Regensburg 2025 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 8: 2D Semiconductors and van der Waals Heterostructures II
HL 8.5: Talk
Monday, March 17, 2025, 16:00–16:15, H15
Two-dimensional semiconductor with tunable bandgap close to the full visible spectrum: a MOCVD study — •Nils Langlotz, Robin Günkel, Tigmanshu Sundiyal, Oliver Maßmeyer, Jürgen Belz, and Kerstin Volz — Department of Physics and Material Sciences Center, Philipps-University Marburg, Germany
Two-dimensional (2D) semiconductors have attracted considerable attention due to their extraordinary thickness-dependent properties. III-VI compounds such as GaSe or GaS exhibit a unique Mexican hat band structure with a van Hove singularity near the valence band maxima (VBM) at the Γ point. Furthermore, 2D GaSe and GaS as bulk material have a direct band gap of 2.0 eV and 2.5 eV, respectively, making a dilute GaSexS1−x system a tunable LED in the visible regime. Tuning the band gap in the few layer regime is also possible, but the indirect band gap has to be overcome, which is suggested by doping. Metal organic chemical vapour deposition (MOCVD) is used for the growth of bulk GaSe, GaS and GaSexS1−x on sapphire (0001). Growth for all materials was performed in an AIX200GFR at 50 mbar at 500∘C in a flow modulated growth mode where the first pulse is 30 s of the gallium species and the second pulse is 30 s of selenium or sulphur, repeated for 150 cycles for the pure crystals. For the diluted crystal the second pulse is replaced by (30−x) s of selenium followed by x seconds of sulphur. The organometallic precursors used were tri-tertiary-butyl-gallium (TTBGa), di-iso-propyl-selenide (DiPSe) and tertiary-butyl-sulphide (TBS). Raman spectroscopy is used to verify the selenium/sulphur incorporation.
Keywords: MOCVD; 2D Crystal growth; GaSeS; GaSe; GaS