Leakage current analysis for dislocations in Na-flux GaN bulk single crystals by conductive atomic force microscopy

Abstract

The mechanisms associated with electrical conduction through individual threading dislocations (TDs) in a Na-flux GaN crystal grown with a multipoint-seed-GaN technique were investigated by conductive atomic force microscopy (C-AFM). To focus on individual TDs, dislocation-related etch pits (DREPs) were formed on the Na-flux GaN surface by wet chemical etching, after which microscopic Pt electrodes were locally fabricated on the DREPs to form conformal contacts to the Na-flux GaN crystal, using electron beam assisted deposition. The C-AFM data clearly demonstrate that the leakage current flows through the individual TD sites. It is also evident that the leakage current and the electrical conduction mechanism vary significantly based on the area within the Na-flux GaN crystal where the TDs are formed. These regions include the c-growth sector (cGS) in which the GaN grows in the [0001] direction on top of the point-seed with a c-plane growth front, the facet-growth sector (FGS) in which the GaN grows with {101¯1} facets on the side of the cGS, the boundary region between the cGS and FGS (BR), and the coalescence boundary region between FGSs (CBR). The local current-voltage (I–V) characteristics of the specimen demonstrate space charge limited current conduction and conduction related to band-like trap states associated with TDs in the FGS, BR, and CBR. A detailed analysis of the I–V data indicates that the electrical conduction through TDs in the cGS may proceed via the Poole-Frenkel emission mechanism.