In the framework of effective mass and single-band approximations, a variational method combined with a self-consistent procedure is adopted to discuss the binding energies of heavy-hole excitons in a strained wurtzite GaN/Al 0.3 Ga 0.7 N quantum well by considering the hydrostatic pressure effect and screening due to the electron-hole gas. The built-in electric field in such a structure produced by spontaneous polarization and strain-induced piezoelectric polarization is considered in our calculation. A simplified coherent potential approximation is extended to calculate the energy gaps of the ternary mixed crystal Al x Ga 1−x N. The result indicates that the binding energies of excitons increase nearly linearly with pressure even when taking into consideration the modification of strain. It is also found that the percentage increase of the binding energy with pressure is influenced by the electron-hole density due to the influence of pressure on the screening and exclusion effects. The excitonic binding energies increase obviously with decreasing barrier thickness due to the built-in electric field.

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The ground state binding energies of donor impurities in strained [0001]-oriented wurtzite GaN / Al x Ga 1-x N asymmetric double quantum wells are investigated using a variational method combined with numerical computation. The built-in electric field due to the spontaneous and strain-induced piezoelectric polarization and the strain modification on material parameters are taken into account. The variations of binding energies versus the width of central barrier, the ratio of two well widths, and the impurity position are presented, respectively. It is found that the built-in electric field causes a mutation of binding energies with increasing the width of central barrier to some value. The results for symmetrical double quantum wells and without the built-in electric field are also discussed for comparison.