Rapid Delineation of Extended Defects in GaN and a Novel Method for Their Reduction

Abstract

Availability of reliable and quick methods to investigate extended defects and polarity in GaN films are of great interest to researchers investigating and exploiting GaN-based structures. The step immediately following the determination of defect density (DD) is to explore ways in which the DD can be reduced. In this paper, we report a systematic investigation of DD determination in GaN which is followed by a novel technique, use of quantum dots, to reduce the DD. We have used photo-electrochemical (PEC) and hot wet etching to determine the DD. We found the density of whiskers formed by the PEC process to be similar to the density of hexagonal pits formed by wet etching and to the dislocation density obtained by transmission electron microscopy (TEM). Hot wet etching was also used to investigate the polarity of MBE-grown GaN films together with convergent beam electron diffraction (CBED) and atomic force microscopy (AFM). We have found that hot H3PO4 etches N-polarity GaN films very quickly resulting in the complete removal or a drastic change of surface morphology. We also report on the improvement in the GaN crystal quality by using multiple layers of quantum dots (QDs) as part of a strain-relieving buffer layer. Samples with QDs generally showed narrower X-ray diffraction peaks and higher photoluminescence efficiency than the control samples without QDs. Insertion of QDs reduced the dislocation density, as determined by a defect revealing etch, from ∼1010 cm—2 to ∼5 × 107 cm—2. Preliminary TEM investigations show that many of the dislocations terminate at QDs.