Growth and structural properties of step-graded, high Sn content GeSn layers on Ge

Abstract

Two approaches have been compared for the low temperature epitaxy of thick, partially relaxed GeSn layers on top of Ge strain relaxed buffers. The benefit of using step-graded instead of constant composition layers when targeting really high Sn contents (16%, here) was conclusively demonstrated. Digermane (Ge 2 H 6 ) and tin-tetrachloride (SnCl 4 ) were used as Ge and Sn precursors, respectively. The growth pressure (100 Torr) and the F(Ge 2 H 6 )/F(SnCl 4 ) mass-flow ratio being constant, it was through a temperature lowering that the Sn concentration in the graded structure was increased. X-ray diffraction, atomic force microscopy and transmission electron microscopy were used to gain access to the Sn concentration, the strain state, the surface morphology and thicknesses of the heterostructures. Using a step-graded approach allowed us to gradually relax the strain in the GeSn layers. It helped us obtain high crystalline quality and avoid Sn segregation/precipitation for high Sn contents.

Experimental Calibration of Sn‐Related Varshni Parameters for High Sn Content GeSn Layers

“…This suggests that epilayers are in fact formed of two distinct layers with different concentration. The situation was confirmed by TEM‐EDX analysis confirmed the presence of layers with two distinct Sn concentrations, a thin lower concentration layer accommodating the plastic strain relaxation between the Ge substrate and the thick high‐Sn layer . With such configuration, we assume that only the highest Sn‐concentrated layer will contribute to the emission as the layer presents the smallest bandgap of the whole stack.…”

“…The Ge x Sn (1− x ) energy bandgap at the Γ point ( is determined by fitting temperature‐dependent PL measurements of the stack described in ref. [] shown in the inset of Figure . Using Equation and bandgap energy calculated for Ge, we are able to plot temperature‐dependent as shown in Figure .…”

Study of Si-Based GeSn Optically Pumped Lasers With Micro-Disk and Ridge Waveguide Structures

“…The Ge buffer layer is almost relaxed, with a nominal thickness of 700 nm (residual strain of ∼−0.1%). A multiple-step Sn-enhanced growth recipe was used, which was developed and reported in our previous study on the spontaneous-relaxation-enhanced (SRE) Sn incorporation process: the gradual relaxation of the material facilitates Sn incorporation [17,27], resulting in an increased Sn composition along the growth direction. Two samples (denoted by A and B) with Sn compositions as high as ∼20.0% were grown.…”

GeSn heterostructure micro-disk laser operating at 230 K

“…GeSn layers were grown on top of a 2.5 µm thick Ge strain relaxed buffer (SRB), which was itself deposited on top of a Si (001) substrate. Ge 2 H 6 and SnCl 4 fluxes were fixed and the temperature gradually lowered -from 349°C down to 313°Cduring the growth at 100 Torr to create discrete Sn concentration steps, known as "GeSn stepgraded epitaxy" in [16,19,20]. Such a strategy limits the number of threading dislocations propagating towards the optically active GeSn 16.0% layer and relaxes it partially.…”