We present the electron capture rates for the double heterostructure GaAs/A
lxGa1-xAs confined between two outer metallic barriers. The capture mechani
sm is assisted by the emission of bulk and dielectric continuum (DC) phonon
s. The alloys generate other phonon resonances compared with the electron c
apture rates, which are evaluated in the case of the GaAs/AlAs heterostruct
ure. This investigation shows that the concentration of aluminium is an imp
ortant parameter to control the electron capture mechanism.