Photo Hall concentration and mobility were measured for two molecular beam epitaxy‐grown samples having a silicon planar‐doped structure in the GaAs layer of a GaAs/AlGaAs heterojunction. The nominal silicon concentration for both samples was 1.5×1013cm−2and the distance between the ideal localization of the doped plane and the interface was adjusted to be 15 A˚. The difference between the two samples is the growth direction. The Hall measurements were carried out at 77 K both in darkness and under illumination using an infrared light emitting diode as light source. Photoexcited effects indicate the presence of silicon atoms inside the undoped AlGaAs layer and that the silicon profile spreads mainly in the growth direction. Self‐consistent electronic structure calculations, in the effective‐mass approximations, were performed assuming doping profiles that simulate both samples. The calculations show that parallel conduction occurs when the growth direction is from GaAs to AlGaAs. This is consistent with the Hall measurements. ©1995 American Institute of Physics.