Enhanced Mg doping efficiency in Al0.2Ga0.8N/GaN superlattices

High p-type conductivity of Mg-doped AlGaN/GaN superlattices is demonstrated. The measured hole concentration at room temperature is over 2.5×1018 cm−3, more than ten times that obtained in bulk AlGaN layers, and lateral resistivity as low as 0.2 Ω cm is realized. The temperature dependence of the resistivity is drastically reduced compared to bulk films, providing evidence of the formation of a confined hole gas. Valence band bending due primarily to piezoelectric and spontaneous polarization is identified as the origin of these effects.