This is a past event.

Rick Mengyan from Northern Michigan University will present at this week's Physics Colloquium. Dr. Rick Mengyan's presentation is titled "Photo-MuSR to study semiconductors".

The seminar will be presented  at 4:00 p.m. on Thursday (Sep.3) in Fisher 139. The coffee hour will be held at 3:30 in the Fisher Hall Lobby.

Abstract  Muons are used in semiconductor research as an experimentally accessible analog to the isolated Hydrogen(H) impurity – a complex that is very difficult (or impossible) to study by other means. Hydrogen impurities of any concentration can modify the electrical, optical, or magnetic properties of the host. For instance, H can be incorporated to remove electrically active levels from the energy gap (i.e. passivation) while some can form isolated centers that tend to be responsible for the trap and release of charge carriers and participate in site and charge-state dynamics which certainly affect the electrical properties of the host. Therefore, it can be quite useful to characterize these impurities in semiconducting materials that are of interest for use in devices. When implanted in a target material, a positively charged muon can behave as a light proton or bind with an electron to form a complex known as Muonium (Mu) with properties that are very similar to that of ionic or neutral H, respectively. A result of these similarities and direct nondestructive implantation is that Mu provides a direct measure of local electronic structure, thermal stability, and charge-state transitions of these impurity centers. Since any material can be subjected to muon implantation and it is the muons themselves that mimic the H impurity centers, these measurements do not depend, at all, on the host’s solubility of H nor do they require some minimum concentration; unlike many other techniques, such as EPR, ENDOR, NMR, or IR vibrational spectroscopy. This presentation focuses on developments in working with semiconductors and muons combined with the relatively new laser on the High Field Muon Spectrometer (HIFI) at Rutherford Appleton Laboratory (UK). Some illumination-based techniques utilizing flashlamps or lasers have been utilized in the past relating to semiconductors. The primary purpose of the illumination has been to vary the carrier concentration to see how the Mu signal responds and further develop an understanding of the (1) stability and dynamics of the Mu states and (2) gain insight into carrier behavior. The new laser system on HIFI opens a range of potential measurements along these same lines but with a different variety of controls. To date, we have worked on measurements such as attempting vibrational spectroscopy (Mu stimulated by the laser); direct ionization of Mu donor/acceptor states; charge-cycles and site change dynamics; carrier mobility and recombination times. This presentation provides a rough overview to studying H defects in semiconductors using the MuSR technique, an introduction to the new laser technique, and brief discussion of a few recent examples where we have been working on both developing the technique and fundamental measurements
that are important for the semiconductor field.

Bio Dr. P. W. Mengyan is a Professor of Physics at Northern Michigan University and an experimental condensed matter physicist. He received his Ph.D. from Texas Tech University in 2014. His research focuses on using Muon Spin Rotation, Relaxation, and Resonance (MuSR) techniques to study semiconductors, magnetic materials, and the role of hydrogen in materials relevant to emerging technologies.