Zeeman Effects in the Edge Emission and Absorption of ZnO

Abstract

Of the more than 20 sharp characteristic emission and absorption lines observed in the edge emission and absorption spectra of ZnO platelets, several typical lines have been examined in detail experimentally at low temperatures (\ensuremath{\sim}1\ifmmode^\circ\else\textdegree\fi{}K). Zeeman effects, in magnetic fields up to 45 000 G, have been studied in singlets as well as zero-field-split doublets. In particular, the magnetic splitting of ${I}_{9}$ (an emission line appearing at 3692.64 \AA{}) has been studied as a function of magnetic field orientation (angular orientation of $c$ axis with respect to field direction). In accordance with the Thomas-Hopfield theory, arguments have been presented for the association of ${I}_{9}$ with a bound-exciton complex; this line has been observed to split linearly as a function of field strength, and an isotropic electron $g$ value of -1.93 has been determined at $C\ensuremath{\perp}\mathrm{H}$. The line ${I}_{9}$ is further characterized by an anisotropic hole $g$ value which has been determined to be -1.24 at $C\ensuremath{\parallel}\mathrm{H}$. A zero-field-split fluorescent doublet, ${I}_{2}\ensuremath{-}{I}_{3}$ (3680.63, 3681.59 \AA{}), which splits nonlinearly as a function of field strength, has been studied as a function of field orientation. The ${I}_{2}\ensuremath{-}{I}_{3}$ doublet has been attributed to an ionized exciton complex, and effective electron and hole $g$ values have been determined. Electron $g$ values are isotropic and essentially the same for all of the lines (about -1.95), while the hole $g$ value is not only anisotropic for each line, but also assumes different values in the different complexes (lines), indicating that the hole is sensitive to its state of binding in the exciton complex.