In the paper, a relationship of detectivity with material parameters is given by a theoretical calculation. An In1-xGaxAs photovoltaic detector structure with x = 0.47 is used as an example for this study. The results show that the detectivity of a photodetector can be enhanced by optimizing the carrier concentration, thickness and surface recombination velocity during the structure growth and device fabrication. (C) 2007 Elsevier Ltd. All rights reserved.