Rapid Characterization of Vertical Threading Dislocations in GaN Using
Chunzhi Jitty Gu, Mike Salmon, Jim Vitarelli
Keywords: GaN, VTD, Dislocation Types, STEM
The purpose of the work is to demonstrate that the vertical threading dislocations (VTDs)in GaN-based materials can be characterized using dedicated Scanning TransmissionElectron Microscopy (STEM). Each dislocation can be readily identified as edge, screw ormixed; distribution and density of each type can be easily evaluated. Comparing toconventional TEM, STEM characterization of dislocations is rapid, simple and easy tointerpret.
Rapid development of light emitting diodes (LEDs) and laser diodes (LDs) for use incommercial applications continuously pressures manufacturers to improve the performanceof their devices. The National Renewable Energy Lab has set goals for increasing theinternal quantum efficiency (IQE) of GaN based LEDs to 90% by 2015 . Research hasshown that the threading dislocation (TD) type has a strong influence on the IQE  of thedevice. As such, there is a growing need to efficiently determine TD types in acommercial environment.
Traditionally, defect or dislocation characterization in various materials is carried out byextensive conventional transmission electron microscopy (TEM) analysis of cross-sectionsamples.[3-5] However, TEM images are complicated by thickness fringes and bendcontours, as well as Kikuchi diffraction patterns (figure 1a). As compared to the TEM, thescanning convergent electron beam of the STEM provides images of dislocations withgreatly simplified contrast (figure 1b).