The Endocyclic Carbon Substituent of Guanidinate and Amidinate Precursors Controlling Atomic Layer Deposition of InN Films

Indium nitride (InN) is an interesting material for future high-frequency electronics due to its high electron mobility. The problematic deposition of InN films currently prevents full exploration of InN-based electronics. We present studies of atomic layer deposition (ALD) of InN using In precursors with bidentate ligands forming In-N bonds: Tris(N,N-dimethyl-N′,N″-diisopropylguanidinato)indium(III), tris(N,N′-diisopropylamidinato)indium(III), and tris(N,N′-diisopropylformamidinato)indium(III). These compounds form a series were the size of the substituent on the endocyclic position decreases from-NMe₂ to-Me and to-H, respectively. We show that when the size of the substituent decreases, the InN films deposited have a better crystalline quality, of better optical quality, lower roughness, and an In/N ratio closer to unity. From quantum chemical calculations, we show that the smaller substituents lead to less steric repulsion and weaker bonds between the ligand and In center. We propose that these effects render a more favored surface chemistry for the nitridation step in the ALD cycle, which explains the improved film properties.