H 2 S-free Metal-Organic Vapor Phase Epitaxy of Coalesced 2D WS 2 Layers on Sapphire
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MRS Advances © 2018 Materials Research Society DOI: 10.1557/adv.2018.669
H2S-free Metal-Organic Vapor Phase Epitaxy of Coalesced 2D WS2 Layers on Sapphire A. Grundmann1, D. Andrzejewski2, T. Kümmell2, G. Bacher2, M. Heuken3, H. Kalisch1 and A. Vescan1 1
Compound Semiconductor Technology, RWTH Aachen University, Sommerfeldstr. 18, 52074 Aachen, Germany
2
Werkstoffe der Elektrotechnik and CENIDE, University Duisburg-Essen, Bismarckstr. 81, 47057 Duisburg, Germany
3
AIXTRON SE, Dornkaulstr. 2, 52134 Herzogenrath, Germany
ABSTRACT The 2D transition metal dichalcogenide (TMDC) tungsten disulfide (WS2) has attracted great interest due to its unique properties and prospects for future (opto)electronics. However, compared to molybdenum disulfide (MoS2), the development of a reproducible and scalable deposition process for 2D WS2 has not advanced very far yet. Here, we report on the systematic investigation of 2D WS2 growth on hydrogen (H2)-desorbed sapphire (0001) substrates using a hydrogen sulfide (H2S)-free metal-organic vapor phase epitaxy (MOVPE) process in a commercial AIXTRON planetary hot-wall reactor in 10 × 2" configuration. Tungsten hexacarbonyl (WCO, 99.9 %) and di-tert-butyl sulfide (DTBS, 99.9999 %) were used as MO sources, nitrogen (N2) was selected as carrier gas for the deposition processes (standard growth time 10 h). In an initial study, the impact of growth temperature on nucleation and growth was investigated and an optimal value of 820 °C was found. The influence of the WCO flow on lateral growth was investigated. The aim was to maximize the edge length of triangular crystals as well as the total surface coverage. Extending gradually the growth time up to 20 h at optimized WCO flow conditions yields fully coalesced WS2 samples without parasitic carbon-related Raman peaks and with only sparse bilayer nucleation. After substrate removal, a fully coalesced WS2 film was implemented into a lightemitting device showing intense red electroluminescence (EL).
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INTRODUCTION: 2D transition metal dichalcogenides (TMDC) such as MoS2 and WS2 are very promising for future (opto)electronics because of their unique properties such as tunable bandgaps and high charge carrier mobilities [1,2,3]. However, one major challenge is the uniform large-area growth of high-quality TMDC monolayers which would enable industrial production of atomically thin high-performance devices. Deposition techniques such as chemical vapor deposition (CVD) have widely been used but control and modulation of source supply as well as uniform deposition on a large scale are challenging. MOVPE can provide a reproducible and easily scalable deposition technology with an excellent homogeneity. Recently, MOVPE has been used to deposit MoS2, WS2 and WSe2 (tungsten diselenide) monolayer and multilayer f
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