Growth and self-organization of SiGe nanostructures

We identify the most important parameters for the growth of ordered SiGe islands on pit-patterned Si(001) substrates. From a multi-dimensional parameter space we link individual contributions to isolate their influence on ordered island growth. This includes the influences of: the pit size, pit depth and pit period on the Si buffer layer and subsequent Ge growth; the pit sidewall inclination on Ge island growth; the amount of Ge on island morphologies as well as the influences of the pit-size homogeneity, the pit period, the Ge growth temperature and rate on island formation. We highlight that the initial pit shape and pit size in combination with the growth conditions of the Si buffer layer should be adjusted to provide suitable preconditions for the growth of Ge islands with the desired size, composition and nucleation position. Furthermore, we demonstrate that the wetting layer between pits can play the role of a stabilizer that inhibits shape transformations of ordered islands. Thus, dislocation formation within islands can be delayed, uniform arrays of one island type can be fabricated and secondary island nucleation between pits can be impeded. These findings allow us to fabricate perfectly ordered and homogeneous Ge islands on one and the same sample, even if the pit period is varied from a few hundred nanometres to several micrometres.

http://iopscience.iop.org/article/10.1088/0957-4484/24/10/105601/pdf

Recipes for the fabrication of strictly ordered Ge islands on pit-patterned Si(001) substrates

Thermodynamic theory of growth of nanostructures

We show that both the morphology and the optoelectronic properties of SiGe islands growing in the pits of periodically pre-patterned Si(001) substrates are determined by the amount of Ge deposited per unit cell of the pattern. Pit-periods (p) ranging from 300 to 900 nm were investigated, and Ge growth was performed by molecular beam epitaxy (MBE) at temperatures of 690 and 760 °C. The ordered SiGe islands show photoluminescence (PL) emission, which becomes almost completely quenched, once a critical island volume is exceeded. By atomic force and transmission electron microscope images we identify the transition from pyramid-shaped to dome-shaped islands with increasing p. Eventually, the nucleation of dislocations in the islands leads to PL quenching. Below a critical Ge coverage a narrowing and a blue shift of the PL emission is observed, as compared to islands grown on a planar reference area of the same sample.

https://iopscience.iop.org/article/10.1088/0957-4484/22/16/165302/pdf

Microphotoluminescence and perfect ordering of SiGe islands on pit-patterned Si(001) substrates.

A new selective strained Si process has been developed incorporating thin (∼200 nm) strain-relaxed SiGe buffers. For the first time, strained silicon and strain relaxed buffer can be deposited selectively on the active area in between preformed shallow trench isolation structures. The combination of in situ chemical vapor etch and selective epitaxial re-growth allows the implementation of strained Si layers in CMOS flow, without the need of chemical mechanical planarisation and without modifications of the standard STI process. NMOSFETs fabricated in selective Strained Si layers on 20% Ge strain relaxed buffers show a carrier mobility increase of ∼50% compared to Si reference devices. The results of first non-optimized devices demonstrate the potential of this strained Si fabrication scheme.

Selective epitaxial deposition of strained silicon: a simple and effective method for fabricating high performance MOSFET devices

There is increasing interest in Si-based optoelectronics using Si/sub 1-x/Ge/sub x/ nanostructures due to the possibility of their integration with the Si technology. To overcome the problem of the indirect character of SiGe one is looking for means to increase the transition probability by realizing structures involving quantum size effects. Several fabrication strategies for semiconductor nanostructures have been proposed. One possible approach involves selective epitaxy to fill-in the small holes in patterned substrates. To realize the lateral confinement below 100 nm the patterned substrates are made either by e-beam lithography or by optical lithography. In the latter case, the sub-100 nm confinement is realized by the development of facets. Another approach for nanostructures is based on self-organized growth which leads to island formation in highly lattice-mismatched layers. In this paper these items are discussed for SiGe as well as device applications such as light emitting diodes. The growth technique used was low pressure chemical vapor deposition.

http://ieeexplore.ieee.org/iel4/6071/16213/00750173.pdf

M. Goryll

Papers

SiGe nanostructures