Growth of p-type GaN – The role of oxygen in activation of Mg-doping

The effects of N₂ and O₂:N₂ (1:1) as ambient gases during activation annealing of Mg as p-type doping of GaN have been investigated. The purpose was to understand the mechanisms involved and especially the impact of O₂ on the resulting hole concentration and hole mobility. The addition of O₂ to the ambient gas during annealing is known to be very effective in reducing the H level of the Mg-doped GaN layer, but the maximum achievable hole concentration and mobility, as determined by Hall characterization, is still higher with pure N₂. The difference is explained by an in-diffusion of O to the GaN layer acting as n-dopant and thus giving rise to a compensation effect.

It is found that to a large degree only the Mg-H complexes at substitutional (Mg_Ga), i.e., the electrically active acceptor sites that provide free holes, are activated by annealing with N₂ only as ambient gas, while annealing with O₂:N₂ (1:1) also dissociates electrically inactive Mg-H complexes resulting in much less residual H. Thus, the residual H level in relation to the Mg level after activation annealing with N₂ only may provide a representative measure of the resulting free hole concentration of the Mg-doped GaN layer.