Synchrotron X-ray topography characterization of high quality ammonothermal-grown gallium nitride substrates
Abstract not provided
Liu, Yafei↗
Engineering topics
Jones, Kenneth A.
Publications and source records attributed to Jones, Kenneth A..
X-ray topography characterization of gallium nitride substrates for power device development
Gallium nitride substrates grown by the hydride vapor phase epitaxy (HVPE) method using a patterned growth process have been characterized by synchrotron monochromatic beam X-ray topography in the grazing incidence geometry. Images reveal a starkly heterogeneous distribution of dislocations with areas as large as 0 3 mm 2 containing threading dislocation densities below 10 3 cm -2 in between a grid of strain centers with higher threading dislocation densities (> 10 4 cm -2 ). Basal plane dislocation densities in these areas are as low as 104 cm -2 . By comparing the recorded images of dislocations with ray tracing simulations of expected dislocations in GaN, the Burgers vectors of the dislocations have been determined. The distribution of threading screw/mixed dislocations (TSDs/TMDs), threading edge dislocations (TEDs) and basal plane dislocations (BPDs) is discussed with implications for fabrication of power devices.
36 MATERIALS SCIENCE↗
Topological and electrical properties of capped and annealed (0001) hydride vapor phase epitaxy GaN films on sapphire
In light of the necessity to anneal GaN to activate implanted dopants, the effects of the annealing temperature and time, the quality of the hydride vapor phase epitaxy grown GaN film, the quality of the annealing cap, and the effects of the stresses generated by the difference in the coefficients of thermal expansion of the film and the substrate are examined topographically using atomic force microscopy, and electrical measurements are made on Schottky diodes fabricated on the annealed samples. Here the results show that thermal decomposition begins at threading edge dislocations that form polygonized small angle grain boundaries during the annealing process; donor defects, probably nitrogen vacancies, are formed near the surface; and the donors are created more quickly when the annealing temperature is higher, the annealing time is longer, and the thermal stresses on the annealing cap are greater. The results suggest that the maximum annealing temperature is ~1300 °C, and at that annealing temperature, the annealing time should not exceed 4 min.
36 MATERIALS SCIENCE↗