Résumé
We have investigated the electron density of the delta -doped conventional AlGaAs/GaAs and pseudomorphic AlGaAs/InGaAs/GaAs heterojunctions. Shubnikov-de Hass (SdH) and quantum Hall effect measurements at 4.2 K have been carried out to investigate the existence of a quasi-two-dimensional gas (2DEG) in delta Si-doped AlGaAs/GaAs heterostructure. Cases have been also examined where the g-doping is placed in a narrow quantum well within the AlGaAs barrier with an Al concentration in the well (x(Al)(well)) less than in the barrier (x(Al)(Barr)). This is intended to increase the electron density. Secondary-ion mass spectroscopy (SIMS) measurements were also performed on one of these structures in order to demonstrate the spreading of the dopants. To improve the electron density, we have combined in only one structure the delta Si, in a narrow quantum well, and the InGaAs layer introduced at the heterointerface between the AlGaAs and the GaAs. A comparison between the theoretical and experimental results was performed. The variation trends of calculated electron density are in good agreement with the experimental ones. (C) 2001 Published by Elsevier Science B.V.