A variety of different transmission electron microscopy techniques, and particularly high-angle annular dark-field scanning transmission electron microscopy, has been used to reveal that V defects or inverted hexagonal pyramid defects in multiple InGaN / GaN quantum well ͑QW͒ layers nucleate on threading dislocations that cross the InGaN QW. The defects have thin walls lying parallel to ͕101 ¯1͖ with the InGaN / GaN QW structure. A formation mechanism for the V defects is proposed taking into account the growth kinetics of GaN and the segregation of In atoms in the strain field around the cores of the threading dislocations.

Thermal stability of InxGa1-xN/GaN multiple quantum wells with InN mole fraction of ∼0.23 and ∼0.30 was investigated by postgrowth thermal annealing. Low temperature photoluminescence spectroscopy was employed to determine the temperature dependence of the interdiffusion coefficient of In and Ga in InGaN/GaN quantum wells. The interdiffusion process is characterized by a single activation energy of about 3.4±0.5 eV and governed by vacancy-controlled second-nearest-neighbor hopping. Due to composition inhomogeneity, lower diffusivity is observed at the early stage of thermal annealing.

Mesa and planar GaN Schottky diode rectifiers with reverse breakdown voltages (V~~) up to 550V and >2000V, respectively, have been fabricated. The on-state resistance, RON, was 6mQ.cm2 and 0.8Llcmz, respectively, producing figure-of-merit values for (VRB)2/RoN in the range 5-48 MW.cm-2. At low biases the reverse leakage current was proportional to the size of the rectifying contact perimeter, while at high biases the current was proportional to the area of thk contact. These results suggest that at low reverse biases, the leakage is dominated by the surface component, while at higher biases the bulk component dominates.On-state voltages were 3.5V for the 550V diodes and 215 for the 2kV diodes. Reverse recovery times were <0.2ysec for devices switched from a forward current density of -500A.cm-2 to a reverse bias of 100V. DISCLAIMER

Gd 2 O 3 has been deposited epitaxially on GaN using elemental Gd and an electron cyclotron resonance oxygen plasma in a gas-source molecular beam epitaxy system. Cross-sectional transmission electron microscopy shows a high concentration of dislocations which arise from the large lattice mismatch between the two materials. GaN metal-oxide-semiconductor field-effect transistors (MOSFETs) fabricated using a dielectric stack of single crystal Gd2O3 and amorphous SiO2 show modulation at gate voltages up to 7 V and are operational at source drain voltages up to 80 V. This work represents demonstrations of single crystal growth of Gd2O3 on GaN and of a GaN MOSFET using Gd2O3 in the gate dielectric.

Postgrowth thermal annealing was applied to investigate the optical and structural properties of InxGa1−xN/GaN multiple quantum wells with high InN mole fraction. Thermal annealing at 900 °C results in a twentyfold increase of the integrated photoluminescence intensity. Photoluminescence emission is also improved from a broad band for the as-grown sample to two dominant peaks for the annealed sample. Cross-sectional transmission electron microscopy shows the existence of quantum dot-like islands in the wells for the as-grown sample but these islands are significantly reduced after thermal annealing at 900 °C.