Shtepliuk I. Regularities of the influence of the cadmium doping on the microstructure, optical, electronic and phonon properties of ZnO films

Nature and mechanisms of the influence of the small cadmium content on the structure, electronic, phonon and emission spectra of the zinc oxide have been investigated. It was also studied the features of the formation of the solid solutions with high cadmium content depending on the growth conditions (substrate type, gas ratio, dc power) and post-growth thermal treatment. It was revealed that the Cd concentration of 0.4 at.% leads to significant enhancement of the CL intensity of ZnO. It suggests the decrease in the number of nonradiative recombination centers and may be used for improvement of the quantum efficiency of ZnO-based devices. It was shown that the change of the gas ratio and dc power may lead to (i) change of cadmium content in resulting film, (ii) red-shift of the absorption edge and (iii) decreasing the optical band gap. It indicates the possibility to control the energetic spectrum of the Zn1-xCdxO. It was found that the substrate type can influence on the cadmium concentration in ternary alloys and their optical characteristics.It was found that the effect of heat treatment on the phonon and luminescence spectra of ternary alloy is strongly depending on the pre-history of the sample. It was revealed that the coupling strength between electrons and LO phonons may be enhanced after annealing. Additionally, it was observed diminishing of the LO-phonons related to second phase after heat treatment and appearance of LO-modes belonging to Zn1-xCdxO ternary alloy. It was identified that the annealing causes the redistribution of the recombination channels, shift of the near-band emission toward low-energy side and vanishing the ZnO-related emission bands. It is explained by the realization of the effective Cd-to-Zn substitution mechanisms in the post-annealed conditions. Obtained results open the way to understanding the phonon and emission features of the Zn1-xCdxО ternary alloys and indicate the possibility to control of the Cd incorporation. The obtained n- Zn1-xCdxO /p-SiC heterostructures exhibited good rectification behaviors and diode characteristics, having turn-on voltages in the range from 3 to 4.4 V and series resistance from 166 to 3865 Om. The results indicate that it should be possible to reduce the values observed for turn-on voltages by decreasing the series resistance. Series resistance can be reduced by improving the quality of metal contacts to p-SiC, and by increasing the boron concentration in p-type SiC.