Investigation of GeSn Strain Relaxation and Spontaneous Composition Gradient for Low-Defect and High-Sn Alloy Growth

Abstract

Recent development of group-IV alloy GeSn indicates its bright future for the application of mid-infrared Si photonics. Relaxed GeSn with high material quality and high Sn composition is highly desirable to cover mid-infrared wavelength. However, its crystal growth remains a great challenge. In this work, a systematic study of GeSn strain relaxation mechanism and its effects on Sn incorporation during the material growth via chemical vapor deposition was conducted. It was discovered that Sn incorporation into Ge lattice sites is limited by high compressive strain rather than historically acknowledged chemical reaction dynamics, which was also confirmed by Gibbs free energy calculation. In-depth material characterizations revealed that: (i) the generation of dislocations at Ge/GeSn interface eases the compressive strain, which offers a favorably increased Sn incorporation; (ii) the formation of dislocation loop near Ge/GeSn interface effectively localizes defects, leading to the subsequent low-defect grown GeSn. Following the discovered growth mechanism, a world-record Sn content of 22.3% was achieved. The experiment result shows that even higher Sn content could be obtained if further continuous growth with the same recipe is conducted. This report offers an essential guidance for the growth of high quality high Sn composition GeSn for future GeSn based optoelectronics.

Si-Based GeSn Photodetectors toward Mid-Infrared Imaging Applications

“…As the Sn composition increases, the emission peak shifts towards longer wavelength due to the bandgap shrinkage of GeSn as more Sn incorporates. 6,41 Note that although sample F has higher Sn composition (22.3%) than that of sample E (20%), the PL peak of sample F was obtained at shorter wavelength, which is attributed to the higher compressive strain of sample F. 41,43 Photoconductor device characterization. As the Sn composition increases, the cut-off wavelength shifts towards longer wavelength due to the bandgap shrinkage.…”

Atomically uniform Sn-rich GeSn semiconductors with 3.0–3.5 μm room-temperature optical emission

“…% is observed in TL. We highlight that a homogeneous Sn composition is obtained across the TL without the presence of a compositional gradient, 19,21 indicating that the introduction of ML-BL layers enhances the strain relaxation, thus facilitating the Sn incorporation in TL. Additionally, a steep change in composition is visible at the TL/ML interface, with a decrease in the Sn content to 13.7 6 0.2 at.…”

“…The recently proposed multilayer growth has emerged as a promising approach to achieve a better control over strain and defects throughout GeSn epitaxy. [19][20][21] However, the observed Sn compositional gradient, resulting from the progressive strain relaxation during growth, may be undesired for the growth of heterostructures with abrupt interfaces and uniform content in each layer. Herein, we demonstrate that this limitation can be overcome by optimizing the growth process leading to GeSn layers with uniform Sn content reaching 18 at.…”

“…2(a) shows the GeSn TL/ ML/BL stack grown on an $650 nm-thick Ge-VS. No threading dislocations propagating toward the GeSn TL are observed, while misfit and edge dislocations are confined at the Ge-GeSn interface and within the first 100 nm of the GeSn stacking. 20,21,24 High-resolution TEM (HRTEM) image of the defect-free TL is shown in Fig. 2(b) with no additional spots in the fast-Fourier transform (FFT) image [ Fig.…”

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

“…This is due to the lattice mismatch between Ge and GeSn, which results in a relatively high threading dislocation density (TDD) [17]. The formation of threading dislocation loops in the 1st GeSn layer prevents the threading dislocations from penetrating the 1st GeSn layer and then propagating into the 2nd GeSn layer, resulting in a relatively low-defect density in the 2nd GeSn layer [30]. From TEM images, the thicknesses of the 1st and 2nd GeSn layers are 450 and 970 nm and 380 and 830 nm for samples A and B, respectively.…”