摘要:

Using picosecond time‐resolved four‐wave mixing we have investigated the turn‐on and turn‐off mechanisms in a photorefractive multiple quantum well spatial light modulator with Stark geometry. We show that holes contribute to the turn‐on time as a slower rise (∼300 ps) of the diffraction efficiency. Furthermore, the diffraction grating is dominated by either electrons or holes, depending on the applied voltage polarity relative to the diffraction of illumination. The grating decays in 0.4–8.5 ns, depending on the grating spacing. We show that the decay is due to lateral transport of carriers at the multiple quantum well/dielectric interfaces, where low‐temperature grown layers can increase the diffraction efficiency and device resolution. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118045

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

In this letter, we report fabrication of pulsed‐shaped phosphorus doping profiles in Si, using a XeCl (&lgr;=380 nm) pulsed excimer laser. Phosphorus buried layers as shallow as 750 A˚ and as deep as 3200 A˚, with peak full width at half‐maximums as narrow as 100 A˚ and as broad as 900 A˚ are demonstrated. It is also demonstrated that the sample is free of point defects and full electrical activation is achieved by using a rapid thermal anneal at 800 °C for 30 s after the laser processing. This process, we demonstrate, afford simplicity, versatility, and independent control over the depth, width, and height of the phosphorus buried layer. Phosphorus buried layers have potential application in the fabrication of metal–oxide–semiconductor field effect transistors and BiPOLAR electronic devices. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118046

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Induced loss spectra in four Al‐coated large‐core optical fibers are measured in the range 380–1000 nm during and after60Co &ggr; irradiation. These fibers had F‐doped‐silica claddings and synthetic silica core materials produced by different technologies. Measurements were carried out independently in Washington and Moscow using differing techniques but yielding very similar results. The highest radiation resistance is exhibited by two fibers with extremely low OH and Cl contents in their cores, one with a core material containing 0.5 mass % of fluorine, fabricated specially for this study, and one based on KS‐4V silica, an original technology developed in Russia. The latter fiber demonstrates a rather flat induced loss spectrum in the visible region at a level of 2–2.5 dB/m for &ggr;‐ray doses of ∼10 MGy(Si). ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118047

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The emission profiles of laser diodes working at 780 nm and 1300 nm are studied by near‐field scanning optical microscopy. As the near‐field probe is scanned across the laser mirror facet, the laser emission induces a transient expansion of the probe tip which is monitored using shear force microscopy. The thermal expansion of the tips reaches absolute values of up to 100 nm per mW of emitted laser power. A fully metallized near‐field probe tip is shown to serve as a local bolometer with a spatial resolution of better than 1 &mgr;m. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118048

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Demixing in an atmospheric‐pressure free‐burning welding arc was investigated using a two‐dimensional numerical model. Simulations of arcs in argon–nitrogen and argon–helium mixtures demonstrated that demixing can have a major influence on the composition of the arc in both the central and edge regions. Convection suppressed the change in composition in the central 0.5 mm of the argon–nitrogen arc only. Furthermore, demixing was found to have only a relatively minor effect on temperature and axial velocity, but it significantly altered thermal transport in the argon–nitrogen mixture. It is concluded that demixing can be important in both chemical and thermal applications of mixed‐gas arcs. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118049

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Diffusion coefficientsDwere measured in nickel under 600 keV Kr++ion irradiation at 77 K and at 800 K using multilayer specimens. At 77 K the diffusion coefficient closely follows the calculated depth dependence of the displacement rateKindicating that athermal atomic mixing with an efficiency ofDmix/K=0.6 nm 2/dpa is responsible for the observed transport at this temperature. At 800 K considerable diffusion is observed far from the irradiated surface in a region where the displacement rate is zero. The exponential slope of the diffusion coefficient measured here indicates annihilation of mobile defects in a microstructure with a sink strength of 7×1013m−2. An upper limit of the fraction of freely migrating defects of 0.05 is estimated. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118050

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

X‐ray powder diffraction and high‐resolution transmission electron microscopy (HRTEM) have found coexistence of three structures of GaN: wurtzite, zinc blende, and rocksalt in the samples prepared through benzene thermal process at 280–300 °C under pressure about 5 MPa. Previously, GaN with rocksalt structure only appeared at high pressure more than 37 GPa. HRTEM showed that there was a transitional region between the two cubic phases of GaN with zinc blende and rocksalt. X‐ray photoelectron spectra analysis of the sample gave the average composition of Ga0.95N. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118051

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The polarity of the lattice of bulk single GaN crystals and the polarity of homoepitaxial and heteroepitaxial‐on‐sapphire GaN thin films has been studied using convergent beam electron diffraction. Diffraction patterns obtained at 200 kV for the ⟨1–100⟩ projection of GaN were matched with calculated patterns. The lattice orientations of two commonly observed bulk single‐crystal facets were identified. It is shown that the smooth facets in single crystals correspond to the (0001), Ga‐terminated, lattice planes, whereas the rough facets correspond to the (0001¯), N‐terminated, planes. It is also shown that metalorganic chemical vapor deposition epitaxy retains the polarity of the substrate, i.e., no inversion boundaries were observed. Heteroepitaxy on sapphire is shown to grow in the (0001), Ga‐terminated orientation. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118052

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

UV irradiation effects on Al chemical vapor deposition on titanium nitride (TiN) was investigated by using dimethylaluminum hydride at 150 °C. Al films grew thermally at a rate of 6.3 nm/min, while the UV light generated by a deuterium lamp reduced the rate to 5.2 nm/min. When TiN surfaces were oxidized, Al films started to grow only under UV irradiation. Using x‐ray photoelectron spectroscopy (XPS), we showed that the adsorbates formed on the oxidized surfaces could be dissociated only when the UV light was irradiated. The XPS results also suggested involvement of photoinduced desorption in reducing the growth rate. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118053

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Long‐wavelength InTlSb photodetectors operating at room temperature are reported. The photo‐ detectors were grown on (100) semi‐insulating GaAs substrates by low‐pressure metalorganic chemical vapor deposition. Photoresponse of InTlSb photodetectors is observed up to 11 &mgr;m at room temperature. The maximum responsivity of an In0.96Tl0.04Sb photodetector is about 6.64 V/W at 77 K, corresponding to a detectivity of about 7.64×108cm Hz1/2/W. The carrier lifetime in InTlSb photodetectors derived from the stationary photoconductivity is 10–50 ns at 77 K. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118054

出版商:AIP    

年代:1996

数据来源: AIP