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Electron tunneling measurements on ultrathin quench-condensed films near the superconductor-to-insulator (SI) transition reveal that the superconducting state degrades with increasing normal state sheet resistance, R□, in a manner that depends strongly on film morphology. In homogeneously disordered films, the superconducting energy gap Δo decreases continuously and appears to go to zero at the SI transition. In granular films the transport properties degrade while Δo remains constant. Measurements in the normal state reveal disorder enhanced e- -e- interaction corrections to the density of states. These effects are strong and depend on morphology in a manner that is consistent with their playing an important role in driving the SI transition.

A method for two-dimensional carrier profiling is presented, based on tunneling from a conducting atomic-force microscope (AFM) probe tip to a semiconductor sample. Current–voltage data are taken during the AFM scan on a cross-sectioned sample consisting of epitaxial InP multilayers. The results show a clear dependence of the current–voltage characteristics on the carrier concentration and different behavior for n-and p-type InP. Modeling of the data enables one to use this method as a quantitative tool for high-resolution two-dimensional dopant profiling.

Determining the cross-sectional doping profile of very small metal–oxide–semiconductor field effect transistors and specifically the direct measurement of their channel length is necessary for true channel engineering to be possible. Scanning capacitance microscopy (SCM) has generated unprecedented images of the cross-sectional doping profiles of very small transistors. The bias voltage dependence of these images has motivated us to investigate the SCM technique in greater detail. Using electrical simulations, we have focused on the pn junction to establish the qualitative and quantitative relationship between the bias voltage and the pn junction location. The ability to confidently interpret the images produced with SCM will allow us to improve simulation models, trouble-shoot process flow, and determine the effective channel length of semiconductor devices.

We have achieved extremely high drive current performance and ballistic (T>0.8) transport using ultra-thin (

As MOSFET channel lengths are scaled to below 100 nm, the determination of the effective channel length, L/sub 0/ becomes increasingly important. We have studied cross-sectioned MOSFETs with gate lengths down to 90 nm using scanning capacitance microscopy (SCM), and show the first images of these state-of-the-art devices. Using a device simulator we have quantitatively established the relation between L/sub 0/ and the SCM response in the channel region, allowing us to determine L/sub 0/ from the SCM measurements. We have explored the ultimate resolution attainable using this technique; experimentally, using very sharp probe tips and with numerical simulations.

With the increased scaling down of MOSFET dimensions, delineation of the p-n junction becomes increasingly important. We have studied cross-sectioned 0.15 micron process MOSFETs using a newly developed technique, scanning capacitance microscopy (SCM), and report the first direct measurement of the channel length for these state-of-the-art devices. Using a device simulator we have quantitatively established the connection between the dopant profile and the SCM response while scanning across a p-n junction. This allows us to determine the position of the p-n junction from the SCM measurements.

We present the first p-channel Vertical Replacement-Gate (VRG) MOSFETs. Like the VRG-nMOSFETs demonstrated last year, these devices show promise as a successor to planar MOSFETs for highly-scaled ULSI. Our pMOSFETs retain the key features of the nMOSFETs and add channel doping by ion implantation and raised source/drain extensions (SDEs). We have significantly improved the core VRG process to provide high-performance devices with gate lengths of 100 nm and below. Since both sides of the device pillar drive in parallel, the drive current per /spl mu/m of coded width can far exceed that of planar MOSFETs. Our 100 nm VRG-pMOSFETs with t/sub ox/=25 /spl Aring/ drive 615 /spl mu/A//spl mu/m at 1.5 V with I/sub OFF/=8 nA//spl mu/m-80% more drive than specified in the 1999 ITRS Roadmap at the same I/sub OFF/. We demonstrate 50 nm VRG-pMOSFETs with t/sub ox/=25 /spl Aring/ that approach the 1.0 V roadmap target of I/sub ON/=350 /spl mu/A//spl mu/m at I/sub OFF/=20 nA//spl mu/m without the need for a hyperthin (

We have investigated the behavior of the superconducting energy gap \ensuremath{\Delta} in ultrathin films of quench condensed Bi near the superconductor-insulator (SI) transition. From electron tunneling measurements on these films, we conclude that \ensuremath{\Delta} becomes very small and approaches zero at the SI transition. We studied high-sheet-resistance films with ${\mathit{T}}_{\mathit{c}0}$'s as low as 0.19 K. This is a factor of 40 lower than the low-sheet-resistance film ${\mathit{T}}_{\mathit{c}0}$ of 6.4 K.

The metal-insulator transition in granular aluminum has been observed. The resistivity has been varied over six orders of magnitude from metallic to a material where the conduction is via variable-range hopping. As the transition is approached from the metallic side, tunneling measurements have shown a ${V}^{\frac{1}{2}}$ dependence of the density of states, in agreement with recent theories.

We report the first systematic study of the corrections to the electron density of states of a 1D system, ultranarrow granular aluminum wires. These corrections do not have the ${\mathrm{V}}^{\mathrm{\ensuremath{-}}1/2}$ dependence predicted by theory, but are significantly larger than the corrections observed in corresponding bulk samples. At high magnetic fields, low temperatures, and very low voltages, we see evidence of a logarithmic gap in the density of states.

We have observed superconductivity in thin films of (La1−xSrx)2CuOy which are fabricated by implanting evaporated La/Cu multilayer films with Sr and annealing in oxygen. The films are insulating and partially transparent as-implanted, but they darken and become conducting at annealing temperatures as low as 500°C. The resistive behavior is very sensitive to the annealing conditions and the superconducting layer appears to be buried beneath the surface. Similarly, implantation of F, O, and Ne into single crystals and high quality (χmin

The resistance of ultrathin films condensed on low-temperature substrates has been measured. All of the materials studied (Au, Cu, Al, Sn, and Pd) show a transition from activated to metallic behavior as the resistance is reduced below 30000 ..cap omega../D/sup 7/Alembertian. This result gives strong evidence is support of the concept of a minimum two-dimensional conductivity. In Pb films with resistance > 30000 ..cap omega../D/sup 7/Alembertian, the onset of superconductivity is marked by an increase in activation energy.

Measurements on the time dependence of the specific heat exist now both at short and long timescales. Below 0.3 K the short time (}10 μs) specific heat of all the materials studied is smaller than the long time specific heat, but larger than the Debye value. Above 0.2 K most of the specific heat is coupled to the phonons already at 10 μs. However, measurements at very long timescales reveal that the specific heat has a component with a logarithmic time dependence, as proposed by the tunneling model, although only part of the total specific heat can be ascribed to it.

By electron tunneling we have studied the superconducting properties of granular aluminum as one approaches the metal-insulator transition. We find that with increasing sample resistivity, the superconducting energy-gap edge broadens because of lifetime effects until that broadening becomes comparable to the gap. At this point, superconductivity disappears.

We have measured the quasiparticle recombination time in the strong-coupled superconductor ${\mathrm{Pb}}_{0.9}$${\mathrm{Bi}}_{0.1}$ directly by measuring the lifetime-broadened energy gap edge. This is done by measuring the $I\ensuremath{-}V$ characteristics of a superconducting tunnel junction of the type ${\mathrm{Pb}}_{0.9}$${\mathrm{Bi}}_{0.1}$-insulator-${\mathrm{Pb}}_{0.9}$${\mathrm{Bi}}_{0.1}$. Agreement with the calculated value is excellent.

The behavior of a superconducting A1 film under conditions of large nonequilibrium injection of quasiparticles is studied by means of a tunnel generator and detector. At a critical injection density, ${n}_{c}$, a second energy gap develops in the superconductor. The relevance to recent theories of nonequilibrium superconductivity is discussed.

We have performed systematic tunneling measurements on two-dimensional quench-condensed films of Sn and Pb to investigate the destruction of superconductivity by localization effects. With increasing sheet resistance of the films, the energy gaps and ${T}_{c}$'s decrease only slightly, but the gap edges broaden until the width becomes comparable to the gap. Associated with this broadening are low-temperature finite-resistance tails in the resistive transitions.

The time-dependent specific heat of amorphous Si${\mathrm{O}}_{2}$ has been measured between 0.1 and 1 K over the range \ensuremath{\sim} 1 sec to 10 \ensuremath{\mu}sec. The decoupling of the roughly $T$-dependent contribution to specific heat is observed in submillisecond time scales, in qualitative agreement with the predictions of the tunneling model. However, the excess ${T}^{3}$-dependent specific heat is not decoupled on the time scales involved.

We have performed tunneling measurements on ultrathin, homogeneous, strong-coupled superconducting Pb films in the regime where ${T}_{c}$ varies with sheet resistance. The energy gap $\ensuremath{\Delta}$ and the strong-coupling corrections to the density of states have been measured as functions of the sheet resistance ${R}_{\ensuremath{\square}}$. We conclude that the standard picture of enhanced Coulomb repulsion with increasing sheet resistance is too naive and that, in the presence of disorder, an analysis more sophisticated than Eliashberg theory is necessary.

We have studied the temperature-dependent resistivity and Hall coefficient of epitaxial $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ films as a function of ion-beam-induced damage. At low ion fluences the films behave like typical metals above the superconducting transition. At higher ion fluences, the material goes continuously through the metal-insulator transition with a resistivity that varies like $\mathrm{exp}({T}^{\ensuremath{-}\frac{1}{2}})$ but with a Hall coefficient that changes very little. This implies that the transition is a result of a reduction in mobility rather than a drop in carrier density.

We have fabricated tunnel junctions between chemically etched single crystals of YBa{sub 2}Cu{sub 3}O{sub 7} and evaporated metal counterelectrodes which exhibit reproducible characteristics. Above the bulk critical temperature of YBa{sub 2}Cu{sub 3}O{sub 7}, {ital T}{sub {ital c}}, the conductance, {ital G}({ital V}), has a linear dependence with voltage and has some asymmetry. Below {ital T}{sub {ital c}}, additional structure associated with the superconductivity appears in {ital G}({ital V}). At {ital T}{much lt}{ital T}{sub {ital c}} there is a reproducible, finite, zero-bias conductance which suggests that there are states at the Fermi energy superconducting YBa{sub 2}Cu{sub 3}O{sub 7}. Junctions with Pb, Sn, Bi, Sb, PbBI, and Au counterelectrodes all show qualitatively similar behavior.

We report the observation of strong line narrowing of microwave radiation (870 MHz) emitted from a continuously operated, dc-pumped ${\mathrm{Bi}}_{92}$${\mathrm{Sb}}_{08}$ semiconducting alloy at 1.6 K. Bandwidths of less than 1 kHz are observed. The origin of the line narrowing is thought to be a maser effect involving the $\frac{3}{2}\ensuremath{\rightarrow}\frac{1}{2}$ nuclear electric-quadrupole transition of the ${\mathrm{Bi}}^{209}$ nucleus. A new dc pumping mechanism is proposed to explain the effect. In this effect the nuclei are pumped by electronic spin levels, saturated as in the Overhauser effect, except that saturation is achieved by carrier avalanche, instead of rf pumping.

High‐quality reproducible Pb oxide tunneling barriers have been grown using thermal oxidation methods. Junctions were made over a conductance range of 104(Ω cm2)−1 by accurately controlling the humidity in a flow of room‐temperature oxygen. An inspection of the I‐V characteristics in the region eV

Buried single‐crystal CoSi2 layers in silicon have been formed by high dose implantation of cobalt followed by annealing. These layers grow in both the (100) and (111) orientations—those in (111) have better crystallinity, but those in (100) are of higher electrical quality. Electrical transport measurements on the layers give values for the resistance ratios and superconducting critical temperatures that are better than the best films grown by conventional techniques and comparable to bulk CoSi2.

Low leakage tunnel junctions have been prepared on (001) oriented YBCO thin films. The junctions were made by evaporating Pb counterelectrodes on chemically etched surfaces of YBCO thin films. The tunneling conductance as a function of voltage shows structure which is reproducible from junction. This structure is very similar to that obtained with etched junctions on single crystal YBCO.

An ultrahigh vacuum system has been constructed which permits deposition of thin films onto 4.2-K substrates. The evaporation mechanism is contained within a small cylindrical vessel which is totally immersed in liquid (4)He. This device has been used to study superconductivity in PbBi and Ga, PdH and PdD, and most recently, transport properties of ultrathin films.

We have observed an interaction between helicon waves and drift currents in a layered lead telluride structure. In the low ωcτ regime of our experiments bulk wave effects are much greater than the surface wave interaction proposed by Baraff and Buchsbaum. Experiments performed on structures which have layers of equal dielectric constants and those with unequal dielectric constants both yield the same result; namely, the attenuation is reduced when the drift and wave propagate in the same direction and is increased when the two are in opposite directions. The observed interaction is strong and although spatial growth of the helicon waves has not yet been achieved with presently available drift velocities (Vdrift < Vphase), wave attenuation has been reduced by as much as 15 dB.

We have measured the superconducting and normal-state properties of ultrathin quench-condensed Pb and Sn films by electron tunneling and transport. The normal-state measurements illustrate a substantial reduction in the electronic density of states about the Fermi surface. Good agreement with theory is obtained for this reduction. The collapse of {ital T}{sub {ital c}} can be accounted for by the reduced density of states but some problems stand in the way of a full description of the superconducting behavior.

Using high dose implantation of 200 keV Co ions followed by high temperature annealing, we have created buried layers of CoSi2 in crystalline Si of both (100) and (111) orientations. For a dose of 3 × 1017 Co/cm2, the layer that forms is ∼1100Å thick and the overlying Si is ∼600Å thick. A lower dose of 2 × 1017 Co/cm2 yields a thinner layer, 700Å thick, under 1200Å of crystalline Si. Rutherford Backscattering and channeling analysis of the layers shows that they are aligned with the substrate (χmin of the Co as low as 6.4%.) and TEM inspection of the (100) CoSi2/Si interfaces shows that they are abrupt and epitaxial (with occasional small facets). Moreover, electrical characterization of these layers yields resistance ratios that are better than epitaxial CoSi2 films grown by more conventional UHV methods.

We present measurements of the temperature dependence of the conductance of a tunnel junction of the form Al/oxide/disordered-granular-Ag-film at low temperatures. From these measurements we deduce that the logarithmic corrections to the two-dimensional density of states due to disorder-enhanced Coulomb interactions depend on temperature. Specifically, for sheet resistances 1.35 k\ensuremath{\Omega}/\ensuremath{\square}${R}_{\ensuremath{\square}}$6.12 k\ensuremath{\Omega}/\ensuremath{\square} and temperatures 0.07 KT6.0 K the logarithmic singularity in the density of states centered on the Fermi energy is sharp at low temperatures and smears out as the temperature increases. Our data are consistent with a model which attributes the temperature dependence of the density of states to a redistribution of the zero-temperature energies of the quasiparticle states over an energy range of the order of ${k}_{B}$T.

Recent progress in the growth of thin epitaxial silicides on silicon has resulted in films of very high quality with especially smooth interfaces. Using a completely different technique, high dose implantation followed by annealing, we have succeeded in creating buried single-crystal layers of CoSi2, NiSi2, and CrSi2 in crystalline silicon. The CoSi2 and NiSi2 layers grow in both the (100) and (111) orientations--those in (111) have better crystallinity, but those in (100) are of higher electrical quality. The CrSi2, on the other hand, only grows in the (111) orientation where its hexagonal structure has an almost perfect lattice match to silicon. We call this new internal growth process “mesotaxy” by analogy with epitaxy which refers to single-crystal growth on surfaces.

We have fabricated tunnel junctions between chemically etched single crystals of YBa2Cu3O7-δ and evaporated metal counterelectrodes which exhibit reproducible characteristics. Above the bulk critical temperature of YBa2Cu3O7-δ, Tc, the conductance, G(V), has a linear dependence with voltage and has some asymmetry. Below Tc, additional structure associated with the superconductivity appears in G(V). At T>>Tc there is a reproducible finite zero bias conductance.

We have prepared low leakage tunnel junctions on epitaxial YBa2Cu3O7 (YBCO) films grown on SrTiO3(001) by evaporating Pb counterelectrodes onto chemically etched YBCO surfaces. Structure in the voltage dependence of the tunneling conductance is reproducible and strongly resembles what has been obtained in similarly etched junctions on YBCO single crystals.

Metal-Insulator-Semiconductor Tunneling Microscopy is a new technique for creating a 2 dimensional map of the carrier concentration in a semiconductor. This is done by measuring the tunneling current between a conducting Atomic Force Microscope tip and a semiconductor sample. Here we present the application of this method to InP. By exploring the current voltage characteristics of p- and n-type InP over a large range of voltages and carrier concentrations we find they are well-described by Metal-Insulator-Semiconductor theory. A fitting procedure of this model to the data gave a maximum deviation of 5%.

It is now possible using scanning capacitance microscopy to directly obtain a two-dimensional profile of the doping in MOSFETs with gate lengths greater than 60 nm. We have accomplished this using highly doped, ultrasharp silicon cantilevers with a tip diameter of less than 10 nm. These tips provide images with very little voltage dependence (over a 1-2 V range), and improved resolution ( 30-50 nm resolution.

The narrowest feature of an integrated circuit is the silicon dioxide gate dielectric (3–5 nm). The viability of future CMOS technology is contingent upon thinning the oxide further to improve drive performance, while maintaining reliability. Practical limitations due to direct tunneling through the gate oxide may preclude the use of silicon dioxide as the gate dielectric for thicknesses less than 1.3 nm, however.

We have studied cross-sectioned n- and p-metal-oxide-semiconductor field effect transistors with gate lengths approaching 60 nm using a scanning capacitance microscope (SCM). In a homogeneous semiconductor, the SCM measures the depletion length, determining the dopant concentration. When imaging a real device there is an interaction between the probe tip and the built-in depletion of the p-n junction. With the help of a device simulator, we can understand the relation between the SCM images and the position of the p-n junction, making the SCM a quantitative tool for junction delineation and direct measurement of the electrical channel length.