Ion beam induced nucleation in amorphous GaAs layers during MeV implantation

To investigate the nonlinear dose dependence of the thickness of the recrystallized layer during ion beam induced epitaxial recrystallization at amorphous/crystalline interfaces GaAs samples were irradiated with 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 degrees C. It has been found that the thickness of the recrystallized layer 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 layer. The size of the crystallites depends on the implantation dose. This nucleation and growth of the crystallites disturbes and at least blocks the interface movement because the remaining surface layer becomes polycrystalline. Choosing temperatures sufficiently below T-max the thickness of the recrystallized layer increases linearly with the implantation dose indicating that the irradiation temperature is too low for ion induced nucleation.