A time-dependent Schrodinger equation is solved numerically for a doub
le-barrier, quantum-well resonant tunnelling structure (RTS), such as
modelling a semiconductor heterostructure, by the fast Fourier transfo
rm method. Results are shown for a resonance tunnelling structure with
barriers doped by a negative delta-function potential (delta-potentia
l) which broadens the widths of the resonances and in turn decrease th
e electron dwell times. The strength of the delta-function can be such
that it may form bound states in the barrier regions, but the states
bound to the delta-potential are very shallow. For this study, the del
ta-potentials are replaced by equivalent barriers of different heights
and widths. It is found that for a certain strength of the delta-pote
ntial or parametric value of a barrier with an equivalent effect in th
e RTS, there are three resonance states very close together. The squar
es of the wave functions trapped in the well region for the states osc
illate in lime for a broad wave packet in k-space, whereas the wave fu
nction trapped in the whole structure decays exponentially. The oscill
ating part resembles quantum beats.