摘要:

Electronic structures of the 8-hydroxyquinoline aluminum(Alq3)/LiF/AlandAlq3/Alinterfaces were measured by ultraviolet photoelectron spectroscopy. Shifts of the highest occupied molecular orbital level and the vacuum level of theAlq3layer due to insertion of a thin LiF layer were observed. This result indicates that the thin LiF layer at theAlq3/Alinterface reduces barrier height for electron injection from the Al toAlq3.We, therefore, conclude that lowering of the driving voltage in an organic electroluminescent device with a thin LiF layer is attributable to the reduction of the barrier height. ©1998 American Institute of Physics. 

ISSN:0003-6951    

DOI:10.1063/1.122583

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Arrays of a few nanometer-size clusters have been realized using a porous silicon (PS) matrix by filling its pores with CdSe. The photoluminescence (PL) peak from the embedded area of the PS samples with different luminescence stabilizes at 1.79 eV. This has been interpreted as due to emission from the CdSe clusters with an average size of about 3–5 nm. Likewise, the PL and Raman scattering spectra of the pure PS area of the samples have been compared with those obtained from the embedded areas. PL spectra were examined as a function of laser irradiation. Finally, to analyze the possibility of the formation of metal/porous semiconductor contacts, cross-section structures have been observed by scanning electron microscopy in the electron-beam-induced current mode. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122584

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The reverse-bias current–voltage characteristics of metal–oxide–silicon tunnel structures containing nonuniform ultrathin oxide layers are analyzed using a numerical three-dimensional quantum mechanical scattering calculation. We find that, in general, roughness at theSi/SiO2interface renders the oxide layer more permeable, but does not qualitatively alterI–Vcharacteristics. In the direct tunneling regime interface roughness induces lateral localization of wave functions which leads to preferential current paths, and is characterized by current densities which increase with island size. In the Fowler–Nordheim tunneling regime, however, interface roughness affects transport primarily through scattering, which increases with island size, and results in current densities which decrease with island size. We have also shown that appropriate one-dimensional models may be used to estimate the effect of interface roughness in limiting cases. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122585

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The technique of transferring patterned ion-cut layers from one Si wafer to another was demonstrated. The starting silicon wafer was masked with checkerboard and line patterns with a 3 &mgr;m thick polymethylmethacrylate/photoresist and was implanted with5×1016 H+ ions/cm2at 150 keV. After stripping off the mask, the wafer was bonded to an oxide-coated receptor wafer through low-temperature direct wafer bonding. Heat treatment of this bonded pair showed that the hydrogen-induced silicon surface layer cleavage (ion cut) could propagate throughout about16 &mgr;m×16 &mgr;mof nonimplanted material with implanted regions only 4 &mgr;m wide. Mask width, spacing, and implantation profiles through the mask shape were shown to have effects on the internal microfracturing mechanisms. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122586

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A simulation of current flow for an InGaN/GaN/AlGaN multiquantum well (MQW) laser showed that generation of the optical gain is inhomogeneous across the MQW due to inhomogeneous carrier injection. Laser diodes with three and five wells in MQW were compared to experimentally investigate inhomogeneous carrier injection. We found that external quantum efficiency was significantly improved by a reduction in the number of wells from five to three. The result was explained quantitatively by the fact that the five-well laser had a larger internal loss and a poorer internal quantum efficiency due to the inhomogeneous carrier injection. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122587

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The energies of photo- and electroluminescence transitions inInxGa1−xNquantum wells exhibit a characteristic “blueshift” with increasing pumping power. This effect has been attributed either to band-tail filling, or to screening of piezoelectric fields. We have studied the pressure and temperature behavior of radiative recombination inInxGa1−xN/GaNquantum wells withx=0.06,0.10, and 0.15. We find that, although the recombination has primarily a band-to-band character, the excitation-power induced blueshift can be attributed uniquely to piezoelectric screening. Calculations of the piezoelectric field in pseudomorphicInxGa1−xNlayers agree very well with the observed Stokes redshift of the photoluminescence. The observed pressure coefficients of the photoluminescence (25–37 meV/GPa) are surprisingly low, and, so far, their magnitude can only be partially explained. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122588

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Highly (100) orientedPb(Zr0.53Ti0.47)O3(PZT) films were prepared on Si substrates with ultrathinSiO2buffer layer by pulsed laser deposition. Hysteresis measurements show that saturation polarization, remnant polarization and coercive field of the films reach26 &mgr;C/cm2,10 &mgr;C/cm2and 70 kV/cm, respectively. The thickness ofSiO2buffer layer is found to play a significant role on phase purity and orientation of PZT as well as the prevention of interdiffusion. It is also found that the grain size and the interdiffusion between PZT and Si are the key factors for the ferroelectric properties of the films, which are discussed together with the synthesis condition in detail. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122589

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We present a mechanism for enhancing the electron impact ionization rate based on the strain-induced polarization fields in a strained multiquantum-well system. To illustrate the concept, the electron ionization rate is calculated for a strained GaN andAl0.3Ga0.7Nmultiquantum-well device. The presence of the polarization fields within theAl0.3Ga0.7Nlayers provides an additional mechanism for carrier heating to the conduction band edge discontinuity of earlier simple multiquantum-well avalanche photodiode designs. It is found that the ionization rate is substantially enhanced over both its bulk GaN value and that for an unstrained multiquantum-well structure. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122590

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The electrostatic interaction between two capacitively coupled, series-connected metal double dots is studied at low temperatures. Experiment shows that when the Coulomb blockade is lifted, by applying appropriate gate biases, in both double dots simultaneously, the conductance through each double dot becomes significantly lower than when only one double dot is conducting a current. The conductance lowering seen in interacting double dots is compared to that caused by an external ac modulation applied to the double-dot gates. The results suggest that the conductance lowering in each double dot is caused by a single-electron tunneling in the other double dot. Here, each double dot responds to the instantaneous, rather than average, potentials on the other double dot. This leads to correlated electron motion within the system, where the position of single electron in one double dot controls the tunneling rate through the other double dot. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122591

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Growth of less than 2 monolayers Ge on a submonolayer amount of predeposited C on Si results in the formation of very small Ge quantum islands. In a photoluminescence study, we compare these C-induced Ge (CGe) dots with carefully chosen reference structures incorporating the same total amount of C and Ge but with different deposition orders and with varied C distribution below the Ge islands. Our investigations imply that the special combination of pregrown low surface mobility C and post-grown high surface mobility Ge constitutes a distinct microstructure within the SiGeC material system, causing dot formation at a very early stage and showing particularly intense photoluminescence signal. Moreover, structures combining CGe dots withSi1−yCyquantum wells are well explained by the model of spatially indirect type-II recombination within the CGe islands. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122592

出版商:AIP    

年代:1998

数据来源: AIP