Dose rate effects in indium implanted GaAs

Lattice disorder produced by 40 keV indium ions has been studied using conventional channelling and Rutherford backscattering of 2.0 MeV helium ions. Plots of lattice disorder as a function of dose are nonlinear and sigmoidal in shape. The lattice disorder saturates for doses approaching 10 14 ions. cm −2 , the higher the implantation dose rate, the higher this saturation level becomes. By varying the nominal dose rate between 2 × 10 10 ions. cm −2 . sec −1 and 10 13 ions. cm −2 . sec −1 a series of damage build up curves may be obtained. The dose rate effects can be described by the Vook and Stein model of annealing during irradiation. Direct observation of implantation beam annealing strongly supports this model. Electron diffraction data indicates that no amorphous gallium arsenide phase is produced under the implantation conditions prevailing in this investigation. The dose rate effects together with the room temperature annealing of implanted samples and the behaviour of several "warm" substrate implants, leads to the conclusion that room temperature lies within a damage annealing stage for implanted gallium arsenide. Preliminary high energy implants indicate that the surface proximity of these low energy implants is also an important factor in their annealing behaviour.