Diversity of contributions leading to the nominally n–type behavior of ZnO films obtained by low temperature Atomic Layer Deposition

• Published in: Journal of alloys and compounds 2017-12, Vol.727, p.902-911
• Main Authors: Krajewski, Tomasz A., Terziyska, Penka, Luka, Grzegorz, Lusakowska, Elzbieta, Jakiela, Rafal, Vlakhov, Emil S., Guziewicz, Elzbieta
• Format: Article
• Language: English
• Subjects: (Photo)luminescence; Atomic layer epitaxy; Defect annealing; Electronic transport; Ellipsometry; Impurities in semiconductors; Low temperature; Luminescence; Photoluminescence; Point defects; Secondary ion mass spectroscopy; Semiconductors; Temperature; Thin films; Zinc; Zinc oxide
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2017.08.206

This paper discusses possible contributions to the nominal n–type behavior of ZnO films grown by the Atomic Layer Deposition (ALD). The room–temperature photoluminescence (RT PL) and Secondary Ion Mass Spectroscopy (SIMS) investigations suggest an important role played by the zinc–related defects in their electrical behavior. This is also supported by increasing electron concentration, which changes from 1.7 × 1017 cm−3 to 8.6 × 1019 cm−3 with increasing ZnO growth temperature. The ellipsometry studies show that the absorption edge shifts with increasing growth temperature from 3.27 eV to 3.34 eV, indicating the self–compensation and the Burstein–Moss effect, whereas the maximal extinction coefficient k remains at the level of k = 0.5. After the rapid thermal processing (RTP) in oxygen and nitrogen–rich atmosphere significant changes in the defect–related RT PL were observed, suggesting the contributions of defects of miscellaneous origin in different spectral range, i.e., RTP annealing in N2 results in the defect–related luminescence peaked at 520–560 nm, i.e. 2.23–2.38 eV (ascribed to the defects involving oxygen vacancies), whereas similar treatment performed in O2 atmosphere activates the luminescence in the vicinity of 650–730 nm, i.e. 1.70–1.90 eV, where the zinc–related (presumably VZn) defects are efficient radiative centers. Comparison of the RT PL spectrum of as grown ALD-ZnO film deposited at 100 °C (1) with the one obtained after RTP process performed on this layer in oxygen-rich conditions (700 °C, 60 s) (2). The presented multi-Gaussian deconvolution illustrates the enhanced role of VZn-related radiative centers occurring after RTP annealing in oxygen. [Display omitted] •ZnO films with low electron concentration were grown by the Atomic Layer Deposition.•Structural optical and electrical properties of the as grown ZnO were investigated.•Photoluminescence results from as grown and RTP-annealed ZnO films were analyzed.•Basing on the PL studies the relevant defects in ZnO films have been identified.•The influence of defects on the properties of the ALD-ZnO films has been discussed.