No abstract

Abstract-In this paper, a simple and reliable method to estimate the channel temperature of GaN high-electron mobility transistors (HEMTs) is proposed. The technique is based on electrical measurements of performance-related figures of merit (I D max and R ON ) with a synchronized pulsed I-V setup. As our technique involves only electrical measurement, no special design in device geometry is required, and packaged devices can be measured. We apply this technique to different device structures and validate its sensitivity and robustness.

We report the improved detectivity of AlxGa1−xN-based solar-blind p–i–n photodiodes with high zero-bias external quantum efficiency. The zero-bias external quantum efficiency was ∼42% at 269 nm, and increased to ∼46% at a reverse bias of −5 V. In addition, the photodiodes exhibited a low dark current density of 8.2×10−11 A/cm2 at a reverse bias of −5 V, which resulted in a large differential resistance. The high quantum efficiency and large differential resistance combine to yield a high detectivity of D*∼2.0×1014 cm Hz1/2 W−1. These results are attributed to the use of an Al0.6Ga0.4N window n region, which allows improved transmission to the absorption region, and to improved material quality.

No abstract

Using the synchrotron Laue method and high-resolution x-ray diffraction, we have revealed the epitaxial tilting effect of gallium nitrite (GaN) films grown on vicinal (0001) surfaces of sapphire and their relationship to the offcut angles and the substrate surface steps. This effect is a consequence of the large outof-plane lattice mismatch between GaN and sapphire, and can be explained by an extended Nagai theory. The large lattice tilts and their formation mechanism indicate that the substrate surface morphology is an important factor that affects the epitaxy process and the crystalline quality of GaN films grown via vicinal-surface epitaxy.

No abstract

Four vanadium-based contacts to n-type Al 0.6 Ga 0.4 N were compared in this work. Both V/Al/Pd/Au and V/Al/V/Au contacts with optimized layer thicknesses provided lower specific-contact resistances than did the previously reported V/Al/Pt/Au ohmic contact. Specific contact resistances of the V/Al/Pd/Au (15 nm/85 nm/20 nm/95 nm) and V/Al/V/Au (15 nm/85 nm/20 nm/95 nm) contacts were 3 ϫ 10 Ϫ6 Ω·cm 2 and 4 ϫ 10 Ϫ6 Ω·cm 2 , respectively. On the other hand, an analogous V/Al/Mo/Au contact never became ohmic, even after it was annealed at 900°C for 30 sec. Compared to the V/Al/Pd/Au contact, the V/Al/V/Au contact required a less severe annealing condition (30 sec at 700°C instead of 850°C). The V/Al/V/Au contact also provided a smoother surface, with a root-mean-square (RMS) roughness of 39 nm.

We have fabricated and investigated high-voltage GaN vertical Schottky-barrier rectifiers grown by metalorganic chemical vapor deposition. A mesageometry Schottky-barrier rectifier having a 5-μm-thick i region, and processed using reactive-ion etching, exhibited a reverse breakdown voltage of −450 V (at 10 mA/cm2) and an on-resistance of 23 mΩ cm2. For comparison, we have also applied wet chemical etching for the fabrication of mesageometry Schottky-barrier rectifiers. The 2-μm-thick i-region GaN mesa-Schottky rectifiers showed a breakdown voltage of −310 and −280 V for wet-etched and dry-etched devices, respectively, and an on-resistance of 8.2 and 6.4 mΩ cm2, respectively. These results indicate that the performance of the wet-etched rectifiers is comparable to or better than that of comparable dry-etched devices.