摘要:

Recently, a complete formulation of the transient surface excitation problem for piezoelectric materials has suggested the existence of a type of electrical sources on the surface not traditionally considered in piezoelectric transduction. This letter shows that these additional sources correspond to electric current dipoles. It is shown that the wave forms, or the frequency dependence, of waves generated by these sources are different from those generated by traditionally studied sources such as mechanical stresses and electric currents. These characteristics can be used to identify the contribution of such sources. Schottky andp‐njunctions on the surface of a semiconductive material are suggested as the experimental implementation of the new sources. In addition to piezoelectric transduction, current dipoles can also be used to generate electromagnetic waves in a nonpiezoelectric medium. ©1995 American Institute of Physics. 

ISSN:0003-6951    

DOI:10.1063/1.114014

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Boron doped superlattices have been used to detect the diffusion of self‐interstitials in Si. Interstitials were generated in the near‐surface region by 40 keV Si implantation followed by diffusion at 670–790 °C. The interstitial diffusion profile at 670 °C is stationary fort≤1 h, demonstrating that the penetration depth of interstitials is limited by trapping. The concentration of traps is estimated to be ∼1017/cm3. For sufficiently long annealing times, interstitials diffuse beyond the trapping length with an effective trap‐limited diffusivity ranging from ∼6×10−15cm2/s at 670 °C to ∼1×10−12cm2/s at 790 °C. The high interstitial supersaturation adjacent to the implant damage drives substitutional B into metastable clusters at concentrations below the B solid solubility limit. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114015

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Phase transitions and dielectric properties of (1−x)Pb(In1/2Nb1/2)O3(PIN)‐xPbZrO3(PZ) solid solution system have been examined as a function of the concentrationx. Two morphotropic phase boundaries were identified: (1) pseudocubic to rhombohedral phase boundary atx=0.35 and (2) rhombohedral to orthorhombic atx=0.8. Forx<0.35, a diffuse phase transition was observed. For 0.35<x<0.8, the relative permittivity &egr;’rshowed a sharp peak atTc. In this regime, the phase belowTcwas confirmed to be ferroelectric by observation squareP‐Ehysteresis loops. Forx≳0.8, a steplike dielectric anomaly appeared atTt(belowTc) as well as the sharp peak in the permittivity. The phase belowTtwas confirmed to be antiferroelectric by the observation of doubleP‐Ehysteresis loops. The maximum permittivity of 15 000 (at 100 kHz) was observed atx=0.35 ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114016

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Numerical finite element calculations have been reported to determine a correction function &Fgr; that describes the reduction of the misfit that occurs when laterally limited structures such as faceted islands or mesa structures are grown on a substrate. The reduction of the average strain energy density is calculated in these three‐dimensional islands and compared to the constant strain energy density in a continuous layer. Ratios &Fgr; are obtained from the calculation of different island geometries, i.e., different facet angles &ggr; and different aspect ratios island widthlto island heighth. These discrete values are fitted by a function which can easily be applied to the full range of aspect ratios (l/h≳0) and facet angles (0°<&ggr;<90°). Faceted Ge(Si) islands on Si(001) substrate, grown from the solution in the Stranski–Krastanov growth mode, serve as an example for the calculation. Experimental and theoretical values for the critical thickness of these islands agree well. This result demonstrates the drastic influence of islanding on misfit strain distribution in island and substrate as well and, consequently, on the strong increase of the critical thickness as determined by the mechanical equilibrium theory of Matthews and Blakeslee. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114017

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Micromachined silicon cantilevers have been prepared using anisotropic etching in conjunction with boron doping. They were driven into resonant vibration for periods of over 2000 h and their natural frequencies and quality factors were recorded as a function of aging time. It has been found that aging has occurred in all of the samples tested and this was manifest as an increase in the quality factor and a small decrease in resonant frequency, with both values eventually stabilizing. The magnitude of this effect was found to increase with increasing levels of boron doping within the structures. The mechanism of aging is not clear but may be linked to dislocation damage and activity of interstitial boron with the crystals. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114018

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Boron diffusion ininsitudoped Si1−xGexand Si, subjected to inert‐ambient furnace annealing at 800 °C, was investigated. For Si1−xGex, the effect of biaxial compressive and tensile strain on boron diffusion was studied using Si1−xGexlayers with a constant Ge content (x≊0.10 andx≊0.20) grown epitaxially on various relaxed Si1−yGey(0≤y≤0.20) substrates. Boron diffusion is primarily a function of Ge content,xin the Si1−xGexlayers, and does not show a strong dependence on macroscopic biaxial strain. For Si, the effect of biaxial tension was investigated using relaxed Si1−yGeylayers as substrate templates for epitaxial Si layers. As in Si1−xGex, boron diffusion in Si does not depend strongly on biaxial strain. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114019

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Smooth and continuous diamond films have been heteroepitaxially grown on &bgr;‐type silicon carbide (&bgr;‐SiC) (001) surfaces. The smooth films can be obtained in the thickness of less than 6 &mgr;m which is the smallest in heteroepitaxial diamonds. The epitaxial growth is composed of three steps; (i) Bias enhanced nucleation on &bgr;‐SiC (001) grown on silicon (001), (ii) ⟨001⟩ fast growth mode for the selection of epitaxially oriented particles, and (iii) ⟨111⟩ fast growth mode for the smoothing of (001) surface. High quality silicon carbide (001) surface is effective for oriented diamond nucleation. The winnowing process of oriented particles and the surface adjustment are due to the high surface energy of diamond. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114020

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Photoluminescence (PL) measurements are reported on modulation‐doped ordered‐GaInP2/ disordered‐GaInP2homojunctions. These junctions exhibit extremely high carrier densities of the two‐dimensional (2D) electron gas. A luminescence peak that involves recombination of these intrinsic 2D electrons and photoexcited holes shows a very large redshift as a result of the spatially separated carriers. However, no inverted S shaped behavior of PL energy is observed for this signal upon increasing temperature. This result affirms that the inverted S PL behavior of bulk ordered GaInP2has an extrinsic nature. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114021

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Data (300 and 77 K) are presented on the photopumped laser operation of AlxGa1−xAs–GaAs vertical cavity quantum well heterostructure crystals that exhibit enhanced hot‐carrier recombination. The mirrors defining the vertical cavity are formed by selective lateral oxidation (H2O+N2, 425 °C, 30 min) of quadruple AlAs layers separated by lower composition AlxGa1−xAs ‘‘stop’’ layers in order to create upper and lower high‐index‐step oxide‐semiconductor distributed Bragg reflector mirrors. The Q of the compact vertical‐cavity (a microcavity) enhances the spontaneous and stimulated recombination of hot carriers, making possible single mode laser operation at an energy corresponding to the second state of the quantum well. The laser operation can be shifted to the first state by cooling to 77 K and shifting the energy gap towards the vertical cavity resonance. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114022

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Metastable pseudomorphic Ge0.12Si0.88films were grown by molecular beam epitaxy on Si(100) substrates and then implanted with 100 keV31P at room temperature for a dose of 5×1013/cm2. Samples were subsequently annealed by rapid thermal annealing (RTA) in nitrogen and by steady‐state furnace annealing in vacuum. Both damage and strain introduced by implantation can be completely removed, within instrumental sensitivity, by RTA at 700 °C for 10–40 s. Vacuum annealing for 30 min at 500–550 °C removes most of the damage and strain induced by the implantation but the activation of the P is poor. At 700 °C, the activation is nearly 100%, but the crystallinity worsens and the pseudomorphic strain begins to relax. We conclude that for a lightly implanted metastable and pseudomorphic GeSi epilayer on Si, steady‐state vacuum annealing cannot achieve good dopant activation without introducing significant strain relaxation to the heterostructure, while RTA can. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114023

出版商:AIP    

年代:1995

数据来源: AIP