Date of Award
Master of Science
Department of Engineering Physics
Michael A. Marciniak, PhD
Micro-Raman (µRaman) spectroscopy is an efficient, non-destructive technique widely used to determine the quality of semiconductor materials and microelectromechanical systems. This work characterizes the stress distribution in wurtzite gallium nitride grown on c-plane sapphire substrates by molecular beam epitaxy. This wide bandgap semiconductor material is being considered by the Air Force Research Laboratory for the fabrication of shock-hardened MEMS accelerometers. µRaman spectroscopy is particularly useful for stress characterization because of its ability to measure the spectral shifts in Raman peaks in a material, and correlate those shifts to stress and strain. The spectral peak shift as a function of stress, known as the phonon deformation potential, is determined by applying strain to the material using a four-point strain fixture while simultaneously monitoring the applied strain and recording the Raman spectrum. The deformation potentials are then used to determine stress distribution; the spectral positions of the E2 Raman mode (v = 569 cm-1) in GaN and A1g Raman mode (v = 418 cm-1) in sapphire are recorded at each spatial position in a raster map. The µRaman spectroscopy is performed using a Renishaw InVia Raman spectrometer with argon ion (λ = 514:5 nm, hv = 2:41eV ) and helium-neon (λ = 633 nm, hv = 1:96 eV ) excitation sources, and the data is collected across the samples with 5- to 10-µm spatial resolution. Inherent stress and evidence of significant damage in the GaN layer due to MEMS processing is discussed.
DTIC Accession Number
Parada, Francisco E., "Characterization of Stress in GaN-on-Sapphire Microelectromechanical Systems (MEMS) Structures Using Micro-Raman Spectroscopy" (2006). Theses and Dissertations. 3367.