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Zinc Malonate Based Precursors for MOCVD of ZnO

ZnO thin films have been investigated extensively because of their interesting electrical, optical and piezoelectric properties. Their superior material properties have played an important role in various applications such as transparent conducting oxides (TCO), photodetectors etc. Metal organic vapor deposition (MOCVD) is a well established process for the growth of high quality thin films for a wide variety of materials. The metal organic precursor plays a key role in the deposition process. The availability of volatile metalorganic precursors possessing sufficient vapor pressure, thermal stability during evaporation process and lower decomposition temperatures are some of the features desired. Diethyl zinc (DEZ) and zinc acetylacetonate [Zn(acac)2] are the most commonly CVD precursors for ZnO growth. However, they exhibit certain disadvantages and there have been several reports where improved precursors for ZnO are explored. Our research efforts concentrate on the development of alternative or improved zinc complexes with the aim of obtaining fluorine free compounds which are volatile, can be easily synthesized, handled and scaled up for practical applications. Bidentate ligands have already been proven to be successful in the cases of ZnO growth by [Zn(hfa)2(tmeda)] [1] and malonate based precursors of Zr, Hf and Ga for the respective metal oxide thin film deposition [2]. Two zinc ketoiminate compounds were recently published that showed one-step decomposition behaviour in the TG and reasonables melting and evaporation temperatures [3]. Here, we focus on the synthesis and evaluation of other potential precursors such as zinc malonates and analogous compounds. Our goal is to investigate the influence of different types of chelating ligands on the precursor properties. Zinc malonates of the type [Zn{C(H)(R1C=O)(R2C=O)}2] (R1, R2: OMe, OEt) were synthesized and evaluated in view of their possible application as precursors for MOCVD of ZnO.