摘要:

The thermal and electrical conductivity of monolithic carbon aerogels was investigated at room temperature. Results showed both the solid thermal conductivity and the electrical conductivity scale with the density in the range between 60 and 650 kg m−3. The scaling exponents for the two conductivities have identical values of 1.5. For a density of 82 kg m−3a thermal conductivity of 0.029 W m−1 K−1in air and 0.018 W m−1 K−1after evacuation was found.

ISSN:0021-8979    

DOI:10.1063/1.353367

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The thickness uniformity of photoresist films deposited by spin coating critically influences the resolution of photolithography. This thickness uniformity depends on uniform evaporation from the film during drying. Simple scaling arguments demonstrate that, if the mass transfer coefficient at the surface of the wafer does not vary with radial position, then the dry coated resist film thickness will be independent of radial position. A model is presented for the compressible, laminar, steady‐state, axisymmetric air flow in a spin coating apparatus for 6‐in.‐diam wafers. Flow fields computed by a finite‐element–Newton method are used to evaluate the radial profile of the mass transfer coefficient at the surface of the rotating wafer, and to calculate the trajectories of particles that are generated as photoresist is flung from the edge of the spinning wafer. At a spin speed of 2000 revolutions/min and exhaust flow rate of 100l/min through the coater, the calculations predict that the mass transfer coefficient should be independent of radius. Comparison with film contours measured from experiments at these conditions indicates radial nonuniformities in the film thickness and suggests the importance of hydrodynamic instabilities in the gas on the uniformity of the coating.    

ISSN:0021-8979    

DOI:10.1063/1.353368

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The general equation for the effective region of doubly curved diffractors for radiation from a point source that was derived by Wittry and Sun [J. Appl. Phys.71, 1 (1992)] has been extended to include the effect of source misalignment. Intensity profiles across an x‐ray topograph recorded on a photographic film located between the diffractor and the focus have been calculated for the Johann case including misalignment effects. Topographs and intensity profiles obtained using TiK&agr; radiation generated by a focused electron beam have confirmed the theoretical calculations and have provided values of the peak reflectivity and rocking‐curve width for graphite, mica, and silicon diffractors of Johann geometry with a radius of curvature of ∼100 mm.

ISSN:0021-8979    

DOI:10.1063/1.353369

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

N‐type andp‐type delta‐doped GaAs grown by molecular beam epitaxy with rather significantly high doses of Si and Be have been investigated by transmission electron microscopy (TEM). The amount of doses ranged from half a monolayer to two monolayers. The microscopic structures of the delta‐doped regions and the adjacent epilayers were directly observed by TEM. The effect of impurity spreading on the heterointerfaces and superlattices was also studied. Si atoms present in Si delta‐doped samples were confined to within a few atomic layers. The Be atoms present in Be delta‐doped samples, however, spread over a quite wide region and caused rough heterointerfaces and wavy superlattices to form. Spreading of Be was attributed to segregation and diffusion which occurred during growth. Stacking faults were found in the delta‐doped samples when they were grown at low temperatures. They could be attributed to local strain caused by heavy doping.

ISSN:0021-8979    

DOI:10.1063/1.353370

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

High‐temperature annealing of semi‐insulating GaAs has been studied. Thermal conversion induced by annealing at 1060–1200 °C can be explained by the causes of both the reduction of EL2 concentration and the generation of deep acceptors during high‐temperature annealing. Both of them can be rationalized by the supposition that the antisite defect, AsGa, breaks into AsIandVGa, and the latter is a deep acceptor.

ISSN:0021-8979    

DOI:10.1063/1.353371

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The onset of misfit dislocation generation is investigated and the critical thickness is determined by transmission electron microscopy using the epitaxial lift‐off technique for InGaAs/GaAs single heterostructures and single quantum wells. The observed geometries of the dislocations in both cases are in good agreement with the predicted models [J. Appl. Phys.41, 3800 (1970) and J. Cryst. Growth27, 118 (1974)]. However, each dislocation undergoes the predicted elongation mechanism [J. Appl. Phys.41, 3800 (1970)] at different strained‐layer thicknesses. A comparison of the predicted and the experimental critical thicknesses is given.

ISSN:0021-8979    

DOI:10.1063/1.353372

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The dynamics of carrier recombination in proton bombarded high‐quality single crystal thin films of InAs grown by molecular beam epitaxy on transparent GaAs substrates are studied using the picosecond pump‐probe technique in the photon energy range 335–483 meV. The effects of extrinsic recombination at the InAs/GaAs interface and of point defects introduced by proton damaging are separated by studying samples ranging from 3.3 to 0.27 &mgr;m in thickness and with proton doses in the range 1011–1015cm−2. The data indicate an interfacial recombination velocity of 2.7×104cm s−1and a defect capture time of 160 ps, and in the regime studied mobility limitations are found to have a negligible effect on the recombination dynamics.

ISSN:0021-8979    

DOI:10.1063/1.353373

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We have used secondary ion mass spectrometry, local vibrational mode infrared absorption, and electrical characterization to study the incorporation of Si delta‐doped planes in GaAs grown by molecular beam epitaxy at 400 °C, in the concentration range 0.01–0.5 monolayers. A correspondence is observed between the density of SiGadonors, the free electron concentration and the total Si coverage, up to a coverage of ∼1013cm−2; however, above this value, the electron density falls, while [SiGa] remains constant up to a coverage of ∼1014cm−2, and then falls below the detection limit at 0.5 monolayer coverage. These effects have been interpreted in terms of a model which takes account of Si migration and aggregation on the delta‐doped plane during deposition.  

ISSN:0021-8979    

DOI:10.1063/1.353374

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Deep level transient spectroscopy has been employed to determine the defect energy levels, capture cross sections, and trap densities in Si‐doped vapor phase epitaxy GaAs both before and after irradiation by 1 MeV electrons at room temperature for electron fluence ranging from 1.1×1014to 5.0×1015e cm−2. The results indicate that the irradiated samples have an electron trap atEc‐0.334 eV(EL6) in addition to the two electron traps atEc‐0.815 eV(EL2) andEc‐0.420 eV(EL3) which are present in the nonirradiated sample. The density of the EL6 trap increases monotonically with irradiation fluence from 6.7×1013to 24.4×1013cm−3as electron fluence is increased from 1.1×1014to 3.1×1014e cm−2. In contrast, both the EL2 and EL3 trap densities were found to be only moderately affected by electron irradiation with trap densities slightly greater than the nonirradiated sample. These results, along with the fact that the EL6 trap was not observed in the nonirradiated sample, strongly suggest that this trap is created by the electron irradiation. In addition to creating the EL6 trap, electron irradiation results in a nonexponential transient for the EL2 deep level atEc‐0.815 eV which can be resolved into the sum of two exponential transients arising from two closely spaced deep levels atEc‐0.815 eV andEc‐0.843 eV.

ISSN:0021-8979    

DOI:10.1063/1.353375

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Annealing of defects introduced by neutron transmutation doping of float‐zone silicon has been investigated by positron lifetime spectroscopy and Doppler‐broadening measurements. It is shown that the main defects anneal out at about 150 and 500 °C. During annealing, the formation of bigger defect complexes can be seen.

ISSN:0021-8979    

DOI:10.1063/1.353346

出版商:AIP    

年代:1993

数据来源: AIP