Nils Fritjof Langlotz

arXiv2026

Localized Excitonic Emission in Wafer-Scale MOCVD-Grown GaSe 2D Nanosheets for Classical and Non-Classical Light Sources

Wafer-scale growth of two-dimensional semiconductors remains a key challenge for their integration into photonic technologies. While most studies of two-dimensional semiconductors have focused on transition metal dichalcogenides and their scalable fabrication, comparatively little attention has been given to III-VI monochalcogenides. Here, we report wafer-scale growth of gallium selenide (GaSe) by metal-organic chemical vapor deposition (MOCVD) and investigate its structural and optical properties for visible-range classical and quantum light emission. Two samples with thicknesses ranging from a few monolayers to several micrometers, controlled via the growth time, were investigated. The 30-minute grown sample yields intense, broad photoluminescence spanning 1.7--2.0$\,$eV, whereas the thinner 3-minute sample exhibits discrete narrow emission lines and single-photon emission with $(g^{(2)}(0) = 0.15 \pm 0.10)$. Remarkably, cathodoluminescence mapping reveals pronounced spatial localization of both spectrally narrow and broad emission centers. Together with temperature-dependent power-law analysis and Raman mapping, our results indicate defect-induced emission rather than intrinsic excitonic recombination. These findings establish wafer-scale MOCVD grown 2D GaSe as a platform for classical and non-classical light sources and highlight defect-engineered localization as a route toward scalable quantum photonics.

cond-mat.mes-hall↗

arXiv2025

Low Temperature MOCVD Synthesis of high-mobility 2D InSe

Two-dimensional (2D) indium selenide (InSe) is a layered semiconductor with high electron mobility and a tunable band gap ranging from 1.25 eV in the bulk to 2.8 eV in the monolayer limit. These properties make these materials strong candidates for future logic and optoelectronic devices. However, growing phase-pure InSe remains challenging due to the complex indium-selenium (In-Se) phase diagram. This complexity and the sensitivity of chemical precursors to growth conditions make it difficult to control which In-Se phase forms during synthesis during, e.g., metal-organic chemical vapor deposition (MOCVD). Despite the challenges, MOCVD is considered the most promising approach for growing InSe, as it enables wafer-scale, uniform, and controllable deposition-key requirements for device integration. In this study, we present a systematic investigation of InSe synthesis via MOCVD on c-plane sapphire substrates at low temperatures, which are highly relevant for various integration schemes. By varying the Se/In precursor ratio and the growth temperature, we create a phase diagram that covers the In-rich, equal stoichiometric, and Se-rich InxSey phases. Raman spectroscopy and atomic force microscopy, supported by energy dispersive X-ray spectroscopy and scanning transmission electron microscopy, confirm conditions, under which the formation of 2D InSe is observed. Atomically-resolved cross-sectional scanning transmission electron microscopy also reveals an epitaxial alignment of the InSe with the sapphire substrate mediated by a specific interface reconstruction. The epitaxial alignment is verified by in-plane X-ray diffraction across large length scales. Samples grown under optimized conditions exhibit a strong optical absorption in the visible range and especially a comparably high electron mobility underlining the potential of the MOCVD-grown material for future applications.

cond-mat.mtrl-sci↗