摘要:

Low‐temperature molecular‐beam epitaxy (MBE) in semiconductors is reviewed, with a focus on limited thickness epitaxy (LTE), the regime where crystalline growth over an epitaxial thicknesshepiis followed by a transition to amorphous deposition. The goal is to summarize the main results on this phenomenon, make the connection to other results on low‐temperature MBE, and present the large body of unpublished data onhepi. Since the problem is still not fully understood, all available data that have a bearing on the understanding of the effect are outlined. The scientific questions and practical problems that have driven interest in low‐temperature growth are outlined, and the phenomenon of LTE and the dependence ofhepion the growth conditions are described. The LTE effect is apparently general, but Si(100) is the model system for which most data are available. Breakdown of epitaxy follows a universal curve that is inconsistent with continuous nucleation of the amorphous phase, implying that growth is truly thickness dependent. The epitaxial thickness is thermally activated in substrate temperatureTashepi=h0 exp(−Eact/kBT), withh0following a weak ln(R) orR1/4dependence on deposition rateR.hepiis also strongly influenced by lattice mismatch strain, residual H in the ultrahigh vacuum, and annealing during growth interrupts. Possible mechanisms for LTE are discussed, with particular emphasis on the roles played by H and kinetic roughening, and the key experiments distinguishing these mechanisms are described. Finally, an attempt is made to draw up the best current picture of the phenomenon. It is concluded that roughening provides the fundamental limit to epitaxy at low temperature, but with H contamination playing an important part in controlling surface diffusion: outstanding problems include the rate dependence and the details of the roughening behavior. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358597

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

It is well known that bimetallic microcantilevers can exhibit static deflection as a result of thermal effects, including exothermic adsorption of chemicals on their surfaces. It is shown here that the resonance frequency of a cantilever can change due to a combination of mass loading and change of spring constant resulting from adsorption of chemicals on the surface. Cantilevers also undergo static bending that is induced by differential surface stress. The magnitude of these effects depends upon the chemical properties of the surface and upon the amount of material adsorbed. Hence cantilever deflection as well as resonance frequency change can be used as the basis for development of novel chemical sensors. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359562

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Unconventional rf traps of the Paul–Straubel type and its variations have found increasing use in ion trapping experiments. Calculations of the properties of these traps are presented. Simple realistic trap geometries are studied for their voltage loss factor, anharmonicity, and radial symmetry breaking. Optimum geometries for these traps are indicated. ©1995 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.358598

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

An on‐shell method that combines plane‐wave and finite‐difference techniques for the calculation of dispersion curves and transmission spectra for electromagnetic fields in photonic band‐gap crystals is presented. The overall problem is decomposed into a field problem of determining the plane‐wave scattering from an individual crystalline layer and a conventional one‐dimensional network problem of combining this scattering to obtain the band structure of the entire crystal or the scattering properties of a crystal with a finite thickness. Results of the calculation are compared with experimental data measured using ultrawideband microwave pulses for a two‐dimensional photonic band‐gap crystal. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358599

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Wide gap II‐VI semiconductors have strong second order susceptibilities &khgr;(2)and are therefore promising materials for efficient second harmonic generation. We have grown high quality single crystalline ZnSe/ZnTe/ZnSe/GaAs (001) waveguides by metalorganic‐vapor‐phase‐epitaxy. Using end‐fire coupling we observe a phase matched signal of the 1170.5 nm fundamental wave. The fundamental beam is generated by a tuneable KTP optical‐parametric‐oscillator pumped by a ps‐Ti:sapphire laser system. Phase matching is achieved by coupling the TE0fundamental mode with the TM2second harmonic mode within the symmetric ZnTe waveguide. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358600

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We report the results from an investigation of the effects of variations in layer thicknesses during the growth of semiconductor Bragg mirrors on their reflectivity spectra. Different types of variations are investigated and an effort is made to point out the sources of such errors in a typical growth process. It is expected that this study will shed light on the critical control parameters for very highly reflecting mirrors and help the interpretation of the measured spectra from a finished growth run and the identification of the possible sources of deviations from the ideal structure. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358601

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

An analytical theory of a high‐pressure gas discharge between two metal electrodes covered with an insulator is presented. The theory is applicable when the voltage applied to the gap between electrodes only slightly exceeds the breakdown voltage. Analytic expressions for the electric field, electron and ion current densities, as a function of time and space, and an analysis of the stability of the discharge are given. A detailed discussion of the role of metastables in the discharge dynamics is included. The discharge in a plasma display cell is used as an example to demonstrate the utility of the theory. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358602

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Plasma dynamics are characterized in a long‐conduction time plasma opening switch [Phys. Fluids B4, 2368 (1992)] operated with densities and currents near the theoretical intersection of the magnetohydrodynamic (MHD) [IEEE Trans. Plasma Sci.PS‐19, 400 (1991)] and electronmagnetohydrodynamic (EMH) [Phys. Fluids B3, 1908 (1991)] regimes. In agreement with MHD theory, a hydrodynamic snowplow is observed to translate axially and reach the load end of the switch at opening. The axial motion of the front agrees with one‐dimensional analytic predictions if the carbon plasma possesses an average ionization of 1, but is significantly less than theory if higher ionization levels are present. The axial motion of the plasma center‐of‐mass is significantly less than that expected from theory for any ionization level. The reduced center‐of‐mass motion is attributed to an ion loss mechanism in the unconfined switch plasma, an effect also observed in the total particle inventory, which saturates while the source plasma flux remains relatively constant. An ion lifetime of 450±15 ns (290±23 ns) forZ=1 (Z=2) results in a predicted center‐of‐mass motion in agreement with the measurements. Only minimal EMH effects are observed indicating, in contrast to theoretical predictions, that the switch is MHD dominated in this regime. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358603

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Nonplanar electrode topographies in plasma etching reactors are known to perturb plasma properties. In this article results from a computational study of plasma etching reactors having nonuniform dielectric structuresbelowthe wafer are presented. The system is an inductively coupled plasma reactor having a 13.56 MHz bias applied to the substrate. The model we have used is a hybrid simulation consisting of electromagnetics, electron Monte Carlo and fluid kinetics modules, and an off‐line plasma chemistry Monte Carlo simulation. We found that the subwafer dielectric adds a series capacitance to the sheath and wafer resulting in voltage division of the applied potential between the sheath, wafer, and dielectric. This produces a smaller sheath potential and smaller sheath thickness above the dielectric. The ion energy distribution is therefore depressed in the vicinity of the dielectric. The effect is more severe at high plasma densities where the capacitance of the sheath is larger compared to the subwafer dielectric. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358604

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The temporal variation of the energy of positive ions deposited in metal electrodes inserted in a plasma to which a negative voltage step is applied is computed. Effects of impurity positive or negative ions upon the plasma source ion implantation process are calculated. ©1995 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.358605

出版商:AIP    

年代:1995

数据来源: AIP