Ion implantation technique for conductivity control of GaN

Ion implantation technique for controlling n- or p-type conduction has been a significant challenge for GaN-based high-power devices to achieve levels approaching their theoretical limits of performance. Previous studies on n-type conduction of GaN through Si ion implantation achieved 86% [1] and approximately 100% [2] of activation rate after annealing at 1250 and 1400°C, respectively. Such high-temperature annealing results in serious surface degradation of GaN(0001) due to decomposition [1], thereby needing a protective layer. However, it is difficult to make a proper choice of a protective layer which remains unaltered and is removable after annealing above 1200°C. Therefore achieving the high-activation rate at lower temperature is a very important practice. On the other hand, the Mg-ion implantation for p-type conductivity is more challenging due to the higher-temperature annealing required for electrical activation, resulting in a major difficulty protecting the surface. The formation energy of Mg on the Ga site (Mg
_Ga
) at the position of Fermi level near the valence band is about 1 eV higher than that of Si
_Ga
at the Fermi level near the conduction band [4, 5], which may explain the difference of required annealing temperature for different conduction types.