摘要:

A comprehensive time‐resolved electronic Raman scattering theory for nonequilibrium carrier excitations in semiconductors is presented. The following are simultaneously taken into account: (i) the effects of the ultrashort laser pulse for probing the excited carrier distribution function; (ii) the fact that the fluctuation‐dissipation theorem is not valid under conditions of nonequilibrium carrier distributions; (iii) the effects of quasiparticle life time via a finite collision time in the Raman scattering cross section; and (iv) the effect of the time‐dependent resonant enhancement factor due to the band structure. The single‐particle scattering spectra for spin‐density fluctuation contribution is found to be significantly broadened by an ultrashort laser pulse, but is substantially narrowed by the finite collision time. The effect of the time‐dependent resonant enhancement factor has been demonstrated to broaden the line shape of single‐particle scattering spectra for the spin‐density fluctuation contribution as the probe photon energy increases.

ISSN:0021-8979    

DOI:10.1063/1.352196

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The deposition of thin films of lithium niobate (LiNbO3) on silicon with rf magnetron sputtering has been investigated. A matrix of experiments was designed to determine the effect of several parameters on the resulting film quality. Under optimized conditions, oriented polycrystalline films of LiNbO3are produced that exhibit a columnar grain structure with the polar axis normal to the substrate surface. Deviations from sputtering parameters optimized for producing LiNbO3, have been shown to produce films of varying proportions of either LiNb3O8or Li3NbO4with LiNbO3. The stoichiometry, microstructure, and electrical properties of selected films have been investigated with Rutherford backscattering, diffractometry, transmission electron microscopy, and a variety of electrical measurement techniques.  

ISSN:0021-8979    

DOI:10.1063/1.352197

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The temperature at the interface between a thin polyimide film and a quartz substrate was monitored as a function of time during KrF (248 nm) laser‐induced heating and ablation using thin film NiSi thermistors. These experimental temperature measurements were coupled with heat flow simulations to obtain time‐resolved temperature profiles in the polyimide. Thermal properties of the polyimide were estimated by requiring that the simulations reproduce experimental temperature profiles. The peak surface temperature of the polyimide at the onset of ablation was subsequently estimated from these constrained simulations and a value of 1660±100 K was obtained for the observed ablation threshold fluence of 36 mJ/cm2.

ISSN:0021-8979    

DOI:10.1063/1.352198

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The reactivity of titanium has been studied in a chlorine containing environment with and without plasma. It has been found that chlorine (atoms or molecules) is not able to remove the native surface oxide unless drastic conditions are realized. Once the oxide is removed, titanium does not appreciably react with molecular chlorine without plasma unless fluorine is present on its surface. Fluorine has a catalytic effect and makes the titanium surface more reactive towards chlorine. Plasma superimposition does not change the reaction pattern, it acts only by increasing the substrate temperature and supplying energy by means of low energy ion bombardment.

ISSN:0021-8979    

DOI:10.1063/1.352199

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Fe films were deposited on (100) GaAs substrates by magnetron sputtering. Bombardment of the films during growth by energetic particles from the plasma had a significant impact on film properties including resistivity, crystallographic orientation, and stress. Preferred orientation of the (200) Fe planes parallel to the substrate surface was observed over a wide range of deposition conditions. The (200) Fe rocking curve widths of these films compare favorably with those of films deposited using molecular beam epitaxy, and the resistivities were comparable to that of bulk Fe. Positions directly in front of the cathode as well as low cathode power appear to favor the formation of (200) Fe texture, however, the rocking curve width and lattice parameter are relatively independent of substrate position and cathode power.

ISSN:0021-8979    

DOI:10.1063/1.352200

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We have developed a new selective‐growth process of InP on exactly (100)‐oriented Si substrate in a conventional low‐pressure metal‐organic vapor‐phase‐epitaxy system. In this process, the InP epitaxial layer was deposited on a photolithographically patterned InP‐buffer film without an additional dielectric mask during the growth. Under our experimental conditions, the InP growth has a very high selectivity and the InP epitaxial layer is antiphase‐domain free. Experimental results show that the undesirable sidewall‐growth interaction in conventional dielectric mask selective‐growth processes is effectively suppressed. Spatially resolved photoluminescence displayed very high optical quality of patterned InP layers compared to those grown on blanket substrates.

ISSN:0021-8979    

DOI:10.1063/1.352201

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Carrier injection and transport in single crystalline paraffin (n‐C36H74) have been investigated on the basis of time‐of‐flight data and dc‐photo injection experiments. The undoped, high‐quality molecular crystal under study represents an isoelectronic analog to polyethylene. Charge‐carrier mobilities in the range &mgr;≤0.1 cm2 V−1 s−1at room temperature have been recorded for both electrons and holes at moderate external electric fields. A clear correlation has been found between transport properties and the molecular structure. Regarding defect properties, significant differences have been observed for both types of carriers in the material. The presence of intrinsic deep traps is crucial to the transport properties of electrons and dominates the overall behavior of the material, but are virtually absent for injected holes. A decrease of the electron mobility with increasing external fields has been observed for electrons, while the opposite behavior has been found for injected holes. Photoinduced avalanching is largely due to a trap‐enhanced field effect, as reported in the literature, where the massive injection of holes from the counter electrode is initiated above a critical external field.

ISSN:0021-8979    

DOI:10.1063/1.352202

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Near‐field optical methods are used, together with the ability of an argon fluoride excimer laser to remove a wide variety of materials without the deposition of detectable heat, to produce structures with nanometer dimensionalities. In this new method of lithography, a hollow glass micropipette is used to guide the 193 nm light of the excimer laser to the surface to be ablated. With such micropipettes, patterns have been produced on photoresists with linewidths that are as small as 70 nm. By investigating the dimensionality of the structures drawn on the photoresist and on the substrate on which the photoresist was deposited, it appears that nonlinear characteristics of the ablation process may allow the near‐field dimensionalities to be maintained at distances that are relatively remote from the tip of the pipette aperture.

ISSN:0021-8979    

DOI:10.1063/1.352203

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

In this paper, some new types ofp‐Si(100) photocathodes withn‐K3Sb,n‐Na3Sb, andp‐Cs3Sb intermediate layers are fabricated. They are the (Si‐K3Sb‐Cs)‐O‐Cs and (Si‐Na3Sb‐Cs)‐O‐Cs negative electron affinity heterojunction photocathodes, and the (Si‐Cs3Sb‐Cs)‐O‐Cs positive electron affinity photocathode. For cathodes withn‐K3Sb,n‐Na3Sb, andp‐Cs3Sb intermediate layers, the maximum photoemission sensitivities attainable are, respectively, 1050, 950, and 150 &mgr;A/lm, and the measured minimum work functions of these cathodes are, respectively, 0.9, 1.0, and 0.85 eV. The photoemission stability of the Si photocathode with an alkali antimonide intermediate layer is better than that of the conventional Si‐O‐Cs and GaAs‐O‐Cs cathodes. The stability of the cathode is also related to the states of the cesium and oxygen during the activation process and the light illumination condition.

ISSN:0021-8979    

DOI:10.1063/1.352204

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We present the analysis of a new mechanism for tunneling real‐space transfer (TRST) in modulation‐doped structures. The conditions for TRST are determined by the quantum thermoelectric properties of the electron systems which results in instabilities. We predict high‐frequency oscillations limited only by the tunneling transfer time and thermalization between electron channels. Negative differential resistance and hysteresis are predicted in theI‐Vcharacteristics of the modulation‐doped structures; recent experiments corroborate the existence of the new mechanism.

ISSN:0021-8979    

DOI:10.1063/1.352205

出版商:AIP    

年代:1992

数据来源: AIP