Abstract: Ultra-wide-band-gap (UWBG) semiconductors have tremendous potential to advance electronic devices as device performance improves superlinearly with increasing gap. Ambipolar doping, however, has been a major challenge for UWBG materials as dopant ionization energy and charge compensation generally increase with increasing band gap and significantly limit the semiconductor devices that can currently be realized. Rutile germanium oxide (r-GeO2) is a promising UWBG (4.68 eV) material, yet has not been explored for semiconducting applications. Using hybrid density functional theory, we demonstrate r-GeO2 to be an alternative UWBG material that can be ambipolarly doped.
“Today, materials scientists and engineers play a critical role in the technological evolution of our society, from using advanced computational modeling to guide the development of lighter and stronger metal alloys, to synthesizing self-assembled nanostructures for energy efficient optoelectronics. The trouble is, unlike mechanical or electrical engineering, students are usually not exposed to materials science until well into higher education, and oftentimes never truly learn what it is.
Since 2017, UM materials science graduate students have been teaming up with engineering diversity and educational outreach experts, physical science education specialists, museum curators, and local teachers to develop and implement materials science curriculum and demonstrations targeting K-12 classes.”
full text available from Bulletin of the American Ceramic Society
Transition metal dichalcogenide (TMD) monolayers, such as WSe2, WS2, MoSe2, and MoS2, possess distinct physical properties due to the strong coupling between spin and valley degrees of freedom.(1, 2) As monolayer TMDs have a direct bandgap lying in visible range, they have been studied extensively by optical methods.(2, 3) Heterostructures of monolayer TMDs with other functional materials are currently attracting significant attention due to the opportunities to access and utilize their spin-valley degrees of freedom through electrical means.(4) For instance, TMD-ferromagnet heterostructures have been employed recently to study spin current generation in TMDs. (4, 5) The quality of atomically thin TMDs, however, is strongly affected by deposition techniques of metallic layers and have not been fully investigated.(6) In this work, we report the fabrication of Pt/Co multilayer using pulsed laser deposition (PLD) on monolayer WSe2 grown bymetalorganic chemical vapor deposition (MOCVD) on single crystalline (0001)-oriented Al2O3 substrates. PLD is a plasma based deposition technique capable of tuning of kinetic and thermodynamic conditions over an expanse range to elucidate and control fundamental structure-property relationships across a wide variety of material classes. (7)Using Raman Spectroscopy, we monitor deposition induced damage on monolayer WSe2. The pressure of Argon process gas is found to suppress deposition induced defects in WSe2, which indicates that the primary source of defect generation comes from ion bombardment. Further, we report on magnetometry and spin torque measurements of our WSe2-ferromagnet heterostructures and demonstrate the generation of spin current from TMD layer. We anticipate that our results will advance the electrical investigation of spin-valley and spin generation phenomena in 2D hybrid heterostructures for spintronics.
New Publication! S. Chae, , J. Lee, K. A. Mengle, J. T. Heron, and E. Kioupakis Appl. Phys. Lett. 114, 102104 (2019)
Abstract: Ultra-wide-band-gap (UWBG) semiconductors have tremendous potential to advance electronic devices as device performance improves superlinearly with the increasing gap. Ambipolar doping, however, has been a major challenge for UWBG materials as dopant ionization energy and charge compensation generally increase with the increasing bandgap and significantly limit the semiconductor devices that can currently be realized. Using hybrid density functional theory, we demonstrate rutile germanium oxide (r-GeO2) to be an alternative UWBG (4.68 eV) material that can be ambipolarly doped. We identify SbGe, AsGe, and FO as possible donors with low ionization energies and propose growth conditions to avoid charge compensation by deep acceptors such as VGe and NO. On the other hand, acceptors such as AlGe have relatively large ionization energies (0.45 eV) due to the formation of localized hole polarons and are likely to be passivated by VO, Gei, and self-interstitials. Yet, we find that the co-incorporation of AlGe with interstitial H can increase the solubility limit of Al and enable hole conduction in the impurity band. Our results show that r-GeO2 is a promising UWBG semiconductor that can overcome current doping challenges and enable the next generation of power electronics devices.
Full text available from Applied Physics Letters
The award comes from the Ceramics program within the NSF Division of Materials Research. The project is to focus on the understanding the roles of defects and disorder on the dielectric properties of entropy-stabilized thin film materials.