Hexacoordinated Gallium(III) Triazenide Precursor for Epitaxial Gallium Nitride by Atomic Layer Deposition

Abstract

Gallium nitride (GaN) is the main component of modern-day high electron mobility transistors due to its favorable electronic properties. As electronic devices become smaller with more complex surface architecture, the ability to deposit high-quality GaN films at low temperatures is required. Herein, we report a new highly volatile Ga(III) triazenide precursor and demonstrate its ability to deposit high-quality epitaxial GaN by atomic layer deposition (ALD). This new Ga(III) triazenide, the first hexacoordinated Ga−N bonded precursor used in a vapor deposition process, was easily synthesized and purified by either sublimation or recrystallisation. Thermogravimetric analysis showed single-step volatilization with an onset temperature of 155 °C and negligible residual mass. Three temperature intervals with self-limiting growth were observed when depositing GaN films. The GaN films grown in the second growth interval at 350 °C were epitaxial on 4H−SiC without an AlN seed layer and found to have a near stoichiometric Ga/N ratio with very low levels of impurities. In addition, electron microstructure analysis showed a smooth film surface and a sharp interface between the substrate and film. The band gap of these films was 3.41 eV with the Fermi level at 1.90 eV, showing that the GaN films were unintentionally n-type-doped. This new triazenide precursor enables ALD of GaN for semiconductor applications and provides a new Ga(III) precursor for future deposition processes.

Synthesis, Structure and Thermal Properties of Volatile Indium and Gallium Triazenides**

“…The coordination geometries of the metal centres are best described as distorted octahedral. These structures are analogous to those previously reported for 1 a and 2 a [33,34] . The diffraction data showed severe disorder for ligands over a multitude of positions.…”

“…However, in those studies their suitability for vapour deposition was not investigated. In contrast, we recently revealed the In(III) and Ga(III) 1,3‐diisopropyltriazenides 1 a and 2 a (Figure 1) and their subsequent use in ALD of InN, GaN, InGaN and In 2 O 3 [33–36] . It should be noted that 2 a was the first example of a homoleptic hexacoordinated M−N bonded compound used for vapour deposition.…”

Synthesis and Thermal Study of Hexacoordinated Aluminum(III) Triazenides for Use in Atomic Layer Deposition

“…Traces of various decom- In previous work, we demonstrated high-quality thin films of indium nitride and gallium nitride by ALD, using the Ga(triaz) 3 and In(triaz) 3 as precursors, respectively. 31,30 From the thermal properties of the compounds, we speculated that the depositions are activated by gas-phase decomposition of the precursor in the ALD reactor. Compounds 1−6 have similar thermal properties as Ga(triaz) 3 and In(triaz) 3 and are therefore expected to undergo a similar decomposition.…”

“…A ligand closely related to the amidinate and guanidinate is the triazenide, differing by the nitrogen atom in the endocyclic position of the ligand backbone. Homoleptic hexacoordinated Al(III) triazenide complexes have previously been reported; 28,29 Recently, we reported the first examples of highly volatile homoleptic 1,3-dialkyltriazenide complexes, tris(1,3diisopropyltriazenide)In(III) (In(triaz) 3 ) 30 and Ga(III) (Ga-(triaz) 3 ), 31 and their use as ALD precursors. These new triazenide precursors underwent gas-phase decomposition at higher temperatures inside the ALD reactor, giving a smaller and more reactive M(III) species.…”

Synthesis, Characterization, and Thermal Study of Divalent Germanium, Tin, and Lead Triazenides as Potential Vapor Deposition Precursors

“…There is no mention of their volatility, and these compounds are most likely not suitable for vapor deposition because of their bulky 1,3-bis­(2,6-diisopropylphenyl)­triazenide ligand. Recently, we explored the 1,3-dialkyltriazenide ligand for group 13 metals and used the In­(III) and Ga­(III) 1,3-diisopropyltriazenide precursors for ALD of InN and GaN. − To further explore the 1,3-dialkyltriazenide ligand, we envisaged its ability to stabilize divalent group 14 elements. This would potentially give a new class of tetracoordinated M–N bonded group 14 precursors for ALD.…”