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

High p-type conductivity of Mg-doped AlGaN/GaN superlattices is demonstrate d. The measured hole concentration at room temperature is over 2.5x10(18) c m(-3), more than ten times that obtained in bulk AlGaN layers, and lateral resistivity as low as 0.2 Omega 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 t he origin of these effects. (c) 1999 American Institute of Physics. [S0003- 6951(99)01824-0].