摘要:

A review is presented of the recent advances in the study of oxygen precipitation and of the main properties of oxide precipitates in silicon. After a general overview of the system ‘‘oxygen in silicon,’’ the thermodynamics and the kinetics of the precipitate formation are treated in detail, with major emphasis on the phenomenology; subsequently, the most important techniques for the characterization of the precipitates are illustrated together with the most interesting and recent results. Finally, the possible influence of oxygen precipitation on technological applications is stressed, with particular attention to recent results regarding device yield. Actually, the essential novelty of this review rests on the attempt to give an extended picture of what has been recently clarified by means of highly sophisticated diagnostic methods and of the influence of precipitation on the properties of semiconductor devices. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359479

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

An optical method is developed for the precise mass determination of submicron size charged particles. The measurement is carried out in a hyperbolic quadrupole ion trap electrode system in vacuum by adjusting particle trajectory star shape patterns. This method does not involve gravity so this may be suitable to use in space applications in weightlessness. Due to the imperfect electrode alignment of the ion trap the mass/charge ratio can now be calculated by means of the corresponding electrical parameters with a relative accuracy of 103. Since the measured parameter is frequency the relative accuracy of the mass measurement could later be increased to 106. Combined with stepwise electron loss events induced by UV radiation it is possible to determine the mass of a single particle in the 109–1012amu range with similar precision. These findings would seem to indicate the feasibility of a novel optical method for high precision mass determination of a single particle in the submicron diameter range. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359480

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

This paper presents a comparative study of the thermal characteristics of four types of vertical‐cavity surface‐emitting lasers (VCSELs). They include the dielectric‐isolated top‐emittingp‐type substrate VCSEL, the ion‐implantation isolated top‐emittingn‐type substrate VCSEL, the dielectric‐isolated bottom‐emittingn‐type substrate VCSEL, and the junction‐isolated etched‐welln‐type substrate VCSEL. Microscale electrical and heat conduction effects are taken into account by employing reduced and anisotropic electrical and thermal conductivities for the Bragg reflectors. Solutions for both the electrical potential and temperature fields are obtained numerically. The calculated device temperature rise compares well with available experimental data. The simulation results show that among the studied lasers thep‐type substrate laser has the best intrinsic thermal performance. Local temperature distributions in these lasers reveal that a large temperature drop occurs across the Bragg reflectors. This study demonstrates that the AlAs concentration and the structure of the Bragg reflectors strongly affect the device temperature rise due to the difference in thermal conductivity. The study also suggests that a thicker top contact should be used to reduce the thermal resistance of these devices. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359481

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The dependence of the characteristic temperatureT0on the cavity length and lasing wavelength is theoretical and experimentally analyzed. The devices are straight separate confinement heterostructure lasers with active layer thickness of 30 and 12 nm grown by low temperature liquid phase epitaxy. The recent observation that for very short lasersT0is an increasing function of the cavity length is confirmed, and explained in terms of the threshold current cavity length dependence. The temperature dependence of the threshold currentIthgivesT0as high as 307 K for a quantum well laser with cavity lengthL=168 &mgr;m. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359482

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A variational approach is used to examine the possibility of bistable behavior in a two‐component metal‐dielectric composite medium with a periodic microstructure where one component has a Kerr‐ type field dependent part in the dielectric constant &egr; while the field independent part of &egr; in both materials is in general complex. It is shown that under certain conditions bistable behavior can occur even though the field dependent nonlinearity is weak everywhere. This is achieved by operating the material sufficiently close to one of its sharp quasi‐static, microgeometric electrical resonances. The physical characteristics of the threshold intensity are worked out and considerations made on how to optimize the chances for observing optical bistability in such a material. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359483

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have measured the lifetimes of the 2.8 &mgr;m emission band for Er3+‐ and Ho3+‐doped fluorides including LiYF4, BaY2F8, LaF3, and KY3F10, and for numerous oxides such as Y3Al5O12, YAlO3, La2Be2O5, and other crystals. Several quantum yields and branching ratios were experimentally evaluated as well, in order to determine the radiative lifetime of the upper laser level for the 2.8 &mgr;m transition. This information was employed to assess the cross sections of the 2.8 &mgr;m infrared emission band for several of these crystals, which involves the4I11/2→4I13/2transition for Er, and the5I6→5I7for Ho. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359449

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A class of conceptual optimum refrigeration cycles is considered with a fixed overall heat conductance and a specified refrigerant operating temperature range to bound the optimization problems. These cycles deal with maximum refrigeration power, maximum refrigeration load, and maximum heat rejection load for the case of a heat pump. The resulting one degree of freedom problems are solved with a variable arithmetic mean temperature difference in the heat exchangers. The maximum refrigeration power solution yields an analytical closed form optimality rule which constitutes a close lower bound solution to the maximum refrigeration load and maximum heat rejection load problems. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359450

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Particles embedded in a plasma acquire a net charge as a result of collisions with electrons and ions. Due to the stochastic nature of encounters between particle and charged species, the instantaneous charge fluctuates. The static properties of the charge fluctuations are quantified for particles surrounded by an undisturbed plasma in orbital motion limit. For particles that satisfy the conditione2/4&pgr;&egr;0RkTe≪1 the charge distribution is a Gaussian function whose average and variance is related to the ion and electron currents toward the particle. For a Maxwellian plasma, in particular, analytical solutions are developed for the average charge and the variance as a function of the parameters of the plasmane/ni,Te/Ti, andMe/Mi. Finally, the methodology is extended to non‐Maxwellian plasmas using the Druyvesteyn as an example. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359451

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A two‐dimensional analytical model for the effect of a nonuniform secondary electron emission coefficient (&ggr;) on the powered electrode of a radio frequency plasma was developed. The nonuniformity was a step change in the value of &ggr;. The ambipolar diffusion equation, including ionization by thermal and secondary electrons, took the form of a Helmholtz equation for which the solution by separation of variables was a series of cosine functions. The discontinuity of &ggr; on the electrode engendered substantial nonuniformity of plasma density. For example, the nonuniformity at the sheath edge of an Ar plasma (50 mTorr, 200 V) was 40% for a substrate having a &ggr; of 0.027 and resting on a platen having a &ggr; of 1.00. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359452

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Compositional disordering of GaAs/AlGaAs quantum wells due to the presence of low‐temperature grown GaAs (by molecular beam epitaxy) was studied. Ga vacancy enhanced interdiffusion was found to be the mechanism underlying the observed intermixing. Diffusion equations were solved numerically to obtain the band profile after intermixing. The transition energies in the quantum wells under various annealing conditions were solved and agree very well with the observed photoluminescence emission peaks. The diffusivity of Ga vacancies and that of induced Al‐Ga interdiffusion were obtained. The vacancy induced interdiffusion diffusivity was found to have an activation energy of 4.08 eV, which is smaller than the activation energy of interdiffusion diffusivity of normal temperature grown GaAs/AlGaAs heterostructures. This is a clear indication of enhanced interdiffusion due to the presence of low‐temperature grown GaAs. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359453

出版商:AIP    

年代:1995

数据来源: AIP