Non-focusing dense plasma focus device based alternative synthesis technology for ZnO thin films

Abstract

Dense plasma focus (DPF) device is conventionally operated in focus mode, to achieve pinch plasma with highest possible temperature and density to maximize the soft and hard x-rays and charged particles. In this paper, we report the first ever application of non-focus mode of DPF device, which is free of magneto-hydrodynamics (MHD) instabilities, for the deposition of zinc oxide thin films (ZnO TFs) on silicon substrates for various number (5, 10, 15 and 20) of non-focused deposition shots (NFDS). The X-ray diffraction (XRD) patterns of as-deposited ZnO TFs confirms the growth along (0 0 2) orientation only. The ZnO TFs are then annealed at 600 °C temperature for 2 h. The XRD patterns of annealed ZnO-TFs confirm the wurtzite phase of ZnO with (1 0 0), (0 0 2) and (1 0 0) planes with improved crystallinity. The up and down shifting of ZnO (0 0 2) diffraction plane indicates the presence of residual stresses which are reduced in annealed ZnO TF. The surface morphology, like shape, size and the distribution of rounded nano-particles, is strongly associated with increasing number of NFDS. Raman analysis shows the development of downshifted E2 (high) and upshifted A1 longitudinal optical (LO) modes centered at 430 cm−1 and 580 cm−1 compared to bulk ZnO (430 and 575 cm−1) indicating the presence of tensile residual stress due to mismatch of thermal expansion coefficient of ZnO TF and Si substrate and due to the presence of oxygen vacancies and Zn interstitials, respectively. The XPS analysis confirms the presence of Zn, Zn–O, C–O, and Zn–OH bonds. The energy band gap and refractive index of annealed ZnO-TF are found to be 3.30 eV and 1.88, respectively. A new method of high quality ZnO TFs synthesis using MHD instability free non-focusing mode of DPF device will open a new alternative synthesis technique.