The Fall 2021 MatSE 590 for graduate students consists of an exciting and jam-packed schedule. MATSE 590 is a colloquium (1-3 credits) consist of a series of individual lectures by faculty, students, or outside speakers.
Graduate students will receive a weekly email with information via @psu.edu email. Graduate students are required to attend all 590 Seminars. If you have any questions, please email Hayley Barnes at firstname.lastname@example.org.
*Due to the ongoing Covid Pandemic this program is being offered virtually through Zoom. Please reference the weekly email from Hayley Barnes (email@example.com) for Zoom link.
Thursday, October 28, 2021
“A Salty Problem: Integration of Alkali Halides with III-Vs”"
Brelon May, Postdoctoral Researcher, National Renewable Laboratory
Expensive single crystalline substrates are at the heart of many semiconduc-tor technologies and limit widespread adoption of area-sensitive technologies such as high-efficiency photovoltaics. Thus, there is a high degree of interest in separating devices from the parent substrate, allowing the wafer to be re-used multiple times. Existing III-V recycling techniques have downfalls such as: high toxicity, slow speed, heterostructure restrictions, but most important-ly the surface after removal is rough, largely negating any cost reductions. Here we demonstrate molecular beam epitaxy of a thin NaCl layer as a sacri-ficial release layer for liftoff and recycling of commonly used GaAs (100). In-situ diagnostic tools reveal that the initial crystallinity of the NaCl is depend-ent on the arrangement of GaAs surface atoms. Overgrowth of GaAs on NaCl thin films is highly complex as NaCl is extremely volatile at typical GaAs growth temperatures. The substrate temperature and exposure to an in-situ electron beam during the early stages of growth have a profound effect on the morphology and crystallinity of the overgrown film. A combination of delib-erate electron-beam exposure and employing methods to increase surface migration of adatoms at low temperature have enabled retaining a NaCl film underneath a (001) GaAs overlayer. NaCl films as thin as 3 nm function as a suitable release layers for GaAs templates. The rapid dissolution of the NaCl when placed in water results in near-immediate liftoff of the overlayer and the parent substrate does not display any obvious surface defects or increased roughness. This work is a promising step toward an alternative method of substrate recycling and rich with scientific questions.
Brelon May received his BS in Chemical Engineering from Clarkson University in 2013 and then moved to the Ohio State University where he received his PhD in Materials Science and Engineering in 2019. Brelon is now a postdoctoral researcher at the National Renewable Energy Laboratory working on integration of alkali halide salts with III-V materials to develop a novel substrate recycling technique. During his PhD he worked on the epitaxial growth of several material systems (nitrides, oxides, selenides) but focused on deposition and fabrication of nanowire-based ultraviolet LEDs. He made the first ultraviolet LEDs directly on metal substrates and worked to understand inhomogeneities in self-assembled devices. Brelon has been granted the Presidential Fellowship and was runner up for the Ohio State University Student Innovator of the Year. Additionally, he has won a number of conference presentation awards and a 3-minute Thesis com-petition. His research has been featured in Semiconductor Today, NSF Science360, and as editorial picks in peer re-viewed journals. Brelon’s research interests include vacuum deposition and epitaxy of various material systems and nanostructures for optoelectronic, magnetic, and energy storage applications.