Bandgap Engineering and Optical Constants of Y sub(x)Al sub(1-x)N Alloys

We study wurtzite Y sub(x)Al sub(1-x)N (0[< or =]x [< or =]0.22) films with (0001) orientation deposited by magnetron sputtering epitaxy on Si(100) substrates and we determine the alloys band gap energies and optical constants. Room temperature spectroscopic ellipsometry (SE) is employed in the energy range from 1 to 6.3 eV, and data modeling based on the standard dielectric function model is used. As a result of the SE data analysis the Y sub(x)Al sub(1-x)N refractive index and extinction coefficient are determined. The band gap of Y sub(x)Al sub(1-x)N is found to decrease linearly from 6.2 eV (x = 0) down to 4.5 eV (x = 0.22). We further observe an increase of the refractive index with increasing Y content; from 1.93 to 2.20 (at 2 eV) for x = 0 and 0.22, respectively, reflecting the increase in material density.