摘要:

The origin of the electronic free charge carriers accumulation/depletion in the porous silicon skeleton contacted with an electrolyte is determined by investigating the limiting step in the conduction process. Experimental evidences, supported by quantitative considerations, show that the porous silicon can be conductive if the free charge carriers flux supplied by the substrate is not the rate determining step of the electrical current conduction. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361180

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The electronic structure of a novel nanometer scale semiconductor quantum wire structure [S. Y. Chou and Y. Wang, Appl. Phys. Lett.63, 788 (1993)] has been calculated self‐consistently. The structure has two control parameters, the voltage applied to a split gate and the voltage applied to a wire gate. The influences of both the split gate and the narrow wire gate which is placed inside the gap of the split gate, on the electronic structure of the system are examined. We show that varying the voltage on either the split gate or the wire gate changes the induced quantum wire confinement potential profile, the energy level spacing, the channel electron density, and the effective channel width. Results for the ballistic conductance of the device as a function of the two control voltages are extracted from the electronic structure calculations and are found to be in satisfactory agreement with experimental data. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361116

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have fabricated GaAs T‐shaped edge quantum wire (T‐QWR) structures by the cleaved edge overgrowth method. The geometries of the samples were designed in such a way that we can separately detect photoluminescence (PL) from T‐QWRs as well as two adjacent quantum wells (QWs) from spatially resolved PL measurements. Each PL peak is unambiguously assigned and analyzed to precisely determine the quantized energy of excitons in T‐QWRs and the adjacent QWs. Special care is made in the cleavage and the growth procedures to realize sharp and efficient PL from these structures. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361117

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Metal‐oxide‐semiconductor capacitors fabricated by dry and wet oxidation at 1150 °C ofn‐type 6H–SiC exhibit a drastic negative charging during Fowler–Nordheim charge injection. This charging strongly depends on the fabrication conditions of the samples. The densities of interface states and oxide charges can be significantly reduced by a postoxidation anneal in Ar for as long as 60 min. A large part of the charge appears to be trapped at the interface. These charges are released from the traps by illumination at photon energies between 2 and 4 eV or by annealing below 300 °C. During charge injection interface states are created near the conduction band edge. Their density is strongly reduced by annealing at 150 °C. For the oxide charging we find capture cross sections in the range of 10−15–10−17cm−2. In unannealed wet oxidized samples the traps exhibit properties similar to those of water‐related traps in SiO2on Si. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361118

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Mesa etched transmission line model (TLM) test structures with different contact lengths have been fabricated on heavily boron doped polycrystalline diamond films. The behavior of the contact and contact end resistance measurements can be fully explained using the TLM. No influence of the grain size on the contact resistivity has been observed. High surface boron doping concentrations led to low contact resistivities, in agreement with numerical calculations. Annealing of Al/Si–diamond contacts at 450 °C in N2leads to lower contact resistivities due the formation of SiC at the metal–diamond interface. The temperature dependence of the specific contact resistivity can be described well with a tunneling model before annealing. After annealing no useful fit is possible, indicative of the fact that the SiC interface layer acts as defect layer. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361119

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We propose a field‐effect tunnel transistor based on the metal–insulator transition. The principle of the switching is the metal–insulator transition, which occurs at the sheet resistanceRQ(∼h/e2=25.8 k&OHgr;). The modulation of the sheet resistance aroundRQby the control gates can be magnified by the phase transition. As a result, high transconductance and high current drivability more than 10 times greater than the ultimate silicon metal‐oxide‐semiconductor transistors are obtained. The device is a thin‐film silicon‐on‐insulator structure with dual gates, one on each side of the channel. A very thin granular metal film is deposited on the Si layer. Each metal island forms a Schottky contact with the Si layer, which is completely depleted. The electrons in the metal tunnel between the islands through the Si. The metal film can have a higher Coulomb gap and current drivability than is obtained with a single tunnel junction. A temperature of less than 1/20 of the Coulomb gap energy is required to reduce the leakage current by three orders of magnitude with the Coulomb blockade mechanism. Using the Wentzel–Kramers–Brillouin approximation, we calculated the tunneling probability between the islands and evaluated the sheet resistance of the metal film. Changing the gate voltage can modulate the sheet resistance in spite of the very narrow spacing between the islands. In the high resistance regime, the Coulomb blockade can operate and the resistance is three orders of magnitude higher than the bare tunnel resistance. In the ‘‘on’’ state, on the other hand, a very low sheet resistance of less than 1 k&OHgr; per square is obtained. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361120

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have compared the charge created inp‐metal–oxide–semiconductor capacitors by Fowler–Nordheim injection from the gate and from the substrate. We have shown that an injection from the gate creates a negative charge, trapped holes, and positively charged slow states whereas an injection from the substrate creates a negative charge, slow states, and amphoteric neutral traps; once charged these neutral traps are discharged irreversibly, as are the trapped holes, by an appropriate gate bias. We have observed that the discharge of the trapped holes, and the charge or discharge of the slow states, obey the same general law, but the time response of the trapped holes is always shorter than the time response of the slow states. This general law is equivalent to the so‐called ‘‘universal law,’’ which is the law which describes the time dependence of current observed in any dielectric in response to a step‐function field. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361121

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Both the ionized impurity scattering rate and its angular dependence inn‐type silicon were theoretically calculated using a full band model, in which a wave‐vector‐ and frequency‐dependent dielectric function was used instead of the dielectric constant of 11.7&egr;0. The number of grid points was determined from the relation between the wave vector and screening length to ensure the validity of the ionized impurity scattering rate. The results show that (1) the calculated overlap integral is small compared with the one used in a nonparabolic band model and (2) the screening effect is strong especially for low energy electrons. The validity of the scattering rate was tested by comparing electron mobilities obtained by a full Monte Carlo simulation with experimental data. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361122

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

(Bi2Sr2Ca3Cu4O12+&dgr;)1(Bi2Sr2CaCu2O8+&dgr;)1superlattice films synthesized by sequential radio frequency magnetron sputtering on MgO substrates were studied by x‐ray diffraction method, Rutherford backscattering technique, magnetization measurements and Hall effect experiments. Superconducting transition temperature observed in the (Bi2Sr2Ca3Cu4O12+&dgr;)1(Bi2Sr2CaCu2O8+&dgr;)1superlattice films (55–58 K) was higher than those of Bi2Sr2Ca3Cu4O12+&dgr;(40–47 K) and Bi2Sr2CaCu2O8+&dgr;(50–52 K) single phase films. The results suggest that optimum carrier concentration is achieved in CuO2layers in the superlattice films by charge transfer from the overdoped Bi2Sr2CaCu2O8+&dgr;units to the underdoped Bi2Sr2Ca3Cu4O12+&dgr;units. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361123

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

An investigation into the phonon contamination of x‐ray sensitive superconducting tunnel junctions arising from the x‐ray photoabsorption in various substrates has been conducted. Results are presented on the design of a superconducting tunnel junction (STJ) which substantially reduces or even eliminates phonon induced noise from the substrate. Such noise is the predominant feature in x‐ray spectra from junctions due to the bulk of the photons being absorbed in the substrate rather than in the thin superconducting film. The design involves the choice of a suitable buffer sandwich between the substrate and the STJ. Such a buffer would appear not only to attenuate the phonons created in the x‐ray photoabsorption in the substrate but also to scatter the phonons inelastically, introducing a frequency down‐conversion. Such a process ensures that few phonons of energy sufficient to break Cooper pairs in the superconducting film of the STJ enter the junction. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361124

出版商:AIP    

年代:1996

数据来源: AIP