摘要:

The kinetics of the C49–C54 phase transformation inTiSi2narrow strips for width in the 0.5–1.3 &mgr;m range was investigated by sheet resistance measurements. The experimental data follow the Johnson–Mehl–Avrami equation for the fraction of the transformed material, with an exponent equal to 1 for all of the analyzed linewidths. Nucleation sites saturation occurs and the growth is one-dimensional along the length of the strip. The characteristic time, as obtained by the fit, increases as1/W,Wbeing the width of the strip, and a nucleation density of about 0.05 sites/&mgr;m2has been obtained. The distribution of the characteristic times around the average value increases with decreasing the linewidth. The amplitude of the dispersion is in quantitative agreement with the statistical fluctuation of the number of nucleation sites. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122918

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We have demonstrated the existence of longitudinal- and transverse-like optical modes of Si–N bond in vibrational absorption spectrum of hydrogenated amorphous silicon nitride thin films. One of the longitudinal-like optical resonances coincides with the transverse-like mode of Si–O bond, and the other closely neighbors the bending mode of N–H bond. We have also shown that the conventionally assigned asymmetric stretching mode of Si–N bond is merely a transverse-like mode of the bond. The microstructures of both longitudinal- and transverse-like modes can well be apprehended by ap-polarized beam at an oblique incidence light, especially at Brewster angle incidence. The spectrum distortion induced by interference fringes can be eliminated at this condition. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122919

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The structural properties of a series of thin (0.2–0.6 &mgr;m) GaN epilayers directly grown on 6H–SiC(0001) by plasma-assisted molecular beam epitaxy are studied. X-ray reciprocal space maps of the GaN(0002) reflection reveal negligible inhomogeneous strain within the layer but a comparatively large orientational spread of the GaNcaxis. X-ray rocking curve measurements show, however, that this mosaicity steadily decreases with film thickness. In fact, the density of threading defects detected by transmission electron microscopy is found to decrease drastically with the distance away from the GaN/SiC interface, finally reaching a value of less than5×109&hthinsp;cm−2at a layer thickness of 0.5 &mgr;m. The formation mechanisms of the threading dislocations in the GaN films are discussed in consideration of the specific GaN/SiC interface structure. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122920

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We demonstrate theoretically that an intense half-cycle terahertz pulse can be used conjunctively with a quantum-well optical amplifier to form the basis of an efficient ultrahigh-speed optical switch. Our procedure implies terahertz and subterahertz switching and recovery rates, respectively. Constraints and practicalities are discussed. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122921

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The implantation of Si ions into undoped high-resistivity GaN films is of interest for the realization of high-performance digital and monolithic microwave integrated circuits. We report the effect of postimplant annealing conditions on the electrical, optical, and surface morphology of Si ion-implanted GaN films. We demonstrate high activation efficiencies for low-dose Si implants into unintentionally doped GaN/sapphire heteroepitaxial films. The Si ions were implanted through an epitaxial AlN cap layer at 100 keV and a dose∼5×1014 cm−2.Samples were subsequently annealed in an open-tube furnace for various times and temperatures. The postanneal electrical activation is correlated with the surface morphology of the film after annealing. The samples annealed at1150 °CinN2for 5 min. exhibited a smooth surface morphology and a sheet electron concentrationns∼6.8×1013 cm−2.©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122922

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The4d-transition metal ruthenium presents a new dopant to fabricate thermally stable semi-insulating InP layers for both electron and hole injection. The layers are grown by low-pressure metalorganic chemical vapor deposition using tertiarybutylphosphine and trimethylindium as source materials for InP growth. Usingbis(&eegr;5-2,4-dimethyl-pentadienyl)ruthenium(II)as precursor Ru doping concentrations of the order of4×1018 cm−3are achieved, determined by means of secondary ion mass spectroscopy. The Ru diffusion coefficient in InP is determined toDRu(800 °C)⩽1×10−15 cm2/swhich is four orders of magnitude smaller than for Fe. Resistivities obtained under electron and hole injection are above6×107 &OHgr; cmand5×108 &OHgr; cm,respectively. In deep level transient spectroscopy measurements under electron emission and hole emission, one deep level each with concentrations around1016 cm−3,is observed. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122898

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The first subband energy at the valence band of self-assembled silicon quantum dots grown by low-pressure chemical vapor deposition on ultrathinSiO2/Sisubstrates has been measured as an energy shift at the top of the valence band density of states by using high-resolution x-ray photoelectron spectroscopy. The systematic shift of the valence band maximum towards higher binding energy with decreasing the dot size is shown to be consistent with theoretical prediction. The charging effects of the silicon dots and theSiO2layer by photoelectron emission during the measurements have been taken into account in determining the valence-band-edge energy. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122923

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We present an experimental approach to determine the intrinsic field-effect mobility in an organic single crystal as a function of the in-plane crystal-axis direction. Using a multiterminal geometry the experiment also excludes the effects of the contact resistances on the transport properties. We have applied the method to quaterthiophene thin films. At gate voltages above the threshold voltage, the channel conductance varies linearly with the applied gate voltage. The resulting charge carrier mobility is1.2×10−3&hthinsp;cm2/V&hthinsp;s.This value is constant over a period of weeks of continuous operation and does not vary from sample to sample, in contrast to the typically observed lower mobilities of polycrystalline quaterthiophene thin-film transistor devices. These results emphasize the need for well-characterized model systems to study the intrinsic transport properties of organic materials. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122924

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Pulsed operation of in-plane laser diodes with InGaN multiple quantum well active regions was achieved. For uncoated chemically assisted ion beam etched facets, we obtained threshold current densities as low as 10.6 kA/cm2. The external differential quantum efficiency dependence on bar length was used to determine the internal optical loss and internal quantum efficiency of these devices and to calculate the modal gain in the device as a function of the terminal current density. Values of facet reflection were determined by a self-consistent analysis. We have measured 90 cm−1of modal gain and estimate material gain exceeding 900 cm−1, at 20 kA/cm2. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122925

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Andreev-reflection dominated transport is demonstrated inAl/n-In0.38Ga0.62Assuperconductor–semiconductor junctions grown by molecular beam epitaxy on GaAs(001). High junction transparency was achieved in low-doped devices by exploiting Si interface bilayers to suppress the native Schottky barrier. It is argued that this technique is ideally suited for the fabrication of ballistic transport hybrid microstructures. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122926

出版商:AIP    

年代:1998

数据来源: AIP