A systematic investigation was made of defect density determination in GaN. Quantum dots were used to reduce the defect density, and photo-electrochemical and hot wet etching were used to measure it. It was found that the density of whiskers formed during the photo-electrochemical process was similar to the density of hexagonal pits formed by wet etching, and also to the dislocation density revealed by transmission electron microscopy. Hot wet etching was also used to investigate the polarity of molecular beam epitaxially grown GaN films; together with convergent-beam electron diffraction andatomic force microscopy. It was found that hot H3PO4 etched the N-polarity films very quickly, thus resulting in the complete removal of, or drastic change in, surface morphology. Improvement in the crystal quality, by using multiple layers of quantum dots as part of a strain-relieving buffer layer was reported. Samples with quantum dots generally had narrower X-ray diffraction peaks and a higher photoluminescence efficiency than did control samples without quantum dots. The insertion of quantum dots reduced the dislocation density (as determined by a defect-revealing etch) from about 1010 to some 5 x 107/cm2. Transmission electron microscopic investigations showed that many of the dislocations terminated at quantum dots.

Rapid Delineation of Extended Defects in GaN and a Novel Method for Their Reduction. P.Visconti, D.Huang, F.Yun, M.A.Reshchikov, T.King, R.Cingolani, J.Jasinski, Z.Liliental-Weber, H.Morkoç: Physica Status Solidi A, 190[1], 5-14