Carrier lifetime and efficiency droop of green light emitting InGaN QWs in LEDs and laser diodes (LD) are discussed in term of Shockley-Read-Hall, radiative, and Auger-like recombination. The carrier lifetime, spectral shift, and carrier density as function of current density was measured by time-resolved electroluminescence with a streak camera. The current density was varied from very low for the LEDs to threshold for the LD. The transition from spontaneous emission in the low carrier density regime to stimulated emission in the high carrier regime is continuous. A comparison with Hakki-Paoli optical gain spectra provides evidence for a significant contribution of stimulated emission already at intermediate current densities. Stimulated emission is discussed as possible contribution to efficiency droop. A wavelength dependency of the lifetime is certainly caused by stimulated emission. Slope efficiency of the laser diode provides a lower limit for the injection efficiency of the LD. Time-resolved electroluminescence spectroscopy with applied bias demonstrates the variation of radiative recombination and consequently carrier lifetime with applied bias. Under certain conditions for modulated operation more light is emitted during times of zero bias than during forward bias.

Date Published: 16 February 2009
PDF: 13 pages
Proc. SPIE 7216, Gallium Nitride Materials and Devices IV, 72161U (16 February 2009); doi: 10.1117/12.803932

Published in SPIE Proceedings Vol. 7216:
Gallium Nitride Materials and Devices IV
Hadis Morkoç; Cole W. Litton; Jen-Inn Chyi; Yasushi Nanishi; Joachim Piprek; Euijoon Yoon, Editor(s)