Activation of free-charge carriers in Be-implanted GaAs annealed at low temperatures

Free-charge carriers in both room- and low-temperature Be-implanted GaAs were generated by annealing at 400, 450, and 475 °C and were observed by using both infrared reflection and electrical measurements. Annealing at 400 °C for 2 h removes homogeneously most of the damage-related changes in the refractive index. Longer annealing (∼50 h) or shorter term annealing at higher temperature produces free carriers. A computer model including plasma effects was used to fit the reflection curves. In general the infrared analysis results and the electric data were in reasonable agreement. Results for the room-temperature-implanted samples show the free-carrier density profile, approximated by joined half-Gaussians, to be (i) a standard deviation for the deeper half-Gaussian (σh≤0.1 μm), which is about the same or smaller than that observed by secondary ion mass spectrometry measurements (∼0.13 μm) for the Be profile, and (ii) a peak position 1.2 μm, which is deeper than the Be ion peak at 0.95 μm. Both peak positions remain essentially unchanged during the anneals. Activation of carriers at these low temperatures is not seen in either Si- or Zn-implanted GaAs. The Zn-implanted material has a weak effect at 500 °C, while the Si-implanted material has none up to 550 °C. The free-carrier profile is considered as the combination of the concentration distributions of dopant ions, Ga vacancies, and possible compensating damage-related states. The discussion centers on the detailed results for the Be case.