Question: why nio is p type semiconductor?
Answer: All of these TCO films are n-type semiconductors with free electrons resulting from extrinsic donors as well as intrinsic donors. ... One metal oxide material, nickel oxide (NiO), is a candidate for p-type transparent conducting films be- cause it is a p-type semiconductor with a band gap energy from 3.6 to 4.0 eV [7, 8].