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Abstract: A feasible mechanism for catalyst- and template-free group III-nitride nanorod growth by hydride vapor phase epitaxy (HVPE) is proposed. The mechanism is composed of random nanoparticle nucleation from stable gas-phase oligomers and subsequent directional growth along the c-axis. A combined study of equilibrium analysis and computational thermochemistry was employed to determine the optimum growth conditions—growth temperature and Cl/group III ratio—based on the proposed mechanism, and the computed values showed good agreement with reported experimental results. The involvement of a group III trichloride as a key species in the proposed mechanism required the Cl/group III ratio to be ∼3 according to stoichiometry. A higher Cl/group III ratio led to etching of the solid phase and a lower ratio favored two-dimensional film growth instead. The zone of GaN and InN nanorod growth by HVPE was shown to lie in the vicinity of the growth–etch transition. A two-temperature approach, employed in GaN nanorod growth, was supported by the deconvolution of two conflicting kinetic and thermodynamic constraints in terms of growth temperature: a high-temperature region for GaCl3 formation that is kinetically limited at low temperature and a low-temperature region for GaN nanorod growth without GaN etching that is thermodynamically favorable in a chlorinated environment at high temperature. The temperature for AlN nanorod growth by chemical vapor deposition using AlCl3 and NH3 was limited only by the thermodynamic constraint of ammonia adduct (Cl3Al:NH3) formation. [Copyright &y& Elsevier]

Abstract: A chemical equilibrium study was performed to investigate the effect of growth parameters on the constitution in ZrC films grown by chemical vapor deposition (CVD). The equilibrium analysis of the Zr–C–H system demonstrated that ZrC (fcc) deposition is favorable and that a certain minimum amount of hydrogen should prevent co-deposition of elemental carbon over a wide range of temperature, pressure, and inlet C/Zr atom ratio. The results of the equilibrium analysis were compared to the phase constitution of films grown by low-pressure metalorganic CVD (<10−4 Torr). Only carbon-rich ZrC films were grown and demonstrated the possibility of an aerosol-assisted CVD approach to stoichiometric ZrC film growth. [Copyright &y& Elsevier]

Abstract: Thin films of zirconium carbide (ZrC) have been grown on Si(111) substrates in the temperature range 400–600°C by aerosol-assisted metalorganic chemical vapor deposition (AA-MOCVD) from tetraneopentylzirconium (ZrNp4) in benzonitrile (PhCN). Preliminary equilibrium calculations suggested that a minimal level of H2 was needed to prevent codeposition of solid carbon, and the minimum level decreased with decreasing temperature. Films were grown at different values of temperature, pressure, and H/Zr inlet molar ratio, as well as carrier gas (H2, He, or N2), and were judged by their X-ray diffraction (XRD) patterns to be amorphous. The trends in the measured composition (Auger electron spectroscopy, AES) of each film were qualitatively consistent with those of the equilibrium calculation, while X-ray photoelectron spectroscopy (XPS) analyses confirmed the formation of Zr–C and Zr–O bonds. It was not possible to grow films in N2 carrier gas or using tetrabenzylzirconium (ZrBn4). The results of density functional theory (DFT) calculations on ZrNp4 and ZrBn4 supported this latter result. [Copyright &y& Elsevier]