The energy dependence of lifetime damage constants in GaAs LEDs for 1-500 MeV protons

The energy dependence of lifetime damage constants have been measured in GaAs LEDs for 1 - 500 MeV protons. At energies below about 100 MeV, the dependence is close to that expected based on proportionality between non-ionizing energy loss (NIEL) and damage constants. In the 150 - 500 MeV range, however, a monotonic decrease in damage constant is found, at variance with published calculations which show an increase with energy. Two possible explanations are suggested; an inadequate model for the calculated energy dependence of NIEL, or the creation of damage clusters which have less effect than the deposition of an equivalent energy in the form of point defects.