Irradiation damage in 1~,53Ch().47AS p-i-n photodiodes by 1-MeV fast neutrons is stuhed as a function of fluence for the first time. The degradation of the electrical and optical performance of diodes increases with increasing fluence. The induced lattice defects in the In0.53Gao.47As epitaxial layers and the InP substrate are studied by DLTS methods. In the In0.53Gao.47As epitaxial layers, hole and electron capture levels are induced by irradiation. The influence of radiation source on device degradation is then discussed by comparison to 1-MeV electrons with respect to the numbers of knock-on atoms and the nonionizing energy loss (NIEL). In order to examine the recovery behavior, isochronal thermal annealing is carried out for temperatures ranging from 75 to 300 O C . After 300 O C thermal annealing, the light current only recovers to 20 % of preirradiation for a fluence of 1 x 1013 n/cm2, while it recovers to 53 % for a fluence of 1 x 1015 e/cm2. The different of recovery behavior is thought to be due a different type of radiation damage.