A comparative structural investigation of GaN implanted with rare earth ions at room temperature and 500 deg C

The crystallographic damage induced in GaN by 300keV rare earth ions implantation has been investigated as a function of the implantation temperature. The defect structure of GaN thin films implanted at 500 deg C with Eu or Er ions with fluences ranging between 1X1015 and 2X1016at./cm2 has been compared with the case of implantation performed at room temperature (RT). Transmission electron microscopy (TEM) investigation shows that less damage is formed during implantation at the higher temperature: basal stacking faults with a majority of I1 type and prismatic stacking faults have been observed as in GaN implanted at RT, but with a lower density. The nanocrystalline layer observed when GaN was implanted at RT with rare earth ion fluences higher than 3X1015at./cm2, did not form for fluences up to 2X1016at./cm2. Implantation of GaN at 500 deg C through an ultrathin AlN cap points out the protective role of this cap against the GaN surface erosion that occurs from 8X1015at./cm2. This method appears as a promising way to reduce the induced damage during the GaN implantation process.