摘要:

We present a study of the fluctuations in the dissolution front observed during the formation of porous silicon, leading finally to layer thickness inhomogeneities. Two types of fluctuations were revealed, one at the millimeter scale (waviness) and the other one at the micrometer scale (roughness). Root mean square amplitudes are comparable. In both cases fluctuations of the dissolution velocity can be invoked and we discuss their dependence on the current density and viscosity of the solution. The large scale fluctuations are attributed to planar resistivity fluctuations in the wafer. The second type of fluctuation displays a typical spatial periodicity comparable to the wavelength of the light so that a statistical characterization can be performed by optical measurements. The Davies–Bennett model quantitatively describes the induced light scattering. Remarkably, these fluctuations increase linearly with the layer thickness up to a critical value where a saturation regime is observed. In order to explain this behavior, we show the importance of the initial surface state of the wafer and of the porous medium. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364400

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The role of the photoexcited state of an azo pigment as a reactant for photocarriers in a layered organic system was investigated using 2,6-anthraquinone bisazo (ABHN) or 1,4-distyrylbenzene bisazo (PDHN) pigment. Both bisazo pigments are highly sensitized by carrier transport molecules involved in the layered device. However, photocarrier generation in the bisazo pigments was quite different in the absence of sensitizing molecules; ABHN never generates, but PDHN generates to some degree by itself. The photocarriers are known to be generated via excitons of the azo pigments in the layered systems from the result of excitation-energy-independent quantum efficiencies. Electromodulated absorption spectra show that ABHN forms a Frenkel exciton and PDHN a charge-transfer-natured exciton. The different types of excitons explain the difference in carrier generation pathways of the optoelectronic systems based on these two azo pigments well. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364401

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Fourier transform infrared photoconductivity spectra of Si donors in GaAs under magnetic field are presented in this paper. Four new spectral lines corresponding to the transitions from hydrogen-like ground state to the metastable states (510), (610), (710), and (810) under nonzero magnetic field were observed. The variational calculation model proposed by Barmby &etal; was applied to the high-lying metastable states. The experimental data of the transition energies agree well with the variational results under high magnetic field and below the resonant polaron region. Deviations due to omitting the bound Landau continuum coupling in the trial wave function were found in the comparison at the low field region for the metastable states with higher Landau index. The ionization energies of the high-lying metastable states were also determined. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364402

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

An accurate method for the determination of the bulk minority-carrier recombination lifetime of crystalline silicon wafers of typical thickness(<0.5mm) is presented. The method consists of two main steps: first, both wafer surfaces are passivated with silicon nitride films fabricated at low temperature (<400 °C) in a remote plasma-enhanced chemical vapor deposition system. Second, the effective minority-carrier lifetime of the wafer is measured by means of the contactless microwave-detected photoconductance decay technique. Due to the outstanding degree of surface passivation provided by remote-plasma silicon nitride films, the bulk minority-carrier lifetime can be very accurately determined from the measured effective minority-carrier lifetime. The method is suited for the bulk minority-carrier lifetime determination ofp-type andn-type silicon wafers with doping concentrations in the1014–1017cm-3range. We demonstrate the potential of the method for commercially available float-zone, Czochralski, and multicrystalline silicon wafers of standard thickness. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364403

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Thermally stimulated current (TSC) and photoconductivity were studied as a function of temperature and light intensity in ann-GaSe single crystal doped with chlorine. TSC measurements were performed in the range 80–450 K, and the results were analyzed by different methods. An electron trapping centre at about 0.38 eV below the conduction band and an electron capture cross section of(8±2)×10−18 cm2were determined. In this centre retrapping is negligible. A strong thermal quenching of photocurrent was observed at various excitation levels. The photocurrent results were analyzed by a simple kinetic model taking into account two different types of centres. In this way a hole centre about 0.20 eV above the valence band was observed. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364404

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Electrical and photoluminescence measurements have been carried out onCuInSe2single crystals. The observed temperature dependence of the Hall coefficient inn-typeCuInSe2single crystals is explained in assuming the existence of an impurity band. The values of the activation energy of the shallow donors, their concentration, and the concentration of the compensating acceptors were calculated. The values of the activation energy of the deep donors (80±10 meV and 110±10 meV) were estimated on the basis of the photoluminescence measurements. The concentration dependence of the activation energy of the shallow donor level and the variation of the Coulomb interaction as a function of the carrier density are determined. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364405

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Electron transport in quantum coherent networks (interacting quantum waveguide arrays) is investigated theoretically with use of the scattering-matrix method. The scattering matrix for the basic unit of networks, the cross junction with square or rounded corners, is derived using the mode-matching technique. The overall scattering matrix for the network is obtained by the composition of the scattering matrices associated with each unit of the network. For a uniform network, the transmission spectra are calculated in the single-mode regime and are found notably dependent on the junction geometry. Small reflection for the input terminal and uniform output for some output ports are obtained, which means that the quantum coherent network can be used as a distributing net for the electron waves. Cross junctions with rounded corners of large radii are found to play a negative role in the device application of quantum coherent networks. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364406

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We study the energy transfer rate for electrons in two parallel quantum wires due to interwire Coulomb interactions. The energy transfer rate between the wires (similar to the Coulomb drag effect in which momentum transfer rate is measured) is calculated as a function of temperature for several wire separation distances. We employ the full wave vector and frequency dependent random-phase approximation at finite temperature to describe the effective interwire Coulomb interaction. We find that the energy transfer rate at intermediate temperatures (i.e.,T∼0.3EF)is dominated by the collective modes (plasmons) of the system. Nonlinear effects on the energy transfer rate is also explored. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364407

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We present the study of the conductance of a quantum nanosystem containing afinite-sizeattractive impurity. A single finite-size attractive impurity introduces multiple quasi-bound states in the channel for a sufficiently strong attractive potential, and these states give rise to multiple resonant peaks before the first plateau in the conductance. These resonant peaks, arising from the resonant tunneling through the multiple quasi-bound levels, have a Lorentzian shape centered around the resonant energy and exhibit a dramatic variation in the linewidths with resonant energy. The strength of the attractive impurity in the constriction is shown to strongly affect the resonant energy and the mean lifetime of each tunneling peak. The temperature dependence of the resonant peaks of conductance is also discussed. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364408

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Tunneling transport assisted by the Coulomb interaction of Wannier–Mott exciton is investigated within the framework of the sequential tunneling formalism. The exciton-assisted tunneling (EAT) probability is derived from Bardeen’s transfer Hamiltonian. The EAT-induced current-voltage(I-V)characteristics are evaluated using a set of three-particle rate equations for double-barrier and triple-barrier tunneling structures. We found that the EAT results in additional current at low bias voltages with respect to the resonant tunneling (RT) current. Their offset in theI-Vspectra is associated to the exciton binding energy. The current intensity of the electron EAT is dependent on the quantum-well hole density as well as the exciton Bohr radius. CalculatedI-Vcharacteristics of electron tunneling via the heavy-hole excitonic states are presented and discussed for typical AlxGa1−xAs/GaAs nanostructures. In particular, the line shape of the EATI-Vspectra is shown to have a fingerprint distinguishable from that of the RT at low temperature. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364409

出版商:AIP    

年代:1997

数据来源: AIP