Inhomogeneously broadened optical gain spectra of InGaN quantum well laser diodes

Abstract

Optical gain of InGaN quantum well laser diodes and its internal field dependences are investigated. Gain spectra are experimentally measured by the Hakki-Paoli method. Inhomogeneous broadening of the gain spectra as well as of the electroluminescence spectra increases with In content of the active layers due to potential fluctuation. From measured carrier decay times and current density, we estimated the carrier density for which modal gain overcomes internal loss. We present gain calculation including quantum confined Stark effect, Coulomb screening and valence band structure simultaneously. Calculated and measured carrier densities are in good agreement. In InGaN quantum well laser diodes working at 470 nm, the quantum confined Stark effect reduces the optical transition probability down to 30% of its value without internal field. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)