This chapter describes the characterization of defects in GaN due to plasma etching, their deleterious impact on the electrical performance of vertical p-n diodes, and methods to remove these defects in p-n diodes formed by etching and subsequent regrowth. Deep level defect energy, concentration, and depth profile can be measured as a function of etch method and post-etch treatment using photocapacitance, and these data correlate well with reverse bias diode performance. Photocapacitance studies of both c-plane and m-plane GaN provide insight to etch-induced defectivity for both the basal plane and sidewalls relevant to patterned selective area regrowth. Electron beam-induced current (EBIC) can also assess the influence of defects by measuring the minority carrier diffusion length for both the p- and n-type regions of etched-and-regrown p-n diodes. Methods to improve the accuracy of carrier diffusion length measurements using EBIC and to improve the spatial resolution of EBIC in vertical p-n diodes are reviewed.