摘要:

Real timein situlaser reflectometry was used to investigate changes in surface morphology observed during the nucleation of oriented diamond on Ni in a hot filament chemical vapor deposition reactor. Characteristic features observed in the intensities of reflected and scattered light were interpreted by comparison with scanning electron micrographs of the diamond seeded substrates quenched at sequential stages of the process. Based on this analysis, a process was developed in which the scattered light signal was used as a steering parameter. Using this process, oriented nucleation and growth of diamond on Ni can be repeatedly achieved. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118756

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

CdZnMgTe/CdZnTe superlattices were doped with nitrogen from a dc plasma source during their growth by molecular beam epitaxy. The samples were investigated by photoluminescence, double crystal x-ray diffraction, and secondary ion mass spectroscopy. A very strong intermixing across the quantum well interfaces was observed, producing a homogeneous alloy. The mixing is attributed to cation diffusion assisted by lattice defects generated by the simultaneous presence of Mg and N atoms. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118757

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A three-dimensional, quasi-simple-cubic, air-hole photonic crystal was fabricated in silicon. The lattice constant is 530&mgr;m and the air-filling factor is 0.84, which corresponds to the simplest structure proposed showing a direct photonic band gap. The observed transmittance in the&Ggr;−Zdirection with five periods along each direction agrees very well with the calculated transmittance. Theoretical calculations indicate that a similar lattice with 8×8×8 periods, which can be fabricated by state-of-the-art techniques, should suffice to observe band gap effects. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118758

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We investigated the optical properties of the saturable absorber3,3′-diethyloxadicarbocyanine iodide incorporated in a matrix of silica-gel glass by the sol-gel technique. Absorption, emission, and fluorescence lifetime were studied as functions of the densification procedures. With respect to the liquid solutions, we observed a strong quenching of the P-isomer luminescence and an increase of the N-isomer fluorescence lifetime. These effects are ascribed to a restriction on the molecular photoisomerization rearrangement caused by the rigidity of the silica cage. Moreover, entrapping reduces intermolecular concentration effects. Finally, different from other glass-embedded dyes, both the absorption and the emission are blue-shifted by about 20 nm. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118759

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Silicon on sapphire wafer pairs are formed by direct wafer bonding of 3-in. silicon and sapphire wafers. Subsequent annealing commonly used to increase the bond energy imposes serious thermomechanical strain. The corresponding bending, recordedin situas a function of temperature, reveals relaxations by de- and rebonding until the silicon wafer cracks into small fragments that mostly remain bonded. After further annealing up to 800 °C and cooling to room temperature, a strong curvature of the fragments indicates a frozen-in high temperature bond state with elastic energies around100 J/m2.Cross-sectional transmission electron microscopy of the interface reveals an amorphous intermediate layer the thickness of which considerably increases with increasing the oxygen partial pressure during annealing. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118760

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have achieved 14.6&percent; initial and 13.0&percent; stable conversion efficiencies using an amorphous silicon-based alloy in a spectrum-splitting, triple-junction structure. These efficiencies have been confirmed independently by the National Renewable Energy Laboratory. Key factors leading to this major advance include improvements made in the low band-gap amorphous silicon–germanium alloy cell, thepntunnel junction between the component cells, and the top conducting oxide. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118761

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report on the band-edge stimulated emission in InGaN–GaN multiple quantum well light-emitting diodes with varying widths and barrier thicknesses of the quantum wells. In these devices, we observe that the stimulated emission peak wavelength shifts to shorter values with decreasing well thickness. From the comparison of the results of the quantum mechanical calculations of the subbands energies with the measured data, we estimate the effective conduction- and valence-band discontinuities at theGaN–In0.13Ga0.87Nheterointerface to be approximately 130–155 and 245–220 meV, respectively. We also discuss the effect of stress on the estimated values of band discontinuities. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118762

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We propose an approach to control the position and the size of semiconductor islands formed by the Stranski–Krastanov growth mode. The method is to perform overgrowth on a cleaved edge of strained multiple quantum wells (SMQW), which give periodically modulated strain to the epitaxial layer. Proper choice of the growth conditions results in the formation of islands selectively on one of the constituents of the SMQW. The usefulness of this method was demonstrated by overgrowing Ge islands on the cleaved edges ofSi0.8Ge0.2/SiSMQW. The Ge islands were selectively formed on the Si layer at 500 °C and on theSi0.8Ge0.2layer at 600 °C. The former reflects the smaller critical thickness of Ge on Si, and the latter is driven by the minimization of strain energy owing to the smaller lattice mismatch between Ge andSi0.8Ge0.2.©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118763

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

DiluteGaAs1−xNxalloys(x<0.3&percent;)were grown by metalorganic vapor phase epitaxy to investigate their photoluminescence and photoluminescence excitation characteristics. Photoluminescence excitation spectra show clear excitonic absorption peaks at low temperatures and their peak energy drastically decreases with increasing nitrogen concentration due to the band-gap bowing in the GaAsN system. This result indicates that the band-gap bowing starts at a nitrogen concentration as low as1018 cm−3,and its bowing parameter is−22 eV.According to this band-gap bowing, the GaAsN alloys show two photoluminescence lines whose peak energy decreases with increasing nitrogen concentration. Their dependence on the nitrogen concentration suggests that these lines correspond to excitonic and carbon-related transitions in the GaAsN alloy. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118764

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Carrier profiles of multiple quantum wells are studied using self-consistent simulations. The free carrier density of the well is found to be distributed nonuniformly and symmetrically, although the doping level in barriers is uniform. The calculated apparent carrier density obtainable from the capacitance-voltage profile is found to be distributed asymmetrically. Simulation results show that, even if electrons are confined in quantum wells, the apparent electron distribution can be flattened if barrier thickness or doping level in barriers are reduced to such an extent that the Debye length is comparable to the barrier thickness. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118765

出版商:AIP    

年代:1997

数据来源: AIP