Computations of scattering rates from strain variations in high-mobility n-channel Si/SiGe heterostructures are presented, and the results compared with experiment. Two sources of strain variation are considered—interface roughness and misfit dislocations—both of which form to relieve strain in the Si channel layer which is under tension. Strain variations induced by interface roughness are demonstrated to provide a source of scattering which, for highly strained systems of the type considered here, is significantly larger than conventional geometrical roughness scattering. Misfit dislocations provide a source of localized scattering centers, and an appropriate formalism is developed to describe this case. For both types of scattering, reasonable agreement with measured mobilities is found for various values of channel thickness.

The formation of disordered regions is observed on the Ge(lll)c2x8 surface, at temperatures in the range 150-350 °C. The disorder occurs by the diffusion of surface adatoms in the (01T) directions. The disordered regions form at domain boundaries, and grow continuously with temperature until the entire surface becomes disordered at 300 °C. We argue that this phase transition is an example of premelting in two dimensions, i.e., "edge melting." PACS numbers: 61.16.Di, 68.35.Rh At room temperature, the lowest-energy structure of the (111) surface of germanium is a centered 2x8 reconstruction, consisting of Ge adatoms bonded on top of a bulk-terminated (111) bilayer. ! " 3 At a temperature near 300°C, the surface is known to undergo a reversible phase transition in which the c2x8 structure disorders, forming a structure characterized by an apparent 1 x 1 diffraction pattern with weak half-order spots. This transition has been studied by a number of techniques, 3 " 7 with the definitive work arguably being the low-energy electron diffraction (LEED) study of Phaneuf and Webb. 3 Above the transition temperature, they find that the weak half-order spots split and broaden, indicating that the disordered phase is actually incommensurate with the underlying lattice. They also argue that the transition is first order, based on an observed hysteresis in the LEED spot intensity between warming and cooling scans. These conclusions were supported by subsequent Monte Carlo simulations. 8 In this work, we use the scanning tunneling microscope (STM) to directly observe the 300 °C phase transition of the Ge(l 11) surface. Since few high-temperature STM measurements have previously been reported, 9 " 11 it is necessary for us to establish the conditions under which atomic motion can be identified from STM images. To this end, we first study the surface at temperatures of 150-220°C, where the motion of individual surface adatoms and rows of adatoms can be clearly seen. As the temperature is increased, this activity accelerates, and the rapidly moving atoms form disordered regions on the surface. These disordered regions are found to form at surface domain boundaries or steps. The regions grow continuously in size as the temperature is increased, and above 300 °C the entire surface is disordered. As discussed below, this type of behavior is precisely what is expected for a two-dimensional phase transition which is first order for an infinite-size domain, but is continuous near domain boundaries due to the occurrence of premelting at the boundaries. 12,13 This work was performed on a newly built STM, incorporating a tube scanner and inch worm 14 approach, with a symmetrical design to minimize thermal drifts.Germanium samples, p-typc with resistivity of 0.1 n cm, were prepared by cleaving and then annealing at a temperature of about 400 °C. Cooling at a rate of 2°C/min following the anneal resulted in

No abstract

The influence of misfit dislocations on the surface morphology of partially strain relaxed Si1−xGex films is studied by atomic force microscopy and transmission electron microscopy. Surface steps arising from the formation of single and multiple 60° dislocations are identified. The role of such steps in the development of a cross-hatch pattern in surface morphology is discussed.

The omission of a key reference (Ref. 2) in the authors’ earlier publication (Ref. 1) is noted. The major conclusion of (Ref. 2) was the same as that of the authors’ in (Ref. 1), namely, that surface steps generated by dislocation glide play an important role in the morphology in Si1−xGex films. (AIP)