|
Close Details
|
|
2012 - 11th Annual NC State Summer Undergraduate Research Symposium
|
|
Session Time :
8/1/12 3:00 PM - 8/1/12 4:14 PM
|
|
Content Area : Advanced Materials for Environmental Sustainability
|
Lead Student Presenters : Jonathan Sami Watson
|
Abstract Title : Stress determination in GaN thin films grown by UHVPLD and MOCVD on sapphire and Si(111) substrates by Raman spectroscopy.
|
Abstract :
GaN devices are promising for use in high temperature, high frequency, and high power devices, as well as blue and green LEDs. Films of GaN grown on nonnative substrates such as silicon and sapphire can introduce a large number of defects and strain which limit the potential of GaN devices. To minimize defects and strain, it is necessary to confine the crystal defects to the interface, so that the rest of the film can grow strain free. In this project Raman spectroscopy was used to characterize the strain in epitaxial GaN films deposited on Sapphire and Silicon substrates. GaN films were deposited by PLD and MOCVD on r-plane sapphire, c-plane sapphire, and Si (111) with an AlN buffer layer. The MOCVD samples were obtained from Veeco. Raman spectroscopy was performed on the GaN films, and on polar and nonpolar bulk GaN samples for comparison. The E2 high and A1 (LO) phonon modes were observed in the Raman spectra from the samples. Shifts in these modes relative to the bulk GaN samples was used to quantify biaxial strain and stress in the films. Using stress coefficients of 2.9GPa-1cm-1 for the E2 high mode and 0.8 GPa-1cm-1 for the A1 (LO) mode, we found stresses in the films ranging from -0.4GPa to -0.8GPa in the MOCVD GaN on Si samples and stresses of 1.0GPa in the PLD GaN on Sapphire and 0.4GPa in the PLD GaN on Si.
|
Mentor and/or Co-Author : Lewis Reynolds
|