MBE-grown ZnSe epilayers on (100) GaAs substrates are optically investigated under moderate to high excitation densities. Below the light-hole and heavy-hole exciton lines Xlh and Xhh, two lines I2 and I'2 are dominant in the luminescence spectra which are related to transitions from a neutral-donor-exciton complex (D0, X). For the first time, comparative excitation spectroscopy and magnetooptics of bound excitons in ZnSe epilayers allowed to determine their term structure, g-values and diamagnetic shifts. In the excitation spectra of the I2 line, a set of resonances located 1.2 meV to 2.9 meV on its high-energy side can be interpreted as specific transitions into excited states of the neutral-donor-exciton complex. For excitation densities until 50 kW/cm2, high-excitation bands appear, superimposing the exciton luminescence. They are discussed to be due to exciton-exciton collision processes and can be compared with high-density transitions known from bulk ZnSe crystals.
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