A surfactant-mediated relaxed Si0.5Ge0.5 graded layer with a very low threading dislocation density and smooth surface

Abstract

A method to grow a relaxed Si0.5Ge0.5 graded layer with a very smooth surface and a very low threading dislocation density using solid-source molecular-beam epitaxy is reported. This method included the use of Sb as a surfactant for the growth of a 2 μm compositionally graded SiGe buffer with the Ge concentration linearly graded from 0% to 50% followed by a 0.3 μm constant Si0.5Ge0.5 layer. The substrate temperature was kept at 510 °C during the growth. Both Raman scattering and x-ray diffraction were used to determine the Ge mole fraction and the degree of strain relaxation. Both x-ray reflectivity and atomic force microscopy measurements show a surface root mean square roughness of only 20 Å. The threading dislocation density was determined to be as low as 1.5×104 cm−2 as obtained by the Schimmel etch method. This study shows that the use of a Sb surfactant and low temperature growth is an effective method to fabricate high-quality graded buffer layers.

Structural characterization of thick, high-quality epitaxial Ge on Si substrates grown by low-energy plasma-enhanced chemical vapor deposition

“…In both samples, the phonon peak is the strongest when both the incident and scattered light are polarized along the (110) direction (solid lines in Fig. The sample was etched using a standard delineation etch, 15,16 and the number of etch pits was counted using an optical microscope. 2).…”

Low Temperature (180°C) Growth of Smooth Surface Germanium Epilayers on Silicon Substrates Using Electron Cyclotron Resonance Chemical Vapor Deposition

“…A smooth surface can enhance the structural and electrical properties and reduce defects at the interface of devices such as photodetectors and solar cells because a better interface between different layers can reduce the carrier recombination effect. In the growth of Ge on Si films, the formation of a rough surface is mainly due to the dislocations threading up to the surface, the strain in the film [21,37], and the Stranski-Krastanov growth mechanism [8]. Figure 9 shows the surface morphology of a 40 nm Ge epilayer on Si when the working pressure is 30 mTorr.…”

Normal-incidence near-1.55-μm Ge quantum dot photodetectors on Si substrate

“…One approach is by growing a sufficient thick graded buffer layer with low grading speed. The use of a graded buffer [21][22] can help to achieve pure Ge or SiGe with high Ge mole fraction with a reduced defect density, but the dislocation still remains problematic for device application. And the long growth time of the thick graded buffer layer also increases the cost.…”