Transition-metal nitride semiconductors

Semiconducting transition-metal nitride alloys emerge as a new category of semiconductors that are stable in hostile environments and are compatible with conventional semiconductor device processing. We report on the epitaxial growth and the electrical and optical properties of Ti_1−xMg_xN, Ti_1−xMg_xC_0.2N_0.8, and (Ti_0.5Mg_0.5)_1−xAl_xN on MgO(001) and (Ti_1−xMg_x)_0.25Al_0.75N on Al₂O₃(0001). X-ray diffraction reciprocal space mapping is used to quantify composition dependent lattice parameters and critical thicknesses for strain relaxation. Ti_0.5Mg_0.5N is a new semiconductor with a bandgap of 0.7-1.7 eV. Reducing the Mg-content in Ti_1−xMg_xN to x < 0.5 leads to a tunable plasmonic response that extends from infrared to visible (930 - 470 nm). The substitutional addition of Al and C on anion and cation sites, respectively, reduces the free carrier density: (Ti_0.5Mg_0.5)_1−xAl_xN layers show a negligible density of states at the Fermi level and a blue-shift of the absorption edge from 1.8 to 2.1 eV for x = 0 - 0.4. Ti_1−xMg_xC_0.2N_0.8 exhibits a metal to semiconductor to insulator transition as x increases from 0.3 to 0.4 to 0.5. Wurtzite-structure (Ti_1−xMg_x)_0.25Al_0.75N(0001) layers have a measured bandgap that increases from 5.1 to 5.2 to 5.9 eV for x = 0.0, 0.5 and 1.0.