The oxygen partial pressure during NiO deposition in reactive sputtering of a Ni target is used to control its carrier type and concentration, obtaining both n- and p-type films. Carrier concentration can be controlled, ranging from 1019 to 1014 cm–3. Films deposition is performed at 200 °C, a relatively low temperature that enables the use of glass as substrate. Experimental band diagrams for n-type NiO are obtained for the first time. Finally, a NiO homojunction is demonstrated by introducing a low carrier concentration layer in between n- and p+-type NiO layers. Layers are deposited in situ, preventing contamination and improving the interface quality, as observed by TEM. The Ni:O ratio for each layer was also obtained by analytical TEM measurements, demonstrating the impact of the oxygen partial pressure on the films’ stoichiometry and the simplicity of our process to control carrier type and carrier concentration in …