Intermediates in Ammonothermal GaN Crystal Growth under Ammonoacidic Conditions

Abstract

Crystals of two new hexammoniates, namely, [Ga(NH3)6]I3·NH3 and [Ga(NH3)6]Br3·NH3, were grown from liquid ammonia solutions of GaI3 and GaBr3 in a wide temperature range. The known compound [Ga(NH3)5Cl]Cl2 and the new triammoniate of gallium fluoride Ga(NH3)3F3 were obtained ammonothermally during the synthesis of GaN from NH4Cl and NH4F, respectively. The compounds are characterized by crystallographic parameters derived from their X‐ray diffraction data. The crystal structures of all the ammoniates feature octahedrally coordinated Ga atoms in complex ions of the general form [Ga(NH3)6–nXn](3–n)+ (n = 0, 1, 2, 4; X = F, Cl, Br, I). The extensive N–H···X hydrogen bonding networks in these compounds are analyzed. The IR and Raman spectroscopy data for [Ga(NH3)6]X3·NH3 (X = Br, I) and Ga(NH3)2F3 are provided, and the IR spectrum of Ga(NH3)3F3 is compared with those published for the monoammoniate Ga(NH3)F3 and the diammoniate Ga(NH3)2F3. Finally, the thermal deamination features of [Ga(NH3)6]X3·NH3 (X = Br, I) and Ga(NH3)3F3 are also discussed.

Determination of GaN solubility in supercritical ammonia with NH4F and NH4Cl mineralizer by in situ x-ray imaging of crystal dissolution

“…In a recent study, Zhang et al characterized solid intermediates in ammonothermal gallium nitride crystal growth formed by reaction with the ammonoacids used as mineralizer [15]. Assuming that using NH 4 Cl as mineralizer the dominating dissolved species containing gallium is [Ga(NH 3 ) 5 Cl]Cl 2 [15] (or more precisely, the ion [Ga(NH 3 ) 5 Cl] 2 þ ), the reaction may proceed as follows:…”

“…The presence of those soluble species is assumed due to the isolation of the solid intermediate Ga(NH 3 ) 3 F 3 , containing those complex ions [15]. Ga (NH 3 ) 3 F 3 was obtained from ammonoacidic conditions at a furnace temperature of 480 1C by Zhang et al [15]. Taking into account the different positions of the thermocouple (furnace temperature vs. temperature inside the autoclave) the synthesis temperature of Ga (NH 3 ) 3 F 3 reported by Zhang Once temperature is kept constant, dissolution quickly slows down and continues with a much lower rate (range III).…”

“…The presence of those soluble species is assumed due to the isolation of the solid intermediate Ga(NH 3 ) 3 F 3 , containing those complex ions [15]. Ga (NH 3 ) 3 F 3 was obtained from ammonoacidic conditions at a furnace temperature of 480 1C by Zhang et al [15].…”

“…Single crystal x-ray intensity data were collected on a Bruker-Nonius Kappa-CCD diffractometer with Mo-K α radiation, powder x-ray diffraction measurements were performed applying a STOE STADI P diffractometer with Mo-K α1 radiation. No hygroscopic products such as Ga(NH 3 ) 3 F 3 (reported previously in the system NH 4 F/Ga/supercritical NH 3 [15]) can be expected to remain due to air contact. Several crystals proved to represent (NH 4 ) 3 [GaF 6 ] [16] according to the unit cell parameters.…”

Defects in Single Crystalline Ammonothermal Gallium Nitride

“…The temperature of the growing crystal directly affects the Ga adatom mobility and attachment/detachment kinetics of the associated molecules. Post-run analysis of powders present in ammonothermal autoclaves would suggest Ga tends to form compounds with ammonia, such as [Ga(NH 3 ) 6-n X n ] (3-n)+ (n = 0, 1, 2, 4; X = F, Cl, Br, I), for acidic solutions [48] and with amides, such as [Ga(NH 2 ) 4 ] − , for basic solutions containing alkali metals. [49,50] While the accurate assessment of GaN solubility in solution during operation is still being explored, solubilities on the order of 0.1% mol Ga /mol NH3 [51] have been measured for basic systems, while higher values have been measured for the acidic systems: 0.1-1% mol Ga /mol NH3 .…”