Availability of reliable and quick methods to investigate extended defects and polarity in GaN films were of great interest to researchers investigating and exploiting GaN-based structures. The step immediately following the determination of defect density was to explore ways in which the defect density could be reduced. A systematic investigation was made here of defect density determination in GaN which was followed by a novel technique, use of quantum dots, to reduce the defect density. Photo-electrochemical and hot wet etching were used to determine the defect density. It was found that the density of whiskers formed by the photo-electrochemical process was similar to the density of hexagonal pits formed by wet etching and to the dislocation density obtained by transmission electron microscopy. Hot wet etching was also used to investigate the polarity of MBE-grown GaN films together with convergent beam electron diffraction and atomic force microscopy. It was found that hot H3PO4 etches N-polarity GaN films very quickly resulting in the complete removal or a drastic change of surface morphology. An improvement in the GaN crystal quality, by using multiple layers of quantum dots as part of a strain-relieving buffer layer, was also reported. Samples with quantum dots generally showed narrower X-ray diffraction peaks and higher photoluminescence efficiency than the control samples without quantum dots. Insertion of quantum dots reduced the dislocation density, as determined by a defect revealing etch, from about 1010 to about 5 x 107/cm2. Preliminary TEM investigations showed that many of the dislocations terminate 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, 2002, 190[1], 5-14