Bound Excitons in Wide-Gap II-VI and Nitride Semiconductors. Comparison of Optical Studies of Shallow Dopants in These Materials

In this paper recent results of optical studies of bound excitons in wide-gap II-VI and nitride semiconductors are surveyed. In the first part latest results about self-compensation mechanisms will be presented. Then, the dynamical characteristics of excitonic transitions are evaluated for various impurities, dopants, and dopant concentrations, and for excitation via particular resonant excitation channels. Relaxation and conversion channels between excitonic systems are analyzed, especially in strained heteroepitaxial systems which show splitting effects of the bands from which the carriers stem. The dynamical behavior of excitons in wide-gap material gives evidence of nonradiative decay channels. Calorimetric spectroscopy at mK temperatures was used to investigate the nonradiative processes and to determine quantum efficiencies. Recent results of transient four-wave mixing experiments at bound-exciton complexes will be shown to demonstrate that shallow defects influence the dephasing in the investigated systems which gives information about the homogeneous and inhomogeneous broadening mechanisms. In the last part negatively charged excitons (trions) were observed in unintentionally donor doped Zn0.90Mg0.10Se/ZnSe single quantum wells by magneto-luminescence experiments. The binding energy of the trion singlet ground state is about 2.7 meV.