Strained SiGe Alloy Research Articles

Strain relaxation in epitaxial Si1-xGex layers during some silicidation processes

Strain relaxation in Si1-xGex epitaxial layers is investigated after the reaction of Co and Pt with strained SiGe alloy. The epitiaxial SiGe alloy studied has a Ge fraction ranging between x = 5% to 22%. The strain in the Si1-xGex is evaluated using multi-crystal high resolution x-ray diffraction mapping in reciprocal space (MC-HRXRD). The results show that for Co in order to keep the strain in Si1-xGex unaffected, a sacrificial Si layer is needed. The direct reaction of 40 nm Co on Si0.9Ge0.1 can lead to defect formation and 40% strain relaxation. This is in contrast to Pt/Si1-xGex reaction, where negligible relaxation was observed.

Amorphization Threshold in Si-Implanted Strained Sige Alloy Layers

AbstractWe have examined the damage produced by Si-ion implantation into strained Si1-xGex epilayers. Damage accumulation in the implanted layers was monitored in situ by time-resolved reflectivity and measured by ion channelling techniques to determine the amorphization threshold in strained Si1-xGex, (x = 0.16 and 0.29) over the temperature range 30-110°C. The results are compared with previously reported measurements on unstrained Si1-xGex, and with the simple model used to describe those results. We report here data which lend support to this model and which indicate that pre-existing strain does not enhance damage accumulation in the alloy layer.

Carrier velocity-field characteristics and alloy scattering potential in Si1−xGex/Si

The alloy scattering potential is an important parameter in SiGe alloys since it not only affects the velocity-field characteristics for carrier transport, but also allows increased optical transitions by relaxing k-selection rules. In this letter, we report on the velocity-field measurements for relaxed and coherently strained SiGe alloys. The alloy scattering potential is obtained from a careful fit to the data. The hole velocity at any field is found to have a bowing behavior as a function of alloy composition. This reflects a strong alloy scattering potential which is calculated to be 0.6 eV for the valence band.

Strained Si/Ge superlattices: Structural stability, growth, and electronic properties.

We present detailed results of self-consistent-field pseudopotential calculations for the stability, structural phase transitions, growth, and the electronic properties of strained Si/Ge semiconductor superlattices and alloys. The metastable structure of (Si${)}_{n}$/(Ge${)}_{n}$ (n\ensuremath{\le}6) superlattices pseudomorphically restricted to the Si(001) surface are determined through total energy minimization and inter- atomic force calculations, and their formation energies are calculated. A simple model for the formation energy of superlattices is developed, whereby the energy of the activation barrier to form a misfit dislocation is estimated. A neostructural phase transition in the strained Si-Ge alloy is studied, and the order of instability for various possible structures is given. It is found that during growth the atoms of the topmost grown layer are dimerized, resulting in a possible short-range order in the alloy. The energy gap of all (Si${)}_{n}$/(Ge${)}_{n}$ superlattices is found to be indirect. A more significant finding, however, is that the energy separation between the direct and indirect gap continues to decrease with increasing n, and is only 0.07 eV for n=6. Conduction-band states of an extended nature located below the confined states point to a new feature of the band offset and quantum-size effect. Localized states lying deep in the valence- and conduction-band continua are another novel result of this study.

Oxidation of Strained Si-Ge Layers Grown by MBE

ABSTRACTThe oxidation of strained SiGe alloy layers grown by Molecular Beam Epitaxy (MBE) was studied. An initial fast growth regime was identified for 800°C steam oxidations, where the growth rate is 2.5 times that of silicon. The oxides formed on SiGe were found to be essentially Ge-free: Ge present in the material is rejected by the oxide, resulting in the formation of a Ge-rich epitaxial layer at the oxide/substrate interface.