Giant Traps on the Surface of Hydride Vapor Phase Epitaxy-Grown Free-Standing GaN

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Extended defects on the top surface of a 250-µm-thick free-standing GaN sample, grown by hydride vapor phase epitaxy (HYPE), were studied by deep level transient spectroscopy (DLTS) and scanning surface potential microscopy (SSPM). For comparison, similar studies were carried out on as-grown HVPE-GaN samples. In addition to the commonly observed traps in as-grown HYPE-GaN, the DLTS measurements on free-standing GaN reveal a very high concentration of deep traps (similar to 1.0 eV) within about 300 nm of the surface. These traps show nonexponential capture kinetics, reminiscent of those associated with large defects, that can accumulate multiple charges. The SSPM measurements clearly reveal the presence of charged microcracks on the top surface of the sample. It appears that the "giant traps" may be associated with these microcracks, but we cannot rule out the involvement of other extended defects associated with the near-surface damage caused by the polishing/etching procedure.