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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]

We propose an optimization method to change the Al component and the thickness of step-graded AlGaN barrier to achieve better electrical performance of the device. Based on the polarization effect, we find that a second potential well occurs while increasing the Al fraction and thickness of the upper AlGaN layer, which contributes to better drain current performance in the simulations. The wafers with different AlGaN barriers were grown to compare their surface morphology and electrical properties. The surface roughness of the wafer is related to the lattice constant of the upper AlGaN layer. According to the Hall and TLM measurements, the electron sheet density and electron mobility of the 20 nm-Al 0.35 Ga 0.65 N/10 nm-Al 0.25 Ga 0.75 N barrier sample are 1593 cm2/Vs and 1.17 × 1013 cm−2 respectively, resulting in a high spacing current of 61.45 mA. Moreover, the maximum drain current density of this barrier device is 589.02 mA/mm under the I–V characteristics, 1.37 times as much as that of the 20 nm-Al 0.25 Ga 0.75 N barrier. The higher gate barrier height of Al 0.35 Ga 0.65 N reduces the gate leakage current. [ABSTRACT FROM AUTHOR]

• Crystallization of GaN:Si,C was carried out to examine the role of C in n-type GaN crystals. • Intentional incorporation of high concentrations of Si and C is possible. • Raman spectroscopy shows low-frequency modes in co-doped crystals, suggesting SiC precipitates. • YL peak's position and intensity vary with dopant specifics, hinting at Si-C complexes or V Ga. In this work co-doping with silicon and carbon in gallium nitride grown by halide vapor phase epitaxy was performed. Native seeds of high structural quality with bowing radii of (0 0 0 1) crystallographic planes higher than 15 m and threading dislocation density on the order of 5 × 104 cm−3 were used. The crystallized material was examined in terms of structural, optical, and electrical properties. For this purpose different characterization methods: X-ray diffraction, Raman spectroscopy, low-temperature photoluminescence, and Hall measurements, were applied. The physical properties of samples doped only with silicon and co-doped with carbon were analyzed and compared. However, during the crystallization process, due to high amount of Si and C, clusters of silicon carbide were unintentionally formed. The formation of these SiC clusters had an impact on the properties of the GaN crystals that were being studied. The research provides an initial insight into the complex studies of co-doping gallium nitride crystals. The results of this paper give us groundwork for more in-depth exploration of this topic. [ABSTRACT FROM AUTHOR]

In this study, magnetron reactive sputtering using a copper oxide target was performed to obtain a series of high-quality CuO x films with high hole concentration. The results of X-ray photoelectron spectroscopy and Hall measurements revealed that the hole concentration exhibited a negative correlation to the Cu + to Cu2+ ratio in the p-type CuO x film. This phenomenon indicated that the hole concentration can be modulated by adjusting film deposition conditions. Considering the high hole concentration and fine surface quality, these CuO x films were used as p-type gates without gate etching and positively shifted the threshold voltage (V th) of AlGaN/GaN high-electron-mobility transistors (HEMTs). This study is the first to achieve quasi-normally off GaN HEMTs using CuO x gates, in which V th positively shifted approximately 2.5 V and reached 0.5 V. Because of the excellent surface quality of the CuO x gate, the off-state current and gate leakage current of GaN HEMTs improved considerably. This study verified that CuO x is a promising gate candidate for fabricating low-cost, normally off AlGaN/GaN HEMTs. [Display omitted] • P-type CuO x gates were obtained through magnetron reactive sputtering of a copper oxide target. • For the first time, a quasi-normally off AlGaN/GaN HEMT with a CuO x gate was achieved. • The Cu+ to Cu2+ ratio in CuO x films was inversely proportional to hole concentration. • Adjustment of Cu+ :Cu2+ in CuO x gates allows the fabrication of AlGaN/GaN HEMTs with different threshold voltages. [ABSTRACT FROM AUTHOR]

Raman and infrared reflectance spectroscopy were used to study GaN single crystals with different doping types and carrier concentrations. In different samples, the characteristic spectra related to LO phonon-plasmon coupled (LOPC) mode are observed as changing regularly with carrier concentration. Furthermore, to obtain the carrier concentration and mobility of GaN crystals, Raman and infrared reflectance spectra with LOPC modes were fitted. The carrier concentration obtained agrees well with that obtained from the Hall measurement, which confirms that these non-contact and non-destructive spectroscopy methods with high spatial resolution are reliable to probe the carrier concentration of doped GaN single crystals. • Getting the carrier concentrations and mobility of GaN with different concentration (1016-1018) by Raman and infrared reflectance spectroscopy. • Verifying the reliability of spectroscopy methods in testing carrier concentration of bulk GaN with different doping types. • Discussing possible reasons for the different mobility obtained by Hall, Raman and infrared reflectance measurements. [ABSTRACT FROM AUTHOR]