The synthesis of a novel tetrameric gallane, [HClGaN3]4 (1),with a heterocyclic cyclooactane-like structure has been demonstrated. A single-crystal X-ray study reveals that the molecule consists of eight-membered Ga4N4 rings with Ga atoms bridged by the α-nitrogens of the azide groups. [HClGaN3]4 crystallizes in the tetragonal space group space group P42 bc, with a = 17.920(3) Å, c = 10.782(3) Å, V = 3462(2) Å3, and Z = 8. On the basis of the mass spectrum, the vapor of the compound consists of the trimer [HClGaN3]3, which is a low-temperature molecular source for growth of GaN layers on sapphire and Si substrates at 500 °C. Solid 1 decomposes exothermically at 70 °C to yield bulk nanocrystalline wurtzite and zinc blende GaN. The reaction between H2GaCl and LiN3 yields the analogous and extremely simple azidogallane (H2GaN3) n (2), which is used to deposit crystalline GaN films at 450 °C. Compound 2 is considerably more reactive than 1, and its decomposition, often initiated at room temperature, yields pure and crystalline nitride material of unusual morphology and microstructure.
We describe the formation and properties of H(2)GaN(3) (1), which is a very simple and stable molecular source for chemical vapor deposition (CVD) of GaN heterostructures. Compound 1 and the perdeuterated analogue D(2)GaN(3) (2) are prepared by the LiGaH(4) and LiGaD(4) reduction of Br(2)GaN(3) (3), respectively. Compound 3 is obtained from the thermal decomposition of the crystalline adduct SiMe(3)N(3).GaBr(3) (4) via loss of SiMe(3)Br. A single-crystal X-ray structure of 4 reveals that the molecule is essentially a Lewis acid-base complex between SiMe(3)N(3) and GaBr(3) and crystallizes in the orthorhombic space group Pna2(1), 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 HBrGaN(3) (5) is also prepared by reaction of appropriate amounts of 3 and LiGaH(4). Both H(2)GaN(3) (1) and D(2)GaN(3) (2) are volatile species at room temperature and can be readily distilled at 40 degrees 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 (H(2)GaN(3))(3) and (D(2)GaN(3))(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 H(2) and N(2) 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 degrees C and the facile decomposition pathway that allows film growth at temperatures as low as 200 degrees C with considerable growth rates up to 800 Å/min.
The formation of a novel Lewis acid-base complex between the silyl azide Si(CH(3))(3)N(3) and GaCl(3) having the formula (H(3)C)(3)SiN(3).GaCl(3)()()(1) is demonstrated. The X-ray crystal structure of 1 shows that the electron-donating site is the nitrogen atom directly bonded to the organometallic group. Compound 1 crystallizes in the orthorhombic space group Pnma, with cell dimensions a = 15.823(10) Å, b = 10.010(5) Å, c = 7.403(3) Å, and Z = 4. Low-temperature decomposition of 1 via loss of (H(3)C)(3)SiCl yields Cl(2)GaN(3) (2), which serves as the first totally inorganic (C,H-free) precursor to heteroepitaxial GaN by ultrahigh-vacuum chemical vapor deposition. A volatile monomeric Lewis acid-base adduct of 2 with trimethylamine, Cl(2)GaN(3).N(CH(3))(3) (3), has also been prepared and utilized to grow high-quality GaN on Si and basal plane sapphire substrates. The valence bond model is used to analyze bond lengths in organometallic azides and related adducts.
We report the development of a simple and highly efficient chemical approach to growing GaN thin films between 150 and 700 °C using a single molecular source, H2GaN3. Uncommonly low-temperature growth of nanocrystalline GaN films with a wurtzite structure is readily achieved at 150–200 °C from the thermodynamically driven decomposition of the precursor via complete elimination of the stable and relatively benign H2 and N2 by-products. Highly oriented columnar growth of crystalline material is obtained on Si at 350–700 °C and heteroepitaxial growth on sapphire at 650 °C. Crucial advantages of this precursor include: significant vapor pressure which permits rapid mass transport at 22 °C; and the facile decomposition pathway of stoichiometric elimination of H2 and N2 over a wide temperature and pressure range which allows film growth at very low temperatures and pressures (10−4–10−8 Torr) with growth rates up to 80 nm per minute.
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