The InN capped with GaN structures is promising for extended visible and infrared absorption. The low growth temperature of GaN/InN epitaxy was fabricated by a low-pressure metal organic chemical vapor deposition system. The strain effect and mixed InxGa1-xN complex of the GaN/InN layer were investigated via Raman and photoluminescence (PL) measurements. The capping GaN with similar growth temperature of previous InN growth induces the gallium diffusion mechanism to form InxGa1-xN complex. The blue-shift phenomenon of multiple GaN/InN peaks with increasing growth temperature was attributed to residual strain and higher Ga content of InGaN. A ZnO/GaN/InN photodetection device is demonstrated with extended IR response, and the quantum efficiency is 2.28%.