after reading 2009 APL paper. It is consistent to the “Intuition” of chemistry: a nitrogen atom doped into ZnO lattice, though being lack of one electron, cannot drag one from an oxygen atom easily: because oxygen has much lower electronegativity. So the nitrogen atom is a “deep” acceptor, and cannot form effect hole conductivity. This is contrast to the successful case of N doped ZnTe. Curiously, solid physicists seldom rely on this kind of chemistry feeling, and they did so many experiments and calculations just leading to a bubble.