The effects of MgO on nitrogen dissolution and p-type conduction of sol-gel Al-N codoped MgxZn1-xO films were investigated. Substitution of MgO for ZnO significantly increased the solubility of nitrogen in the MgxZn1-xO films. The formation energies of NO and (N-2)(O) were found to decrease with increasing MgO content, resulting in higher concentrations of NO and (N-2)(O). The acceptor levels of NO were estimated to be about 114 and 163 meV above the valence band maximum, respectively, for x = 0 and x = 0.05 films. The bandgap and the acceptor ionization energy increase with the MgO content, leading to a reduction in hole concentration and an increase in resistivity. The homojunction formed between a Al-N codoped MgxZn1-xO and a n-type Ga0.01Zn0.99O film displayed a typical rectifying behavior with a turn-on voltage of 2V, confirming the p-type conduction of the Al-N codoped MgxZn1-xO films. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.049202jes] All rights reserved.