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The improved control of lattice strain in the quantum-dot (QD) region of p – i – n structures using a modified epitaxial growth procedure has been observed and analyzed. Strain in the QD region was managed by (a) inserting a correction layer (CL) with a lattice constant that was intermediate between the lattice constant of the QD region and the lattice constant of the underlying substrate, (b) capping the QD islands with a layer that had the same lattice constant as the CL, and (c) the utilization of only three atomic elements in the growth of the QD intrinsic region. These results were demonstrated in In x Ga 1− x As/InAs/In x Ga 1− x As p–i–n devices with five InAs QD layers and then compared with In x Ga 1− x As p–n (HOM) devices with identical ternary alloy compositions and no quantum dot layers. The layers in all of the devices were grown by molecular beam epitaxy. X-ray diffraction (XRD) measurements showed the interface dislocations in the QD samples were fewer than in the HOM samples and were isolated at the In x Ga 1− x As–GaAs interface, away from the optically active QD region. Cross-sectional, high-resolution transmission electron microscopy (HRTEM) images showed no evidence of threading dislocations in the QD region. Post-growth calculations of the average lattice constant of the QD region, using atomic force microscopy, XRD, and HRTEM data, indicated the QD region experienced a ∼3× reduction in its lattice misfit while increasing its critical thickness by more than 3×. Although the total misfit in the QD samples increased with the insertion of the CL and the average lattice constant of the QD region was not matched to the CL, the strain energy nevertheless was absorbed successfully without creating deleterious dislocations as seen in QD devices exhibiting lower dark current densities than in HOM control devices.

Atomically controlled epitaxy of semiconductor-on-semiconductor is important for the construction of nanometer-scale devices such as quantum dots, qubits for quantum computing, nanoelectromechanical systems (NEMS) oscillators, and nanobiomedical devices. For instance, patterned atomic layer epitaxy (ALE) using a scanning tunneling microscopy tip to depassivate an area of a H-terminated Si(001) surface, creating a pattern for subsequent Si growth, should lead to a new generation of atomically precise structures. Vapor phase epitaxy is well-suited to achieve controlled deposition, as the precursors are not reactive with the H-terminated background, unlike Si atoms from solid-source evaporation. Disilane (Si2H6) is arguably the best precursor for Si ALE on Si or Ge surfaces at moderate temperatures; yet, its adsorption configuration and subsequent decomposition pathways are not well understood. Combining experimental data from in situ infrared absorption spectroscopy (IRAS), scanning tunneling microscopy (ST...

The inversion layer electron mobility in n-channel In"0"."5"3Ga"0"."4"7As MOSFET's with HfO"2 gate dielectric with several substrate impurity concentrations (~1x10^1^6cm^-^3 to ~1x10^1^8cm^-^3) and various surface preparations (HF surface clean, (NH"4)"2S surface clean and PECVD a-Si interlayer with a HfO"2 gate dielectric) have been studied. The peak electron mobility is observed to be strongly dependent on the surface preparation, but the high field mobility is observed to be almost independent of the surface preparation. A detailed analysis of the effective mobility as a function of electric field, substrate doping, and temperature was used to determine the various mobility components (surface roughness, phonon, and coulombic scattering limited mobility components). For the substrates with high doping concentration, the electron mobility at low vertical electric field is dominated by Coulomb scattering from the substrate dopants, whereas, for lower substrate doping the Coulombic scattering is dominated by the disorder induced gap states. Low temperature measurements were used to determine the surface roughness scattering and phonon components. The results show that room temperature mobility of In"0"."5"3Ga"0"."4"7As surface channel MOSFETs with HfO"2 gate dielectric at high electric field is limited primarily by remote phonons whereas the Al"2O"3 gate dielectric is limited by surface roughness scattering.

CdSeTe epilayers were grown by molecular beam epitaxy on (1 0 0)-oriented vicinal silicon wafers. By controlling the growth conditions, either multiple-phase or single-phase epilayers could be deposited. In this paper we present a detailed investigation of the structure of a single-phase CdSeTe epilayer using X-ray diffraction, Rutherford back scattering, and transmission electron microscopy. Photoreflectance and photocurrent results are also presented.

An in-situ high-vacuum process has been developed for the preparation of ultrathin Al2O3 films on monolayer Se passivated Si(100) surface. The in-situ high-vacuum process prevents the Si surface from adsorbed moisture or native oxide, leading to an Al2O3/Si(100) interface without any low-k interfacial layer at 400oC. The Se monolayer terminates the dangling bonds on Si(100) before the formation of the high-k dielectric. The electrical properties of the Al2O3 film on Se passivated Si(100) are significantly improved in comparison to control samples without Se passivation. The interface trap density is about 5 times lower to 2×1011 eV-1/cm2. The C-V hysteresis is reduced to 80 mV from 160 mV. The leakage current for the same physical dielectric thickness is reduced by more than an order of magnitude.

High-resistance phases of Ni-rich Ni silicide are formed on Si(100) below 400/spl deg/C, while high-resistance phases of Si-rich Ni silicide are formed above 600/spl deg/C. The desired low-resistance NiSi is formed between 400/spl deg/C and 600/spl deg/C. In this paper, the authors report the suppression of high-resistance phases of Ni silicide by passivating the Si(100) surface with a monolayer of Se. A 500-/spl Aring/ Ni on n-type low 10/sup 15/ cm/sup -3/ doped Si(100) wafers, passivated with Se, shows a sheet resistance of /spl sim/2.55 /spl Omega//square upon annealing between 200/spl deg/C and 500/spl deg/C, while the sheet resistance of the 500-/spl Aring/ Ni on identical wafers without Se-passivation jumps to /spl sim/7.92 /spl Omega//square between 300/spl deg/C and 350/spl deg/C. Between 600/spl deg/C and 700/spl deg/C, the sheet resistance of the Se-passivated samples is /spl sim/ 10% lower than that of the control samples. Transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy all confirm that the suppression of high-resistance Ni silicides below 500/spl deg/C is attributed to the suppression of silicidation and above 600/spl deg/C to the delay in Si-rich Ni silicide formation at the Ni/Se-passivated Si(100) interface.

We reported selenium passivation of silicon (001) surface and showed the ohmic nature of the interface between magnesium and selenium-passivated n-type silicon (001). In this paper, we present a detailed study on the thermal stability of this interface. Magnesium contacts on selenium-passivated silicon (001) are annealed from 200°C to 500°C at an interval of 50°C and then characterized by current–voltage measurements. Schottky barrier heights of the contacts are measured by capacitance–voltage and activation-energy methods. Schottky behaviour sets in only when the interface is subjected to annealing above 375°C. On the contrary, magnesium contacts on bare silicon (001) turn from ohmic to Schottky at much lower temperatures. The temperature difference is 50–150°C. We deduce that selenium passivation suppresses silicidation between magnesium and silicon, because it reduces the surface reactivity of silicon by eliminating dangling bonds and relaxing strained bonds.

It is experimentally shown that, by terminating dangling bonds on Si(001) with a monatomic layer of selenium, the chemical reactivity of the surface is suppressed. In the case of nickel silicidation, transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy reveal that Se passivation suppresses Ni silicidation by over 100 °C as compared to the bare Si(001) surface. The formation of Ni subsilicide (Ni 2 Si) is not observed on Se-passivated Si(001). This interfacial silicidation appears to be linked with changes in electrical behavior of the interface between titanium and Se-passivated Si(001), which we reported previously.

Usually, numerical self-consistent calculations predict a much larger intrinsic bistability region than actually is measured in resonant tunneling diodes (RTDs). In addition, numerical calculations have shown that scattering in the well reduces bistability. We used a unified treatment of current flowing from continuum states and emitter quasi-bound states to show numerically and analytically that not only the scattering in the quantum well but also the scattering in the emitter reduces bistability. Moreover, within the Hartree approximation, bistability occurs by tunneling resonantly between emitter quasi-bound state and well quasi-bound state as a pitchfork bifurcation.

The thermal stability of the interface between Ti and Se-passivated n-type Si(001) is investigated. As-deposited Ti contacts show ohmic characteristics. After annealing at temperatures from 200 °C to 480 °C in air, the Se-passivated samples are much more resistant to Schottky transition as compared to the bare samples. The bare samples turn to Schottky below 300 °C, whereas the passivated samples are ohmic all the way to 400 °C. A difference of over 100 °C is observed between the two types of samples. Schottky barrier heights are determined using capacitance–voltage and activation–energy methods. The bare samples reach a maximum barrier height of 0.39 eV as determined by activation–energy measurements, while the passivated samples maximize at 0.19 eV. We deduce that a monolayer of Se suppresses silicidation between Ti and Si by eliminating dangling bonds on Si(001).

A metal–semiconductor contact should have a negative Schottky barrier if the metal has a work function less than the electron affinity of the semiconductor. Such a contact would behave ohmically with a low internal resistance. In reality, the electronic states on the semiconductor surface pin the surface Fermi level and make almost all the metals to show a positive Schottky barrier. By eliminating surface states on Si(0 0 1) with a monolayer of selenium, ohmic contacts with a negative Schottky barrier are demonstrated between titanium and n-type Si(0 0 1). These contacts are found to be thermally stable up to 400 °C.

A biomimetic strategy is used to bridge the gap from the molecular scale to the microscale. Dendritic, conformationally rigid ruthenium(II)polypyridyl complexes have been synthesized to form a set of nanometer-sized building blocks (NBBs) (1.6– 5.0 nm ) with discrete ‘tertiary’ structures. We postulate that thin films constructed from NBBs with differing tertiary structures will form ordered arrays with differing ‘quaternary’ structures and, presumably, differing electronic properties. Experimental studies show that thin films of these molecules are conductive, display electric field-modulated conductivity, and enhanced conductivity upon visible irradiation. Significantly, changes in the molecule's overall shape (tertiary structure) have a measurable effect on the electrical properties of the films prepared from them. Importantly, these NBBs are chemically robust and structurally tunable. We intend to exploit these properties as well as their newly discovered electronic, optical, and, potentially even, chiro-optical properties so as to provide a new, added dimension in molecular electronics and chiral optical devices.

Incoherent scattering degrades the peak-to-valley ratio in resonant tunneling diodes (RTDs). In addition, scattering reduces intrinsic bistability, which is a hysteresis in current–voltage ( I – V ) characteristics. Previous numerical calculations considered only incoherent scattering in the well. In this work, by a unified treatment of current flowing from emitter continuum states and emitter quasi-bound states, we study also the effect of emitter scattering on intrinsic bistability. An analytical model that retains the salient features of intrinsic bistability is given. It is shown numerically that: (a) broadening induced by incoherent scattering in the emitter reduces intrinsic bistability; and (b) emitter scattering is on same footing with well scattering. This result may explain the discrepancy between numerical simulators and experimental facts regarding the presence of intrinsic bistability in such devices like RTDs.

We studied the time evolution of a two-level electron system interacting with a single-mode bosonic field (i.e. photons, phonons). We found that in the adiabatic limit (i.e. electron motion fast and boson motion slow) it is possible to obtain a reduction in fluctuation for the position coordinate of boson and momentum coordinate as well, depending on the adiabatic potential. If the system is on a lower adiabatic sheet we obtain a reduction in momentum fluctuations. However, if the system is on an upper sheet the fluctuation in position coordinate (associated with the bosonic field) is reduced. The maximum reduction is for a range of parameters given by g 2 / v ≈1, where g is the electron–photon (phonon) coupling strength and 2 v is the electron energy level splitting. Moreover, it is possible to generate squeezed light at a frequency different from the pump frequency. The output frequency is mainly given by the curvature of the adiabatic potential. The system is interesting because it can be implemented in nanoscale systems like a single or double quantum well system interacting with a laser field of radiation. The degree of squeezing can be improved either by time modulating the energy of the electron levels inside the quantum well or by modulating the laser field.

The effect of monolayer roughness on the peak-to-valley ratio of Si / SiO 2 resonant tunnel diodes is numerically modeled. Atomic scale roughness is shown to be acceptable. As the roughness, that is the island size increases above the atomic scale, the peak-to-valley ratio quickly degrades to less than 5 for 1 nm roughness and less than 2 for 2 nm roughness.

Epitaxial films of the wide-bandgap II–VI beryllium chalcogenide semiconductors, BeTe, BeSe, and BeSeTe were grown on arsenic-terminated silicon substrates by MBE. Silicon was also epitaxially regrown on Be-chalcogenide films. Initial structural characterization revealed the desired smooth two-dimensional nature of the layer growth. The composition of BeSeTe ternary films was governed by the Be/Se flux ratio during deposition rather than by the Se/Te flux ratio. The variation in Be/Se flux ratio or in the sticking coefficients due to temperature gradients led to radial compositional inhomogeneity. Current versus temperature measurements of the Be-chalcogenide films at elevated temperatures analyzed assuming thermionic emission over the heterojunction barrier, showed conduction band offsets of 1.2 eV for the BeSe 0.41 Te 0.59 /As/Si and 1.3 eV for the BeSe/As/Si heterostructures. At room temperature, current density through BeSe/Si and BeSe 0.41 Te 0.59 /Si films was mid-10 − 9 A cm − 2 at 0.1 MV cm − 1 , similar to previously reported values for ZnS/Si, while BeTe/Si films had orders of magnitude higher current density, possibly due to interfacial recombination.

We report a detailed study of molecular beam epitaxial growth of ZnS films on bare and arsenic-passivated vicinal Si(100) surfaces. This study elucidates the initiation of microtwinning and stacking-fault defects on double-stepped substrate surfaces. The study also sheds light on the function of arsenic passivation in reducing crystal defects in ZnS epitaxial layers. Three substrate surfaces, Si(100) 2×1, Si(100):As 2×1, and Si(100):As 1×2, were used for the ZnS epitaxial growth studies. Adsorption experiments were performed to demonstrate the chemical passivation effect of an arsenic overlayer. Reflection high-energy electron diffraction was used to study growth modes and the epitaxial relationship of the ZnS layers to the substrates. Transmission electron microscopy was used to study the crystal-defect structures. Secondary ion mass spectroscopy was used to determine the chemical profiles of the heteroepitaxial interfaces of ZnS layers grown on arsenic-passivated surfaces. One of the main results demons...

The lattice misfit at the island-cap interface in two In0.15Ga0.85As p-i-n devices, with 5 layers of InAs quantum dots (QDs), was modified by depositing 2.1 and 3.2 ML of InAs while maintaining near identical capping layers. The device with 35 ± 3 nm island size distribution exhibited photoluminescence activity in the near infra-red range from 975 to 1150 nm while the device with 42 ± 12 nm size islands recorded lower PL intensity over a narrower range of 1000-1100 nm suggesting (a) increased island-cap interface misfit, (b) truncation of the islands, and (c) generation of structural defects.

Epitaxially formed indium arsenide quantum dot (QD) structures formed by the Stranski-Krastanov growth mode have been investigated with respect to how quantum confinement and lattice strain behavior affects the optoelectronic performance in p-i-n type InGaAs devices. The introduction of a correction layer and the proper selection of the QD capping layer’s alloy and thickness parameters allowed the control and management of the lattice misfit in two QD structures, which led to reduced defects and improved dark current behavior under forward bias conditions when compared to an InGaAs p-n homojunction (HOM) device without quantum-dots. Although the dark-current of the HOM devices behaved as expected under forward and reverse biases, the QD device structures displayed an apparent anomalous behavior in their dark-current densities under forward and reverse biases. Closer analysis reveals that this behavior is not anomalous; instead the information gained can be used to extract greater understanding about how to optimize the optoelectronic performance in quantum confined structures. In addition, the analysis suggests that lattice strain behavior continues to be a critical benchmark for defining and optimizing the performance of epitaxially formed= QD devices.

It has been reported that no metal shows a Schottky barrier of less than 0.4 eV on n-type silicon (001). This is attributed to interface states between metal and silicon (001), which pin the interface Fermi level and make the Schottky barrier more or less independent of the metal work function. We demonstrate that, by terminating dangling bonds and relaxing strained bonds on the silicon (001) surface with a monolayer of selenium, low Schottky barriers can be obtained on n-type silicon (001). Aluminum and chromium show barrier heights of 0.08 and 0.26 eV on n-type silicon (001), respectively. These results agree well with the ideal Schottky barrier heights for aluminum and chromium on n-type silicon (001), but are significantly different from the experimental barrier heights known for four decades for these metals on n-type silicon (001).

Dangling bonds and surface states are inherent to semiconductor surfaces. By passivating dangling bonds on the silicon (001) surface with a monolayer of selenium, surface states are removed from the band gap. Magnesium contacts on selenium-passivated silicon (001) behave ohmically, as expected from the work function of magnesium and the electron affinity of silicon. After rapid thermal annealing and hot-plate annealing, magnesium contacts on selenium-passivated silicon (001) show better thermal stability than on hydrogen-passivated silicon (001), which is attributed to the suppression of silicide formation by selenium passivation.

A newly devised misfit management method was used to deftly balance the lattice strain in an InAs quantum dot (QD) based In 0.15 Ga 0.85 As p-i-n device. The photovoltaic behavior under AM0 conditions exhibited higher V oc and lower J sc in the QD-based device as compared to a control p-n device without quantum dots. To our knowledge, both of these observations are new and seemingly conflict with some of the current understanding of quantum-dot-based PV device physics. The PV behavior under infrared illumination confirms that the quantum-confined carriers of the InAs islands in the intrinsic region contribute to the photocurrent.

Graphene is a possible candidate for post CMOS applications and mobility is a material characteristic that has been utilized to gauge the quality of the material[1]. Mobility of exfoliated graphene transferred on SiO 2 has been reported to range from 2,000 to 25,000 cm2/V·s [1, 2]. The large variation is typically attributed to factors such as scattering by defects in the underlying substrate, residue from processing, charged impurity scattering and phonon scattering [3]. In most previous studies one of the primary assumptions made is that the mobility is independent of channel dimensions. In this study, we performed room temperature effective mobility measurements as a function of channel dimensions. The mobility exhibits clear channel length (L ch ) and width (W ch ) dependence and varies from less than 1,000 cm2/V·s to 7,000 cm2/V·s. Theoretical analysis of the conductivity (σ) in graphene devices as a function of W ch performed by Vasko et al [4]. is in agreement with our experimental results. Mobility values for back gated devices with well defined channel dimensions in literature [5] are seen to be consistent with the trend that we report here.

A stack of 10 InAs quantum dot layers has been incorporated into an In x Ga 1-x As(p doped)/InAs/In x Ga 1-x As(n doped) heterojunction semiconductor device using molecular beam epitaxy. Atomic force microscopy revealed quantum dots of sizes 20 to 50 nm and heights of 2 to 5 nm. The density was 2x1010 quantum dots per cm2 per layer. This device, when compared to In x Ga 1-x As (p doped)/In x Ga 1-x As(n doped) homojunction device with no InAs quantum dot layers, showed a 20 fold increase in the photocurrent density under 50 W lamp illumination however the open circuit voltage dropped. Exponential increase in the photocurrent might have been an effect of multiple exciton generation (carrier multiplication) due to discrete electronic wave functions in the nanometer sized InAs quantum dots.

The II–VI semiconductor cadmium selenide telluride CdSeTe was grown by MBE on silicon. The large lattice mismatch to the silicon was accommodated in smaller steps using a beryllium telluride - zinc telluride buffer layer. A CdTe film grown on this buffer had about three times narrower x-ray diffraction peak than a CdSe 0.40 Te 0.60 alloy. Photojunction devices were formed into mesa structures with n+Si / p+BeTe p-type bottom contacts and n-type CdSe top emitter layers, with thin (≪1 μm) CdSeTe base layers. The photocurrent of junctions with CdTe base layers was about an order of magnitude greater than those with the CdSe 0.40 Te 0.60 alloy, most likely due to short minority carrier lifetime in the ternary.

The chemical and electronic passivation of semiconductors is an important issue for the fabrication of electronic devices. In this work we use angle resolved x-ray photoelectron spectroscopy to study the chemical passivation of silicon (001) surface with selenium at a surface coverage close to 1 monolayer. The interaction of Se with silicon breaks the Si–Si dimers leading to a change in the surface reconstruction from a (2×1) to (1×1) symmetry. The silicon surface covered with a selenium monolayer was exposed to dry oxygen at 300°C for 80min. We find that the presence of the Se monolayer does not appreciably reduce the formation of a SiO2 layer.

We have calculated electronic and optical properties of Si/BeSe$_{0.41}$Te$_{0.59}$ heterostructures by a semiempirical $sp^{3}s^{*}$ tight-binding method. Tight-binding parameters and band bowing of BeSe$_{0.41}$Te$_{0.59}$ are considered through a recent model for highly mismatched semiconductor alloys. The band bowing and the measurements of conduction band offset lead to a type II heterostucture for Si/BeSe$_{0.41}$Te$_{0.59}$ with conduction band minimum in the Si layer and valence band maximum in the BeSe$_{0.41}$Te$_{0.59}$ layer. The electronic structure and optical properties of various (Si$_{2})_{n }$/(BeSe$_{0.41}$Te$_{0.59})_{m}$ [001] superlattices have been considered. Two bands of interface states were found within the bandgap of bulk Si. Our calculations indicate that the optical edges are below the fundamental bandgap of bulk Si and the transitions are optically allowed., 16 pager, 7 figures

We report a new model for highly mismatched semiconductor (HMS) alloys. Based on the Anderson impurity Hamiltonian, the model generalizes the recent band anticrossing (BAC) model, which successfully explains the band bowing in highly mismatched semiconductors. Our model is formulated in empirical tight-binding (ETB) theory and uses the so-called $s{p}^{3}{s}^{*}$ parameterization. It does not need extra parameters other than bulk ones. The model has been applied to $\mathrm{Be}{\mathrm{Se}}_{x}{\mathrm{Te}}_{1\ensuremath{-}x}$ alloy. BeTe and BeSe are wide-band gap and highly mismatched semiconductors. Calculations show large band bowing, larger on the Se rich side than on the Te rich side. Linear interpolation is used for an arbitrary concentration $x$. The results are applied to calculation of electronic and optical properties of $\mathrm{Be}{\mathrm{Se}}_{0.41}{\mathrm{Te}}_{0.59}$ lattice matched to Si in a superlattice configuration.

BeTe and BeSe are wide‐band gap and highly mismatched semiconductors (HMS). The band bowing of BeSexTe1−x originates in the mismatch of size and orbital energies between Te and Se and is under‐predicted by virtual crystal approximation. The recent band anti‐crossing (BAC) model explains the band bowing in highly mismatched semiconductors. We extend the BAC model to empirical tight‐binding (ETB) theory. We use the sp3s* model and calculate the band bowing of the on‐site (self‐) energies for an arbitrary concentration x. The results are applied to calculation of electronic and optical properties of BeSe0.41Te0.59 lattice matched to Si in a superlattice configuration.

The Schottky barrier height at a metal/Si interface is ideally determined by the difference between metal work function and Si electron affinity for n-type Si. In reality, interface states between metal and Si pin the interface Fermi level, making the barrier height more or less independent of the ideal barrier height. We demonstrate that, by terminating dangling bonds on n-type Si(100) with a monolayer of Se, interface states are significantly reduced between metal and Si. As a result, low Schottky barriers are obtained for metals with low ideal barrier heights, such as Al and Cr. A negative Schottky barrier is demonstrated between Si and Ti, a metal commonly-used in the semiconductor industry. The negative Schottky barrier is thermally stable up to 400/spl deg/C. For metals with high ideal barrier heights, inconsistency is observed between ideal barrier height and measured barrier height even with Se passivation.

Valence mending of a semiconductor surface, such as the Se-passivated Si(001) surface, improves the chemical and thermal stability of the surface as compared to the bare Si(001) surface. In this paper, we report the suppression of Ni silicide formation between Ni and Si(001) through monolayer passivation of Si(001) by Se. Ni was deposited on both Se-passivated and bare Si(001) surfaces. The samples were annealed at temperatures from 400°C to 700°C. Cross-sectional TEM (Transmission Electron Microscopy) revealed that Ni on bare samples reacted with Si at 400°C and formed silicide, whereas Ni on Se-passivated samples did not react with Si at 500°C. Surface composition analysis by XPS (X-Ray Photoelectron Spectroscopy) showed pure Ni surface on Se-passivated samples annealed at 400°C and 500°C, but silicide surface on bare samples annealed at the same temperatures. Hence, Se passivation suppresses the formation of Ni silicide on the Si(001) surface by over 100°C as compared to the bare Si(001) surface. These results may have important implications in source/drain engineering in sub-100 nm Si CMOS (Complementary Metal Oxide Semiconductor) devices.

Schottky source/drain (S/D) in Si-CMOS provide an alternative to current approaches in S/D, channel, and gate-stack engineering. The Schottky S/D PMOS has been demonstrated at a number of university and industrial laboratories. The bottleneck for the Schottky S/D NMOS is the fact that none of the common metals or metal silicides has a low enough barrier height (~0.2 eV) on n-type Si. A method to produce low Schottky barriers on n-type Si with common metals including aluminum (Al) and chromium (Cr) is reported in this paper. The interface between metal and Si(100) is engineered at the atomic scale with a monolayer of selenium (Se) to reduce the density of interface states, and the engineered interface shows inertness to chemical and electronic processes at the interface. One consequence of this electronic inertness is that the Schottky barrier is now more dependent on the metal work function. Al and Cr both have work functions very close to the Si electron affinity. It is found that the Schottky barrier of Al on Se-engineered n-type Si(100) is 0.08 eV, and that of Cr is 0.26 eV. These numbers agree well with the ideal Schottky barrier heights for Al and Cr on n-type Si(100), but are significantly different from the barrier heights known for four decades for these metals on n-type Si(100). These results bring new hope for the Schottky S/D NMOS with a metal commonly used in the Si industry.

Experiments were performed to determine the effect of radiation on quantum devices. The devices included resonant tunneling devices and two-dimensional electron gas devices. None of the devices were radiation-hardened prior to testing. The radiation used in the tests included gamma rays, protons, neutrons, and heavy ions. Resonant tunneling devices were found to possess significant radiation tolerance. None of these devices showed any systematic effects as a result of irradiation up to 1 Mrad of gamma rays, 3.5x10(exp 11) protons/cm2 at 55 MeV, 5x10(exp 10) neutrons/cm2 with energies from 1.5 to 800 MeV, and to 1x10(exp 7) Kr ions/cm2 with an LET = 35 MeV-cm2/mg. Two-dimensional electron gas devices, including quantum transistors and MODFET structures, were irradiated by gammas to 50 krad, protons to 5x10(exp 10) protons/cm2, and neutrons to 3x10(exp 10) neutrons/cm2. These devices displayed transient effects due to gamma and proton irradiation. Gamma irradiation produced a depression of the device current that recovered completely over periods of hours. Proton bombardment produced an enhancement of the device currents that did not anneal completely over similar periods. Neutron irradiation produced no effects on the devices. Taken as a whole, these results indicate that quantum devices represent a prime candidate for application in radiation-harsh environments.

Direct bandgap InP, GaAs, CdTe, and Ga0.5In0.5P solar cells containing backside mirrors as well as parasitically absorbing substrates are analyzed for their limiting open circuit voltage and power conversion efficiency with comparison to record solar cells. From the principle of detailed balance, it is shown quantitatively that mirror solar cells have greater voltage and power conversion efficiency than their substrate counterparts. Next, the radiative recombination coefficient and maximum radiative lifetime of GaAs mirror and substrate solar cells are calculated and compared to the nonradiative Auger and Shockley-Read-Hall (SRH) lifetimes. Mirror solar cells have greater radiative lifetime than their substrate variants. Auger lifetime exceeds radiative lifetime for both substrate and mirror cells while SRH lifetime may be less or greater than radiative lifetime depending on trap concentration and capture cross section. Finally, the change in free energy of the photogenerated carriers is analyzed in a comparison between InP, GaAs, CdTe, and Ga0.5In0.5P mirror and substrate solar cells in order to characterize the relationship between solar photon quality and free energy management in solar cells with differing bandgaps. Wider bandgap visible threshold Ga0.5In0.5P solar cells make better use of the available change in free energy of the photogenerated charge carriers, even when normalized to the bandgap energy, than narrower bandgap near-IR threshold InP, GaAs, and CdTe solar cells.

A detailed analysis of the extracted back gated FET mobility as a function of channel length, channel width, and underlying oxide thickness for both exfoliated and chemical vapor deposited (CVD) graphene is presented. The mobility increases with increasing channel length eventually saturating at a constant value for channel lengths of several micrometers. The length dependence is consistent with the transition from a ballistic to diffusive transport regime. The mobility as a function of channel width first increases and then decreases. The increase in mobility for very small channel widths is consistent with a reduction in edge scattering. The decrease in mobility for larger channel widths is observed to be strongly dependent on the oxide thickness suggesting that electrostatics associated with fringing fields is an important effect. This effect is further confirmed by a comparative analysis of the measured mobility of graphene devices with similar channel dimensions on oxides of different thicknesses. The observed electrical measurements are in excellent agreement with theoretical studies predicting the width dependence of conductivity and mobility. The mobility of CVD grown graphene is slightly lower than that of exfoliated graphene but shows similar trends with length and width. The mobility values reported in the literature are in agreement with the trend reported here.

The effective electron mobility of In0.53Ga0.47As metal-oxide-semiconductor field-effect-transistors with HfO2 gate oxide was measured over a wide range of channel doping concentration. The back bias dependence of effective electron mobility was used to correctly calculate the vertical effective electric field. The effective electron mobility at moderate to high vertical effective electric field shows universal behavior independent of substrate impurity concentration. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3588255]

Publicity Co-Chairs Hai Jin, Huazhong University of Science and Technology, China Antonio Coronato, ICAR-CNR, Italy Damien Sauveron, Universite de Limoges/CNRS, France Hua Liu, Xerox Corporation, USA Kevin Raymond Boyce Butler, Pennsylvania State University, USA Guojun Wang, Central South University, China Tao Jiang, Huazhong University of Science and Technology, China Gang Wu, UESTC, China Yoshiaki Hori, Kyushu University, Japan

Tip based nanofabrication (TBN) processes promise unprecedented degrees of control and precision for the manufacture of nanostructured materials and devices. These processes use atomic force microscope or scanning tunneling microscope tips to create localized electric fields, electron beams, and other catalyzing conditions to control and detect the position, size, dimension, and orientation of nanostructures. Tip based approaches have deposited metals, oxides, and organic molecules to name a few. Often, a gas phase precursor is required to provide the material for the deposit. The TBN conditions for gas dosing are unique compared to other fabrication processes, e.g., chemical vapor deposition. The manufacture of precision nanostructures requires a contamination-free environment, and hence ultrahigh vacuum conditions must be maintained in the chamber. This can cause a gas jet from a doser to spread into a wide fan resulting in a small precursor flux with a broad distribution. This makes it difficult to mee...

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Giant magnetoresistance was observed in a disordered two‐dimensional electron system in a variable‐range hopping regime. The possibility of utilizing the phenomenon as a magnetic field sensor was demonstrated by the detection of trapped vortices in a superconducting Pb film. The minimum size of such a device is discussed.