Crystallization of isolated amorphous zones in semiconductors.

摘要

The amorphous-to-crystalline transition of isolated amorphous zones in semiconductors was investigated in Si, Ge, GaAs, GaP and InP. Crystallization was induced by low energy electrons, photons and thermal annealing with experiments performed in-situ using transmission electron microscopes at Argonne National Laboratory and at the Center for Microanalysis of Materials in the Frederick Seitz Materials Research Laboratory at the University of Illinois at Urbana-Champaign. Spatially isolated amorphous damage was created by low dose (≈1011 cm−2) ion implantations (typically 50 keV Xe+ at 300 K) using the IVEM-Tandem Accelerator Facility at ANL. Electron-induced crystallization irradiations were performed at energies from 25 to 300 keV at temperatures between 90 and 300 K in a Philips CM30 TEM at ANL. The effects of varying ion energy and crystal orientation was studied, but the electron energy had the strongest effect on crystallization rates. The dependence of crystallization rate on electron energy was similar in all the semiconductors studied. As the electron energy was lowered from 300 K the rate initially decreased and reached a minimum below the threshold displacement energy. As the electron energy was lowered further the crystallization rate increased, reaching a maximum at 25 keV, the lowest voltage attempted. Low temperature electron irradiations, thermal annealing experiments and theoretical calculations of temperature rise demonstrate that crystallization is not caused by electron beam heating. Sub-threshold electron-induced crystallization shows that displacive mechanisms and point defects are not required to stimulate regrowth of isolated amorphous zones. The rate dependence on electron irradiation stimulated amorphous zone regrowth in each material, again suggesting that a non-displacive mechanism is operating. The photon-induced crystallization rates scaled with the number of electron-hole pair defects generated.; Software was developed to detect, measure and track individual amorphous zones throughout a series of irradiation micrographs. Characteristic zone shrinkage behaviors were observed. A simple shrinkage model suggests that the defects responsible for regrowth are created very near the crystalline/amorphous interface. In the sub-threshold electron energy regime, crystallization is thought to be initiated by an electronic excitation which creates a dangling bond pair. By migrating along the crystalline/amorphous interface these dangling bonds are capable of reconstructing to the crystal a large number of atoms through a mechanism similar to that for thermally activated solid phase epitaxial growth.