The electron concentration, the wavefunctions and the energy levels of a n-AlxGa1-xAs/GaAs/n-AlxGa1-xAs double heterojunction are evaluated by solving Schrodinger and Poisson equations self-consistently. The authors investigate, at zero temperature, the dependence of the sheet electron concentration, and the subband populations on the well width, spacer thickness and doping concentrations, for Al mole fraction x=0.3. They give physical interpretations of some interesting characteristics observed. The transition from a 'perfect' square well to a system of 'two separated heterojunctions' is systematically studied. The results are in excellent agreement with previous experiments.

Experiment shows that in AlGaAs/GaAs heterostructures the sheet electron concentration remains almost constant up to a certain temperature, while it increases at higher temperatures. We attempt an interpretation of this temperature dependence, taking into account the fact that in the bulk, n-AlGaAs deep and shallow donors exist, which independently and by different mechanisms provide electrons to the different conduction band minima of the bulk n-AlGaAs, and contribute to the formation of the Q2DEG. We calculate the electronic states of this structure, the Q2DEG and the bulk concentrations, and the corresponding mobilities as a function of temperature. Our numerical results are in an excellent agreement with experimental data.