Terrace grading of SiGe for high-quality virtual substrates

Abstract

Silicon germanium (SiGe) virtual substrates of final germanium composition x=0.50 have been fabricated using solid-source molecular beam epitaxy with a thickness of 2 μm. A layer structure that helps limit the size of dislocation pileups associated with the modified Frank–Read dislocation multiplication mechanism has been studied. It is shown that this structure can produce lower threading dislocation densities than conventional linearly graded virtual substrates. Cross-sectional transmission electron microscopy shows the superior quality of the dislocation network in the graded regions with a lower rms roughness shown by atomic force microscopy. X-ray diffractometry shows these layers to be highly relaxed. This method of Ge grading suggests that high-quality virtual substrates can be grown considerably thinner than with conventional grading methods.

Photoluminescence study of interband transitions in few-layer, pseudomorphic, and strain-unbalanced Ge/GeSi multiple quantum wells

“…Unfortunately, heteroepitaxial strain, arising from the 4.2 % lattice mismatch between Ge and Si, results in crystal defects, such as threading dislocations, that behave as non-radiative recombination centers and their presence is then detrimental for the efficiency of optoelectronic devices 23,24 . To achieve high-x Ge x Si 1−x layers with low threading dislocations density (TDD), relatively thick GeSi reverse-graded virtual substrates (RG-VS), where the lattice mismatch is gradually distributed among several layers, are commonly used [25][26][27][28] . Employing so many substrate layers with different concentrations results in complicated PL spectra.…”

Inhomogeneous distribution of dislocations in a SiGe graded layer and its influence on surface morphology and misfit dislocations at the interface of strained Si∕Si0.8Ge0.2

“…The surface fine lines were probably related to the slip steps arising from the formation of dislocation pileups in the graded SiGe layer. [13][14][15] Examining the TEM images ͑Fig. 1͒ in detail, we can see that the dislocations tended to be arranged in dislocation pileups.…”

Introduction of Terraces into a Reverse Linearly Graded SiGe Buffer on Si(001) Substrate and Their Effect on the Buffer's Structural Properties

“…In this paper we will investigate the properties of an RTG buffer, throughout its heterostructure, for use as a buffer for these applications. The idea of (forward) terrace grading was originally proposed by Capewell et al 12 where insertion of constant composition layers allow an analysis of the graded region throughout the buffer. In the previous work, we showed a small reduction in threading dislocation density (TDD) when RTGs were compared to RLG buffers.…”