Structural studies reveal that heavy ion bombardment of GaN causes amorphiz
ation and anomalous swelling of the implanted region as a result of the for
mation of a porous structure. Results strongly suggest that such a porous s
tructure consists of N-2 gas bubbles embedded into a highly N-deficient amo
rphous GaN matrix. The evolution of the porous structure in amorphous GaN a
ppears to be a result of stoichiometric imbalance where N- and Ga-rich regi
ons are produced by ion bombardment. Prior to amorphization, ion bombardmen
t does not produce a porous structure due to very efficient dynamic anneali
ng processes in the crystalline phase. (C) 2000 American Institute of Physi
cs. [S0003-6951(00)03349-0].