Electron-microscope study of 10.6-μm laser damage in GaAs

Abstract

The nature of the damage to GaAs caused by exposure to a 10.6-μm laser beam at power densities of 1130, 2260, and 5650 W/cm2 was determined by transmission electron microscopy. At 5650 W/cm2 damage was observed at the surface in the form of craters of 80 μm or larger in diameter. Within the craters were found concentric zones spreading out from the center and consisting of (1) an amorphous region, (2) a region showing striations and skeletal crystalline walls in an amorphous matrix, and (3) a mixed amorphous-crystalline region containing small rounded clusters of dislocations, some of which were helical. In one case crystalline arsenic was found near the central zone. The results observed at this power level indicate that thermal effects have caused melting, evaporation, and decomposition. It is suggested that the skeletal walls and the striations parallel to {110} planes are caused by preferential evaporation or decomposition and may be related to the presence of small precipitates or chemical inhomogeneities along {110} planes of GaAs as observed by others. Damage near the entrance surface at low power densities, and at the exit surface for the highest power density, consisted of unique clusters of dislocations spreading out along orthogonal 〈110〉 directions up to 3 μm. Although the direct cause of these dislocations could not be determined, it suggested that they result from cracking or cleavage of the crystal due to stresses caused by localized heating at sites of precipitates, occlusions, or other faults in the crystal.