A New Single Source Precursor Approach to Gallium and Aluminum Nitride
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Current address is IBM, Watson Research Center, Yorktown Heights, NY 10598 85 Mat. Res. Soc. Symp. Proc. Vol. 395 0 1996 Materials Research Society
MC13 + 2 R1 R2NLi
Et2 °C -78
(RR2N)2MCI + LiCl
(1)
(RjR 2N) 2MN 3 + NaCl
(2)
25 °C (RIR 2N) 2MCI + NaN 3
CH 2 CI2 dibenzo- 18-crown-6
2: R=R2 =Me M=Ga 3: RI=R 2 =Me M=A1 Film growth experiments with compounds 1, 2, and 3 were conducted in a low pressure hot wall reactor MOCVD reactor (Analysis Reactor) attached to a X-ray photoelectron spectroscopy (XPS) tool to enable in-situ sample transfer without exposure to ambient conditions. GaN and AIN films were grown on Si [001] substrates which were mounted on molybdenum stubs with indium foil. Substrates were cleaned with methanol and acetone before use. Precursors were sublimed from a glass saturator at 65-84 °C. Ultra-high purity nitrogen was used as the carrier gas flowing at 250 sccm. The N 2 was prewarmed and scrubbed by a Puratrem metal alloy getter operating at 250 oC. Substrate deposition temperatures varied between 480500 °C, reactor pressure was maintained at 10 torr for all depositions. XPS analyses were performed using a VG ESCALAB Mark I spectrometer with Mg Kct (1253.6 eV) and Al Kct, (1486.6 eV) x-rays as the excitation sources, operating at 275 W and 450 W, respectively. The base pressure of the analysis chamber was 6 x 10-11 Torr and during sample irradiation never exceeded 5 x 10-10 Torr. Sputter cleaned Ag[ 100] was used for calibration of the spectrometer. The Ag(3d 5 / 2 ) peak had a full width at half maximum value of 1.7 eV and a binding energy of 368.2 eV when the spectrometer is operated at a pass energy of 50 eV. The GaN standard was grown by atmospheric pressure MOCVD ex-situ of the Analysis Reactor with triethylgallium 5 and ammonia at 1050 °C. RESULTS Compounds 1,4 and 22 are colorless nonpyrophoric solids (m.p. = 60 oC). They do not enflame in air, but slowly decompose when exposed to ambient conditions. Compound 1 is a polymer in the solid state. The basic repeating unit (CH 3 )2 GaN 3 forms a spiral along the a-axis of the orthorhombic unit cell. The gallium atoms in the chain are bridged by a single nitrogen of the azide group. Compound 2 which combines labile amido ligands and an azide nitrogen delivering substituent is a polymeric chain of dimers with the azide substituent bridging two gallium centers. Compound 2 (0.01 Torr at 90 °C) has a lower vapor pressure than compound 1 (0.05 Torr at 60 °C). Compound 3 is a colorless solid with a low melting point, 65-67 °C, and is readily decomposed. Careful Schlenk technique is necessary during synthesis and handling to prevent premature decomposition. A dimeric structure for compound 3 is suggested by similarity arguments with compound 2, the detection of the dimer by mass spectroscopy and the 3 1 equivalence of the 1 H and 13 C{ H} resonances. Pyrolysis experiments with compounds 1,6 and 22 were conducted. The azide ligand of compound 1 was observed to decompose at 375 °C and the methyl-gallium bond to cleave at 425 °C. Decomposition of
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