Seminarium Fizyki Ciała Stałego

As recently established in experimental and theoretical works, defect complexes including native point defects, hydrogen and possibly a dopant determine electrical conductivity of ZnO in a wide range as they introduce shallow and deep donor and acceptor states in the bandgap. This knowledge seems discouraging because the control of conductivity, and in particular the achievement of acceptor conductivity, requires the simultaneous tuning of point defects and dopants, which is difficult to achieve. Our investigations indicate, however, that this goal seems to be achievable, but it requires very conscious approach to the growth procedure and appropriate post-processing. In the presentation we will show the experimental cathodoluminesence (CL) and scanning photoelectron microscopy (SPEM) measurements performed on ZnO:N layers that allow sampling of a single microcrystallite in the films cross-section [1-3]. The results account for grouping acceptor and donors in separate domains/crystallites. This phenomenon is found to be very common provided the ZnO films are grown under O-rich conditions and nitrogen is introduced in the form of the –NH chemical group. Density Functional Theory calculations point out that the complexes involving zinc vacancy (VZn), hydrogen and nitrogen provide complexes-related acceptor states [4]. Hydrogen stabilizes formation of the VZnNO complex, but the appearing VZnNOH complex is found to be a deep acceptor. DFT calculations show that compressive strain and/or surface proximity facilitate the formation of acceptor complexes, so they are easily created under appropriate strain/microstrain conditions or near the surface. This theoretical finding may explain the origin of acceptor and donor grouping in different crystallites. Additionally, a closer insight into the electronic structure of a single crystallite performed by scanning photoemission experiment reveals that carbon present in a form of –CH group facilitates the formation of acceptor states, as seen by the modification of the valence band shape. According to DFT calculations, CiHx group is stable in the ZnO crystal lattice and creates C-H-O bond states. The calculated migration properties show that complexes such as VZn(NH)O are easily formed in the presence of the interstitial CiH2 group as it leads to lowering of the migration energy of VZn by 0.8 eV and to 0 eV in the ZnO and ZnO:N, respectively [5]. Acknowledgements The study was supported by the Polish NCN Project DEC-2018/07/B/ST3/03576 [1] E. Guziewicz, O. Volnianska et al., Phys. Rev. Appl. 18 044021 (1-13) (2022)[2] E. Guziewicz, E. Przezdziecka et al., ACS Appl. Mat. Interfaces 9, 26143-26150 (2017)[3] S. Mishra, B.S. Witkowski et al., Phys. Stat. Sol. A 2022, 2200466 (1-11)[4] O. Vonianska, V.Yu. Ivanov, L. Wachnicki, E. Guziewicz, ACS Omega 2023, 8, 43099[5] E. Guziewicz, S. Mishra, M. Amati, L. Gregoratti and O. Volnianska, Nanomaterials 2025, 15, 30