Structural properties of self-organized semiconductor nanostructures

TLDR: In this paper, 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.

Abstract: 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.

Figures

FIG. 4. Evolution of a stepped surface calculated using the strain model for step bunching: sad time evolution of the average bunch size; sbd growth time expressed in arbitrary units. Adapted from Tersoff et al., 1995.

FIG. 11. Typical Ge island shapes obtained by STM during Si capping of Ge domes grown on Sis001d: sad,sbd, domes; scd pyramids; sdd–sfd prepyramids. The Si coverages are 0, 1, 2, 4, 8, and 16 ML’s for panels sad–sfd. From Rastelli et al., 2001.

FIG. 10. The size distribution of several island types occurring during deposition of Ge on Sis001d. The inset shows the time evolution of the island density for different types. Adapted from Vailionis et al., 2000.

FIG. 29. Energy-selective imaging sESId: sad conventional TEM bright-field image of InAs islands in GaAs; sbd In concentration map obtained from ESI; scd line profiles of In concentration along the growth direction averaged over the stripes indicated in sbd. From Walther et al., 2001.

FIG. 49. sColor in online editiond Photoluminescence sPLd spectra from SiGe hut clusters overgrown at different energies. Inset: the PL line position saturates for Tgrowth,360 °C. From Denker et al., 2003b.

FIG. 50. Photoluminescence from dome-shaped SiGe islands as a function of growth temperature during Si capping. From Schmidt, Denker, et al., 2000.

Frequently asked questions

Q1. What have the authors contributed in "Structural properties of self-organized semiconductor nanostructures" ?

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. 

Q2. What is the effect of the surface reconstruction on the formation of self-assembled nanostructures?

Elastic energy relief is important for the formation of self-assembled nanostructures, and this in turn depends substantially on layer thickness: 

Q3. How did this group grow the nanowires?

Using prefabricated catalytic nanoparticles, e.g., size-selected gold aerosol particles, this group grew 2D arrays of vertically oriented nanowires of various materials sSi/Ge, InAs/InP, etc.d epitaxially. 

Q4. Why have x-ray scattering techniques gained importance?

x-ray scattering techniques have gained importance due to the abilities offered by thirdgeneration synchrotron sources. 

Q5. Why are dome-shaped islands considered as quantum wells?

Because of their larger size, lateral confinement effects are not observed, and dome-shape islands can be regarded as quantum wells with confinement only along the growth direction. 

Q6. What is the way to characterize the shape of self-assembled islands?

With a typical resolution of several nm laterally and several Å vertically, AFM is ideally suited to characterize the shape of self-assembled islands. 

Q7. What is the reason for the improved signal from the surface layer compared to that from the substrate?

The improved signal from the surface layer compared to that from the substrate in grazing-incidence diffraction is due not to an enhancement of the former, but to a reduction of the latter, as most of the x-ray beam is specularly reflected at the surface. 

Q8. What is the important parameter affecting the optical performance of self-organized semiconductor islands?

An important parameter affecting the optical performance of self-organized semiconductor islands is the homogeneity of their size and shape. 

Q9. What are the different means of contrast used in x-ray scattering?

Different means of contrast can be used, e.g., differences in the refractive index are exploited in x-ray reflectivity and grazing-incidence small-angle x-ray scattering, while the strain fields are measured in coplanar x-ray diffraction and grazing-incidence diffraction. 

Q10. How did Eisenberg and Kandel s2002d explain the growth of the island?

In order to explain planar growth for low coverages, Eisenberg and Kandel s2002d considered the elastic anisotropy of the growing layer. 

Q11. What is the intensity maxima of the reciprocal island lattice?

If the primary x-ray beam is well collimated both in the scattering plane and in the direction perpendicular to it, the intensity maxima are cross sections of the reciprocal island lattice with the scattering plane. 

Q12. What is the effect of strain field on the formation of step bunches?

During growth, the strain field due to a step bunch in a buried strained layer influences the formation of step bunches in subsequent strained layers. 

Q13. How does the value of hydrostatic stress at the surface of the island apex vary?

The value of hydrostatic stress at the surface above the island apex varies as D−1, where D is the thickness of the spacer layer. 

Q14. Why is it not possible to form an image out of the diffraction pattern?

Due to the lack of x-ray lenses, however, it is not possible to form an image out of the diffraction pattern; the pattern itself is recorded. 

Q15. What is the rate of change of potential with thickness?

From the three-dimensional representation of the unitcell vectors, which form a plane ellipse, the rate of change of projected potential with thickness can be deduced. 

Q16. What is the resolution of AFM, STM, and TEM?

X-ray diffraction sXRDd or photoluminescence may also be used to determine size and shape, but in general the resolution of AFM, STM, and TEM is higher. 

Q17. What is the difference between grazing-incidence diffraction and x?

In contrast to GISAXS and x-ray reflectivity, grazing-incidence diffraction measures the crystalline lattice roughness rather than morphological roughness alone, as it is sensitive to contrast in xh instead of x0, but the general features of diffuse scattering remain the same.