ION-IMPLANTATION IN GAN AT LIQUID-NITROGEN TEMPERATURE - STRUCTURAL CHARACTERISTICS AND AMORPHIZATION

This paper deals with the results of a systematic investigation of dam age generation and accumulation until amorphization induced by 180 keV Ca+ and Ar+ implantation in GaN films at liquid-nitrogen temperature. The structure of GaN films before and after implantation was characte rized by Rutherford backscattering/channeling, cross-sectional transmi ssion electron microscopy, and high-resolution x-ray diffraction. The as-implanted GaN films exhibits an expanded lattice. Its texture was d etermined by pole figure measurement. An amorphous component has been found after Ca+ implantation at doses not less than 3X10(14) cm(-2). T his suggests that Ca+ implantation for p-type doping be carried out be low this dose, in order to avoid unrecoverable structural damage and t o achieve better transport properties. On the other hand, implantation with higher doses is generally needed to compensate for the native el ectron background of GaN and to realize p-type reversal. This conflict uncovers the essential difficulty for p-type doping of GaN by ion imp lantation. The maximum damage concentration exists in a depth of 100 n m below the surface, which corresponds to the mean projected range, an d broadens gradually towards surface and greater depth with increasing ion fluence. The thresholds for the amorphization of GaN films are re vealed to be 6x10(15) cm(-2) for both Ca+ and Ar+ implantation. The am orphization mechanism is discussed and the accumulation of amorphous c lusters seems to be the reason for the collapse of GaN crystalline. [S 0163-1829(98)02904-X].