The photoluminescences of ion-implanted (I/I) and epitaxial Mg-doped GaN (GaN:Mg) are compared. The intensities and lifetimes of the near-band-edge and ultraviolet luminescences associated with a MgGa acceptor of I/I GaN:Mg were significantly lower and shorter than those of the epilayers, respectively. Simultaneously, the green luminescence (GL) became dominant. These emissions were quenched far below room temperature. The results indicate the generation of point defects common to GL and nonradiative recombination centers (NRCs) by I/I. Taking the results of positron annihilation measurement into account, N vacancies are the prime candidate to emit GL and create NRCs with Ga vacancies, (VGa)m(VN)n, as well as to inhibit p-type conductivity.
A simple and feasible method for fabricating high-quality and highly reliable GaN-based metal-oxide-semiconductor (MOS) devices was developed. The direct chemical vapor deposition of SiO 2 films on GaN substrates forming Ga-oxide interlayers was carried out to fabricate SiO 2 / GaO x /GaN stacked structures. Although well-behaved hysteresis-free GaN-MOS capacitors with extremely low interface state densities below 10 10 cm %2 eV %1 were obtained by postdeposition annealing, Ga diffusion into overlying SiO 2 layers severely degraded the dielectric breakdown characteristics. However, this problem was found to be solved by rapid thermal processing, leading to the superior performance of the GaN-MOS devices in terms of interface quality, insulating property, and gate dielectric reliability.
Mg-doped p-type gallium nitride (GaN) layers with doping concentrations in the range from 6.5 × 1016 cm−3 (lightly doped) to 3.8 × 1019 cm−3 (heavily doped) were investigated by Hall-effect measurement for the analysis of hole concentration and mobility. p-GaN was homoepitaxially grown on a GaN free-standing substrate by metalorganic vapor-phase epitaxy. The threading dislocation density of p-GaN was 4 × 106 cm−2 measured by cathodoluminescence mapping. Hall-effect measurements of p-GaN were carried out at a temperature in the range from 130 to 450 K. For the lightly doped p-GaN, the acceptor concentration of 7.0 × 1016 cm−3 and the donor concentration of 3.2 × 1016 cm−3 were obtained, where the compensation ratio was 46%. We also obtained the depth of the Mg acceptor level to be 220 meV. The hole mobilities of 86, 31, 14 cm2 V−1 s−1 at 200, 300, 400 K, respectively, were observed in the lightly doped p-GaN.
Lateral GaN MOSFETs on homoepitaxial p-GaN layers with different Mg doping concentrations ([Mg]) have been evaluated to investigate the impact of [Mg] on MOS channel properties. It is demonstrated that the threshold voltage (Vth) can be controlled by [Mg] along with the theoretical curve. The field effect mobility also shows [Mg] dependence and a maximum field effect mobility of 123 cm2 V−1 s−1 is achieved on [Mg] = 6.5 × 1016 cm−3 layer with Vth = 3.0 V. The obtained results indicate that GaN MOSFETs can be designed on the basis of the doping concentration of the p-GaN layer with promising characteristics for the realization of power MOSFETs.
Abstarct
The impact of controlling Ga-oxide (GaO
x
) interlayers in SiO2/GaO
x
/GaN gate stacks is investigated by means of physical and electrical characterizations. Direct deposition of SiO2 insulators produces thin GaO
x
interlayers, and subsequent oxidation treatment attains high-quality insulator/GaN interface. However, the Ga diffusion into the SiO2 layers severely degrades the breakdown characteristics of GaN-MOS devices. To improve reliability of such devices, we proposed a two-step procedure with the initial SiO2 deposition conducted under nitrogen-rich ambient, followed by thick SiO2 capping. We found that this two-step procedure enables nitrogen incorporation in the insulator/GaN interface to stabilize GaN surface. Consequently, the Ga diffusion into the SiO2 overlayer during the oxidation annealing is effectively suppressed. The proposed method allows us to achieve a SiO2/GaO
x
/GaN stacked structure of superior electrical property with improved Weibull distribution of an oxide breakdown field and with interface state density below 1010 cm−2 eV−1.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.