A detailed investigation on dual-band （mid- and far-） infrared detection and photon frequency upconversion in GaN/AlGaN heterojunction structures is carried out. We deduce the Al composition in intrinsic AlGaN barrier layer through photoluminescence spectroscopy, and evaluate the conduction bandgap interfacial workfunction in GaN/AlGaN with different Al compositions. Based on the mid- and far-infrared responsivity simulation of single-period GaN/AlGaN heterojunction detector, we investigate the mid- and far-infrared photon frequency upconversion efficiencies of multi-period GaN/AlGaN heterojunction detectors integrated with GaN/AlGaN violet light emitting diodes in relation to the GaN emitter layer thickness, intrinsic AlGaN barrier layer thickness, violet photon extraction efficiency, internal quantum efficiency, spatial frequency, and GaN emitter doping concentration. The results show that GaN-based infrared upconversion devices have high upconversion efficiency and good optoelectronic application prospect.