A Simple Approach to the Energy of Bound Exciton Complexes

From some basic properties of excitons bound to ionized impurities a rough estimate and an approximation is obtained of the energy of the complex. Especially the upper limit of the estimate reflects the available experimental data quite well. The critical σ = m e /m h value, above which the complex becomes unstable, is found to be 0.462 ≦ σ c ≦ 0.576. For the region σ ≦ 1 we compute both upper and lower limits and an approximation of the energy of excitons bound to neutral impurities. From the limiting cases σ → 0, ∞ the forbidden region 2.1 ≦ σ F ≦ 12 is obtained where the upper value is certainly too large.