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The InAlN alloy system has bandgap energies that span the entire visible range and is a promising candidate for bandgap engineering. To facilitate bandgap engineering, the bandgap bowing for the entire composition range must be well characterized. In rich InxAl1−xN (x > 0.60), films were grown via plasma assisted molecular beam epitaxy on freestanding GaN substrates. The InxAl1−xN film compositions were determined using high resolution X-ray diffraction. On-axis 0002 ω-2θ scans were used to determine the c spacing of the films, reciprocal space maps of the 1 ¯ 015 peaks were used to determine that the films were completely relaxed, and the film compositions were calculated from that information assuming Vegard's law. The bandgaps were independently measured using absorbance spectroscopy and fitting to the linear region of a Tauc plot (dependence of α2 hν on hν) as determined by interpolating the second derivative of the data and selecting a region of low curvature. Compared with the literature, the data were fit to a composition-independent bandgap bowing model, and a bowing parameter of b = 4.0 ± 0.2 eV was calculated, which is consistent with previous results. [ABSTRACT FROM AUTHOR]

The dependence of electron mobility on growth conditions and threading dislocation density (TDD) was studied for n--GaN layers grown by ammonia-based molecular beam epitaxy. Electron mobility was found to strongly depend on TDD, growth temperature, and Si-doping concentration. Temperature-dependent Hall data were fit to established transport and charge-balance equations. Dislocation scattering was analyzed over a wide range of TDDs (∼2×106 cm-2 to ∼2×1010 cm-2) on GaN films grown under similar conditions. A correlation between TDD and fitted acceptor states was observed, corresponding to an acceptor state for almost every c lattice translation along each threading dislocation. Optimized GaN growth on free-standing GaN templates with a low TDD (∼2×106 cm-2) resulted in electron mobilities of 1265 cm2/Vs at 296K and 3327 cm2/Vs at 113 K. [ABSTRACT FROM AUTHOR]

Responses to 1.8 MeV proton irradiation and 10-keV X-ray irradiation under typical bias conditions are investigated for AlGaN/GaN HEMTs fabricated with different types of process technologies. We find that, in contrast to previous generations of process technologies, total ionizing dose effects can be significant in these devices. For proton irradiation, worst-case bias for transconductance degradation for GaN-on-SiC substrate devices is ON bias, and for devices built on free-standing GaN substrates, the worst-case bias condition is semi-ON bias. Low-frequency noise measurements demonstrate that these differences result from differences in defect types and energy distributions for the different types of devices, both before and after irradiation. These results emphasize the need to test devices under a wide range of conditions during characterization and qualification testing. [ABSTRACT FROM PUBLISHER]

A small degradation of threshold voltage and a significant reduction in dc and RF transconductance are observed for AlGaN/GaN high-electron-mobility transistors fabricated via three different process techniques and subjected to high voltage stress in the semi-ON bias condition. Low-frequency noise measurements as a function of temperature show peaks at ∼0.2, ∼0.5, ∼0.7, and/or ∼0.8 eV that increase with the magnitude and duration of high-field stress. The dehydrogenation of passivated Fe and O impurity defects and/or N antisite defects leads to increased charge trapping, noise, and transconductance degradation. Density functional theory calculations show that Ga vacancy motion and dehydrogenation of substitutional Fe complexes in the GaN buffer layer also contribute significantly to the poststress degradation of these devices. At higher stress voltages, these defects also likely contribute to device failure. [ABSTRACT FROM PUBLISHER]

We have examined the effect of an indium surfactant on the growth of p-type GaN by ammonia-based molecular beam epitaxy. p-type GaN was grown at temperatures ranging from 700 to 780 °C with and without an indium surfactant. The Mg concentration in all films in this study was 4.5-6 × 1019 cm-3 as measured by secondary ion mass spectroscopy. All p-type GaN films grown with an indium surfactant had higher p-type conductivities and higher hole concentrations than similar films grown without an indium surfactant. The lowest p-type GaN room temperature resistivity was 0.59 Ω-cm, and the highest room temperature carrier concentration was 1.6 × 1018 cm-3. Fits of the temperature-dependent carrier concentration data showed a one to two order of magnitude lower unintentional compensating defect concentration in samples grown with the indium surfactant. Samples grown at higher temperature had a lower active acceptor concentration. Improvements in band-edge luminescence were seen by cathodoluminescence for samples grown with the indium surfactant, confirming the trends seen in the Hall data. [ABSTRACT FROM AUTHOR]

AlGaN/GaN high electron mobility transistors (HEMTs) irradiated with 1.8-MeV protons show more relative degradation in RF power/current gain, cutoff frequency f_T, and maximum oscillation frequency fmax than DC transconductance. These result from radiation-induced increases in fast bulk and surface trap densities, as well as increasing impedance mismatch at high frequencies with increasing proton fluence. NH3-rich MBE devices show less degradation in DC transconductance, but more degradation in RF gain than Ga-rich devices. [ABSTRACT FROM PUBLISHER]

Metal-polar In0.17Al0.83N barriers, lattice-matched to GaN, were grown under N-rich conditions by plasma-assisted molecular beam epitaxy. The compositional homogeneity of these barriers was confirmed by plan-view high-angle annular dark-field scanning transmission electron microscopy and atom probe tomography. Metal-polar In0.17Al0.83N/(GaN)/(AlN)/GaN structures were grown with a range of AlN and GaN interlayer (IL) thicknesses to determine the optimal structure for achieving a low two-dimensional electron gas (2DEG) sheet resistance. It was determined that the presence of a GaN IL was necessary to yield a 2DEG sheet density above 2 × 1013 cm−2. By including AlN and GaN ILs with thicknesses of 3 nm and 2 nm, respectively, a metal-polar In0.17Al0.83N/GaN/AlN/GaN structure regrown on a GaN-on-sapphire template yielded a room temperature (RT) 2DEG sheet resistance of 163 Ω/□. This structure had a threading dislocation density (TDD) of ∼5 × 108 cm−2. Through regrowth on a free-standing GaN template with low TDD (∼5 × 107 cm−2), an optimized metal-polar In0.17Al0.83N/GaN/AlN/GaN structure achieved a RT 2DEG sheet resistance of 145 Ω/□ and mobility of 1822 cm2 V−1 s−1. High-electron-mobility transistors with output current densities above 1 A mm−1 were also demonstrated on the low-TDD structure. [ABSTRACT FROM AUTHOR]

The responses to 1.8 MeV proton irradiation of AlGaN/GaN HEMTs grown under Ga-rich and ammonia-rich conditions are investigated in this work. Changes in defect energy distributions of AlGaN/GaN HEMTs during proton irradiation are characterized via temperature-dependent low-frequency noise measurements. Density functional theory calculations show these changes are consistent with the reconfiguration and/or dehydrogenation of oxygen-related defects in Ga-rich devices. [ABSTRACT FROM PUBLISHER]

AlxGa1-xN/GaN (x = 0.06, 0.12, 0.24) and AlGaN/AlN/GaN heterostructures were grown on 6 H-SiC, GaN-on-sapphire, and free-standing GaN, resulting in heterostructures with threading dislocation densities of ∼2 × 1010, ∼5 × 108, and ∼5 × 107 cm-2, respectively. All growths were performed under Ga-rich conditions by plasma-assisted molecular beam epitaxy. Dominant scattering mechanisms with variations in threading dislocation density and sheet concentration were indicated through temperature-dependent Hall measurements. The inclusion of an AlN interlayer was also considered. Dislocation scattering contributed to reduced mobility in these heterostructures, especially when sheet concentration was low or when an AlN interlayer was present. [ABSTRACT FROM AUTHOR]