Instabilities in semiconductor heterostructure growth can be exploited for the self-organized formation of nanostructures, allowing for carrier confinement in all three spatial dimensions. Beside the description of various growth modes, the experimental characterization of structural properties, such as size and shape, chemical composition, and strain distribution is presented. The authors discuss the calculation of strain fields, which play an important role in the formation of such nanostructures and also influence their structural and optoelectronic properties. Several specific materials systems are surveyed together with important applications.

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Structural properties of self-organized semiconductor nanostructures

Low energy electron microscopy (LEEM) is a surface imaging technique in which the surface is illuminated by an approximately parallel electron beam at near normal incidence. The image is formed with those electrons which are elas- tically backscattered into a small angular region around the surface normal. The limitation to a small angular region is necessary because of the large aberrations of the objective lens which produces the primary image. This lens is a so-called cathode lens which not only has imaging properties but at the same time decelerates the fast electrons of the illuminating beam to the desired low energy at the specimen and re-accelerates the backscattered electrons to high energies again. In order to achieve this, the specimen is at a high negative potential which differs from the potential of the emitter of the electron gun of the illumination system by V 0 = E 0/e, where E 0 is the energy of the electrons at the specimen. Typical energy values are E = eV = 15−20 keV for the fast electrons and 0 < E 0 < 50 eV at the specimen. There are three fundamental quantities which are important in LEEM: resolution, intensity and contrast. These will be discussed in Sect. 12.1. Section 12.1 also describes how LEEM can be combined with other surface characterization techniques, such as low energy electron diffraction (LEED), photoemission electron microscopy (PEEM) and other emission microscopies. Section 12.2 illustrates the applications of LEEM and of the associated techniques to the study of clean surfaces, while Sect. 12.3 presents examples of the power of LEEM in the study of surface layers. Section 12.4 gives an outlook for possible future developments. A brief summary (Sect. 12.5) concludes this chapter.

https://iopscience.iop.org/article/10.1088/0034-4885/57/9/002/pdf

Low energy electron microscopy

Clustering on surfaces

Steps on surfaces: experiment and theory

Elastic effects on surface physics

Surface studies by low-energy electron microscopy (LEEM) and conventional UV photoemission electron microscopy (PEEM)

Vicinal Si(111) surfaces misoriented towards the [211] direction facet reversibly upon cooling through the (1×1) to (7×7) reconstructive phase transition. We have used low-energy electron microscopy to examine the kinetics of this phase separation. Nucleation and growth of facets occur when the surfaces are quenched just below the phase boundary. However, at lower temperatures we find evidence for the existence of a spinodal which divides the faceting kinetics into unstable and metastable regions. The location of the spinodal is consistent with previous measurements of Si(111) step energetics

Crossover from metastable to unstable facet growth on Si(111)

The low‐energy electron microscopy work on the structure and dynamics of semiconductor surfaces, in particular of Si(111) and Si(100) is reviewed. The phenomena studied include the (7×7) ↔ (1×1) phase transition of the Si(111) surface, the sublimation of Si from Si(100) and the growth of Si on Si(100). Interactions between steps and between steps and impurities are also discussed as are metal–silicon interactions, illustrated by the formation of CoSi2 by cobalt deposition.

Low-energy electron microscopy of semiconductor surfaces

The Si{100} and Si{111} surfaces are studied by low-energy electron microscopy. Atomic step and terrace structure formed by misorientation of Si wafers is investigated as well as various migration patterns of atomic steps formed during sublimation. Slip traces ending typically at screw dislocations form along ‘110’ directions in the surface and create additional atomic steps. Analysis of migration patterns near slip traces implies that both partial and perfect dislocations (or their equivalent, namely two partials) form on Si {100}. Perfect dislocations are seen on Si{111}. Regions with the (7×7) structure on Si{111}, which contain stacking faults, are imaged. Surface domain structure and domain boundaries are seen on Si{111}. On Si{100} the partial dislocations create two new types of surface domain displaced relative to the two pre-existing (2 × 1) and (1 × 2) domains. The potential for in situ studies of process-induced defects on Si wafers is demonstrated.

W. Swiech

Papers

Surface studies by low-energy electron microscopy (LEEM) and conventional UV photoemission electron microscopy (PEEM)

Crossover from metastable to unstable facet growth on Si(111)

Low-energy electron microscopy of semiconductor surfaces

Atomic step and defect structure on surfaces of Si{100} and Si{111} observed by low-energy electron microscopy

Low energy electron microscopy of surface processes