Rare Earth manganites (RMnO3) systems have been widely studied both as polycrystalline ceramics and as single crystals [1]. Thin films present additional degrees of freedom to explore, like substrate induced strain and interface modifications, opening practical pathways for designing multifunctional devices. Several physical-based techniques can be used to prepare thin films, such as pulsed laser deposition [2], RF sputtering, molecular beam epitaxy. On the other hand, chemical methods [1] have the advantage of comparative low cost, providing versatility on precursors composition and thus prompt control of films stoichiometry. In particular, the metal organic chemical vapour deposition (MOCVD) method allows to investigate a series of relevant parameters in order to establish the suitable deposition conditions to synthetize RMnO3 thin films.
In this work, we explore MOCVD conditions aiming to synthetize thin films with the hexagonal LuMnO3 phase as a potential low band gap ferroelectric material. Main parameters investigated are metalorganic precursors ratios, substrate temperature and annealing effect. The study uses two different substrates, silica glass (SiO2) and platinized silicon (Si(100)/SiO2/TiOx/Pt). To investigate the thermodynamic stability and quality of the developed phases, a detailed analysis of the films crystal structure, microstructure, morphology and roughness were carried out by X-ray diffractometer, scanning electron microscopy (SEM), Energy Dispersive Spectrometry (EDS), Raman spectroscopy and piezo force microscopy (PFM). The results showed the relevance of deposition temperature and precursors composition molar ratio as critical parameters to grow P63cm h-LuMnO3 phase. It was found that formation of the h-LuMnO3 single phase can be obtained within a window 0.93 < |Lu|/|Mn| < 1.33 [3] of the film composition. In addition, the series of films XRD patterns indicate that amorphous films deposited at 700 °C become crystalized after annealing at 800 °C in air. Optimization of deposition conditions and in-situ thermal treatments for long periods further improves the quality of the film phase (Figure1). These films exhibit a relatively narrow band gap around 1.75 eV within the values reported for the h-LuMnO3 system [4].