Optical Modal Gain Saturation of Exciton-Exciton Scattering and Electron-Hole Plasma in ZnO

Abstract

The optical modal gain spectrum for a ZnO thin film was measured by using a variable stripe length method. Using the dierential equation for amplified spontaneous emission in a stripe geometry, we obtained stripe-length-dependent gain spectra, which enabled us to investigate the gain saturation in long stripe lengths. When the stripe was shorter than the saturation length, our analysis was in a good agreement with the gain obtained by commonly-used analysis [1]. For intermediate density ( nMott). Both gains saturate with increasing stripe length, but the electron-hole plasma becomes relatively dominant for long stripe lengths ( 1000 µm) while the exciton-exciton scattering is relatively suppressed. This result suggests that exciton-exciton scattering gain saturation is more vulnerable to increase in the stripe length increase since the excitonic stimulated emission occurs on a coherence scale of the localized area.