摘要:

This paper proposes a very small switching device, called an atom relay, which would supersede present metal‐oxide‐semiconductor devices for the next decade. The basic configuration of an atom relay consists of an atom wire, a switching atom, and a switching gate, with total dimensions below 10 nm, and an operation speed at more than terahertz level. The operation principle of the atom relay is that a switching atom is displaced from the atom wire by the electric field supplied from the switching gate, and the atom relay exhibits an ‘‘off’’ state. The switching characteristics of the atom relay are demonstrated by simulation, and it is shown that the electron propagation is successfully cut if a gap of about 0.4 nm is formed in the atom wire by the displacement of the switching atom. A self‐relay structure, in which the switching atom is displaced by the electric field from the atom wire itself, enables a dynamic memory cell, and the functions are ascertained by simulation. Fundamental logic circuits as NAND and NOR gate constitutions are also proposed. These logic and memory circuits can integrate a supercomputer in a 200‐&mgr;m‐square of area, with 107gates of logic circuit and 109bits of memory, and operate at more than 1012Hz. The atom relay is evaluated on the basis of the characteristics necessary for integrated circuit devices, together with several nanoscale devices, and is found to be the most promising candidate device for future integrated circuits.

ISSN:0021-8979    

DOI:10.1063/1.354999

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Electron coincidence spectroscopy in an ultrahigh vacuum scanning transmission electron microscope has been used to study the generation pathways for secondary (SE) and Auger electrons (AE) excited by high‐energy incident electrons. Energy and momentum transfer of inelastically scattered 100 keV primary electrons have been correlated with energy selected SE and AE for both thin ⟨111⟩ oriented Si crystals and amorphous C films. Coincidence spectra from the valence excitation region indicate that bulk plasmon decay is not the primary production channel for SE in Si(111) and that SE result partially from the decay of ionizations from deep in the valence band. Energy deposition by the primary beam is responsible for SE production at excitation energies above the valence region. At most one SE is emitted from the entrance surface of a thin film for each inelastically scattered 100 keV primary electron. An enhancement in both the SE yield and generation probability is observed at the CKionization edge. Correlations between energy loss electrons in the vicinity of the CKionization edge and energy selected SE near the CKLLAE energy show a very sharp threshold in the generation probability. High‐momentum transfer (spatially localized) inelastic scattering events are more efficient at creating SE than low‐momentum transfer events. The high‐spatial resolution obtained in SE images is explained using the Heisenberg uncertainty principle and the scattering angle dependence of the SE generation probability.

ISSN:0021-8979    

DOI:10.1063/1.355000

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Capacitance measurements as a function of bias provide evidence for the redistribution of electrons above the pressure induced type I to type II transition in a 43, 72, and 40 A˚ AlAs/GaAs double barrier structure (DBS). Measurements at 77 K for pressures up to 16 kbar allow the identification of low and high pressure regimes. In the low pressure regime the DBS exhibits a capacitance whose characteristic length includes both the barriers and the well, and any surrounding depletion regions. In the high pressure regime, the behavior is like that of a ‘‘quantum capacitor,’’ with plates only ∼70 A˚ apart. This causes a marked increase in the zero bias capacitance, which is explained by electron transfer to theXwells in the AlAs regions. The subsequent variation of the capacitance with bias is consistent with a band bending model introduced previously, in which the Fermi level is pinned to the lowestXlevel in each well at low bias, but where the collector well is eventually depleted at larger bias.  

ISSN:0021-8979    

DOI:10.1063/1.355001

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

This work refers basically to the detailed understanding of the natural phenomena in real tunneling metal‐semiconductor contacts. A mechanism of forming extremely low‐resistance nonalloyed Ti/Pt/Au ohmic contacts to a variety of III‐V compound semiconductors, e.g., InGaAs, InAs, and GaAs, is presented. Epitaxial layers of either type with different doping levels ranging from 1×1019to 2×1020cm−3were employed in order to determine electrical parameters that guarantee pure tunneling behavior of the contacts. Ti/Pt/Au contacts formed onp‐InGaAs Zn doped to 1×1020cm−3and onn‐InGaAs Si doped to 5×1019cm−3yielded a specific contact resistance of 4.8×10−8and 4.3×10−8&OHgr; cm2, respectively. The same metallization scheme applied to 4×1019cm−3Si‐dopedn‐InAs gave a specific contact resistance of 1.7×10−8&OHgr; cm2for the as‐deposited and annealed samples. An extremely low value of 2.8×10−8&OHgr; cm2was evaluated for contacts onp‐GaAs doped with Be to 2×1020cm−3. The contact properties are discussed in relation to the effect of ion‐beam cleaning and postdeposition annealing. Of particular concern was the cleaning of the semiconductor surface with low‐energy (60 eV) Ar+ions for 40 s prior to the metallization process. This opens also the possibility to investigate ion damage defects and trap‐assisted increase of the depletion depth. The contact design was based on the concept that the detrimental influence of the ion beam on the semiconductor properties can be neutralized with a proper annealing. It has been demonstrated that even very rapid thermal processing for 1 s at elevated temperatures was sufficient to restore the stoichiometry in the As‐depleted subsurface layer arising as a result of ion damage.The fabrication sequences used provide formation of intimate contacts without interfacial films and carrier compensation effects. Optimal processing conditions have been empirically established that stimulate substantially the ohmic behavior of the contacts. It was possible to achieve an absolute control over the contact formation mechanism without crucial adjustment of annealing parameters. Closer examination of the temperature dependence of the contact resistances reveals a good agreement with the theoretical approach based on the tunneling model. Metallurgical studies of the contacts confirm their unreacted, abrupt metal‐semiconductor configurations if optimal annealing temperatures are used. Experimental evidence manifests a definite relationship between electrical properties and interfacial compositional modifications affected by different forming conditions. The trend for structural changes occuring at annealing temperatures above the optimal ones was found to be in correlation with the chemical reactivity of III‐V compounds. The observed thermal stability of the contacts can be fully explained in this way. In contrast to chemical precleaning the controllable elimination of interface inhomogeneities during ion etching results in contacts with improved homogeneity and uniformity. The demonstrated universality and reliability make the fabrication technique suitable to meet specific needs of modern semiconductor devices.

ISSN:0021-8979    

DOI:10.1063/1.355002

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

This article proposes a novel Schottky junction structure on (100) GaAs, which has a thin nonstoichiometric GaAs interface layer. A 10‐ to 20‐A˚‐thick As‐rich or Ga‐rich interface layer was grown by low‐temperature molecular beam epitaxy at 200 °C, and placed at the metal‐GaAs junction interface. Independent of metal work functions, the interlayer insertion causes a wide variation in barrier heights in the range of 0.5–1.0 eV onn‐GaAs, and 0.4–0.9 eV onp‐GaAs. The barrier height variation is attributed to a strong Fermi‐level pinning controlled by stoichiometric defect levels in the interlayer. The levels were characterized by isothermal capacitance transient spectroscopy of a metal‐insulator‐semiconductor structure having a nonstoichiometric interlayer between an aluminum nitride insulating film and GaAs. High concentrations of defect levels were confirmed around 0.4 eV below the conduction band edge in the As‐rich interlayer and around 0.3 eV above the valence band edge in the Ga‐rich interlayer. An anomalous transient response, exhibiting what appears to be low activation energy and a small capture cross section, was found in addition to the normal response. This anomaly can be explained by variable range hopping conduction via defect sites along the interlayer. In diodes with dense interfacial defects, this relaxation process for trapped carriers is considered to proceed faster than the usual emission to the conduction or valence band, at low temperatures.

ISSN:0021-8979    

DOI:10.1063/1.355003

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

By considering the decomposition of water‐related bonds at the silicon/oxide interfaces, theoretical expressions for the hot‐electron induced interface state generation and threshold‐voltage shift are developed. Results demonstrate that the relation between the threshold‐voltage shift and the hot‐electron fluence needs not follow the power law. The developed expression of the threshold‐voltage shift is a function of the initial interface trap density, interface hardness, density of water‐related chemical bond, and the capture cross section of interface trap and can be used to explain most of the reported experiments. When the trapping rate and the generation rate are close to each other, a power law dependence of the threshold‐voltage shift will be observed in a wide range of injection fluence. However, if the trapping rate is greater than the generation rate or for a sample with large hardness and small initial trap density, a quasi‐saturation region is observed because of most of the interface trap being filled and the small amount of generated traps. Saturation of the threshold‐voltage shift will occur when most of the water‐related bonds are dissociated and the created traps are filled.

ISSN:0021-8979    

DOI:10.1063/1.355004

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A formalism based on the superlattice crystal coordinate representation, which is valid for arbitrary well and barrier widths, is developed and applied to the Wannier exciton problem. A simple model for the electron‐hole Coulomb interaction within the independent subband approximation permits nonvariational calculation of exciton binding energies, oscillator strengths, and optical absorption of both bound and continuum exciton states. The effects of growth axis directed electric and magnetic fields are emphasized. Numerical results for GaAs/ Ga1−xAlxAs and In1−xGaxAs/GaAs exciton binding energies and oscillator strengths as functions of well width, barrier width, and electric and magnetic field strengths show excellent agreement with experiment.

ISSN:0021-8979    

DOI:10.1063/1.355005

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A theoretical study of resonant interband tunneling in GaAs &dgr;‐doped inducing homostructure and polytype GaSb/AlSb/InAs heterostructure is presented in this article. The resonant interband tunneling in such homo‐ and heterostructures is modeled by an energy‐ and spatial‐dependent effective mass equation incorporating the general transfer matrix method. The present formalism is based on the envelope function approximation as done to date, but contains two significant improvements: a more realistic treatment of the spatial and energy dependence of effective‐mass and bandstructures; and the avoidance of plane‐wave, Airy function or Wentzel–Kramers–Brillouin approximations for calculating the envelope function in favor of direct numerical evaluation. The transmission coefficients of the unipolar and bipolar resonant interband tunneling structures are calculated and the symmetric and asymmetric multiple quantum well resonant interband tunneling structures are also discussed.

ISSN:0021-8979    

DOI:10.1063/1.355006

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The phase decomposition in high quality Bi2Sr2CaCu2Oy(2212) single crystals annealed in air at 400–750 °C is studied by x‐ray diffraction and scanning electron microscopy. It is found that the Bi2Sr2CaCu2Oyphase of the as‐grown single crystals readily decomposes even at temperatures as low as 450 °C. With the annealing temperature increasing, phases of bismuth oxides, strontium bismuth oxide, and the Bi2Sr2CuOx(2201) are segregated successively from the air annealed single crystals and are found to be temperature dependent. Combining with the enhancement of the superconducting onset temperatures and the very narrowness of the diamagnetic transitions observed for the annealed crystals, it is suggested that the structural change indicated by the surface phase decomposition may play an important role in the variations of superconductivity in Bi2Sr2CaCu2Oysingle crystals.

ISSN:0021-8979    

DOI:10.1063/1.355007

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The real and imaginary parts of the alternating current volume susceptibility are simultaneously measured on a cylindrical sample of ceramic superconducting YBa2Cu3O7−&dgr;in the frequency range from 0.5 to 1×103Hz. A relatively small frequency dependence of the shielding diamagnetism is observed below 2 Hz and above 250 Hz. A logarithmic dependence of the peak loss temperature is observed which is characteristic of an activated process with an activation energy of 2.5 eV. A weak decrease of the shielding signal takes place when the amplitude of the alternating current magnetic field is increased from 0.002 to 0.02 G. Above 0.02 G this shielding signal is field independent. The data are interpreted in terms of flux creep and viscous drag effects.  

ISSN:0021-8979    

DOI:10.1063/1.355008

出版商:AIP    

年代:1993

数据来源: AIP