N. Rosson, A. Fischer, R. Scott
Lawrence Semiconductor Research Laboratory,
United States
Keywords: optoelectronics group IV GeSn lasers, detectors, direct bandgap
Summary:
For the past decade, researchers in the U.S. and abroad have ramped up efforts to develop group IV, Si-based alloys of (Si)GeSn for optoelectronic devices operating in the SWIR, MWIR and LWIR portion of the electromagnetic spectrum, including detectors, imagers, and lasers. Traditionally, III-V and II-VI materials have been used for these applications, but monolithic integration of group IV-based device structures on a silicon platform is highly advantageous for system performance and cost. Given the differences in lattice parameter and coefficients of thermal expansion (CTE) when comparing group IV to III-V and II-V materials, hybridizing III-V materials with Si requires elaborate materials coupling methods including flip chip bonding and Indium bumping. In addition, processing compound semiconductor materials is very costly. Many of the precursors used for CVD deposition of III-V and II-VI materials are toxic, pyrophoric and have stringent waste effluent regulations necessitating costly abatement systems. In addition, the III-V and II-VI substrates needed for epitaxial growth are not always commercially available. Hence, top notch research institutions, national laboratories and industry partners are converging in an effort to develop group IV alloys that meet or exceed the performance of III-V and II-VI device analogs. To that end, Lawrence Semiconductor Research Laboratory, Inc. (LSRL), a Tempe, Arizona based company that has been providing novel group IV (Si, Ge, SiGe, and SiGeC) epitaxial growth services since 1992, has recently expanded its capability to develop and supply SiGeSn GeSn device structures. This in part is due to a subcontract award to LSRL from the Office of Naval Research (ONR) and internal motivation to add this material capability to their repertoire of epitaxial device structures using group IV alloys. In 2023, LSRL dedicated and modified an ASM E2500 CVD reactor and clean room for the growth and characterization of these novel group IV materials. Here we report progress in developing these GeSn-based device structures. To date, LSRL has grown GeSn on a Ge buffer layer with specular, defect free surface morphology across a 200 mm wafer with Sn compositions ranging from a few percentages up to approximately 20% Sn, corresponding to a band edge of approximately 1585 to greater than 3750 nm. Based on temperature dependent photoluminescence from 300K to 20K, direct bandgap behavior has been demonstrated for Sn compositions above approximately 10 atomic percent.