X-ray topographic observation of subsurface line defects in GaAs on Si substrate

Abstract

Defects in GaAs epilayers on Si substrates grown by MOCVD have been studied. Subsurface defects in both epilayers and substrates generated during the device fabrication process were observed, using X-ray double crystal topography. In order to clarify the defect formation mechanism, the influence of Si preheating prior to epitaxial growth on the defect formation was also examined. It was found that the defects in the GaAs epilayer occur simultaneously with defect formation in Si substrates and the defect density decreased with the lowering of the preheating temperature of the Si substrate in AsH 3 gas flow. These defects extended along the [011] or [01 1 ] direction with respect to substrate misorientation in the [011] direction and were revealed as images with peculiar contrasts in X-ray topographs. The images can be explained in terms of lattice plane distortion caused by crack formation. These results indicate that microcracks first form at the epilayer-substrate interface and then propagate in both the GaAs epilayer and the Si substrate in the slip mode.