Synthesis of 2D Gallium Sulfide with Ultraviolet Emission by MOCVD.

Two-dimensional (2D) materials exhibit the potential to transform semiconductor technology. Their rich compositional and stacking varieties allow tailoring materials' properties toward device applications. Monolayer to multilayer gallium sulfide (GaS) with its ultraviolet band gap, which can be tuned by varying the layer number, holds promise for solar-blind photodiodes and light-emitting diodes as applications. However, achieving commercial viability requires wafer-scale integration, contrasting with established, limited methods such as mechanical exfoliation. Here the one-step synthesis of 2D GaS is introduced via metal-organic chemical vapor deposition on sapphire substrates. The pulsed-mode deposition of industry-standard precursors promotes 2D growth by inhibiting the vapor phase and on-surface pre-reactions. The interface chemistry with the growth of a Ga adlayer that results in an epitaxial relationship is revealed. Probing structure and composition validate thin-film quality and 2D nature with the possibility to control the thickness by the number of GaS pulses. The results highlight the adaptability of established growth facilities for producing atomically thin to multilayered 2D semiconductor materials, paving the way for practical applications.

Metal Organic Vapor Phase Epitaxy in a Transmission Electron Microscope.

In situ transmission electron microscopy (TEM) observations of the metal-organic vapor phase epitaxy (MOVPE) growth promise to enhance the understanding of this complex process. However, a new experimental approach is required, capable of live imaging at the atomic scale and simultaneously reflecting this method's elevated pressures. To this end, a closed gas cell in situ TEM setup is used as a micrometer-scaled MOVPE reactor to grow GaP using tertiary butyl phosphine (TBP) and trimethyl gallium (TMGa). To prove the MOVPE reactor ability of the in situ TEM holder, the thermal decomposition of TBP and TMGa is shown to proceed similarly to conventional reactor setups. Decomposition temperatures align with susceptor temperatures in MOVPE machines. Formed products and their temperature decomposition curves are comparable to previous investigations performed in conventional reactors, even though the setups significantly differ. The obtained results are exploited to grow GaP nanostructures via the MOVPE growth process inside the TEM. To prepare a substrate surface for GaP growth, which is highly challenging, Au-catalyzed vapor-liquid-solid-grown GaP nanowires are grown in the reactor cell. Subsequently, the nanowire's sidewalls serve as MOVPE substrates. These results lay the foundation for crystal growth observation under MOVPE conditions in a TEM.

Revealing the Significance of Catalytic and Alkyl Exchange Reactions during GaAs and GaP Growth by Metal Organic Vapor Phase Epitaxy.

Tertiarybutylarsine (TBAs) and tertiarybutylphosphine (TBP) are getting more and more established as group V precursors for the growth of V/III semiconductors by metal organic vapor phase epitaxy (MOVPE). Due to this development, the thermal decomposition of these precursors was studied during the growth of GaAs and GaP utilizing the Ga precursors, trimethylgallium (TMGa), triethylgallium (TEGa), and tritertiarybutylgallium (TTBGa), in a horizontal AIXTRON AIX 200 GFR MOVPE system. The decomposition and reaction products were measured in line with a real-time Fourier transform quadrupole ion trap mass spectrometer from Carl Zeiss SMT GmbH. The decomposition temperatures and the related activation energies were determined for all the mentioned precursors under comparable reactor conditions. The decomposition curves suggest, on the one hand, a catalytic effect of the GaAs surface on the decomposition of TBAs. On the other hand, the decomposition products indicate alkyl exchange as a relevant step during the bimolecular decomposition of TBAs and TBP with the Ga precursors TMGa, TEGa, and TTBGa. The catalytic reaction reduces the decomposition temperature of TBAs and TBP by up to 200 °C. In addition, for the growth of GaAs with TBAs and TEGa and for the growth of GaP with TBP and TEGa, a significant decrease of the decomposition temperature with an increasing V/III ratio is observed. This behavior, which is related to an alkyl exchange reaction, gives insights into the low-temperature growth of GaAs and GaP and is converted into an effective V/III ratio. Finally, the growth of GaAs with TTBGa and TBAs is realized at 300 °C below the unimolecular decomposition temperature of TBAs, underlining the catalytic effect of the GaAs surface. Altering the growth surface with trimethylbismuth led to the prevention of the catalytic effect.