Carrier Dynamics Determined by Carrier-Phonon Coupling in InGaN/GaN Multiple Quantum Well Blue Light Emitting Diodes

Phonon sidebands in the electrolumiescence (EL) spectra of InGaN/GaN multiple quantum well blue light emitting diodes are investigated. S-shaped injection current dependence of the energy spacing (ES) between the zero-phonon and first-order phonon-assisted luminescence lines is observed in a temperature range of 100-150 K. The S-shape is suppressed with increasing temperature from 100 to 150K, and vanishes at temperature above 200K. The S-shaped injection dependence of ES at low temperatures could be explained by the three stages of carrier dynamics related to localization states: (i) carrier relaxation from shallow into deep localization states, (ii) band filling of shallow and deep localization states, and (iii) carrier overflow from deep to shallow localization states and to higher energy states. The three stages show strong temperature dependence. It is proposed that the fast change of the carrier lifetime with temperature is responsible for the suppression of S-shaped feature. The proposed mechanisms reveal carrier recombination dynamics in the EL of InGaN/GaN MQWs at various injection current densities and temperatures.