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Maskless pendeo-epitaxy involves the lateral and vertical growth of cantilevered "wings" of material from the sidewalls of unmasked etched forms. Gallium Nitride films grown at 1020°C via metalorganic vapor phase epitaxy on GaN/AlN/6H-SiC(0001) substrates previously etched to form -oriented stripes exhibited similar vertical [0001] and lateral growth rates, as shown by cross-sectional scanning electron microscopy. Increasing the temperature increased the growth rate in the latter direction due to the higher thermal stability of the surface. The surface was atomically smooth under all growth conditions with a root mean square (RMS)=0.17 nm. High resolution X-ray diffraction and atomic force microscopy of the pendeo-epitaxial films confirmed transmission electron microscopy results regarding the significant reduction in dislocation density in the wings. This result is important for the properties of both optoelectronic and microelectronic devices fabricated in III-Nitride structures. Measurement of strain indicated that the wing material is crystallographically relaxed as evidenced by the increase in the c-axis lattice parameter and the upward shift of the E2 Raman line frequency. A strong D°X peak at 3.466 eV was also measured in the wing material. However, tilting of the wings of ≤0.15° occurred due to the tensile stresses in the stripes induced by the mismatch in the coefficients of thermal expansion between the GaN and the underlying substrate.

Gallium nitride films of increasing thickness have been grown on either AlN or AlGaN substrates. The state of stress of these biaxially stressed layers gradually changed from compression to tension with regard to both their average strain and their local strain along the [0001] growth direction. The components of both the compressive and tensile stresses are caused by the mismatch in lattice parameters between the GaN and the buffer layer and the mismatch in the coefficients of thermal expansion between GaN and SiC, respectively. The compressive stress is partially relieved within the first 20 nm in the GaN film grown on the AlN buffer layer. The relief of the remaining stress follows an exponential dependence on the thickness of the GaN layer with values for the characteristic decay length of 0.24 μm and 0.64 μm for the AlN and AlGaN buffer layer, respectively. The relaxation mechanism is discussed in terms of the formation of misfit dislocations via surface undulations.

The cracking of GaN films and the associated cracking of substrates are described. The geometry, structure, and evolution of fracture demonstrate that GaN films crack under tensile stress during growth and are subsequently overgrown and partially healed. The film cracks channel along the (1010)_GaN planes and also extend a distance of ~5 μm into the sapphire substrate. These incipient cracks in the substrate form a set of initial flaws that leads to complete fracture through the sapphire during cooling for sufficiently thick films. Each stage of this cracking behavior is well described by a fracture mechanics model that delineates a series of critical thicknesses for the onset of cracking that are functions of the film and substrate stresses, thicknesses, and elastic properties. Similar cracking behavior is found to occur independently of the choice of substrate between sapphire and SiC and is traced to a tensile stress generation mechanism early in the growth process, such as that provided by island coalescence. Cracking is the dominant stress relief mechanism, as opposed to dislocation generation or diffusion, because of the island growth mode and because of optimized growth temperatures at or below the brittle-to-ductile transition. Lateral epitaxial overgrowth (LEO) of GaN is shown to minimize substrate fracture even though film cracking remains unaffected. This effect explained in terms of the limits placed on the initial extent of insipient substrate cracks due to the LEO geometry.

Ultra-thin body Double Gate MOS structures with strained silicon are investigated by solving the 1-D Schrödinger and Poisson equations, with open boundaries conditions on the wave functions in the gate electrodes. The electrostatics of this device architecture and its dependence on the amount of strain and on the thickness of the silicon layer is analyzed in terms of subband structure, subband population, carrier distribution within the strained-silicon layer, charge-voltage characteristics and gate tunneling current.

SOI technology offers ample room for scaling, performance improvement, and innovations. The current status is reviewed by focusing on several technological options for boosting the transport properties in SOI MOSFETs. The impact of series resistance, high-K dielectrics, and metal gate in advanced transistors is discussed. Carrier mobility measurements as a function of channel length and temperature reveal the beneficial effect of strain, mitigated however by various types of defects. The experimental data is exclusively collected from state-of-the-art, ultrathin body, fully depleted MOSFETs. Simple models are presented to clarify the mobility behavior.

GaN-based pseudomorphic heterostructures with their demonstrated superior thermal performance suggest an alternative to the standard GaAs-based technology to realize high power lasing at THz frequencies. A larger electron effective mass in GaN based system results in the energy levels lying deeper within the quantum well compared to its GaAs counterpart resulting in longer carrier lifetimes assisting transitions required for THz radiation while reducing tunneling current. However, the presence of spontaneous and piezoelectric polarization and dependence of bandgap and band offsets on structural and bias induced strain reduces carrier lifetime.

We have investigated the residual in-plane strain and width of the surface misfit dislocation free zone in linearly-graded GaAs_1-yP_y metamorphic buffer layers as approximated by a finite number of sublayers. For this purpose we have developed an electric circuit model approach for the equilibrium analysis of these structures, in which each sublayer may be represented by an analogous configuration involving a current source, a resistor, a voltage source, and an ideal diode. The resulting node voltages in the analogous electric circuit correspond to the equilibrium strains in the original epitaxial structure. Utilizing this new approach, we show that the residual surface strain in linearly-graded epitaxial structures increases monotonically with grading coefficient as well as the number of sublayers, and is strongly dependent on the width of the misfit dislocation free zone, which diminishes with an increasing grading coefficient.

Chirped superlattices are of interest as buffer layers in metamorphic semiconductor device structures, because they can combine the mismatch accommodating properties of compositionally-graded layers with the dislocation filtering properties of superlattices. Important practical aspects of the chirped superlattice as a buffer layer are the surface strain and surface in-plane lattice constant. In this work two basic types of InGaAs/GaAs chirped superlattice buffers have been studied. In design I (composition modulated), the average composition is varied by modulating the composition of one of the two layers in the superlattice period, but the individual layer thicknesses were fixed. In design II (thickness modulated), the individual layer thicknesses were modulated, but the compositions were fixed. In this paper the surface strain and surface in-plane lattice constant for these chirped superlattices are presented as functions of the top composition and period for each of these basic designs.

Halide perovskite materials such as FAPbI3 are of great interest for photovoltaic applications and could replace silicon cells if problems of chemical instability, strain and crystal defects are solved. In this paper we present a preliminary modeling study of lattice relaxation in epitaxial FAPbI₃ on MAPbCl_xBr_3-x (001).

The mechanical and electronic properties of GaP nanowires are investigated by computing the Young’s modulus, Poisson’s ratio, energy band gap and effective carrier masses using first-principles calculations based on density functional theory. The wurtzite structural nanowires with diameters upper limited to $\sim 27$Å are strained by uniaxial strains in the range of $-7.5$–$7.5\%$. The Young’s moduli of nanowires are found to be decreased with increase of the size in the direction of the Young’s modulus of the bulk GaP. The Poisson’s effect is determined to be stronger in GaP nanowires than in the bulk. The energy band gaps of the unstrained and strained nanowires are obtained to be enlarged with decrease of the size due to the quantum size effect. The confinement effect is found larger in the compressed nanowires than in the stretched ones. All the unstrained nanowires except the largest one are indirect band gap materials. Indirect to direct band gap transition is determined to be size and strain dependent. The effective carrier masses in all unstrained nanowires are found small compared to the ones in the bulk GaP. The effective electron and hole masses are obtained to be modulated in nanowires of this work by the compressive and both compressive/tensile strains, respectively.

Using the ab initio plane-wave ultrasoft pseudopotential method based on the generalized gradient approximation (GGA), we investigate the bandgap tuning in monolayer phosphorene in terms of applying external electric fields perpendicular to the layers. The bandgap continuously decreases with the applied electric fields, eventually rendering them metallic. The phenomenon is explained by the giant stark effect. The interlayer P-P distance also result in the semiconductor-to-metal transition. The phosphorene exhibits the significant bandgap tuning ability under different strains with 5% variation. Our investigations show the bandgap change for the fabrication of novel electronic and photonic devices.

On the basis of the finite element approach, we systematically investigated the strain field distribution of conical-shaped InAs/GaAs self-organized quantum dot using the two-dimensional axis-symmetric model. The normal strain, the hydrostatic strain and the biaxial strain components along the center axis path of the quantum dots are analyzed. The dependence of these strain components on volume, height-over-base ratio and cap layer (covered by cap layer or uncovered quantum dot) is investigated for the quantum grown on the (001) substrate. The dependence of the carriers' confining potentials on the three circumstances discussed above is also calculated in the framework of eight-band k·p theory. The numerical results are in good agreement with the experimental data of published literature.

In this study, a system for non-contact in-situ measurement of strain during tensile test of thin films by using CCD camera with marking surface of specimen by black pen was implemented as a sensing device. To improve accuracy of measurement when CCD camera is used, this paper proposed a new method for measuring strain during tensile test of specimen with micrometer size. The size of pixel of CCD camera determines resolution of measurement, but the size of pixel can not satisfy the resolution required in tensile test of thin film because the extension of the specimen is very small during the tensile test. To increase resolution of measurement, the suggested method performs an accurate subpixel matching by applying 2nd order polynomial interpolation method to the conventional template matching. The algorithm was developed to calculate location of subpixel providing the best matching value by performing single dimensional polynomial interpolation from the results of pixel-based matching at a local region of image. The measurement resolution was less than 0.01 times of original pixel size. To verify the reliability of the system, the tensile test for the BeNi thin film was performed, which is widely used as a material in micro-probe tip. Tensile tests were performed and strains were measured using the proposed method and also the capacitance type displacement sensor for comparison. It is demonstrated that the new strain measurement system can effectively describe a behavior of materials after yield during the tensile test of the specimen at microscale with easy setup and better accuracy.

In this paper, we have proposed a step separate confinement heterostructure (SCH) based lasing nano-heterostructure In_0.90Ga_0.10As_0.59P_0.41/InP consisting of single quantum well (SQW) and investigated material gain theoretically within TE and TM polarization modes. In addition, the quasi Fermi levels in the conduction and valence bands along with other lasing characteristics like anti-guiding factor, refractive index change with carrier density and differential gain have also been investigated and reported. Moreover, the behavior of quasi Fermi levels in respective bands has also been correlated with the material gain. Strain dependent study on material gain and refractive index change has also been reported. Interestingly, strain has been reported to play a very important role in shifting the lasing wavelength of TE mode to TM mode. The results investigated in the work suggest that the proposed unstrained nano-heterostructure is very suitable as a source for optical fiber based communication systems due to its lasing wavelengths achieved at ~1.35 μm within TM mode, while ~1.40 μm within TE mode.

Electron group velocity for graphene under uniform strain is obtained analytically by using the tight-binding (TB) approximation. Such closed analytical expressions are useful in order to calculate the electronic, thermal and optical properties of strained graphene. These results allow to understand the behavior of electrons when graphene is subjected to strong strain and nonlinear corrections, for which the usual Dirac approach is no longer valid. Some particular cases of uniaxial and shear strain were analyzed. The evolution of the electron group velocity indicates a break-up of the trigonal warping symmetry, which is replaced by a warping consistent with the symmetry of the strained reciprocal lattice. To do this, analytical expressions for the shape of the first Brillouin zone (BZ) of the honeycomb strained reciprocal lattice are provided. Finally, the Fermi velocity becomes strongly anisotropic, i.e., for a strong pure shear strain (20% of the lattice parameter), the two inequivalent Dirac cones merge and the Fermi velocity is zero in one of the principal axis of deformation. We found that nonlinear terms are essential to describe the effects of deformation for electrons near or at the Fermi energy.

The effects of biaxial strain parallel to the (001) plane on the electronic structures and optical properties of Ge are calculated using the first-principles plane-wave pseudopotential method based on density functional theory. The screened-exchange local-density approximation function was used to obtain more reliable band structures, while strain was changed from −4% to $+$4%. The results show that the bandgap of Ge decreases with the increase of strain. Ge becomes a direct-bandgap semiconductor when the tensile strain reaches to 2%, which is in good agreement with the experimental results. The density of electron states of strained Ge becomes more localized. The tensile strain can increase the static dielectric constant distinctly, whereas the compressive strain can decrease the static dielectric constant slightly. The strain makes the absorption band edge move toward low energy. Both the tensile strain and compressive strain can significantly increase the reflectivity in the range from 7 eV to 14 eV. The tensile strain can decrease the optical conductivity, but the compressive strain can increase the optical conductivity significantly.

In this study, we propose a new bilayer-laminated magnetoelectric (ME) composite consisting of magnetostrictive Ni and Tb${}_{0.3}$Dy${}_{0.7}$Fe₂ (Terfenol-D) plates and piezoelectric Pb(Zr,Ti)O₃ (PZT) plate. The Ni–Terfenol–D-Ni/PZT composite is constructed and compared with the traditional Terfenol-D/PZT composite. The bias magnetic field and the electric field frequency dependences of the converse ME (CME) coefficient were investigated. It is shown that the Ni–Terfenol-D–Ni/PZT exhibits a large CME coefficient of 6.2 × 10${}^{-7}$ s/m at the electric field frequency of 42 kHz under a low bias magnetic field of 230 Oe, which results from the highly concentrated flux induced by Ni and the stress-interaction between Ni and magnetostrictive Terfenol-D.

The stability and electronic properties of the hexagonal, trigonal and rectangular cross-sectional GaP nanowires in wurtzite (WZ) phase are investigated using full potential linear augmented plane waves method. The rectangular cross-sectional nanowires are found more stable than the hexagonal and trigonal ones. The indirect bandgap structure of the nanowires is transformed into the direct bandgap one at a critical size connected to the geometry of the cross-section. The energy bandgap of the nanowires in the same cross-sectional group is enlarged by the quantum size effect. The effective carrier masses in the nanowires, calculated to be larger than those in bulk GaP, are found to slightly increase with the decrease in the size of the nanowires in the same cross-sectional groups. The mechanical strain effect on the electronic band structure is investigated for the rectangular GaP nanowires under the uniaxial and lateral strains. It is found that the indirect bandgap structures of the rectangular nanowires are transformed into the direct bandgap ones by the uniaxial high compression strains. It is also found that this transformation can be triggered by small uniaxial tensile and high lateral tensile strains in addition to the effect of size increase. The energy bandgap of the rectangular nanowires is determined to be narrowed by the uniaxial/lateral strains. It is obtained that the small rectangular nanowire is in the indirect bandgap structure for all the lateral strains and the larger one can be transformed into the direct bandgap structure more easily by the $x$-directional lateral tensile strains compared to the $y$-directional ones. The effective electron and hole masses are found to be reduced by the uniaxial highest tensile and compression strains of this work. It is determined that the lateral strains are not effective in making the electrons of the nanowires more mobile, but the $y$-directional lateral high tensile strains make the holes more mobile by reducing the effective hole mass in the small rectangular nanowire.

The effect of high-energy electron beam on the silicon carbide nanopowder’s structural parameters, strain and powder size was studied. The sample was irradiated with $\sim$2-MeV electron beam energy under different fluencies such as 1.13 ⋅ 10${}^{17}$, 1.89 ⋅ 10${}^{17}$, 2.79 ⋅ 10${}^{17}$ and 3.69 ⋅ 10${}^{17}$ cm${}^{-2}$ at the linear electronic accelerator. Initial and irradiated samples at various doses have been analyzed in the XRD. The nanostructural effects within FullProf are treated using the pseudo-Voigt profile function. The dependences of maximum strain and nanocrystallite size on irradiation dose were obtained and analyzed.

In this study, a molecular dynamics (MD) study has been performed on composition and temperature dependences of mechanical properties of CdTe${}_{1-x}$Se${}_x$ ($x=0.25$, 0.50 and 0.75) nanowires with a diameter of 6.93 nm. The simulation results show that CdTe${}_{0.75}$Se${}_{0.25}$ nanowire seems to be more ductile, whereas CdTe${}_{0.25}$Se${}_{0.75}$ nanowire seems to be more brittle at 1 K. Moreover, the temperature and composition exert significant effects on the mechanical properties of CdTeSe nanowires under stretching. We conclude that the dominancy of Se atoms yields a higher stability and strength at the lower temperature of 1 K, whilst it is the same for the nanowires with both higher Te and Se contents at the higher temperature of 300 K. The radial distribution functions (RDFs) have also been calculated for the CdTeSe nanowires based on the pair separation distance at 1 and 300 K.