Effect of substrate temperature on migration of Si in planar-doped GaAs

Quantum oscillations in the magnetoresistance of GaAs δ (or planar) doped with Si are analyzed to obtain the electron densities of the electric subbands. We compare these densities with the results of self-consistently calculated subband structures of δ-doped GaAs in which the spread of the dopant atoms (Si) in the growth direction is a fitting parameter. The results indicate that there is negligible spread in structures grown at a substrate temperature T_S ≲530°C, while in structures grown at higher T_S there is measurable spread which increases with T_S. For T_S =640°C, the Si spread is determined to be ≅220 Å. An examination of the three-dimensional Si densities in these layers indicates that the dominant mechanism for the spreading of Si for T_S >600°C is the migration of Si to satisfy the solid solubility limit.