The use of substituted gallium hydrides (gallanes) (including gallium hydrides-azides) in materials science is reviewed in [342]
Gallium dihydride-azide GaH2(N3) has been reported as a very simple and stable molecular source for chemical vapor deposition (CVD) of GaN. Significant vapor pressure permits its rapid mass transport at 22°C; the compound is readily distilled at 40°C/ 0.20 Torr without decomposition. Facile decomposition pathway (elimination of only H2 and N2) at low temperatures allows to grow pure and highly stoichiometric GaN thin films at temperatures as low as 200°C with considerable growth rates up to 800 Å/min.
However, its commercial application is difficult because of ease of instant decomposition often accompanied with spontaneous ignition. The remaining residue is always crystalline GaN free of Cl or any other impurities. The sample used for CVD experiments was first dissolved in benzene and then transferred to the appropriate container. The solvent was removed in the vacuum line and the sample was attached to the vacuum chamber. The gaseous precursor was transported into the reactor under vacuum through a leak valve. Even in solvents it should be handled with extreme care. GaH2(N3) can be stabilized by adduct formation with pyridine and trimethylamine (both are liquids); however only the adduct with Me3N can be volatilised without disproportionation [426]
The IR spectrum of the product displays two distinct and very intense bands at 2130 cm -1 and 1980 cm-1 assigned ν as N3 and ν as Ga--H respectively. Other notable features include ν sym N 3 at 1238 cm-1 , ν(Ga--N) at 475 cm -1 , ν(N--Ga--N) at 345 cm-1 and a strong absorption at 710-675 cm-1 corresponding to GaH 2 scissoring deformations (FIG. ). The latter is very prominent in molecules containing terminal Ga--H 2 units such as (H 2 GaCl) 2 , as described in Goode et al., J. Chem. Soc. Chem. Commun. 768, 1988 and (Me 2 NGaH 2 ) 2 as described in Baxter et al., Chem. Soc. Dalton, Trans. 807, 1985; Harrison et al., Chem. Soc. Dalton 1554, 1972, but it is not observed in the spectrum of (HClGaN3)4 . The weak bands at 3360 cm -1 and 2470 cm-1 , are overtones and correspond to ν as N 3 +ν sym N 3 and 2×ν sym N 3 respectively. These features are common for organometallic azides of Al, Ga, and In and have been previously observed in the IR spectra of X 2 MN 3 , (XCl, Br, I), and MAl and Ga. as described in Muller et al., J. Organomet. Chem. 12:37, 1968; Dechnicke et al., Z. anorg. allg. Chem. 444:71, 1978.
The 1H NMR spectrum at 20° C. in toluene-d 8 revealed a rather broad Ga--H resonance at δ4.87, a value significantly different than that found for (HClGaN 3 ) 4 (δ5.25) and for H2GaCl (δ5.40) as reported in Goode et al., J. Chem. Soc. Chem. Commun. 768, 1988. The peak sharpens considerably at -50° C. but its position remains the same. After several hours, at room temperature an additional sharp peak was observed at δ4.51 and was accompanied by formation of a very small amount of a white precipitate (FIG. 4). This feature at δ4.51 has been previously attributed to dissolved H2 and its presence suggests minor decomposition with loss of hydrogen as previously reported in Wells et al., Inorg. Chem. 36:4135, 1997. In contrast, the 1 H NMR spectrum in THF-d 8 shows a single, relatively sharp, resonance at δ4.86, and does not indicate any dissolved H 2 or precipitate formation for solutions that remained at room temperature for several days, indicating that a THF complex of the compound may be responsible for the remarkable stability of H 2 GaN 3 over time. (The combination band at 3360 cm-1 should not be confused with an N--H stretch. There was no obervation of N--H type vibrational modes in the IR or N--H resonances in the NMR).
The mass spectrum displays the calculated isotopic patterns for the ions (H 2 GaN 3 ) + at 114 amu, [(H 2 GaN 3 ) 2 + -H] at 227 amu, [Ga 3 N 9 ] at 334, and [(H 2 GaN 3 ) 3 + -H 2 ] at 340 amu [427]