Abstract
Coherent phonon spectroscopy of wurtzite InN epitaxial thin films was carried out with time-resolved second-harmonic generation technique. In addition to the bulk A1 (LO) phonon and A1 (LO) -plasmon coupling modes, a phonon mode at 543 cm-1 was identified and characterized. It is found that this phonon mode is localized in the topmost few atomic layers and sensitive to surface modification. This vibration mode is described as the opposite motion between the In and N atoms along the c axis. This phonon mode is assigned to the surface optical phonon of InN. © 2007 American Institute of Physics.