摘要:

The effects of ion implantation and ultrasonic cavitation on the near‐surface region of MgO single crystals were investigated. For 150 keV, room‐temperature implantations of Ar+or K+at 5×1016–1017ions cm−2into a (100)‐oriented surface of MgO, a dilatometric swelling of the implanted layer is observed perpendicular to the implanted surface. When these strained surface layers are then subjected to an ultrasonic (∼20 kHz) cavitation treatment, uniform layers (∼100–200 nm) can be removed from the MgO surface in a controlled manner. The thickness of the removed layer is directly related to the duration of the ultrasonic irradiation, but does not exceed the depth of the implanted species. When MgO implanted with Ar+or Kr+at fluences of 5×1016–1017ions cm−2is subsequently irradiated with 2 MeV He+ions at 1016–1017ions cm−2, the region exposed to the He+beam is effectively ‘‘stabilized’’ and is not removed by the ultrasonic treatment. K+or Ar+implantations at <5×1016ions cm−2produced no swelling of the layer, and subsequent ultrasonic irradiation with an energy flux of ∼120 W cm−2did not remove the crystal surface as determined by profilometry. For MgO implanted with ≳2×1017ions cm−2, the implanted layer is highly strained and detaches from the underlying crystal without exposure to ultrasonic‐cavitation effects. These findings are discussed in terms of the stressed states of the implanted layers, and their potential applications to the mechanical ‘‘etching’’ of ceramics are considered.

ISSN:0021-8979    

DOI:10.1063/1.363195

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The dependence of x‐ray or neutron specular reflectance on the scattering density has been linearized by modifying the Born approximation. This makes it possible to analyze the reflectivity curves by the Fourier transform method by using the box refinement technique. Thus, the phases of the scattered waves are iteratively obtained, by which the scattering density profile in layered systems can be directly evaluated. The validity of these modifications is demonstrated by some numerical examples. The box refinement technique requires fewer constraints to obtain the physically realistic scattering density than the least‐squares‐fitting method does. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363196

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The microstructure of the diamond and the &bgr;‐SiC interlayer grown on Si substrates was studied in synchrotron x‐ray scattering experiments. In the process of growing diamond using microwave plasma chemical vapor deposition, a &bgr;‐SiC interlayer was always formed epitaxially regardless to the orientation and the pretreatment of substrates. The crystalline axes of the &bgr;‐SiC interlayer were parallel to the substrate crystalline axes. The pretreatment of the silicon substrates greatly enhanced the growth rate of the &bgr;‐SiC. Meanwhile, the diamond particles were preferentially grown along both the ⟨111⟩ and the ⟨001⟩ directions on all the pretreated substrates. The diamond particles that were grown with the preferred growth direction matching to the substrate normal crystalline axis direction exhibited partial epitaxy, while others were grown nonepitaxially. The substrate pretreatment also enhanced the growth of diamond particles significantly. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363197

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Thin films of SrTiO3were grown by pulsed laser deposition on Si and SiO2/Si at 35 and 650 °C in a 50 mTorr oxygen discharge (300 V). The effect of introducing a SiO2buffer layer between the Si substrate and the complex oxide on the crystallinity and microstructure of the SrTiO3films was investigated at both deposition temperatures. All films grown at 35 °C were amorphous. Surface morphology examination by scanning electron microscopy (SEM) showed that these films were continuous and homogeneous when grown on Si, but were porous and had low‐density noninterconnecting lines when grown on SiO2/Si. Films prepared at 650 °C were polycrystalline and their x‐ray‐diffraction patterns exhibited peaks corresponding to the (001), (110), (111), and (002) reflections of the SrTiO3cubic phase (a=3.904 A˚). The films deposited on SiO2/Si were found to grow with a high degree of preferred orientation along the (110) direction. SEM studies on the surface morphology of the films grown at high temperature showed the presence of a ‘‘rosette’’ structure. The mean size of the rosettes was ∼80 nm in 40‐nm‐thick films grown on Si and ∼100 nm in films of similar thickness grown on SiO2/Si. Additional atomic force microscopy studies on the topography of these samples indicated that the rosettes were constituted by ∼35‐nm‐diam grains. Typical peak‐to‐valley surface roughness of these films was 0.5–2 nm. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363198

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A novel linear prediction based parameter estimation algorithm is developed for analyzing deep level transient spectroscopy (DLTS) signals. The algorithm performs significantly better than a current linear prediction based algorithm used in DLTS because it accurately accounts for the effects of noise and any underlying baseline constant. The algorithm is developed for any digitized isothermal capacitance transient. It does not rely on overmodeling or require baseline nulling hardware. The superior performance of the algorithm is verified on synthesized, as well as challenging actual DLTS signals. It is shown to consistently extend the linear regions and resolve closely spaced activation energies on Arrhenius plots.

ISSN:0021-8979    

DOI:10.1063/1.363133

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The effects of phonon confinement on electron–acoustic‐phonon scattering is studied in cylindrical semiconductor quantum wires. In the macroscopic elastic continuum model, the confined‐phonon dispersion relations are obtained for several crystallographic directions with the two cardinal boundary conditions: free‐surface and clamped‐surface boundary conditions. The scattering rates due to the deformation potential interaction are obtained for these confined phonons and are compared with those of bulk‐like phonons for a number of quantum wire materials. The results show that the inclusion of acoustic phonon confinement effects may be crucial for calculating accurate low‐energy electron scattering rates in nanostructures. It is also demonstrated that the scattering rates may be significantly influenced by the direction of phonon propagation, especially for low‐energy electrons. Furthermore, it has been found that there is a scaling rule governing the directional dependence of the scattering rates: the directions characterized by small Poisson ratios exhibit large scattering rates. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363199

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Strain‐relaxed, compositionally graded Ge0.3Si0.7/Si heterostructures grown by ultrahigh vacuum chemical vapor deposition at 650 °C are shown to display a consistent change fromp‐type ton‐type conductivity as a function of rapid thermal annealing (RTA) temperature in the range 700–850 °C. Cross‐sectional transmission electron microscopy, spreading resistance, and electron beam induced current (EBIC) studies eliminate the dislocations themselves as a possible source of this type conversion, by demonstrating that the spatially invariant hole concentration of 2×1014cm−3is not correlated to the dislocation density, which decreases from ∼108cm−2in the graded region to 7×105cm−2in the 30% Ge cap. To identify the source of type conversion, a systematic investigation was performed on 650 °C as‐grown and annealed samples with deep‐level transient spectroscopy (DLTS), photoluminescence (PL) and capacitance–temperature (C–T) measurements. DLTS measurements on as‐grown samples reveal a complex spectrum of deep and shallow hole traps, whileC–Tstudies reveal a prominent temperature dependence of the zero bias capacitance, indicating that thep‐type background conductivity is associated with a high degree of compensation. Post‐growth RTA atT≥800 °C eliminates this compensation, and yields backgroundn‐type films, consistent with the backgroundn‐type conductivity that is always observed in graded films grown atT≳800 °C in the same reactor. This change in conductivity type is accompanied by a strong increase in EBIC signal strength and a significant simplification of DLTS and PL spectra. These results are discussed in terms of dislocation interaction within the graded layers which generates nonequilibrium concentrations of intrinsic point defects that form extended complexes at growth temperatures ≤800 °C. These complexes are associated with thermally unstable acceptor‐like defect states in the energy rangeH(0.05)–H(0.30) that convert low growth temperature, relaxed, graded GeSi/Si films from backgroundntype to backgroundptype. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363200

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

CdNiTe nanostructured thin films were prepared by radio frequency sputtering from a target of CdTe and nickel compressed powders. The structural and electrical film properties were studied as a function of the atomic nickel concentration in the films (x=0.05, 0.10, and 0.15). X‐ray diffraction patterns showed a cubic CdTe parent structure with a (111) preferential orientation. The microcrystalline grain size in the films showed a systematic decrease with the increase of Ni content, starting with grain sizes of around 35 nm forx=0.05, down to an average of 26 nm forx=0.15. From scanning electron microscopy micrographs, a fine granular morphology with a random distribution of grain sizes in the films was observed. The film electrical resistivity was measured as a function of the temperature in the rangeT: 26–473 K. The temperature dependence of the dark resistivity over this wide temperature range showed a clear deviation from a simple thermally activated carrier transport mechanism. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363201

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

To model high injection phenomena in P–N junction devices it is usually necessary to use numerical analysis. This is because the standard procedure of dividing the structure into neutral zones and depletion layer (regional approximation) fails. In a recent paper, Yueetal. [J. Appl. Phys.77, 1611 (1995)] proposed an extension of the Shockley theory, retaining the form of the conventional diffusion current‐only model for the conduction mechanism. Their solution was based on the resolution of the ambipolar transport equation in the base. It is shown here by a numerical simulation of the complete structure, within the framework of the drift‐diffusion model, that both the exponential current dependence:J&agr; exp(eVa/2kT) as well as the Yueetal. approximation are valid only in the limiting case of a strongly extrinsic short base diode. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363134

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The hole transport properties of gallium antimonide with various degrees of tellurium compensation have been investigated in the temperature range of 4.2–300 K. For the undoped GaSb, thep‐type conductivity arises from a doubly ionizable native defect VGaGaSb. In the Te compensated samples, apart from the Te‐donor level and the VGaGaSbcenter, an acceptor level resulting from complexation of VGaGaSbwith TeSbhas been found. This acceptor level lies ∼70 meV above the valence band edge. The concentration of this center depends on the melt composition and the level of Te present in the melt during growth of crystals. Most interestingly, at very low level of Te concentration, an additional triple native acceptor (VGaGaSbVGa) has also been observed. With the increase in Te concentration, the mobility decreases and a shift in the mobility peak to higher temperature is observed. The low‐temperature mobility is limited by ionized impurity scattering. At higher temperatures, the scattering mechanisms depend on Te concentration in the sample. In this regime, significant contributions from acoustic, nonpolar optical, and polar optical phonon scattering are observed for samples with low levels of Te. In contrast, the impurity scattering dominates even at room temperature for highly compensated crystals. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363135

出版商:AIP    

年代:1996

数据来源: AIP