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, 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 3 v 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.