H₂GaN₃ and Derivatives: A Facile Method to Gallium Nitride

We describe the formation and properties of H₂GaN₃ (1), which is a very simple and stable molecular source for chemical vapor deposition (CVD) of GaN heterostructures. Compound 1 and the perdeuterated analogue D₂GaN₃ (2) are prepared by the LiGaH₄ and LiGaD₄ reduction of Br₂GaN₃ (3), respectively. Compound 3 is obtained from the thermal decomposition of the crystalline adduct SiMe₃N₃·GaBr₃ (4) via loss of SiMe₃Br. A single-crystal X-ray structure of 4 reveals that the molecule is essentially a Lewis acid-base complex between SiMe₃N₃ and GaBr₃, and crystallizes in the orthorhombic space group Pna2₁, with a = 14.907(5) Å, b = 7.759(3) Å, c = 10.789(5) Å, V = 1248(1) Å,³ and Z = 4. The new azidobromogallane HBrGaN₃ (5) is also prepared by reaction of appropriate amounts of 3 and LiGaH₄. Both H₂GaN₃ (1) and D₂GaN₃ (2) are volatile species at room temperature and can be readily distilled at 40°C (0.20 Torr) without decomposition. Normal-mode analysis and ab initio theoretical calculations suggest that the vapor phase IR spectra of 1 and 2 are consistent with a trimeric (H₂GaN₃)₃ and (D₂GaN₃)₃ molecular structure of C_3v symmetry. On the basis of the mass spectrum, 1 is a trimer in the vapor phase and decomposes readily at low temperatures by elimination of only H₂ and N₂ to yield pure and highly stoichiometric GaN thin films. Crucial advantages of this new and potentially practical CVD method are the significant vapor pressure of the precursor that permits rapid mass transport at 22°C and the facile decomposition pathway that allows film growth at temperatures as low as 200°C with considerable growth rates up to 800 Å/min.