Approaching Dissolved Species in Ammonoacidic GaN Crystal Growth: A Combined Solution NMR and Computational Study

Abstract

Solutionso fg allium trihalidesG a X 3 (X = F, Cl, Br,I ) and their ammoniatesi nl iquid ammonia were studied at ambient temperature under autogenousp ressure by multinuclear ( 71 Ga, 35 Cl, 81 Br) NMR spectroscopy.T ou nravel the role of pH, the analysesw ere done both in absence and in presence of ammonium halides, which are employed as mineralizers during ammonoacidic gallium nitride crystal growth. While gallium trifluoride and its ammoniate were found to be too sparingly soluble to give rise to aN MR signal, the spectra of solutions of the heavier halides reveal the presence of as ingle gallium-containing species in all cases. DFT calculations and molecular dynamics simulations suggest the identification of this species as consisting of a [Ga(NH 3 ) 6 ] 3 + cation and up to six surrounding halide anions, resultingi na no verall trend towards negative complex charge. Quantitative 71 Ga NMR studies on saturated solutions of GaCl 3 containing variousa mountso fa dditional NH 4 Cl revealed an ear linear increase of GaCl 3 solubility with mineralizer concentrationo fa bout 0.023 mol GaCl 3 per mol NH 4 Cl at room temperature. These findings reflect the importance of Coulombic shielding fort he inhibition of oligomerization and precipitation processes and help to rationalize both the low solubility of gallium halides in neutral ammonia solution and, in turn, the proliferating effect of the mineralizer during ammonoacidic gallium nitride formation.

On the Role of Amides and Imides for Understanding GaN Syntheses from Ammonia Solution: Molecular Mechanics Models of Ammonia, Amide and Imide Interactions with Gallium Nitride

“…The common GAFF2 force-field is well suited for modelling ammonia and ammonia solutions of halides, mono-and divalent metal ions. [8,24] Moreover, we recently extended the GAFF2 force-field for modeling the interactions of ammonium and amide ions in ammonia solution. [25] On this basis, an intuitive estimate of (NH) 2À interactions with NH 3 and (NH 2 ) À is given by adopting the Lennard-Jones parameters from the amide model to describe the van-der-Waals interactions of imides.…”

Numerical Simulation of Ammonothermal Crystal Growth of GaN—Current State, Challenges, and Prospects

“…Figure 1 schematically illustrates the functionality of ammonothermal growth in the current common understanding, for growth in the temperature range of retrograde solubility. It should be noted that the transport of gallium requires the assistance of a mineralizer to promote its solubility, likely by the formation of complex ions [35][36][37][38], which appear to aggregate under ammonothermal process conditions [38,39]. The temperature dependence of solubility depends on the mineralizer and may comprise both a range of normal solubility at lower temperatures and retrograde solubility at higher temperatures.…”

“…A combination of further clarification of solution chemistry, numerical modeling, and experimental validation of selected conditions may eventually provide comprehensive data on ammonothermal solutions with sufficient accuracy for the use in growth process modeling. Both experimental and numerical investigations in the context of ammonothermal solution chemistry have recently been conducted [38,120,121] and represent important first steps in this direction. [46] with added data from new publication [117]).…”

Festkörperchemie

“…Ihre Ergebnisse unterstützten sie mit DFT-Rechnungen und Molekulardynamiksimulationen. 25) Demnach besteht die Mehrheit der Galliumhalogenide in flüssigem Ammoniak als Komplexe {[Ga(NH 3 ) 6 ]X n }( n-3 )-(n = 4-6), wenn NH 4 X als Mineralisierungsmittel dient.…”