Role of Lithium in the Formation of Exciton Luminescence of Zinc Oxide

A detailed interpretation of exciton lines caused by the presence of a lithium impurity in ZnO crystals (T = 4.2 K) was carried out. The 368.5-nm line is caused by radiative recombination of excitons bound on neutral donor states ${Li}_i^{\times }$. The 371.2-nm line is caused by the same process but occurring simultaneously with the transition of the donor to the excited state. The 368.2-nm line occurs when excitons bound on ionized ${Li}_i^{+}$ states emit. The 369.7-nm line is the emission of excitons bound on acceptor complexes of the form (${Zn}_i^{+}{Li}_{Zn}^{\mid }$), (${In}_{Zn}^{+}{Li}_{Zn}^{\mid }$), (${Li}_i^{+}{Li}_{Zn}^{\mid }$), etc. The measurements also made it possible to calculate the ionization energy of shallow donors ${Li}_i^{\times }$ as E_d = 0.033 eV. Thus, a method for exciton spectroscopy of lithium states affecting the optical and electrophysical characteristics of zinc oxide has been developed.