Simon Phillip Cooil

The earth‐abundant II‐IV‐nitrides ZnSnN ₂ and ZnGeN ₂ are direct bandgap semiconductors with a wurtzite‐derived crystal structure. Their alloys, ZnSn _x Ge _{1 − x} N ₂ , have bandgaps tunable across the full visible spectrum, making them interesting for many optoelectronic applications. Here, electrical, structural, and optical properties of near‐stoichiometric ZnSn _x Ge _{1 − x} N ₂ alloys, i.e., where [Zn]/([Zn]+[Ge]+[Sn]) ≈ 0.5, are reported, for samples synthesized by reactive magnetron sputtering. These results reveal unprecedentedly high electrical mobilities in Ge‐rich alloys, with values of 136 and 400 cm ² /Vs at room‐temperature and ≈100 K, respectively. The bandgaps are determined from optical absorption measurements combined with hybrid density functional calculations and reveal a significant Burstein–Moss shift in the Sn rich alloys. Finally, band alignments are determined in the sputter‐grown thin films by combining optical transmission measurements, hybrid density functional calculations, and UV photoelectron spectroscopy measurements, where the bandgap variation is predominantly caused by a shift of the conduction band edge. This work elucidates in unprecedented detail the tuning of optical and electrical properties in ZnSn _x Ge _{1 − x} N ₂ by variation of the chemical composition, where bandgap values of alloys with x ∈ [0.5−0.7] are suitable for top cell absorbers in two‐terminal tandem solar cells assuming a Si bottom cell.

In the Comment by Goletti [], concerns are raised regarding the interpretation of our experimental findings, as well as the application of basic ground-state density functional theory (DFT) models pertaining to the C ( 111 ) − ( 2 × 1 ) surface presented in our earlier publication [Reed , ]. These concerns are addressed and our interpretation of the results is ultimately reconfirmed. We present further analysis of the original data and introduce new measurements on previously unreported regions of the surface reconstructed ( 2 × 1 ) Brillouin zone, aiding in the evaluation of the dispersion relation at other high-symmetry points. We gain insights relating to the current use of DFT calculations that include many-body theories when relating to the occupied electronic structure of this surface as measured by angle-resolved photoelectron spectroscopy.

Understanding the collective behavior of the quasiparticles in solid-state systems underpins the field of nonvolatile electronics, including the opportunity to control many-body effects for well-desired physical phenomena and their applications. Hexagonal boron nitride (hBN) is a wide-energy-bandgap semiconductor, showing immense potential as a platform for low-dimensional device heterostructures. It is an inert dielectric used for gated devices, having a negligible orbital hybridization when placed in contact with other systems. Despite its inertness, we discover a large electron mass enhancement in few-layer hBN affecting the lifetime of the π-band states. We show that the renormalization is phonon-mediated and consistent with both single- and multiple-phonon scattering events. Our findings thus unveil a so-far unknown many-body state in a wide-bandgap insulator, having important implications for devices using hBN as one of their building blocks.

The large-scale formation of patterned, quasi-freestanding graphene structures supported on a dielectric has so far been limited by the need to transfer the graphene onto a suitable substrate and contamination from the associated processing steps. We report μm scale, few-layer graphene structures formed at moderate temperatures (600–700 °C) and supported directly on an interfacial dielectric formed by oxidizing Si layers at the graphene/substrate interface. We show that the thickness of this underlying dielectric support can be tailored further by an additional Si intercalation of the graphene prior to oxidation. This produces quasi-freestanding, patterned graphene on dielectric SiO₂ with a tunable thickness on demand, thus facilitating a new pathway to integrated graphene microelectronics.