The Chemical Vapor Deposition of Aluminum Nitride:  Unusual Cluster Formation in the Gas Phase

Abstract

An ab initio investigation of the chemical vapor deposition of AlN from the AlCl3NH3 adduct is presented. Geometries, harmonic vibrational frequencies and relative energies for the AlCl3NH3 adduct, its dissociation products AlCl n , NH n (n = 1−3), and ring and cluster compounds [(Cl2AlNH2) n (n = 1, 2), (ClAlNH) n (n = 1, 2, 3, 4, 6)] are discussed. The Al−N bond lengths in the investigated compounds are strongly dependent on the coordination numbers of the aluminum and nitrogen centers, decreasing from 2.0 Å for 4-coordinated Al/N centers to 1.79 and 1.68 Å for 3- and 2-coordinated Al/N centers, respectively. Thermodynamic analysis shows that dissociation of Cl x AlNH x (x = 2, 3) compounds with elimination of HCl and simultaneous formation of oligomeric forms is preferable to the process of dissociation into components or simple HCl detachment. Under standard conditions gaseous 4-coordinated Al/N compounds (ClAlNH)6 and (ClAlNH)4 are more stable than 3-coordinated (ClAlNH)2 and (ClAlNH)3 compounds. In 4-membered rings and clusters, the electrostatic repulsion between nearby Al−Al and N−N atoms makes reorganization to 6-membered rings extremely favorable. The suggested mechanism of AlN deposition involving cluster formation in the gas phase is discussed.

Theoretical spectroscopic constants of the GaN molecule

“…For example, Langho et al [19] calculated that the ground state of AlN is 3 P, using the complete-active-space self-consistent-®eld (CASSCF) [22] and multi-reference con®guration interaction (MRCI) methods. Their assignment has been in accord with experimental observation and later calculations [20,21]. Langho et al showed that the adiabatic excitation energy (T e ) for the 3 S A ®rst excited state of AlN is less than 0.1 eV, where its energetic separation depends on the level of theory.…”

Growth of thick-film AlN substrates by halide vapor transport epitaxy

“…In fact, the AlCl 3 and NH 3 molecules can form a monoamine adduct even at room temperature that dissociates at about 700 C. The AlCl 3 and NH 3 molecules can also form a long line of other adducts with structures from dimers to hexagons with increasing stability [7]. Keeping the reactants separated as long as possible would help prevent the unwanted gas phase reactions but this also has a problem.…”

“…The formation of AlCl 3 2NH 3 in the gas phase as shown in Eq. (2) is desirable due to its clean and relatively well-understood decomposition to AlN [7]. Additionally, the aluminum chloride-alkyl amine lets AlCl 3 2NH 3 decompose much later thus providing a better carrier which reduces the chance of formation of the lower temperature adducts.…”

Growth mechanism of catalyst‐ and template‐free InN nanorods

“…The InCl 3 forms an ammonia adduct (Cl 3 In:NH 3 ) with NH 3 and the subsequent monomer formation (Cl 2 InNH 2 ) via a HCl elimination leads to the formation of innate In-N bond in monomer [18][19][20][21][22]. The oligomer species ([Cl 2 InNH 2 ] n ), an aggregate of monomers, has been identified to be stable in the gas phase below a certain high temperature (up to 1000 K) [18][19][20][21][22]. The strong intramolecular H-Cl hydrogen bonding and dipoledipole interactions are known to favor the formation of larger oligomer species [21].…”