Science Diliman (Dec 2004)
Two-Photon Optical Beam-Induced Current Microscopy of Light-Emitting Diodes
Abstract
We demonstrate two-photon optical beam-induced current (2P-OBIC) microscopy of light-emitting diodes (LEDs). We utilized a Ti:Sapphire femtosecond laser source operating at 800 nm to derive the 2P-OBIC signal from a 605 nm band-gap LED. The spatial confinement of free carrier generation only at the focus and the quadratic dependence of the 2P-OBIC signal on excitation power are the key principles in two-photon excitation. As a consequence, superior image quality evident in the 2P-OBIC images of LEDs are obtained. These features decrease the linear absorption and wide-angle scattering effects plaguing single-photon optical beam-induced current (1P-OBIC) technique, thereby increasing the resolution of the imaging system in the axial and lateral directions. Thus, the attainment of good axial discrimination in the LED samples is obtained even without a confocal pinhole. In addition, 2P-OBIC images reveal local variations in free carrier densities which are not evident in the single-photon excitation.
