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

Ewa Przeździecka,Aleksandra Wierzbicka,Abinash Adhikari,Adrian Kozanecki,Anastasiia Lysak,Piotr Sybilski,Krzysztof Morawiec,Piotr Dłużewski

doi:10.1021/acs.cgd.1c01065

Ewa Przeździecka, Aleksandra Wierzbicka + Show 6 more

Open Access

https://doi.org/10.1021/acs.cgd.1c01065

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Abstract

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.

Highlights

Zinc oxide (ZnO) has received considerable attention as a potential candidate for short-wavelength optoelectronic devices such as ultra-violet/blue detectors,[1,2] light-emitting diodes, and laser diodes.[3]
We explore short-period {Cadmium oxide (CdO)/ ZnO}n SLs with different thicknesses of ZnO and CdO layers, which were grown by plasma-assisted molecular beam epitaxy (PA-MBE) on m-oriented sapphire substrates
high-resolution transmission electron microscopy (HRTEM) images proved the wurtzite structure of ZnO layers and the rocksalt structure of CdO layers

Summary

■ INTRODUCTION

Zinc oxide (ZnO) has received considerable attention as a potential candidate for short-wavelength optoelectronic devices such as ultra-violet/blue detectors,[1,2] light-emitting diodes, and laser diodes.[3]. New approaches to “ultra-high” efficiency solar cells include devices such as multiple quantum wells and SL systems.[20] SLs give us a unique opportunity to obtain quasicrystals with precise control of the energy gap[21,22] while maintaining the high-quality crystal structure of the layers.[19,23,24] Good control of the energy gap of quasi-ternary alloys can give a chance to obtain semiconductor laser diodes or photodetectors for the dedicated spectral range from green to UV wavelengths by controlling CdO to ZnO sublayer thicknesses. There are no reports in the literature about the growth and deep crystallographic analysis of these kinds of structures (Figure 1)

EXPERIMENTAL SECTION

RESULTS AND DISCUSSION

■ CONCLUSIONS

■ REFERENCES