Zinc　nitride　(Zn3N2)　thin　films　were　deposited　on　glass　substrates　by　reactive　radio-frequency　magnetron　sputtering　from　a　pure　Zn　target　in　nitrogen-argon　ambient.　X-ray　diffraction　analysis　indicates　that　the　films　just　after　the　deposition　are　polycrystalline　with　a　preferred　orientation　of　(400).　With　increasing　substrate　temperature,　the　grain　size　in　zinc　nitride　film　increases　from　26.5　nm　(100　degrees　C)　to　33.6　nm　(200　degrees　C),　and　then　decreases　to　17.8　nm　(300　degrees　C).　Atomic　force　microscopy　reveals　that　the　film　surface　morphology　is　dependent　on　the　substrate　temperature.　With　reflective　spectroscopic　ellipsometry,　the　ellipsometric　parameters　psi　and　Delta　of　Zn3N2　films　are　measured.　Then,　a　new　model　for　Zn3N2　films　is　built.　With　the　Tauc-Lorentz　dispersion　formula,　the　ellipsometric　data　are　fitted,　and　both　the　thickness　and　optical　constants　(refractive　index　and　extinction　coefficient)　of　the　films　are　obtained　at　a　wavelength　of　430-850　nm.　The　optical　band　gap　is　calculated　from　the　extinction　coefficient　by　using　the　Tauc　formula,　and　a　direct　band　gap　of　1.73-1.79　eV　is　obtained.