Thermal Control of Metathesis Reactions Producing GaN and InN

The addition of lithium amide (LiNH 2 ) and ammonium chloride (NH 4 Cl) to metathesis (exchange) reactions between gallium triiodide (GaI 3 ) and lithium nitride (Li 3 N) produces crystalline gallium nitride (GaN) in seconds at ambient pressure. A specially designed rate cell incorporating multiple thermocouples enables both the reaction velocity and temperatures to be measured. Without the additives, the GaI 3 /Li 3 N reaction propagates at >100 cm/s with a reaction temperature above 1300 K, which exceeds the 1150 K decomposition temperature of GaN. By adding an optimal ratio of LiNH 2 and NH 4 Cl, the reaction velocity slows to about 3 cm/s with a reaction temperature near 1200 K. Rapid heat dissipation is found to be very important in these reactions in preventing the decomposition of GaN. By using a specially designed thermal dissipation cell, the yield of GaN can be increased up to 78.8%. Applying the concepts developed in the synthesis of GaN, crystalline InN has been synthesized for the first time using solid-state metathesis reactions.