Decomposition of supercritical ammonia and modeling of supercritical ammonia–nitrogen–hydrogen solutions with applicability toward ammonothermal conditions

Abstract

Ammonothermal growth of nitrides occurs at temperatures in excess of 800 K and pressures greater than 150 MPa. For this region, no experimentally verified equation of state (EOS) exists for ammonia, nor is there any accurate description available for the equilibrium constant of the ammonia decomposition reaction for

Ammonothermal Synthesis of Earth‐Abundant Nitride Semiconductors ZnSiN2 and ZnGeN2 and Dissolution Monitoring by In Situ X‐ray Imaging

“…ZnSiN 2 and ZnGeN 2 were obtained as pale beige and light yellow powders, respectively. We observed that pressures above 100 MPa were necessary to obtain well‐crystallized products, which can be explained with higher NH 3 mole fractions and better solubilities of ionic compounds with increasing pressures . Zn was used in 25 % excess due to a higher expected solubility of Zn(NH 2 ) 2 and ternary zinc amides in comparison to Si, Ge, or respective intermediates.…”

“…Since KNH 2 exhibits the highest solubility of the investigated mineralizers, we assume that a higher basicity of the supercritical ammonia solution might support crystal growth . The reactions were conducted in two steps taking the preferential formation of amides at lower temperatures and the significant decomposition of ammonia beyond 850 K into account: Reactive intermediate compounds were formed at 570–670 K which were gradually decomposed to the nitrides at temperatures up to 1070 K. After the reaction, the residual mineralizer and zinc intermediates were removed by washing the product with water and 1 m HCl. ZnSiN 2 and ZnGeN 2 were obtained as pale beige and light yellow powders, respectively.…”

Defects in Single Crystalline Ammonothermal Gallium Nitride

“…Recent thermodynamic equilibrium calculations of ammonia at equilibrium with nitrogen and hydrogen under ammonothermal conditions [53] suggest the possibility of hydrogen partial pressures exceeding 10 MPa during growth, which is ≈100× higher than common vapor phase growth techniques for GaN (<0.1 MPa H 2 ). Thermodynamic favored reconstruction and termination of the crystal surfaces with hydrogen may also lead to a naturally hydrogen terminated structure.…”

Ammonothermal Synthesis and Optical Properties of Ternary Nitride Semiconductors Mg‐IV‐N2, Mn‐IV‐N2 and Li‐IV2‐N3 (IV=Si, Ge)

“…Ammonobasic mineralizers MNH 2 (M=Li, Na, K) were added to increase solubility of the starting materials. [23] All Si-containingp roducts were synthesized at up to 1070 Kw ith an autogenous pressure of 170 MPa. Residuala lkali or alkaline earth metal amides were easily washed out after the reactions (see below).…”