摘要:

Freshly produced red, yellow and green emitting porous Si specimens have been studied by NEXAFS and EXAFS (near edge and extended x‐ray absorption fine structure). The emission peaks are at 690, 580, and 520 nm, which almost covers the full visible range that direct anodization can achieve. The correlation between the co‐ordination numbers of the first, second and third Si neighbor shells from Fourier transform fitting of EXAFS and both emission peak energies and optical band gaps estimated by PLE (photoluminescence excitation dependence) suggests that the nanostructures of the PS are nanowires, rather than nanocrystalline. Two types of quantum nanowire with one and one‐plus‐a‐fraction dimensionality are proposed to interpret the correlation. The order factors of the theoretical fits suggest the nanowires of the freshly produced PS have crystalline cores. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361032

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Localized {100} fiber textured diamond films were grown by addition of 20–200 ppm nitrogen into the gas phase during hot‐filament chemical‐vapor deposition (CVD). Cathodoluminescence indicates the presence of the nitrogen‐vacancy system in the {100} textured diamond, whereas a blue ‘‘band A’’ luminescence is normally observed in diamond films grown without nitrogen addition. The results demonstrate that the nature of the substrates used for growth has no appreciable influence on the {100} texture, which implies that this fiber texture is obtained by competitive growth and selection of facets. The interaction of nitrogen with the {100} surface is a highly important factor in this process. Homoepitaxial growth shows that the addition of a small amount of nitrogen greatly enhances the growth rate of the {100} faces, making ⟨100⟩ the fastest growth direction in comparison with the ⟨110⟩ and ⟨111⟩ directions. This is attributed to breaking of a part of the dimers on the (2×1) reconstructed {100} surface by nitrogen compounds. The {100} texture in narrow, ring‐shaped areas on diamond layers grown by the flame technique can also be attributed to the occurrence of a certain amount of nitrogen in the gas phase. It is demonstrated that the flame grown polycrystalline diamond layers have morphologies and cathodoluminescence features that are consistent with those observed in the hot‐filament CVD diamond films grown with the addition of nitrogen. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361033

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

p‐type ion‐implantation doping of Al0.75Ga0.25Sb is reported. The surface morphology and electrical properties of Al0.75Ga0.25Sb are shown by atomic force microscopy and Hall measurements to be degraded after rapid thermal annealing of 650 °C. Implantation of Be and Mg results in sheet hole concentrations twice that of the implanted acceptor dose of 1×1013cm−2following a 600 °C anneal. This is explained in terms of double acceptor or antisite defect formation. Implanted C acts as an acceptor but also demonstrates excess hole conduction attributed to implantation‐induced defects. Implanted Zn requires higher annealing temperatures than Be and Mg to achieve 100% effective activation for a dose of 1×1013cm−2probably as a result of more implantation‐induced damage created from the heavier Zn ion. Secondary ion mass spectroscopy of as‐implanted and annealed Be, Mg, and C samples are presented. Diffusion of implanted Be (5×1013cm−2, 45 keV) is shown to have an inverse dependence on temperature that is attributed to a substitutional‐interstitial diffusion mechanism. Implanted Mg (1×1014cm−2, 110 keV) shows dramatic redistribution and loss at the surface of up to 56% after a 600 °C anneal. Implanted C (2.5×1014cm−2, 70 keV) displays no redistribution even after a 650 °C anneal. This work lays the foundation for using ion‐implantation doping in high performance AlGaSb/InGaSb‐basedp‐channel field‐effect transistors.

ISSN:0021-8979    

DOI:10.1063/1.361034

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Zinc incorporation into InP grown by atmospheric pressure metalorganic vapor phase epitaxy has been studied systematically as a function of Zn source flow rate, substrate orientation, and growth temperature. Within the growth conditions for device quality layers, a Zn saturation level exists which varies with substrate orientation. The incorporation kinetics is analyzed using a surface adsorption‐trapping model. We demonstrate that the Langmuir state of adsorption–desorption process is not established during growth due to the interruption of the surface processes by layer growth. The existence of a saturation level at a given growth condition indicates that Zn atoms incorporate at defect sites instead of the normal growth sites for In. Two parameters are used to characterize the properties of the surface defect, i.e., the capture cross section and the time of desorption for Zn atoms. The implication of these parameters and their substrate orientation and growth temperature dependencies are discussed. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361035

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Longitudinal stress profiles have been measured in polycrystalline silicon carbide (SiC) shocked to peak stresses from 7.3 to 23 GPa. Dispersive wave fronts, consistent with the expected inelastic response, were observed beyond the previously reported Hugoniot elastic limit (HEL) of 11.7 GPa. Detailed numerical analyses were carried out to interpret the observed inelastic response using both a strain‐hardening, plasticity model and a pressure‐dependent strength, stress relaxation model. Both models show good agreement with the data; the latter provides a better fit to the transient features in the measurements suggesting rate dependence in the material response. The computed Hugoniot curve matches all of the peak state data for two different types of SiC that display more than 20 % variation in HEL. This suggests that the measured HEL for SiC is not a proper indicator of the material strength in the shocked state. The results also show that the longitudinal data and analyses are insufficient to resolve issues related to material strength and mechanisms governing inelastic deformation in shocked SiC. The need for a more complete characterization of the shock response of a high‐strength brittle material is discussed. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361036

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We model the indiffusion of arsenic vacancies and their interaction with the midgap electron trap EL2 in GaAs samples that occurs during unprotected and proximity high‐temperature anneals. From fits to existing data we find the diffusive capture ofVAsby EL2 to be inhibited by a large (≳1 eV) repulsive barrier of unknown origin. In conjunction with other results from the literature we estimate the diffusivity ofVAsto be 4×10−3exp(−1.8 eV/kT) cm2/s, a value uncertain by at least an order of magnitude. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361037

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Thin films of CuInSe2and CuGaSe2were grown by molecular‐beam epitaxy. Domain structures in these films were examined by transmission electron microscopy. We demonstrate that orientation domains may not form by the use of (001)GaAs substrate while antiphase domains can be eliminated by annealing the films in the presence of a Se beam. The annealing temperatures were 400 °C for CuInSe2and 450 °C for CuGaSe2. Photoluminescence measurements on an annealed CuInSe2film exhibited a decrease in intensity of optical emissions associated with antisite defects and an enhancement in near‐band‐edge emission intensity. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361038

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have calculated the effect of misfit stress on the compositional stability of strained‐layer hetero‐epitaxial compound semiconductor structures. For uniformly stressed layers, a simple formula is derived for the change in chemical potential of the lattice atoms diffusing across the hetero‐interface. An increase in the total chemical potential indicates that interdiffusion of the specific elements is thermodynamically unfavorable and therefore the composition of the structure is stable with respect to the misfit stress‐induced interdiffusion of the specific elements. On the other hand, a decrease in the total chemical potential indicates that the interdiffusion will be driven by the misfit stress and the composition of the heterostructure is unstable. Various strain‐layer systems of III–V compound semiconductors such as In1−xGaxAsyP1−y/InP, In1−xGaxAsyP1−y/GaAs, (Al1−xGax)yIn1−yP/GaAs, (Al1−xGax)yIn1−yAs/GaAs, In1−xGaxP/GaAs, In1−xGaxSb/InP, etc., are examined and their stability is discussed. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361039

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Experimental evidence is presented to verify the quantitative predictions of interfacial defect theory as applied to strain relief in epitaxial PbTiO3thin films through the formation of 90° domains. Epitaxial PbTiO3thin films grown by metal‐organic chemical vapor deposition on MgO(001), SrTiO3(001), LaAlO3(001), and SrRuO3(001)/SrTiO3(001) substrates are examined using four‐circle x‐ray diffraction and transmission electron microscopy. The data represents a detailed examination of the ...c/a/c/a... 90° domain patterns that develop during the paraelectric to ferroelectric (PE→FE) phase transition as the film is cooled from the growth temperature. Three independent measurements of the relative coherency strain (er) are reported. The data quantitatively and self‐consistently verify the crystallographic rotations predicted by the concept of the relative coherency strain and demonstrate the validity of domain stability maps in understanding the phase transformation history in epitaxial ferroelectric thin films. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360978

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Highly tetrahedral, dense amorphous carbon (ta‐C) films have been deposited using rf sputtering of graphite by an unbalanced magnetron with intense dc Ar‐ion plating at low temperatures (<70 °C). The ratio of the argon ion flux to neutral carbon flux &Fgr;i/&Fgr;nis about 5. The film density and compressive stress are found to pass through a maximum of 2.7 g/cm3and 16 GPa, respectively, at an ion plating energy of about 100 eV. Experiments with higher ion flux ratios of &Fgr;i/&Fgr;n=10 show that it is possible to deposit carbon films with densities up to 3.1 g/cm3andsp3contents up to 87%. Deposition of ta‐C in this experiment when the energetic species is Ar appears to require a minimum stress of 14 GPa to create significantsp3bonding, which contrasts with the continuous increase insp3content with stress when the energetic species is C ions themselves. These results are used to discuss possible deposition mechanisms. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360979

出版商:AIP    

年代:1996

数据来源: AIP