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

TLDR: In this paper, the structural and optical properties of II-VI oxide alloys, MgxZn1−xO and CdyZn 1−yO, grown by pulsed-laser deposition, were described.

Abstract: We describe the structural and optical properties of II–VI oxide alloys, MgxZn1−xO and CdyZn1−yO, 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 (y=0.07) to 4.0 eV (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 Cd0.07Zn0.93O and Mg0.33Zn0.67O 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 Cd0.01Zn0.99O grown on a lattice-matched ScAlMgO4 substrate.

Figures

FIG. 2. Concentration(y) dependence of absorption spectra of CdyZn12yO epilayers obtained at room temperature. The curves, from right to leftrespond to those of the samples withy50, 0.0013, 0.027, 0.043, and 0.073

FIG. 1. Cadmium content dependence of~a! FWHM values of the~0002! peak in XRD v and v22u scanned curves,~b! dependence of the cel volume, and~c! dependence of thea- and c-axis lattice lengths of the CdyZn12yO films grown on sapphire substrates. The solid lines in~c! are fitted lines obtained by usinga53.25210.143y20.147y2 and c55.204 10.956y25.42y2.

FIG. 4. ~a! Absorption spectra in a CdyZn12yO (y50.01) epilayer grown on a lattice-matched ScAlMgO4 substrate obtained at 5 K.~b! Temperature dependence of absorption peak energy in~Cd,Zn!O ~open circles! and ZnO ~closed circles!. Solid curves are the fitted results obtained using Eq.~1!.