Inhibition of Mg activation in p-type GaN caused by thin AlGaN capping layer and impact of designing hydrogen desorption pathway

Thermal activation of a Mg-doped GaN layer with a thin AlGaN capping layer was investigated by means of systematic electrical characterization. Two-dimensional electron gas generated at the AlGaN/GaN interface greatly inhibited activation of the underlying Mg-doped GaN layer. This finding is attributed to the charge states of the interstitial hydrogen atoms being released from the Mg–H complexes and their diffusivity being dependent on the Fermi level position in GaN-based heterostructures. Reasonable electrically active acceptor concentration in Mg-doped GaN was achieved by designing a hydrogen desorption pathway.