Strain relief of metastable GeSi layers on Si(100)

Abstract

Highly metastable pseudomorphic Ge0.3Si0.7 layers 570 nm thick were grown on Si(100) at ∼300 °C by molecular-beam epitaxy. The relief of strain in such metastable layers upon ex situ thermal annealing in vacuum is investigated by double-crystal x-ray diffractometry and MeV 4He channeling spectrometry. Upon isochronal annealing of 30 min, the strain relieves sharply at (375±25) °C, and reaches the thermal equilibrium value above 400 °C. Under isothermal annealing between 300 and 400 °C, the time evolution of the strain relief has the characteristics of a nucleation and growth transformation. The strain relief is very slow initially, increases approximately linearly as the strain is partially relieved, and saturates upon approaching equilibrium strain state. Two important results are drawn from the experimental data. First, a deformation-mechanism map is constructed from which the strain relief rate of a metastable GeSi/Si can be extrapolated for given stress state and temperature. Second, the rate of the strain relief when the strain is partially relieved increases with rising temperature, and follows an Arrhenius behavior as a function of the inverse temperature with a slope of 2.1±0.2 eV. This value coincides with the activation energy for dislocation glide in Ge0.3Si0.7. Furthermore, the strain-relief equation of a plastic flow model is solved and fits well the experimental strain-time dependence. One of the two fitting parameters, the time constant, has an Arrhenius temperature dependence. The slope, 1.9±0.2 eV, is assumed to be the activation energy for dislocation motion, and agrees with the previous value extracted from the simple rate-temperature dependence. In addition, as the strain is relieved, the x-ray-diffraction peak from the layer broadens and the channeling yield increases, confirming that the generation of misfit dislocations associated with the strain relief is accompanied by the generation of threading dislocations in the layer.

Electrical properties of the Ti(SiGe)2/Si0.89Ge0.11/Si(001) contact system

“…These effects when driven by a high ͑800°C͒ annealing temperature enhance generation of vacancies, annealing of points defects, and agglomerations of defects in the depletion region. 33,34 This is also supported by the presence of a high GR rate of minority carriers at all measurement temperatures in specimens annealed at 800°C, as it seen from the observed reverse currents in Fig. 1.…”

Strain relaxation of GeSi/Si(001) heterostructures grown by low-temperature molecular-beam epitaxy

“…The Matthews and Blakeslee critical thickness of the beginning of misfit-dislocation insertion 25 for a film with such a fraction of Ge is about 13 nm. 26 In growing stressed films at low temperatures, the equilibrium critical thickness can be exceeded by a factor of dozens, 27 which is observed in our case with the heterostructures grown on a dislocation-free Si substrate. Figure 4 shows the x-ray rocking curve of the D16 sample with a 0.2 fraction of Ge (the D16 sample is a typical representative of such films).…”

Interface roughness in SiGe quantum-cascade structures from x-ray reflectivity studies

“…It is well known that the SiGe critical layer thickness can be strongly increased by growing at low temperatures. 10,11 Annealing of our samples for 10 min at 600°C leads to plastic relaxation, demonstrating that the asgrown samples are metastable. In order to probe a much larger volume of the sample as that accessible with TEM and to prove the pseudomorphic growth, high-resolution XRD reciprocal space maps were recorded.…”