The structural evolution in Ge+ implantation amorphous Si has been investigated by high-resolution transmission electron microscopy in conjunction with auto-correlation function (ACF) analysis. Si(0 0 1) wafers were implanted with 5 keV Ge+ to a dose of 5 X 10(15) ions/cm(2). A high density of embedded nanocrystallites was found to be present in as-implanted amorphous Si. After 350 degreesC annealing, the density of nanocrystallites was found to decrease, but increase after annealing at 400 degreesC or higher temperatures. The observation indicated that the implanted silicon became more randomized upon annealing up to 350 degreesC. The results are discussed in terms of energy variation in the system. (C) 2003 Elsevier Science B.V. All rights reserved.