摘要:

We report on luminescence properties of porous silicon emitting efficient light only a few tens of meV above the band gap of bulk Si. This emission band has a well-defined low-energy limit coincident with the position of the lowest possible luminescing exciton state of bulk silicon. The resonant photoluminescence spectrum exhibits all possible combinations of zero-phonon and momentum-conserving TA- and TO-phonon assisted absorption and exciton emission processes known for bulk silicon. We found that TO-phonon assisted processes give a major contribution to the light emission. We discuss the implications of these studies for the understanding of the origin of porous silicon photoluminescence. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122099

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A coherently strained stressor structure is used to create a one-dimensional periodic potential in the two-dimensional electron gas at a AlGaAs/GaAs heterointerface. We demonstrate that from magnetotransport the Fourier coefficients of the conduction band modulation can be determined. In contrast to conventional electrostatic patterning, “hard” potential modulation with dominant contributions of higher harmonics is achieved. In the regime of narrow stressor-stressor distance, the strain-induced potential modulation can be calculated analytically from elasticity theory. The calculated magnetoresistance which can be derived from the stressor-induced potential is in good agreement with the experimental data. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122100

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We have observed single-electron charging effects in heavily doped polycrystalline silicon nanowires at 4.2 K. Wires of approximately 20 nm by 30 nm active cross section were defined by electron-beam lithography and thermal oxidation in standard polycrystalline silicon material. We have measured a Coulomb staircase and periodic current oscillations with gate bias, attributed to localized carrier confinement resulting from a statistical variation in the intergrain tunnel barriers. A sharp change in the current oscillation period is seen and we speculate that it is due to electrostatic screening of the gate bias by grain boundary defect states. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122101

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The charge distribution and junction voltage on an indirect-band-gap semiconductor tunnel junction (that is in parallel with a resistor and current source) were obtained by solution of the master equation. Expressions for the tunneling rate in a silicon degeneratepnjunction are presented. Phonon-assisted tunneling permits relaxation of a requirement (that the external resistance be much larger than the resistance quantum) for the observation of single electron tunneling oscillations. Consequently, that process may enable observation of such oscillations in practical single junction circuits. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122102

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A new Si di-interstitial model is derived from theSi-P6electron paramagnetic resonance spectrum observed in neutron-, proton-, or ion-implanted silicon. Two Si interstitials lie in the {100} plane at a position considerably off from two tetrahedral interstitial sites nearby, sharing one Si lattice atom. The di-interstitial disappears at 170 °C annealing and can form the ⟨110⟩ interstitial chains which are considered to be a “building block” of the {311} extended defects frequently observed in ion-implanted Si.

ISSN:0003-6951    

DOI:10.1063/1.122116

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Oxygen vacancies (O vacancies) are considered to be charge trap centers inSiO2.This letter explores possible terminators of Si-dangling bonds associated with the O vacancies by performing first-principles total energy calculations. The present exploration is focused on the terminators which retain their chemical bonds after hole trapping. We have found that Cl atoms, NH and OH molecules firmly terminate the Si-dangling bond while H atoms are dissociated from aSi&sngbnd;Hbond after hole trapping. The H dissociation is accompanied by the generation of gap states which can contribute to the leakage currents in theSiO2films. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122103

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Focused ion-beam milling has been used to fabricate field-ion specimens from a multilayer film structure containing 100 repetitions of a(Cu2 nm/Co2 nm)bilayer deposited directly onto a planar substrate. The as-deposited films showed a magnetoresistance ratio of ∼5&percent; over a 250 Oe range at room temperature, and a coercivity of ∼60 Oe. The magnetic data suggest that the films are coupled ferromagnetically. Successful field-ion specimen preparation has allowed the observation of these layers by field-ion imaging and three-dimensional atom probe compositional analysis. Examination of the multilayer images reveals that, in some regions, the layers are nonparallel, but the interfaces are chemically quite sharp, with a diffuse interface region of ∼3 atomic layers. In addition, in some areas adjacent cobalt layers appear to be in contact. The fact that the layers are wavy suggests that the ferromagnetic coupling may be a result of Ne´el “orange peel” type magnetostatic coupling between adjacent cobalt layers. The relatively high coercivity may be a result of the poor layer planarity leading to a high number of domain wall pinning sites. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122104

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We have systematically studied the influence of Si doping on the characteristics of InGaN/GaN multiple quantum wells (MQWs) by means of high-resolution x-ray diffraction (HRXRD), photoluminescence (PL), PL excitation (PLE), and time-resolved PL spectroscopy. The twelve- period MQWs were grown by metalorganic chemical vapor deposition. Si doping in the GaN barriers was varied from1×1017to3×1019 cm−3.Information on the structural quality of the MQWs as a function of Si doping was extracted from the linewidth broadening of the higher-order superlattice satellite peaks measured in HRXRD. The HRXRD measurements indicate that increased Si doping results in better interface properties of the MQWs. PL and PLE measurements show a decrease in the Stokes shift with increasing Si doping concentration. The 10 K radiative recombination lifetime was observed to decrease from ∼30 ns (forn<1×1017 cm−3)to ∼4 ns (forn=3×1019 cm−3)with increasing Si doping concentration. The reduced Stokes shift, the decrease in radiative recombination lifetime, and the increase in the interface quality indicate that Si doping results in a decrease in carrier localization at potential fluctuations in the InGaN active layers. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122105

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We have observed an extremely narrow absorption spectrum due to bound-to-continuum transition inGaAs/AlxGa1−xAsmultiple quantum wells (MQWs). Its linewidth is only about one tenth of the values reported previously. Our calculation indicates that the broadening of the excited state in the continuum has little contribution to the absorption linewidth. We have grown a sample whose MQW region contains two kinds of wells with a minor thickness inhomogeneity. Its resultant absorption linewidth is six times as large as that of homogeneous well sample, which is in good agreement with our theoretical analysis. Thus we can suggest that the wider absorption spectra reported by many authors may be due to the well width inhomogeneity. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122106

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We have imaged the Abrikosov vortex lattice on the surface of a conventional superconductor with a low-temperature magnetic force microscope, which is based on commercially available piezoresistive cantilevers. The heat dissipation at low temperature is limited by operating the cantilevers at higher mechanical resonances, allowing one to improve the signal-to-noise ratio by a factor of 3. Using a Co/Au multilayer for the magnetic tip coating, the interaction with the vortices can be kept small, and it is possible to observe a stable vortex lattice on the surface of a cleavedNbSe2crystal. The stability of the vortex lattice can be understood in terms of collective pinning effects. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122107

出版商:AIP    

年代:1998

数据来源: AIP