hydrochloric acid as the etchant and H2O2 as the oxidant. Subsequently, the sample is outgassed and exposed to an oxygen plasma for 30 min followed by thermal desorption of the newly formed oxide layer. Reflection high-energy electron diffraction shows a clear 2 × 1 reconstruction of the germanium surface. In situ x-ray photoelectron spectroscopy measurements confirm that the cleaned surface is free of carbon contamination and that no GeO2 remains. Angle-resolved photoemission spectra of the cleaned Ge show the peak associated with the Ge surface state indicating a very clean surface. Atomic force microscope images further indicate a smooth germanium surface with a mean surface roughness of approximately 3 A after plasma cleaning.

Dependence on proton energy of degradation of AlGaN/GaN high electron mobility transistors

Abstract: The effects of proton irradiation energy on dc, small signal, and large signal rf characteristics of AlGaN/GaN high electron mobility transistors (HEMTs) were investigated. AlGaN/GaN HEMTs were irradiated with protons at fixed fluence of 5 × 1015/cm2 and energies of 5, 10, and 15 MeV. Both dc and rf characteristics revealed more degradation at lower irradiation energy, with reductions of maximum transconductance of 11%, 22%, and 38%, and decreases in drain saturation current of 10%, 24%, and 46% for HEMTs exposed to 15, 10, and 5 MeV protons, respectively. The increase in device degradation with decreasing proton energy is due to the increase in linear energy transfer and corresponding increase in nonionizing energy loss with decreasing proton energy in the active region of the HEMTs. After irradiation, both subthreshold drain leakage current and reverse gate current decreased more than 1 order of magnitude for all samples. The carrier removal rate was in the range 121–336 cm−1 over the range of proton energies employed in this study.

Residue-free plasma etching of polyimide coatings for small pitch vias with improved step coverage

Abstract: The authors have found that patterning polyimide coatings containing organosilane adhesion promoter using pure oxygen plasma resulted in a thin silicon-rich residue layer. They show in this paper that adding small amounts of fluorine-containing gas to the etching gas mixture is necessary in order to achieve residue-free polyimide plasma etching. They report residue-free plasma etching of polyimide coatings with both isotropic and anisotropic profiles, using either metal or oxide hard masks. These etching methods are however not sufficient for the fabrication of high density metal filled vias in 10 μm thick polyimide coatings. In order to improve the metal step coverage over the vias while keeping the pitch as small as possible, the authors have developed a two-step etching recipe combining both isotropic and anisotropic profiles, resulting in wine-glass shaped vias.

Ozone priming of patterned carbon nanotube forests for subsequent atomic layer deposition-like deposition of SiO2 for the preparation of microfabricated thin layer chromatography plates

Abstract: The authors report the ozonation of patterned, vertically aligned carbon nanotube (CNT) forests as a method of priming them for subsequent pseudo atomic layer deposition (ψ-ALD) (alternating layer deposition) of silica to produce microfabricated, CNT-templated thin layer chromatography (TLC) plates. Gas phase ozonation simplifies our deposition scheme by replacing two steps in our previous fabrication process: chemical vapor deposition of carbon and ALD of Al2O3, with this much more straightforward priming step. As shown by x-ray photoelectron spectroscopy (XPS), ozonation appears to prime/increase the number of nucleation sites on the CNTs by oxidizing them, thereby facilitating conformal growth of silica by ψ-ALD, where some form of priming appears to be necessary for this growth. (As shown previously, ψ-ALD of SiO2 onto unprimed CNTs is ineffective and leads to poor quality depositions.) In conjunction with a discussion of the challenges of good peak fitting of complex C 1s XPS narrow scans, the authors present an analysis of their C 1s data that suggests an increase in oxidized carbon, particularly the C=O group, with increasing oxygen content of the CNT forests. After coating with SiO2, the CNTs are removed by elevated temperature air oxidation, the SiO2 is rehydrated, and the plates are coated with 3-aminopropyltriethoxysilane (APTES). The resulting APTES-coated plates separate various fluorescent dyes giving results that are generally at least as good as those the authors reported previously with their more complicated fabrication/priming scheme. TLC plates with different geometries are microfabricated, where plates with narrower channels show longer run times (lower mobile phase velocities) and plates with narrower features appear to give higher efficiencies.

Impact of low-k structure and porosity on etch processes

Abstract: The fabrication of interconnects in integrated circuits requires the use of porous low dielectric constant materials that are unfortunately very sensitive to plasma processes. In this paper, the authors investigate the etch mechanism in fluorocarbon-based plasmas of oxycarbosilane (OCS) copolymer films with varying porosity and dielectric constants. They show that the etch behavior does not depend on the material structure that is disrupted by the ion bombardment during the etch process. The smaller pore size and increased carbon content of the OCS copolymer films minimize plasma-induced damage and prevent the etch stop phenomenon. These superior mechanical properties make OCS copolymer films promising candidates for replacing current low-k dielectric materials in future generation devices.

Double-layered passivation film structure of Al2O3/SiNx for high mobility oxide thin film transistors

Abstract: The optimization of the passivation process for oxide thin film transistors with high carrier mobility was investigated. Hydrogen incorporation into oxide channels during the deposition of SiNx could degrade device stability and uniformity, especially for high-mobility devices. A novel double-layered passivation film structure composed of Al2O3/SiNx was proposed, in which thin and dense Al2O3 film prepared by atomic layer deposition was introduced underneath the SiNx layer. In-Ga-Zn-O TFT passivated with the proposed double-layered films showed no significant negative shift in turn-on voltage, even after passivation. The field-effect mobility and subthreshold swing were typically measured as 27.7 cm2 V−1 s−1 and 0.11 V/dec, respectively. Hydrogen doping was effectively protected by the introduction of Al2O3 as thin as 15 nm.

Impact of proton irradiation on dc performance of AlGaN/GaN high electron mobility transistors

Abstract: The effects of high energy proton irradiation dose on dc performance as well as critical voltage of the drain-voltage step-stress of AlGaN/GaN high electron mobility transistors (HEMTs) were investigated to evaluate the feasibility of AlGaN/GaN HEMTs for space applications, which need to stand a variety of irradiations. The HEMTs were irradiated with protons at a fixed energy of 5 MeV and doses ranging from 109 to 2 × 1014 cm−2. For the dc characteristics, there was only minimal degradation of saturation drain current (IDSS), transconductance (gm), electron mobility, and sheet carrier concentration at doses below 2 × 1013 cm−2, while the reduction of these parameters were 15%, 9%, 41% and 16.6%, respectively, at a dose of 2 × 1014 cm−2. At this same dose condition, increases of 37% in drain breakdown voltage (VBR) and of 45% in critical voltage (Vcri) were observed. The improvements of drain breakdown voltage and critical voltage were attributed to the modification of the depletion region due to the intro...

MBE grown GaAsBi/GaAs double quantum well separate confinement heterostructures

Abstract: GaAsBi/GaAs double quantum wells and double quantum well separate confinement heterostructures are grown at low temperatures using molecular beam epitaxy. Methods of achieving identical quantum wells in double quantum well structures without growth interruption are proposed and implemented. Cross-sectional transmission electron microscopy and room temperature photoluminescence measurements indicate that the samples have excellent structural and optical properties. The high optical quality of the samples is attributed to the surfactant effect of Bi throughout the low temperature growth of GaAs and AlGaAs layers. The proposed approach can be extended to grow laser diode structures with multiple quantum well separate confinement heterostructures containing more identical quantum wells.

Fabrication of large dimension aluminum air-bridges for superconducting quantum circuits

Abstract: Proper grounding between different ground planes in coplanar superconducting qubit circuits is important to avoid spurious resonances which increase decoherence. Here, the authors present a possible solution to suppress such undesired modes using superconducting aluminum air-bridges which have been fabricated on top of aluminum coplanar waveguide transmission lines. 3D electromagnetic simulations were done to guide the design of the air-bridges such that the input reflection (S11) of the bridges was kept at a minimum level. A fabrication method based on optical lithography techniques was developed and it resulted in air-bridges with a height of approximately 10 μm and lengths of up to 500 μm. The method can be generalized to arbitrary length air-bridge with heights even exceeding 15 μm.

Metal–semiconductor–metal photodetector on as-deposited TiO2 thin films on sapphire substrate

Abstract: TiO2 thin films are prepared on c-plane sapphire substrates by the RF magnetron sputtering method. The performance of the Pt contact metal–semiconductor–metal (MSM) photodetector fabricated on as-deposited films is studied. The dark current density and the responsivity obtained were 1.57 × 10−9 A/cm2 at 5 V bias and 1.73 A/W at 50 V bias, respectively. Breakdown is not observed up to 50 V bias. Rise and fall times for the photocurrent were 7 and 3 s, respectively. Our results show that high quality MSM photodetectors can be fabricated without high temperature and complicated fabrication steps.

Active-matrix nanocrystalline Si electron emitter array with a function of electronic aberration correction for massively parallel electron beam direct-write lithography: Electron emission and pattern transfer characteristics

Abstract: A planar nanocrystalline silicon (nc-Si) electron emitter array compatible with an active-matrix large-scale integrated (LSI) driving circuit has been developed for massively parallel electron beam direct-write lithography. The electron-emitting part of the device consists of a 50-μm-pitch and 200 × 200 arrays of nc-Si dots fabricated on a Si substrate, and via-first-processed through-silicon-via (TSV) plugs of poly-Si connected with the dots from behind the substrate. Tapered emitter-array etching and electrochemical-oxidation with subsequent annealing and super-critical rinsing and drying processes significantly enhanced the electron emission current by improving and stabilizing uniformity and reducing the process temperature. When the emitter array was driven, electrons were effectively injected into the nc-Si layer through the TSV plugs and quasiballistically emitted through the gold surface electrode. The nc-Si emitter responded to the input signal within times of 0.1 μs or less. A 1:1 pattern transf...

Effect of electron irradiation on AlGaN/GaN and InAlN/GaN heterojunctions

Abstract: AlGaN/AlN/GaN/sapphire, AlGaN/GaN/sapphire, AlGaN/GaN/Si, and InAlN/GaN/sapphire heterojunctions (HJs) were irradiated with 10 MeV electrons to fluences of 2 × 1015 to 3.3 × 1016 cm−2. The main effects on the electrical properties were a decrease in two-dimensional electron gas (2DEG) mobility and the shift of capacitance–voltage (C-V) characteristics to more positive values. The 50% 2DEG mobility decrease occurred at a similar fluence of 3.3 × 1016 cm−2 for all AlGaN/GaN and AlGaN/AlN/GaN HJs, but at a much lower fluence of 1.3 × 1016 cm−2 for InAlN/GaN, which is in line with previous observations for neutron irradiated HJs. The shift of C-V characteristics is due to increased concentration of deep acceptor traps in the barrier/interface region. In AlGaN/GaN/Si transistors, the increase of concentration of deep barrier/interface traps with activation energy of 0.3, 0.55, and 0.8 eV was observed. This increase correlates with the observed degradation of gate lag characteristics of transistors after irradiation with 1.3 × 1016 cm−2 electrons.

Fabrication of arbitrarily shaped silicon and silicon oxide nanostructures using tip-based nanofabrication

Abstract: The authors report fabrication of arbitrary shapes of silicon and silicon oxide nanostructures using tip-based nanofabrication (TBN). A heated atomic force microscope (AFM) tip deposits molten polymer on a substrate to form polymer nanostructures that serve as etch mask to fabricate silicon or silicon oxide nanostructures. The authors demonstrate how TBN can be combined with conventional wet etching as well as metal-assisted chemical etching, in order to fabricate these nanostructures. The size of the TBN-fabricated silicon nanostructures is around 200 nm. Silicon nanostructures fabricated using metal-assisted chemical etch can have very smooth sidewalls with, roughness as small as 2 nm. The authors show fabrication of arbitrary shapes of silicon and silicon oxide nanostructures including those with curved and circular shapes. Our results show that TBN using a heated AFM tip can function as an additive nanolithography technique with minimum contamination, and is compatible with existing nanofabrication methods.

Coexistence of weak ferromagnetism and polar lattice distortion in epitaxial NiTiO3 thin films of the LiNbO3-type structure

Abstract: The authors report the magnetic and structural characteristics of epitaxial NiTiO3 films grown by pulsed laser deposition that are isostructural with acentric LiNbO3 (space group R3c). Optical second harmonic generation and magnetometry demonstrate lattice polarization at room temperature and weak ferromagnetism below 250 K, respectively. These results appear to be consistent with earlier predictions from first-principles calculations of the coexistence of ferroelectricity and weak ferromagnetism in a series of transition metal titanates crystallizing in the LiNbO3 structure. This acentric form of NiTiO3 is believed to be one of the rare examples of ferroelectrics exhibiting weak ferromagnetism generated by a Dzyaloshinskii–Moriya interaction.

Performance comparison of front- and back-illuminated AlGaN-based metal–semiconductor–metal solar-blind ultraviolet photodetectors

Abstract: In this work, AlGaN-based metal–semiconductor–metal solar-blind ultraviolet photodetectors (PDs) with low dark current were fabricated on sapphire substrates. In both front- and back-illumination operation modes, the PDs exhibited sharp photoresponse cutoffs at ∼280 nm with solar-blind/ultraviolet rejection ratios of more than 103. The quantum efficiency of the back-illuminated PD was observed to generally be higher than that of the front-illuminated PD. Nevertheless, at very low bias range, the front-illuminated PD exhibited greater photoresponsivity. The observed performance differences of the PDs in the different illumination modes are discussed in terms of surface reflectivity and photocarrier collection efficiency.

Deep centers and persistent photocapacitance in AlGaN/GaN high electron mobility transistor structures grown on Si substrates

Abstract: Deep trap spectra in AlGaN/GaN high electron mobility transistor structures grown on Si by metalorganic chemical vapor deposition show four major electron traps (Ec—0.15, 0.29, 0.40 and 0.76 eV) in the AlGaN barrier/interface region and three (Ec—0.18, 0.27 and 0.45 eV) in the undoped GaN buffer region. The presence of a high density of deep acceptor traps was observed in the AlGaN barrier region, as determined by hysteresis in low temperature capacitance-voltage (C-V) characteristics. The spectral dependence of persistent photocapacitance shifts showed two optical thresholds of 1.5 V and 3.1 eV, with the second being specific to structures grown on Si substrates. Comparison of results obtained on transistors and on large-area Schottky diodes prepared on heterostructures from which transistors are fabricated show that measurements on test large-area diodes are representative of the main characteristics important for transistor performance.

Bipolar resistive switching in an amorphous zinc tin oxide memristive device

Abstract: The integration of amorphous zinc tin oxide (ZTO) into crossbar memristor device structures has been investigated where asymmetric devices were fabricated with Al (top) and Pt (bottom) electrodes. The authors found that these devices had reproducible bipolar resistive switching with high switching ratios >104 and long retention times of >104 s. Electrical characterization of the devices suggests that both filamentary and interfacial mechanisms are important for device switching. The authors have used secondary ion mass spectrometry to characterize the devices and found that significant interfacial reactions occur at the Al/ZTO interface.

Flexible substrate and release layer for flexible MEMS devices

Abstract: In this letter, the authors report a process for flexible substrate fabrication on silicon carrier wafers and the subsequent release of the flexible substrate from the carrier wafer. Polyimides with relatively high glass transition temperatures (>400 °C) are employed for the flexible substrate. The fabrication steps utilize the low adhesion strength, high glass transition temperature (360 °C) HD Microsystems PI2611 as the release layer. The PI2611 release layer is protected from exposure to common solvents and "remover" used during lift-off or wafer cleaning processes by creating a seal with the HD Microsystems PI5878G substrate around the perimeter of the wafer. This flexible MEMS fabrication technique allows conventional fabrication equipment to be used.

Atomic-scale silicon etching control using pulsed Cl2 plasma

Abstract: Plasma etching has been a key driver of miniaturization technologies toward smaller and more powerful devices in the semiconductor industry. Thin layers involved in complex stacks of materials are approaching the atomic level. Furthermore, new categories of devices have complex architectures, leading to new challenges in terms of plasma etching. New plasma processes that are capable to etch ultra-thin layers of materials with control at the atomic level are now required. In this paper, the authors demonstrate that Si etching in Cl2 plasma using plasma pulsing is a promising way to decrease the plasma-induced damage of materials. A controlled etch rate of 0.2 nm min−1 is reported by pulsing the chlorine plasma at very low duty cycles. Using quasi-in-situ angle resolved XPS analyses, they show that the surface of crystalline silicon is less chlorinated, the amorphization of the top crystalline silicon surface is decreased, and the chamber wall are less sputtered in pulsed plasmas compared to continuous wave plasmas. This is attributed to the lower density of radicals, lower ion flux, and lower V-UV flux when the plasma is pulsed.

Epitaxial NiInGaAs formed by solid state reaction on In0.53Ga0.47As: Structural and chemical study

Abstract: Thin epitaxial layers of NiInGaAs formed by solid state reaction of Ni on (100) In0.53Ga0.47As are used as metal source and drain regions for In0.53Ga0.47As metal oxide field effect transistors. Here, the authors present a structural and chemical analysis of this phase. The stoichiometry of the layer was determined as Ni2In0.53Ga0.47As. Transmission electron microscopy revealed an abrupt interface and a detailed x-ray diffraction analysis showed that the layer is of a hexagonal lattice, which grows epitaxially with the orientation relations of {100}InGaAs||{100}NiInGaAs; ⟨011¯⟩InGaAs||[001]NiInGaAs. Only one domain can be observed in this epitaxial growth. Understanding the structure of these layers is a crucial step not only in their incorporation into InGaAs based devices but also a step toward novel devices.

Influence of barrier form on Fowler–Nordheim plot analysis

Abstract: Recent research has described an improved method of Fowler–Nordheim (FN) plot analysis, based on the definition and evaluation of a slope correction factor and a new form of intercept correction factor. In this improved approach, there exists a basic approximation that neglects certain terms in the general theory, and focuses on the influence of the form of the tunneling barrier on the values of basic slope (σB) and intercept (ρB) correction factors. Simple formulae exist that allow these to be evaluated numerically for a barrier of arbitrary well-behaved form. This paper makes an initial exploration of the effects of barrier form on FN plot analysis. For a planar emitter, two models for the correlation-and-exchange (C&E) potential energy (PE) are used. For the Schottky–Nordheim barrier, it is shown that numerical and analytical approaches generate equivalent results. This agreement supports the validity of the numerical methods used. Comparisons with results for the Cutler–Gibbons barrier show that small...