Molybdenum carbonitride films prepared by plasma enhanced atomic layer deposition were studied for use as Schottky contacts to n-type gallium nitride. Deposited using bis(tertbutylimino)bis(dimethylamino)molybdenum and a remote plasma N2/H2 plasma, the diodes capped with Ti/Au displayed excellent rectifying behavior with a barrier height of 0.87 ± 0.01 eV and an ideality factor of 1.02 ± 0.01 after annealing at 600 °C in N2. These characteristics surpass those of pure metal nitride Schottky diodes, possibly due to work function engineering due to the incorporation of C and use of a remote plasma to avoid process-induced defects. According to x-ray photoelectron spectroscopy and energy-dispersive x-ray spectroscopy, the film composition is approximately MoC0.3N0.7. Grazing incidence x-ray diffraction and plan-view transmission electron microscopy selected area electron diffraction are consistent with a rock salt structure with a lattice parameter of 0.42 nm.

This work presents electroless deposition of palladium films onto gallium nitride from aqueous palladium dichloride using sodium L-ascorbate as the reducing agent in an acidic bath. Profilometry, four-point probe measurements, energy dispersive x-ray spectroscopy (EDS), and x-ray photoelectron spectroscopy (XPS) were used to measure film thickness, sheet resistance, resistivity, morphology, and composition. The resistivity of Pd was 1-3 x 10 -5 Ω cm. Schottky diodes were produced from plated films, and the barrier heights and ideality factors were determined from current-voltage measurements. Average barrier heights were 1.13-1.26 eV, with ideality factors from 1.02-1.05, depending on the gallium nitride epilayer and substrate. Also presented is a method for depositing palladium-gallium alloy films onto gold surfaces from palladium dichloride and gallium (III) sulfate using sodium hypophosphite as the reducing agent; however, palladium-gallium alloys were not readily deposited on gallium nitride.

Materials composed of nitrogen-doped carbon are useful as catalyst supports due to their low cost, low density, and enhanced metal–support interaction. One way to synthesize catalytic single atoms and nuclei on these supports is via vapor phase deposition processes. Here, density functional theory (DFT) was used to evaluate the effects of N doping and oxidation of graphene on the adsorption and dissociation of trimethyl­(methylcyclopentadienyl) platinum (MeCpPtMe3), which is a commonly used precursor in vapor deposition of platinum. DFT calculations confirmed that oxygen incorporation into graphene via oxidation of vacancies is thermodynamically favorable with and without N dopants. N doping was found to elongate substrate–oxygen bonds, thereby enhancing the interaction between MeCpPtMe3 and oxidized defective graphene. According to nudged elastic band calculations, MeCpPtMe3 dissociation on all oxidized substrates, with or without N doping, displayed positive enthalpies of reaction and activation energies. However, N doping drives the reactions by lowering the enthalpy of reaction and activation energy for the dissociation of MeCpPtMe3 and the enthalpy of reaction for the subsequent chemisorption of MeCpPtMe2, which was exothermic in all cases. Finally, the entire reaction beginning with MeCpPtMe3 and two unreacted oxidized monovacancies and ending with MeCpPtMe2 and a methyl group each bound to an oxidized monovacancy is exothermic for substrates containing pyridinic-N dopants.

Although silicon (Si) currently dominates the semiconductor industry, its small 1.1 eV band gap limits its maximum operating temperature, which restricts its use in high-temperature, high-power devices. Gallium nitride (GaN) is an attractive semiconductor with its wide bandgap (3.4 eV), high electron mobility (1700 cm2/Vs), high electron saturation velocity (3 x 107 cm/s), large critical breakdown field (2 MV/cm), and thermal stability. The high-power capabilities of GaN allow for a reduction in device size, which can conserve physical space if used to replace conventional Si power devices. While the semiconductor itself can endure harsh operating conditions, the reliability of the metal/semiconductor contacts can be a limiting factor for its use. Schottky contacts should provide a high barrier height and low reverse leakage current, and they must be electrically stable over the lifetime of the device. In this study, three materials reported to have high work functions are compared as Schottky diodes to n-type GaN, each selected for its anticipated thermodynamic stability with GaN1 or the potential to minimize process-induced defects in the diodes or both. Rhenium (Re) diodes fabricated via electron beam deposition, molybdenum nitride (MoNx) diodes via remote plasma atomic layer deposition (ALD), and palladium (Pd) diodes via electroless deposition were investigated. Ti/Al-based ohmic contacts were employed. The Re/n-GaN Schottky diode was chosen for study because of its thermodynamic stability against metallurgical reactions1 and high work function (4.96 eV)2. The barrier heights were investigated by current–voltage (I-V) and capacitance–voltage (C-V) measurements at room temperature. Both techniques demonstrated that the barrier height increased after an anneal at 400°C for 5 min, yielding a barrier height of 0.88 eV and ideality factor of 1.02 from by I-V measurements, while the C-V measurements revealed a barrier height of 0.91 eV. These barrier heights and reverse leakage currents remained stable upon annealing in N2 at 600°C. The MoNx/n-GaN Schottky diode was chosen for study because of the reported high work function of MoNx (5.33 eV)3, its conductive and refractory nature, and its thermodynamic equilibrium with GaN4. Films were deposited with bis (tert-butylimido)-bis (dimethylamido) molybdenum and a 300 W remote N2/H2 plasma. Four-point probe measurements and x-ray photoelectron spectroscopy (XPS) were used to measure sheet resistance and composition. Barrier heights from the I-V measurements were 0.41 eV, and ideality factors were 1.4, with good stability upon annealing at 600°C. The Pd/n-GaN Schottky diode was chosen because of its high work function (5.12 eV)2 and its potential to be electrolessly deposited, offering a gentle technique to minimize process-induced defects in the GaN, although Pd is not expected to be in thermodynamic equilibrium with GaN. A new method for electroless deposition of Pd films onto GaN surfaces used palladium dichloride with sodium L-ascorbate as the reducing agent was developed. Profilometry, four-point probe measurements, energy dispersive x-ray spectroscopy, and XPS were used to measure film thickness, sheet resistance, resistivity, morphology, and composition. The process provided conductive and pure Pd films, but some challenges with nucleation of the film on GaN makes the process less robust. Barrier heights from the I-V measurements were 1.13–1.26 eV, and ideality factors were 1.02–1.05. However, Pd is not in thermodynamic equilibrium with GaN. Among the candidates tested so far, the Re diodes were overall the strongest candidate. Future work will involve stress testing followed by materials characterization to provide more information on stable metallizations for high-power GaN devices. The authors are grateful to Sandia National Laboratories (Andrew Allerman) for providing GaN epilayers. This work was funded by the Office of Naval Research under Grant N000141812360, distribution A, approved for public release, distribution is unlimited (DCN# 43-7434-20). S. E. Mohney and X. Lin, J. Electron. Mater, 25, 811–818 (1996). H. Michaelson, J. Appl. Phys. 48, 4729-4733, (1977): H. Matsuhashi and S. Nishikawa, Jpn. J. Appl. Phys., 33, 1293, (1994). H. S. Venugopalan and S. E. Mohney, Z Metallkd., 89, 184-186, (1998).