The availability of new manufacturing methodology in solid state physics makes it possible to grow nano-photonic devices for better performance and unique properties. In this thesis work, we use I-V and FTIR spectroscopy to study the electrical and optical properties of InAsP/InP nanowire-based array avalanche photodetectors for near infrared applications. Measurements are performed at 300K and 5K for different applied biases under darkness and illumination conditions. I-V curves are plotted to understand the charge carrier transport in nanowire photodetectors and also to improve the device fabrication. I-V characteristics display non-optimal diode properties with large dark leakage currents. From spectrally resolved photocurrent measurements, peaks appear at photon energies of 1.34eV and 1.4eV respectively, corresponding to the bandgap of zinc blende (ZB) and wurtzite (WZ) InP. An additional photocurrent peak at 1.25eV agrees with the bandgap of the included InAsP segments. The Schottky-like contacts present at the top of the nanowires most likely generate additional photocurrent at higher photon energies. No breakdown effect is observed for the array devices. Complementary single-nanowire devices indicate an avalanche breakdown effect at  V_R=-35V.