The fabrication and comparative studies of vertically-grown and horizontally-dispersed fully nanowire-based photodetectors are reported. The detectors both consist of transparent electrodes made by Ag nanowires and active region fabricated by GaN nanowires. The performances of the nanowire-based detectors are strongly affected by desorption and absorption of oxygen. Although the photocurrent sensitivity are similar, the horizontal structured photodetector owns larger of both of photo- and dark current which is due to the better carrier pathways and larger area that can be illuminated. The vertically structured photodetector shows a self-powered effect which is caused by diversity of the two GaN-Ag Schottky contacts. (C) 2015 Elsevier B.V. All rights reserved.