Tunable Wavelength GeSn Laser and Photodetector on Lattice-Matched InAl(Ga)As Buffers for Group-IV Photonics

In line with the recent CHIPS and Science Act of 2022 and the push for quantum technology, group IV-based GeSn semiconductor materials have potential in photonics due to their unique and wide range of optical characteristics achieved by bandgap engineering via control of tin (Sn) composition in the GeSn alloy. The continued development of compact and affordable laser light sources and detection based on GeSn materials is important in many areas such as communication, biomedical, and defense applications.

However, one needs to synthesize device-quality, low-defect density tunable Sn compositional GeSn materials on a lattice-matched buffer. Furthermore, there is a lack of low-threshold current density GeSn-based laser light source due to the low carrier lifetime and weak carrier confinement on silicon that demand investigation of an alternative GeSn heterostructure design, which can achieve much higher conversion efficiency, thereby enhancing the integrated photonic device performance.

The latticed-matched combination of GeSn and InAl(Ga)As heterostructures for laser and photodetector offers a new path for highly efficient tunable light emission and detection. The central thrust of the proposed research is to investigate the design of tunable Sn compositional GeSn-based laser and mid-wavelength infra-red (MWIR) photodetector architectures that combine GeSn quantum-well (QW) or absorber layer lattice-matched to underlying InAl(Ga)As buffer.

Our objective is to develop tunable wavelength laser light sources that can exhibit lower threshold current density and higher quantum efficiency than existing group IV-based light sources as well as MWIR detection that will benefit a wide range of applications.

To demonstrate the feasibility of the proposed approach, several key technical and scientific challenges must be addressed, including (i) low-defect density tunable Sn compositional GeSn layer on lattice-matched InAl(Ga)As buffer with enhanced carrier lifetime; (ii) increased band offsets between GeSn and large bandgap InAl(Ga)As barrier layer for superior carrier confinement in a GeSn QW; (iii) design and simulation of the proposed wavelength tunability of GeSn/InAl(Ga)As-based QW laser and MWIR GeSn-based photodetectors; (iv) materials synthesis and analysis of lattice-matched InAl(Ga)As/GeSn/InAl(Ga)As QW laser structure on GaAs for modified bandgap of GeSn; and (v) fabrication and demonstration of GeSn QW laser and photodetector. To address (i), (ii), (iv), and (v), the proposed research will utilize the state-of-the-art in-house epitaxial growth (interconnected III-V and group IV molecular beam epitaxy chambers), comprehensive materials characterization and simulation (e.g., high-resolution x-ray diffraction, transmission electron microscopy, photoconductive decay, photoluminescence spectroscopy, atom probe tomography, x-ray photoelectron spectroscopy, and electronic band structure simulation by QuantumATK), and in-house fabrication facilities.

To address (iii), a combination of numerical simulations (Synopsys TCAD) and density functional theory will be leveraged to develop experimentally-calibrated InAl(Ga)As/GeSn/InAl(Ga)As QW device models necessary for light emission in MWIR range and photodetection. By investigating these topics, this research will elucidate numerous as-of-yet unexplored avenues of fundamental research, including (a) the synthesis of high Sn compositional GeSn alloy on lattice-matched InAl(Ga)As buffer; (b) the role of GeSn layer thickness to optical gain and emission wavelength; (c) the reduction of threshold current density arising from recombination losses; (d) carrier lifetime and interatomic diffusion in a GeSn alloy on InAl(Ga)As buffer.

Through a comprehensive examination and understanding of the above challenges, this research will establish a pathway to achieve high-performance group IV lasers and detectors that will benefit society and industry. Furthermore, this project will train and mentor undergraduate and graduate students in the field of photonics. These students will experience a research environment in PI’s laboratories.

Outcomes of the proposed research results will be disseminated to the public and be incorporated into the course curriculum. In addition, the project will provide hands-on experience to undergraduates through Virginia Tech ECE Department major design experience.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.