Measurements of deep-level transient spectroscopy (DLTS) have been made on the n-GaP before and after electron irradiation at 10 MeV. The density of an electron trap with an activation energy of 0.38 eV, which originally exists in the as-grown crystal, is reduced by the irradiation at an average reduction rate of 0.07 cm-1. The DLTS spectrum for this trap is broadened with irradiation and sharpened with successive annealing. The level broadening ΔE t of the trap is estimated by the simulation technique. ΔE t increases (decreases) with increasing (decreasing) width of the DLTS spectrum according to the introduction (annihilation) of radiation defects. The calculated average potential fluctuation is close to ΔE t(=70 meV) for the irradiated sample with 1 × 1017 electrons/cm2, implying that the level broadening arises from the band-edge broadening.

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Two-dimensional density distributions of damage, introduced into GaP by irradiation of the electron beams collimated by a slit with a 0.5 mm gap at incident energies of 10 and 16 MeV, were obtained by using optical density measurements. The lateral profile of damage can be approximated by a Gaussian profile for a depth z>2 mm; its lateral spread Δp increases from 0.29 to 2.35 mm for z=0.01 to 6.1 mm for 10 MeV. The increase in Δp is larger for a 10 MeV-electron beam than for a 16 MeV beam. This is explained by the larger lateral spread of traversing electrons for 10 MeV. The damage does not spread laterally as much as the electrons, which leads to a decrease of the lateral damage introduction rate. This is discussed in terms of the energy distribution and the scattering angle of electrons in matter.