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Neutron transmutation doping (NTD) has demonstrated its initial feasibility in offering precisely controlled and highly uniform dopants within bulk gallium nitride (GaN) wafers. This study aims to assess the doping efficacy of NTD applied to heteroepitaxial GaN films and address the technical challenges related to neutron damage and impurity activation through a comprehensive investigation of neutron irradiation parameters and annealing temperatures. Heteroepitaxial GaN films on sapphire were exposed to neutrons with varying thermal to fast neutron flux ratios in a fission reactor. The results highlight the successful application of the NTD process to heteroepitaxial GaN films, utilizing a relatively harder neutron spectrum with nearly equal thermal and fast neutron fluxes. Notably, a significant activation yield of 95.4 % was achieved through annealing at 1100 °C. Furthermore, the lattice damage and electrical conduction properties of heteroepitaxial GaN films show a strong correlation with the fast neutron fluence and annealing temperature. Elevated annealing temperature promotes the recovery from neutron-irradiated damage and enhances the activation of transmuted dopants. However, some residual defects still persist in neutron-irradiated GaN crystal after annealing. The outcomes of this study are expected to be useful for the establishment of optimal process parameters for NTD-GaN. [ABSTRACT FROM AUTHOR]

To suppress the electric-field crowding at the edge of GaN-based power devices and enhance the breakdown voltage as well, argon ion (Ar+) implantation has been demonstrated an efficient process of edge termination for n-type GaN, that is realized by the introduction of radiation-induced defects to modify electric-field distribution around the edge of devices. However, a high fluence of Ar+ irradiation inevitably causes radiation damage, which is absolutely detrimental to the electrical and material properties of GaN crystal. Therefore, the purpose of this study is to investigate the effects of radiation damage arising from Ar+ implantation on n-type GaN epitaxial layer. 180 keV Ar ions with various fluences ranging from 4.8 × 1013 to 6 × 1015 cm−2 were implanted, forming a thin damaged area near the surface of GaN epitaxial layer. The characteristics of Ar+-implanted GaN epitaxial layer were then thoroughly investigated by Hall effect measurement, X-ray diffraction (XRD), photoluminescence (PL), and Raman scattering spectroscopy. The results indicated that the electron concentration of GaN decreases with the increase of Ar+ fluence. About 32.5 % of carriers in GaN are removed after Ar+ irradiation to a maximum fluence of 6 × 1015 cm−2. As revealed by PL spectra, Ar+ implantation-induced defects would trap free carriers and behave like non-radiative recombination centers. An abrupt increase in lattice strain derived from XRD spectra implies a localized amorphous layer that may be formed in GaN crystal when Ar+ fluence is higher than 1.2 × 1015 cm−2. The Raman spectra also evidenced that Ar+ implantation into GaN leads to N sublattice damage and degradation in electrical conduction properties. The results obtained in this study are expected to be useful for the design of Ar+-implanted edge termination for GaN power devices. [ABSTRACT FROM AUTHOR]

• Quasi-vertical Schottky barrier diodes were fabricated on GaN on Si substrate. • The diodes exhibited ultra-low turn on voltage of 0.23 V and ideality factor of 1.02 being close to the ideal value. • Schottky barrier height was extracted from both current–voltage and capacitance–voltage curves. • Experimental current–voltage characteristics are consistent with the simulation results obtained using Silvaco TCAD software. • Temperature dependent reverse leakage current is attributed to variable range hopping mechanisms through dislocations. Quasi-vertical Schottky Barrier Diodes (SBDs) with near to ideal turn-on voltage and ideality factor (n) of 1.02, were fabricated on a GaN on Si substrate. The average turn-on voltage and on-resistance values were found to be 0.23 ± 0.005 V (at 1 A/cm2) and 1.76 ± 0.11 mΩcm2, respectively with diode series resistance of 11 Ω. The analysis of the current–voltage curve revealed a temperature-independent barrier height, however the capacitance–voltage method showed a negative temperature coefficient. This discrepancy is discussed in the paper. Variable range hopping through dislocations is shown to be the dominant reverse current leakage mechanisms identified in the fabricated diode, with a characteristic temperature, T 0 of 2 × 1010 K. [ABSTRACT FROM AUTHOR]