Band gap engineering based on MgxZn1−xO and CdyZn1−yO ternary alloy films

Abstract

We describe the structural and optical properties of II–VI oxide alloys, ${\mathrm{Mg}}_x{\mathrm{Zn}}_{\text{1−x}}\mathrm{O}$ and ${\mathrm{Cd}}_y{\mathrm{Zn}}_{\text{1−y}}\mathrm{O},$ grown by pulsed-laser deposition. Single-phase alloyed films of (Mg,Zn)O and (Cd,Zn)O with c-axis orientations were epitaxially grown on sapphire (0001) substrates. The maximum magnesium and cadmium concentrations (x=0.33 and y=0.07, respectively) were significantly larger than the thermodynamic solubility limits. The band gap energies systematically changed from 3.0 $\text{(y=0.07)}$ to 4.0 eV $\text{(x=0.33)}$ at room temperature. The photoluminescence peak energy deduced at 4.2 K could be tuned from 3.19 to 3.87 eV by using ${\mathrm{Cd}}_{\mathrm{0.07}}{\mathrm{Zn}}_{\mathrm{0.93}}\mathrm{O}$ and ${\mathrm{Mg}}_{\mathrm{0.33}}{\mathrm{Zn}}_{\mathrm{0.67}}\mathrm{O}$ at both ends, respectively. The lattice constants of the a axis were monotonically increasing functions of the concentrations of both alloys. The exciton–phonon coupling strength was determined in ${\mathrm{Cd}}_{\mathrm{0.01}}{\mathrm{Zn}}_{\mathrm{0.99}}\mathrm{O}$ grown on a lattice-matched ${\mathrm{ScAlMgO}}_{\mathrm{4}}$ substrate.