Amorphous GaP produced by ion implantation

Abstract

Two types of non-crystalline states (“disordered” and “amorphous”) of GaP were produced by using ion implantation and post annealing. A structural-phase-transition-like annealing behaviour from the “disordered” state to the “amorphous” state was observed. The ion dose dependence and the annealing behaviour of the atomic structure of GaP implanted with 200 keV − N + ions were studied by using electron diffraction, backscattering and volume change measurements. The electronic structure was also investigated by measuring optical absorption and electrical conductivity. The implanted layer gradually loses the crystalline order with the increase of the nitrogen dose. The optical absorption coefficient α and electric conductivity σ of GaP crystals implanted with 200 keV−N + ions of 1 × 10 16 cm −2 were expressed as αhν = C( hν − E 0) n and log σ = A − BT - 1 4 , respectively. Moreover, the volume of the implanted layer increased about three percent and the electron diffraction pattern was diffused halo whose intensity monotonically decreases along the radial direction. These results indicate that the as-implanted layer has neither a long range order nor a short range order (“disordered state”). In the sample implanted at 1 × 10 16 cm −2, a structural phase-transition-like annealing stage was observed at around 400°C. That is, the optical absorption coefficient α abruptly fell off from 6 × 10 4 to 7 × 10 3 cm −1 and the volume of the implanted layer decreased about 2% within an increase of less than 10 degrees in the anneal temperature. Moreover, the short range order of the lattice structure appeared in the electron diffraction pattern. According to the backscattering experiment, the heavily implanted GaP was still in the non-crystalline state even after annealing. These facts lead us to believe that heavily implanted GaP, followed by annealing at around 400°C, is in the “amorphous” state, although as-implanted Gap is not in the “amorphous” state but in the “disordered” state.