The Band-Gap Studies of Short-Period CdO/MgO Superlattices

Abstract

Trends in the behavior of band gaps in short-period superlattices (SLs) composed of CdO and MgO layers were analyzed experimentally and theoretically for several thicknesses of CdO sublayers. The optical properties of the SLs were investigated by means of transmittance measurements at room temperature in the wavelength range 200–700 nm. The direct band gap of {CdO/MgO} SLs were tuned from 2.6 to 6 eV by varying the thickness of CdO from 1 to 12 monolayers while maintaining the same MgO layer thickness of 4 monolayers. Obtained values of direct and indirect band gaps are higher than those theoretically calculated by an ab initio method, but follow the same trend. X-ray measurements confirmed the presence of a rock salt structure in the SLs. Two oriented structures (111 and 100) grown on c- and r-oriented sapphire substrates were obtained. The measured lattice parameters increase with CdO layer thickness, and the experimental data are in agreement with the calculated results. This new kind of SL structure may be suitable for use in visible, UV and deep UV optoelectronics, especially because the energy gap can be precisely controlled over a wide range by modulating the sublayer thickness in the superlattices.

DFT-1/2 and shell DFT-1/2 methods: electronic structure calculation for semiconductors at LDA complexity

“…DFT-1/2 has also been applied to diamond [179], Gecontaining semiconductors [180,181], SiC [182,183], III-V semiconductors , spinel nitrides [217], EuS [218], MgTe [219], doped K 0.5 Na 0.5 NbO 3 [220,221], halide perovskites [222][223][224][225][226][227][228][229][230][231][232][233][234][235], II-VI semiconductors [236][237][238][239][240][241][242][243][244], WO 3 [245], LiGa 5 O 8 [246], silicon surfaces [247][248][249][250][251][252][253][254][255], alkaline earth fluorides [147], Ca oxides [256], SnO 2 [257], Be-VI polymorphs…”

Europium doped Sr2YNbO6 double perovskite phosphor for photoluminescence and thermoluminescence properties

“…These were attributed to the charge transfer excitation of electrons that occurred from the 2 p orbital of O 2− to the empty 4 f orbital of Eu 3+ and the transition between the host excitation level to the 7 F 0 → 5 H 3 / 5 H 6 excitation of Eu 3+ . [ 25–28 ] The excitation spectra exhibited discrete sharp lines at 396 nm and 467 nm that were attributed to the characteristic excitation transitions of Eu 3+ from 7 F 0 – 5 L 6 and 7 F 0 – 5 D 2 , respectively, and that were prominent at the 4 mol% concentration of Eu 3+ . The spectra revealed that the Eu 3+ doped Sr 2 YNbO 6 phosphors were excited either by 396 nm or 467 nm wavelengths.…”

“…5 H 3 / 5 H 6 excitation of Eu 3+ . [25][26][27][28] The excitation spectra exhibited discrete sharp lines at 396 nm and 467 nm that were attributed to the characteristic excitation transitions of Eu 3+ from 7 F 0 -5 L 6 and 7 F 0 -5 D 2 , respectively, and that were prominent at the 4 mol% concentration of Eu 3+ . The spectra revealed that the Eu 3+ doped Sr 2 YNbO 6 phosphors were excited either by 396 nm or 467 nm wavelengths.…”

Nanoscale Morphology of Short-Period {CdO/ZnO} Superlattices Grown by MBE

“…For pure ZnO, the energy gap is expected to be 3.3 eV, whereas for pure CdO, the reported direct energy gap is about 2.2 eV. 37 The energy gap of the short-period SLs depends on the thickness of sublayers, 21,38,39 whereas in the case of random alloys like Cd x Zn 1−x O, it depends on the Cd concentration in the ZnO matrix. Single-phase hexagonal Cd x Zn 1−x O can be obtained for limited values of Cd concentration, while for higher Cd concentrations, the cubic phase is detected.…”