The carbon nanotubes (CNTs) are an ideal material for infrared applications due to its excellent electronic and optoelectronic properties, suitable bandgap, mechanical and chemical stabilities. In this paper, we demonstrate a photovoltaic infrared detector which is based on aligned single-walled CNT (SWCNT) arrays. The device is fabricated by asymmetrically contacting the two ends of the SWCNT arrays with Pd and Sc of different work functions, which are known to form ohmic contacts with the valence and conduction bands of semiconducting SWCNTs respectively. The device is characterized at room temperature, exhibiting excellent diode characteristics, high responsivity of 9.87 × 10 A/W and infrared spectral detectivity of 1.09 × 10 cmHz /W. The demonstration of the SWCNT arrays based infrared detector which is fabricated using a doping-free process paves the way to applications of CNT in such field as high-performance infrared sensors. © 2012 Optical Society of America. -5 7 1/2