Spatial correlations of DX charges and electron mobility in AlxGa1-xAs

The low-temperature electron mobility mu in Si-doped Al x Ga 1-x As (x=0.25) is not a single-valued function of the free electron density n, mu being larger if a given n value is reached through capture rather than photoionization processes. This difference is reduced by lowering the Si doping level. The result is interpreted as due to spatial correlations amongst charges at the DX centres. Analysis of mobility transients during isothermal capture processes in the temperature range 110-140 K indicates that the fast initial stage of the capture is marked by an increasing order in the spatial distribution of the scattering centres. On the contrary, the slow final stage of the capture process is characterized by a diminishing order in the distribution.