Migration of Si IN δ-doped GaAs and Al_xGa_{1 - x} As: Effect of substrate temperature

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. Determinations of the extent of Si migration were made through analysis of quantum oscillations in the magnetoresistance and independently by using secondary ion mass spectroscopy (SIMS). Analysis of magnetotransport data in δ-doped GaAs samples indicates that there is negligible spread in structures grown at T_S≤530 °C, while in structures grown at higher T_S there is a measurable spread which increases with T_S. For T_S=640 °C, the Si spread is determ be = 180 Å. A similar analysis performed on the magnetoresistance of δ-doped Al_0.25Ga_0.75As samples reveals that the Si spreads further in Al_0.25Ga_0.75As than in GaAs (for a comparable T_S). SIMS measurements performed on the same structures confirm these findings.