Resonant hydrogenic impurity states and 1s−2p₀ transitions in coupled double quantum wells

Calculations of the 1s and resonant 2p₀ states of a shallow donor in double-quantum-well structures are performed. The variational method is used to calculate the localized part of the impurity states, taking into account the effect of intersubband mixing. The resonance coupling of the 2p₀ state with the first subband is then dealt with using the Green function technique. The results show that for an asymmetric double-quantum-well structure the 1s state has a maximum binding energy as the donor is around the center of the wider well while the 2p₀ state has in general a maximum binding energy as the donor is in the narrower well. The resonant coupling of the 2p₀ state is stronger for the structures with a stronger intersubband mixing, where the 2p₀ energy level is closer to the first subband bottom. The resonance-induced broadening of the 2p₀ state can be as large as 6 meV, corresponding to a lifetime of ∼0.1 ps. The resonance in general causes a negligibly small blueshift but can give a redshift of the order of 1 meV when the resonance is strong. A phase transition of the 2p₀ state can occur from the resonant nature to the bound nature by modulation of the interwell coupling. The 1s−2p₀ transition energy is also calculated. The possibility of population inversion between the 1s and 2p₀ states is discussed.