Optical damage performance of conductive widegap semiconductors: spatial, temporal, and lifetime modeling

The optical damage performance of electrically conductive gallium nitride (GaN) and indium tin oxide (ITO) films is addressed using large area, high power laser beam exposures at 1064 nm sub-bandgap wavelength. Analysis of the laser damage process assumes that onset of damage (threshold) is determined by the absorption and heating of a nanoscale region of a characteristic size reaching a critical temperature. This model is used to rationalize semi-quantitatively the pulse width scaling of the damage threshold from picosecond to nanosecond timescales, along with the pulse width dependence of the damage threshold probability derived by fitting large beam damage density data. Multi-shot exposures were used to address lifetime performance degradation described by an empirical expression based on the single exposure damage model. A damage threshold degradation of at least 50% was observed for both materials. Overall, the GaN films tested had 5-10 x higher optical damage thresholds than the ITO films tested for comparable transmission and electrical conductivity. The route to optically robust, large aperture transparent electrodes and power optoelectronics may thus involve use of next generation widegap semiconductors such as GaN.