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.
The nanoscale morphology
of short-period {CdO/ZnO}
n
superlattices
(SLs) grown by plasma-assisted molecular
beam epitaxy on m-oriented sapphire substrates is
studied. The SL structures consist of 25 repetitions of subsequently
deposited ZnO and CdO layers. X-ray diffraction (XRD) and transmission
electron microcopy (TEM) studies confirm the presence of 2D SL structures
with the wurtzite phase of ZnO sublayers and the rocksalt structure
of CdO sublayers. For thicker ZnO sublayers, the (11̅.3) twinning
was observed. The SL periods are calculated based on high-resolution
XRD and TEM analyses. By varying the thickness of the CdO and ZnO
sublayers, it is possible to control the energy gap in these quasi-alloys.
These results suggest the promising potential of their optical properties
for light emission and/or applications in the detection of visible
to ultra-violet light.
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