Deposition of II/VI thin films from Novel Single-Source Precursors
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M5.21.1
DEPOSITION OF II/VI THIN FILMS FROM NOVEL SINGLE-SOURCE PRECURSORS
Mohammad Afzaal, Mohammad Azad Malik, Paul O’Brien and Jin-Ho Park The Manchester Materials Science Centre and Department of Chemistry, University of Manchester, Oxford Road, Manchester, M13 9PL, UK. E-mail: [email protected]; [email protected] ABSTRACT The compound [MeCd(SePiPr2)2N]2 is used as a single-source precursor to cadmium selenide films in a low-pressure chemical vapour deposition process. Thermogravimetric analysis (TGA) shows that the precursor is reasonably volatile, making it suitable for the deposition of thin films. As-deposited films were identified as CdSe confirmed by X-ray powder diffraction (XRPD) and their morphologies were studied by scanning electron microscope (SEM). INTRODUCTION In recent years, there has been a rapid development in the field of II-VI semiconductors for their use in photovoltaic devices due to their intermediate energy band gaps e.g. cadmium/zinc chalcogenides are useful materials for solid-state solar cells,1 photoconductors, field effect parameters, sensors and tranducers.2 A number of reports have appeared concerning single-source precursors for the deposition of II/VI materials, and systems studied have included thiocarbamates,3 selenocarbamates,4 thiophosphinates,5 thiolates,6 2,4,6-tri-tert-butylphenyl chalcogenides,7 silicon-based systems (e.g. M[ESi(SiCH3)3]2: M = Zn, Cd, Hg; E = Se, Te),8 and alkylmetal thio- and selenocarbamates.9,10 We have previously identified a new class of organometallic single-source precursors based on NH(EPiPr2)2 (E = S or Se) ligands (an analogue of the β-diketonates), Cd[(EPiPr2)2N]2 (E = S or Se) complexes and have been recognised as suitable precursors for cadmium chalcogenide films by LP-MOCVD.11 In this study, we report the synthesis and characterisation of [MeCd(SePiPr2)2N]2 complex, which is one of the first examples of mixed alkyl diselenoimidodiphosphinate complex and its use as a single-source precursor to deposit metal selenide films by LP-MOCVD. EXPERIMENTAL DETAILS Precursor Synthesis The complex [Cd(SePiPr2)2N]2 was prepared according to previously reported methods.12 Dimethylcadmium was a gift from Epichem Ltd. Toluene (BDH) was distilled over Nabenzophenone and degassed prior to use. All manipulations and reactions were carried out in an inert atmosphere using Schlenk techniques and a vacuum line.
M5.21.2
[MeCd(SePiPr2)2N]2: A solution of [Cd(SePiPr2)2N]2 (2.4 g, 2.59 mmol) in dry toluene (~ 50 ml) was stirred with dimethylcadmium (0.38 g, 2.59 mmol) at room temperature for 1 hour. After removal of solvent under vacuum, a white colour solid was obtained. Some of this product was recrystallised in toluene to give clear crystals. Yield: 2.4 g (87%). mp 191 oC. 1H NMR (δ, C6D6, 300 MHz): 0.10 [6H, s, Cd-CH3]; 0.8 [48H, m, C-CH3]; 1.5 [8H, m, C-H]; 31P NMR (δ, C6D6, 400 MHz): 54.76 [m]. Microanalysis: Calculated for [C26H62N2P4Se4Cd]: C, 29.28; H, 5.81; N, 2.63%. Found: C, 30.40; H, 6.12; N, 2.84%. FT-IR (major bands and tentative assignmen
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