ION-BEAM-INDUCED NUCLEATION IN AMORPHOUS GAAS-LAYERS DURING MEV IMPLANTATION

To investigate the nonlinear dose dependence of the thickness of the r ecrystallized layer during ion beam induced epitaxial recrystallizatio n at amorphous/crystalline interfaces GaAs samples were irradiated wit h 1.0 MeV Ar+, 1.6 MeV Ar+ or 2.5 MeV Kr+ ions using a dose rate of 1. 4 x 10(12) cm(-2) s(-1) at temperatures between 50 degrees C and 180 d egrees C. It has been found that the thickness of the recrystallized l ayer reaches a maximum value at T-max = 90 degrees C and 135 degrees C for the Ar+ and Kr+ implantations, respectively. This means that the crystallization rate deviates from an Arrhenius dependence due to ion beam induced nucleation and growth within the remaining amorphous laye r. The size of the crystallites depends on the implantation dose. This nucleation and growth of the crystallites disturbes and at least bloc ks the interface movement because the remaining surface layer becomes polycrystalline. Choosing temperatures sufficiently below T-max the th ickness of the recrystallized layer increases linearly with the implan tation dose indicating that the irradiation temperature is too low for ion induced nucleation.