Prepyramid-to-pyramid transition of SiGe islands on Si(001)

The morphology of the first three-dimensional islands appearing during strained growth of SiGe alloys on Si(001) was investigated by scanning tunneling microscopy. High resolution images of individual islands and a statistical analysis of island shapes were used to reconstruct the evolution of the island shape as a function of size. As they grow, islands undergo a transition from completely unfacetted rough mounds (prepyramids) to partially {105} facetted islands and then they gradually evolve to {105} facetted pyramids. The results are in good agreement with the predictions of a recently proposed theoretical model

X-ray Diffraction Mapping Of Strain Fields And Chemical Composition Of Sige:si(001) Quantum Dot Molecules

A variety of surface morphologies can be formed by controlling kinetic parameters during heteroepitaxial film growth. The system reported is a Si0.7 Ge0.3 film grown by molecular beam epitaxy at 550°C and a 1 s deposition rate, producing quantum dot molecule (QDM) structures. These nanostructures are very uniform in size and shape, allowing strain mapping and chemical composition evaluation by means of anomalous x-ray diffraction in a grazing incidence geometry. Tensile and compressed regions coexist inside QDMs, in accordance with the finite-element calculations of lattice relaxation. The Ge content was found to vary significantly within the structures, and to be quite different from the nominal composition. © 2006 The American Physical Society.7312Chen, K.M., (1995) Appl. Phys. Lett., 66, p. 34. , APPLAB 0003-6951 10.1063/1.114172Goldfarb, I., (1997) Phys. Rev. Lett., 78, p. 3959. , PRLTAO 0031-9007 10.1103/PhysRevLett.78.3959Mo, Y.-W., (1990) Phys. Rev. Lett., 65, p. 1020. , PRLTAO 0031-9007 10.1103/PhysRevLett.65.1020Tomitori, M., (1994) Appl. Surf. Sci., 76-77, p. 322. , ASUSEE 0169-4332Floro, J.A., (1998) Phys. Rev. Lett., 80, p. 4717. , PRLTAO 0031-9007 10.1103/PhysRevLett.80.4717Ross, F.M., (1998) Phys. Rev. Lett., 80, p. 984. , PRLTAO 0031-9007 10.1103/PhysRevLett.80.984Medeiros-Ribeiro, G., (1998) Science, 279, p. 353. , SCIEAS 0036-8075 10.1126/science.279.5349.353Chaparro, S.A., (1999) Phys. Rev. Lett., 83, p. 1199. , PRLTAO 0031-9007 10.1103/PhysRevLett.83.1199Denker, U., (2005) Appl. Phys. Lett., 772, p. 599. , APPLAB 0003-6951Gray, J.L., (2002) Appl. Phys. Lett., 81, p. 2445. , APPLAB 0003-6951 10.1063/1.1509094Vandervelde, J.T.E., (2003) Appl. Phys. Lett., 83, p. 2505. , APPLAB 0003-6951Jesson, D.E., (1996) Phys. Rev. Lett., 77, p. 1330. , PRLTAO 0031-9007 10.1103/PhysRevLett.77.1330Gray, J.L., (2004) Phys. Rev. Lett., 92, p. 135504. , PRLTAO 0031-9007 10.1103/PhysRevLett.92.135504Schülli, T.U., (2003) Phys. Rev. Lett., 90, p. 066105. , PRLTAO. 0031-9007. 10.1103/PhysRevLett.90.066105Malachias, A., (2003) Phys. Rev. Lett., 91, p. 176101. , PRLTAO 0031-9007 10.1103/PhysRevLett.91.176101Magalhães-Paniago, R., (2002) Phys. Rev. B, 66, p. 245312. , PRBMDO. 0163-1829. 10.1103/PhysRevB.66.245312Krause, B., (2005) Phys. Rev. B, 72, p. 085339. , PRBMDO 0163-1829 10.1103/PhysRevB.72.085339Zhang, Y., (2001) J. Appl. Phys., 90, p. 4748. , JAPIAU 0021-8979 10.1063/1.1407311Gray, J.L., (2005) Phys. Rev. B, 72, p. 155323. , PRBMDO 0163-1829 10.1103/PhysRevB.72.155323Tersoff, J., (1998) Phys. Rev. Lett., 81, p. 3183. , PRLTAO 0031-9007 10.1103/PhysRevLett.81.318

First-principles calculation of the effect of strain on the diffusion of Ge adatoms on Si and Ge (001) surfaces

First-principles calculations are used to calculate the strain dependencies of the binding and diffusion-activation energies for Ge adatoms on both Si(001) and Ge(001) surfaces. Our calculations reveal that the binding and activation energies on a strained Ge(001) surface increase and decrease, respectively, by 0.21 eV and 0.12 eV per percent compressive strain. For a growth temperature of 600 degrees C, these strain-dependencies give rise to a 16-fold increase in adatom density and a 5-fold decrease in adatom diffusivity in the region of compressive strain surrounding a Ge island with a characteristic size of 10 nm.Comment: 4 pages, 4 figure

GaN Stress Evolution During Metal-Organic Chemical Vapor Deposition

The evolution of stress in gallium nitride films on sapphire has been measured in real- time during metal organic chemical vapor deposition. In spite of the 161%0 compressive lattice mismatch of GaN to sapphire, we find that GaN consistently grows in tension at 1050"C. Furthermore, in-situ stress monitoring indicates that there is no measurable relaxation of the tensile growth stress during annealing or thermal cycling

Stress and Defect Control in GaN Using Low Temperature Interlayers

In organometallic vapor phase epitaxial growth of Gail on sapphire, the role of the low- temperature-deposited interlayers inserted between high-temperature-grown GaN layers was investigated by in situ stress measurement, X-ray diffraction, and transmission electron microscopy. Insertion of a series of low temperature GaN interlayers reduces the density of threading dislocations while simultaneously increasing the tensile stress during growth, ultimately resulting in cracking of the GaN film. Low temperature AIN interlayers were found to be effective in suppressing cracking by reducing tensile stress. The intedayer approach permits tailoring of the film stress to optimize film structure and properties