Secondary-ion mass spectrometry study of the migration of Si in planar-doped GaAs and Al_0.25Ga_0.75As

We have investigated the effect of substrate temperature T_s during growth by molecular beam epitaxy on the migration of Si atoms in δ-(or planar) doped GaAs and Al_0.25Ga_0.75As using secondary-ion mass spectrometry (SIMS). Our results for δ-doped GaAs illustrate a measurable spread of Si that increases by ∼80 Å as T _s is varied from 580 to 640°C. For comparable T_s, the Si spreads further (by ∼350 Å) in δ-doped Al _0.25Ga_0.75As. For T_s<580°C, the width of the Si profiles is determined by the resolution of our SIMS measuring technique. Magnetotransport measurements were also performed on these structures in order to determine the spreading of the dopants. The Si migration measured by SIMS is in qualitative agreement with the transport results; however, the SIMS data indicate larger Si areal densities. Two mechanisms, autocompensation and the electron localization by a DX center, are believed to be responsible for the latter observation.