John L. Lyons

ZUSAMMENFASSUNG: Zinnhalogenidperowskit Quantenpunkte (ZHP QP) sind aussichtsreiche Alternativen für ihre Bleianaloge im Hinblick auf rote und nah‐infrarote Lichtemission. ZHP sind jedoch durch Kationenleerstellen intrinsisch stark p‐dotiert, was die Photolumineszenzquantenausbeute (PLQA) von ZHP QP limitiert. Die niedrigen Kationenleerstellenbildungsenergien erlauben keine ausreichende stöchiometrische Kontrolle über den Grad der Dotierung, und effektive aliovalente Dotierungsstrategien zur extrinsischen Regulierung der Ladungsträgerkonzentration sind nicht bekannt. Diese Arbeit etabliert organische Dikationen wie Ethylendiammonium (EN) als effektive Elektronendonatoren für ZHP QP. Die aliovalente A‐Kationensubstitution kompensiert die p‐Dotierung und steigert dadurch die PLQA um mehr als zwei Größenordnungen. 4 bis 16 nm CsSnI ₃ ‐EN QP emittieren bei Wellenlängen größer als 750 nm mit PLQA von bis zu 38%. Dieses Konzept funktioniert sowohl mit diversen Dikationen als auch für hybride FASnI ₃ QP. Die ursprünglichen, p‐dotierten ZHP QP zeigen ein größenabhängiges infrarotes Absorptionsband, das Intrabandübergängen im Valenzband zugeschrieben wird und bei Kompensationsdotierung durch EN verschwindet. Röntgenphotoelektronenspektroskopie (PES) zeigt erhöhte Kernniveaubindungsenergien aller Perowskitbestandteile, die mit einer Verschiebung des Ferminiveaus um 0.1 eV weg vom Valenzband übereinstimmen. Der Befund wird von der Darstellung der Fehlstellengleichgewichte durch Dichtefunktionaltheorieberechnungen bestätigt. Diese Ergebnisse etablieren organische Dikationen als Donatoren zur Herstellung von nah‐infrarot emissiven ZHP QP.

Tin halide perovskite quantum dots (THP QDs) are promising alternatives to their lead analogs for red and near‐infrared emission. However, cation vacancies cause strong p ‐doping, limiting the photoluminescence quantum yields (PLQYs) of quantum‐confined THP QDs. Low formation energies of charged cation vacancies hinder doping control through stoichiometry alone, while effective aliovalent doping strategies for extrinsic control of carrier concentrations remain lacking. Here, we establish organic dications, such as ethylenediammonium (EN), as effective electron‐donor dopants for THP QDs. Aliovalent A‐cation substitution compensates the p ‐character, enhancing the PLQY by over two orders of magnitude. CsSnI ₃ ‐EN QDs ranging in size from 4 to 16 nm emit beyond 750 nm with PLQYs up to 38%. Enhancements extend to various dications and hybrid FASnI ₃ QDs. The pristine, hole‐doped THP QDs exhibit a size‐dependent infrared absorption band arising from valence‐to‐valence intraband transitions, which disappears upon compensatory EN doping. X‐ray photoelectron spectroscopy reveals increased core‐level binding energies for all three perovskite constituents, consistent with a Fermi level shift of approximately 0.1 eV away from the valence band. Density functional theory calculations corroborate this finding and elucidate the defect equilibria. These results establish organic dications as donor dopants for near‐infrared emissive THP QDs.

Sub-bandgap optical absorption (OA) in AlN between 2 and 4 eV is widely observed, but its microscopic origin remains contested. Using photo-induced electron paramagnetic resonance (photo-EPR) and OA spectroscopy on the same samples, we demonstrate a correlation between this absorption band and the neutral charge state of substitutional carbon on the nitrogen site (CN). Hybrid functional calculations of the OA spectra show that a transition involving CN and the valence band occurs near 3.3 eV, which agrees well with a peak identified within the measured OA between 2 and 4 eV. This conclusion requires the combined ability to manipulate the charge state of carbon using photo-EPR and to use first-principles calculations of the absorption line shape that account for the dispersion of the valence band and the energy dependence of the optical matrix elements.

Tin halide perovskite quantum dots (THP QDs) are highly compelling contenders for their lead analogs when it comes to light emission in the red and near-infrared regions. However, THPs are inherently highly p-doped due to cation vacancies, limiting the photoluminescence quantum yields (PLQYs) of quantum-confined THP QDs. The low formation energies of charged cation vacancies hinder synthetic control of doping levels by stoichiometry alone, and effective aliovalent doping strategies to extrinsically control carrier concentrations are lacking. This work establishes that organic dications, such as ethylenediammonium (EN), are effective electron-donor dopants for THP QDs. The aliovalent A-cation substitution compensates the p-character, thereby enhancing the PLQY by over two orders of magnitude. 4 to 16 nm CsSnI ₃ -EN QDs emit beyond 750 nm with PLQYs up to 38%. Enhancements are found for various dications and for hybrid FASnI ₃ QDs. X-ray photoelectron spectroscopy shows increased core-level binding energies for all three perovskite constituents, consistent with a Fermi level shift away from the valence band by circa 0.1 eV. This finding is corroborated by density functional theory calculations, which elucidate the defect equilibria. These results establish organic dications as donor dopants to produce near-infrared emissive THP QDs.

DX behavior limits n -type carrier concentrations in ultrawide-bandgap nitrides such as aluminum nitride (AlN) and cubic boron nitride ( c -BN). Instead of acting as effective-mass donors, DX centers capture two electrons, stabilizing a negative charge state that leads to self compensation. Silicon is the most effective n -type dopant in this class of materials; in AlN, its DX level [i.e. the (+/ − ) transition level] is ∼ 270 meV from the conduction-band minimum. This implies that many silicon impurities incorporated into AlN will be negatively charged and compensate the intended n -type doping. By combining density functional theory calculations of temperature-dependent band gaps and Si dopant transition levels, we show here that significant compensation occurs in silicon-doped AlN, even in the absence of any other defects. This compensation strongly limits free electron concentrations which become independent of doping concentration, and donor activation is only significant for light doping scenarios. Higher free carrier concentrations can be achieved in AlGaN alloys or in c -BN, where the DX level sits closer to the conduction-band minimum.

Efficient single-photon emitters are desirable for quantum technologies including quantum networks and photonic quantum computers. We investigate the T center, a telecommunications-band emitter in silicon, and find a strong isotope dependence of its excited-state lifetime. In particular, the lifetime of the deuterium T center is over five times longer than the common protium variant. We measure an isotope-dependent shift of the local vibrational carbon-hydrogen stretch mode energy and show through explicit first-principles calculations that the dramatic lifetime difference is consistent with strong suppression of nonradiative decay due to the reduced energy of this mode for deuterium T centers. Our results imply that the deuterium T center approaches unit quantum efficiency, enabling more efficient single-photon sources and quantum memories and improved readout of the T center electron spin.

Nearly all ultrawide-bandgap oxides are affected by hole localization that limits $p$-type conductivity and thus potential applications for these materials. Highly localized holes, also known as hole polarons, trap in the vicinity of acceptor dopants, giving rise to large ionization energies and severely constraining free hole concentrations. Though this hole-trapping behavior affects wurtzite zinc oxide, rocksalt zinc oxide was recently found to be resistant to the formation of hole polarons. Moreover, $p$-type doping using lithium acceptors was predicted to be achievable. While rocksalt zinc oxide is metastable and has a band gap near $\sim$3 eV, here it is found that zinc magnesium oxide (Zn$_{\rm x}$Mg$_{\rm 1-x}$O) alloys remain $p$-type dopable within the stable rocksalt crystal structure, in addition to exhibiting band gaps in excess of 4 eV. As in rocksalt zinc oxide, alkali acceptors are shallow in zinc magnesium oxide and do not appear to be affected by donor compensation. These results indicate that alkali-doped Zn$_{\rm x}$Mg$_{\rm 1-x}$O alloys are a promising system for achieving a $p$-type dopable ultrawide-bandgap oxide.

The inorganic tin halide perovskites (such as Cs Sn Br 3 and Cs Sn I 3 ) exhibit high hole concentrations, which have been attributed to the presence of intrinsic defects such as cation vacancies. Despite their promise as photovoltaic materials, this high intrinsic conductivity limits deployment. Using hybrid density functional theory, we examine the impact of these intrinsic defects on the electronic properties of Cs Sn Br 3 and Cs Sn I 3 . We find that tin and cesium vacancies have low formation energies, especially under Sn -poor conditions, in agreement with prior work, and that the presence of these native acceptor defects can lead to high hole concentrations. However, effective donor doping of these systems can be obtained via Sc or Y incorporation. These impurities substitute on the Sn site, where they act as single donors. By examining the formation energy of these dopants versus the native defects, we show that Sc or Y doping should lead to a strong compensation, reducing hole concentrations under Sn -rich conditions. Published by the American Physical Society 2025