摘要:

A new technique was developed to predict the unknown in-plane stress state and the magnitude of the stress components in (111) silicon wafers using micro-Raman spectroscopy. The approach is based on analyzing the combined signal from the initially degenerate peaks of theF2gmode in silicon as a function of the angle between the incident laser polarization and the polarization selected from the scattered beam using an analyzer. The peak position of the combined signal when plotted as a function of the angle was found to contain the information required to estimate the magnitude of the individual stress components in the plane-stress condition. The development of this technique is described in this paper for (111) silicon wafers. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366072

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have studied low temperature grown GaAs by electromodulation reflectance spectroscopy for growth temperatures between 200 and 320 °C. The reflectance spectra can be observed only when the concentration of the arsenic antisite defect is lower than3.4×1019 cm−3.The absence of the signal for a rich defect sample is related to the short carrier lifetime and surface depletion width. The transition energies ofE0andE1are found to increase with the decrease of the growth temperatures. The increase of the transition energies is attributed to lattice mismatch and deviation of the stoichiometry. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366073

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Room temperature photoreflectance (PR) measurements have been carried out on a series of pseudomorphic AlGaAs/InGaAs/AlGaAs high electron mobility transistor (HEMT) structures with different doping profiles grown by molecular beam epitaxy. The GaAs and AlGaAs features in the PR spectrum were studied and their origins were determined by a sequential etching method. It was found that the GaAs buffer layer and AlGaAs barrier layer dominate the GaAs and AlGaAs features in the PR spectrum, respectively. The electric fields for Franz-Keldish oscillations (FKOs) associated with theE0transition of both GaAs and AlGaAs are affected by the doping on both sides of the InGaAs channel, but are not directly related to the channel carrier concentration. The aluminum composition in theAlxGa1−xAslayers was determined and compared with the results of FKO energy and the critical-point energy methods. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366074

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have performed a detailed numerical reinvestigation of the photoluminescence peak position data given by G. Oelgart &etal; [J. Appl. Phys.74, 2742 (1993)] for the ground state heavy-and light-hole excitons in a high quality molecular beam epitaxially grownGaAs/Al0.3Ga0.7Asmultiple quantum well structure. Appropriate fittings of the measured temperature dependencies of exciton peak positions from 4.2 up to 340 K are shown to be provided by a novel analytical four-parameter representation developed recently by one of the authors for the gap shrinkage effect in semiconductors. The magnitude of the limiting(T→∞)shrinkage coefficient, &agr;=0.475 meV/K, and the associated average phonon temperature, &THgr;=222.4 K, have been determined. Characteristic qualitative differences and basic deficiencies of earlier three-parameter models are discussed and illustrated numerically by comparisons with various experimental observations from low to high temperatures. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366098

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Piezoelectric polymer gauge measurements were performed on the rear surface of plane copper and aluminum foils irradiated by infrared laser pulses of 1.5 ns duration, with intensities up to about 7 T W/cm2, using recently developed transducers made of a vinylidene-fluoride and trifluoroethylene copolymer. Some gauge records have indicated that incipient spall damage occurs in the samples subjected to very intense shocks. This was confirmed by post-test examination of the targets. The experiments were simulated using two computer codes: one describes laser–matter interaction and provides input to the second code that handles wave propagation. A spall model for ductile metals is integrated in the wave code. The ability of those computer models to predict the experimental results was thereby tested. Overall agreement was obtained between the gauge measurements and calculations, except for some discrepancies that are discussed. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366075

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A treatment that lowers the threshold field for field emission and increases the emission site density from a nominallyn-type diamondlike carbon film is described. The film was deposited using an rf plasma of methane and nitrogen gases. The treatment involved deposition of cesium followed by a low temperature anneal. Field emission measurements were used to characterize the threshold field and emission site density before and after cesium treatment. Ultraviolet photoemission was used to study the effect of cesium on the work function. Dramatic improvements to field emission by cesiation cannot be generalized to all diamondlike samples, as similar treatment of a type IIb single-crystal (p-type) diamond did not produce as pronounced an improvement in turn-on field or emission site density. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366076

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The work function, field emission property (turn-on field), and Auger electron spectroscopy of cesiated carbon films on Si (100) have been investigated for codeposition of Cs neutral andC−ion beams at different energies (25–150 eV). The higher energy (150 eV)C−ion beam produces the lower work function surface (1.1 eV) as well assp3rich carbon film. The work function depends both on cesium concentration as well as on thesp3fraction in the carbon films. The turn-on field of the film can be as low as 7 V/&mgr;m. The thermal stability of the low work function surface has been investigated for postdeposition annealing up to 600 °C. An extremely high stability cold cathode has been made by forming cesium carbide. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366077

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Molybdenum disulfide(MoS2)has been used in industrial applications as a dry lubricant. Although this material initially improves anti-wear properties, as surfaces move against each other the lubricating particles tend to spread out from the asperity points. To reduce this spread of lubricant,MoS2platelets were made magnetic by replacing the unsaturated or loosely bonded sulfur atoms (located mainly on the edges of the platelets) with magnetic elements such as Fe, Ni, or Co particles. Under appropriate experimental conditions these elements form stable bonds with the partially free Mo atoms of the edges and are protected from oxidation in air by the basal planes of the overlapping neighboring layers. When compared to the friction coefficient of pureMoS2,the incorporation of magnetic Fe particles for example, increases the friction depending on the Fe/Mo ratio, but the overall result is in an improved lubricant with unique magnetic properties when the Fe/Mo ratio is properly optimized. In this application at least one of the surfaces must be ferromagnetic to hold the lubricant in place. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366078

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Raman scattering has been used to study the variation of surface barriers in GaAs due to sulfur passivation in solutions of ammonium sulfide[(NH4)2S]in different alcohols (ethanol, isopropanol, andtert-butanol). It has been found that the surface barrier height and the depletion layer width decrease considerably with the decrease of the dielectric constant of the passivating solution. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366079

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A study on the effect of substrate conditions was performed for the plasma beam deposition of amorphous hydrogenated carbon (a-C:H) from an expanding thermal argon/acetylene plasma on glass and crystalline silicon. A new substrate holder was designed, which allows the control of the substrate temperature independent of the plasma settings with an accuracy of 2 K. This is obtained via a combination of a good control of the holder’s yoke temperature and the injection of helium gas between thermally ill connected parts of the substrate holder system. It is demonstrated that the substrate temperature influences both thea-C:H material quality and the deposition rate. The deposition rate and substrate temperature are presented as the two parameters which determine the material quality.In situstudies prove that the deposition process is constant in time and that thermally activated etching processes are unlikely to contribute significantly during deposition. Preliminary experiments with an additional substrate bias reveal that an energetic ion bombardment of the growing film surface does not influence the deposition process. A tentative deposition model is proposed based on the creation and destruction of active sites, which depend on the particle fluxes towards the substrate and the substrate temperature. This model allows the qualitative explanation of the observed deposition results. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366080

出版商:AIP    

年代:1997

数据来源: AIP