Mechanical Deformation Behavior of Nonpolar GaN Thick Films by Berkovich Nanoindentation

In this study, the deformation mechanisms of nonpolar GaN thick films grown on m-sapphire by hydride vapor phase epitaxy (HVPE) are investigated using nanoindentation with a Berkovich indenter, cathodoluminescence (CL), and Raman microscopy. Results show that nonpolar GaN is more susceptible to plastic deformation and has lower hardness than c-plane GaN. After indentation, lateral cracks emerge on the nonpolar GaN surface and preferentially propagate parallel to the < 11 (2) over bar0 > orientation due to anisotropic defect-related stresses. Moreover, the quenching of CL luminescence can be observed to extend exclusively out from the center of the indentations along the < 11 (2) over bar0 > orientation, a trend which is consistent with the evolution of cracks. The recrystallization process happens in the indented regions for the load of 500 mN. Raman area mapping indicates that the distribution of strain field coincides well with the profile of defect-expanded dark regions, while the enhanced compressive stress mainly concentrates in the facets of the indentation.

Elastic deformation of wafer surfaces in bonding

A model has been proposed for describing elastic deformation of wafer surfaces in bonding. The change of the surface shape is studied on the basis of the distribution of the periodic strain field. With the condition of diminishing periodic strain away from the interface, Airy stress function has been found that satisfies the elastic mechanical equilibrium. The result reveals that the wavy interface elastically deforms a spatial wavelength from the interface. (C) 2000 American Institute of Physics. [S0021-8979(00)04219-5].

Triclinic deformation and anisotropic strain relaxation of an InAs film on a GaAs(001) substrate measured by a series of symmetric double crystal X-ray diffraction

We presented a series of symmetric double crystal X-ray diffraction (DCXD) measurements, (0 0 4), (2 2 0) and (2 - 2 0) diffraction, to investigate the strain relaxation in an InAs film grown on a GaAs(0 0 1) substrate. The strain tensor and rotation tensor were calculated according to the DCXD results. It is found that the misfit strain is relaxed nearly completely and the strain relaxation caused a triclinic deformation in the epilayer. The lattice parameter along the [1 1 0] direction is a little longer than that along the [1 - 1 0] direction. Furthermore, a significant tilt, 0.2 degrees, towards the [1 1 0] direction while a very slight one: 0.002 degrees, towards [1 - 1 0] direction were discussed. This anisotropic strain relaxation is attributed to the asymmetric distribution of misfit dislocations, which is also indicated by the variation of the full-width at half-maximum (FWHM) of (0 0 4) diffraction along four azimuth angles. (C) 1998 Elsevier Science B.V. All rights reserved.

INTERVALLEY-GAMMA-CHI DEFORMATION POTENTIALS IN III-V ZINCBLENDE AND SI SEMICONDUCTORS BY AB-INITIO PSEUDOPOTENTIAL CALCULATIONS

Intervalley GAMMA - X deformation potential constants (IVDP's) have been calculated by first principle pseudopotential method for the III-V zincblende semiconductors AlP, AlAs, AlSb, GaP, GaAs, GaSb, InP, InAs and InSb. As a prototype crystal we have also carried out calculations on Si. When comparing the calculated IVDP's of LA phonon for GaP, InP and InAs and LO phonon for AlAs, AlSb, GaAs, GaSb and InSb with a previous calculation by EPM in rigid approximation, good agreements are found. However, our ab initio pseudopotential results of LA phonon for AlAs, AlSb, GaAs, GaSb and InSb and LO phonon for GaP, InP and InAs are about one order of magnitude smaller than those obtained by EPM calculations, which indicate that the electron redistributions upon the phonon deformations may be important in affecting GAMMA - X intervalley shatterings for these phonon modes when the anions are being displaced. In our calculations the phonon modes of LA and LO at X point have been evaluated in frozen phonon approximation. We have obtained, at the same time, the LAX and LOX phonon frequencies for these materials from total energy calculations. The calculated phonon frequencies agree very well with experimental values for these semiconductors.

INTERVALLEY GAMMA-CHI DEFORMATION POTENTIALS IN III-V ZINCBLENDE SEMICONDUCTORS BY ABINITIO PSEUDOPOTENTIAL CALCULATIONS

Intervalley GAMMA-X deformation-potential constants (IVDP's) have been calculated by use of a first-principles pseudopotential method for the III-V zinc-blende semiconductors AlP, AlAs, AlSb, GaP, GaAs, GaSb, InP, InAs, and InSb. When the calculated IVDP's of LA phonons for GaP, InP, and InAs and of LO phonons for AlAs, AlSb, GaAs, GaSb, and InSb are compared with results of a previous calculation that used the empirical pseudopotential method (EPM) and a rigid-ion approximation, good agreement is found. However, our ab initio pseudopotential results on IVDP's of LA phonons for AlAs, AlSb, GaAs, GaSb, and InSb and of LO phonons for GaP, InP, and InAs are about one order of magnitude smaller than those obtained by use of EPM calculations, indicating that the electron redistribution accompanying crystal-lattice deformation has a significant effect on GAMMA-X intervalley scattering for these phonon modes when the anions are being displaced. In our calculations the LA- and LO-phonon modes at the X point have been evaluated in the frozen-phonon approximation. We have also obtained the LAX- and LOX-phonon frequencies for these materials from total-energy calculations, which agree very well with experimental values for these semiconductors. We have also calculated GAMMA-X hole-phonon scattering matrix elements for the top valence bands in these nine semiconductors, from which the GAMMA-X IVDP's of the top valence bands for the longitudinal phonons and transverse phonons are evaluated, respectively.

SHEAR-DEFORMATION-POTENTIAL CONSTANT OF THE CONDUCTION-BAND MINIMA OF SI - EXPERIMENTAL-DETERMINATION BY THE DEEP-LEVEL CAPACITANCE TRANSIENT METHOD

The shear-deformation-potential constant XI-u of the conduction-band minima of Si has been measured by a method which we called deep-level capacitance transient under uniaxial stress. The uniaxial-stress (F) dependence of the electron emission rate e(n) from deep levels to the split conduction-band minima of Si has been analyzed. Theoretical curves are in good agreement with experimental data for the S0 and S+ deep levels in Si. The values of XI-u obtained by the method are 11.1 +/- 0.3 eV at 148.9 K and 11.3 +/- 0.3 eV at 223.6 K. The analysis and the XI-u values obtained are also valuable for symmetry determination of deep electron traps in Si.

Deformation behaviour of electrodeposited nanocrystalline Ni with broad grain size distribution

In the present work, nanocrystalline Ni (nc-Ni) with a broad grain size distribution (BGSD) of 5-120 nm and an average grain size of 27.2 nm was prepared. The BGSD nc-Ni sample shows a similar strength and good ductility in comparison with electrodeposited nc-Ni with a narrow grain size distribution. The intracrystalline dislocation network was observed in the post-deformed microstructure confirming the conventional intracrystalline dislocation sliding mechanism in BGSD nc-Ni. The uniaxial tensile loading-unloading-loading deformation shows BGSD nc-Ni has the capability to store dislocations in the grain interior, which is very limited compared with that of coarse grained metals. For BGSD nc-Ni, the strain rate sensitivity of flow stress m enhances with decreasing strain rate. At the strain rate of 5 x 10(-6) s(-1), m was estimated to be 0.055. At the corresponding strain rate, the enhanced ductility along with the decreased strength was achievable, indicating activation of other deformation mechanisms, e. g. grain boundary sliding or diffusion.