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Very strong nonlinear optical absorption in green GaInN/GaN multiple quantum well structures
Author(s) -
Zhao W.,
Zhu M.,
Xia Y.,
Li Y.,
Senawiratne J.,
You S.,
Detchprohm T.,
Wetzel C.
Publication year - 2008
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.200778686
Subject(s) - materials science , optoelectronics , absorption (acoustics) , free carrier absorption , absorption edge , two photon absorption , wavelength , laser , light emitting diode , diode , quantum well , optics , physics , band gap , composite material
The efficiency of green GaInN/GaN light emitting diodes (LEDs) is known to drop under high current densities. To explore the reason, 535 nm emitting GaInN/GaN multiple quantum well (MQW) and GaN epilayers were characterized using Z‐scan techniques under comparable excitation conditions with a continuous wave laser. Two wavelengths, 514 nm and 488 nm, were selected right below and above the apparent optical absorption edge. At 514 nm, a very large nonlinear absorption coefficient β = 2.6 cm/W was obtained. This leads to a 20% absorption enhancement at a photon flux of 21 kW/cm 2 . We attribute this to nonlinear free‐carrier absorption. On the other hand, at 488 nm, a nonlinear saturable absorption with β = –1.7 cm/W was observed. This induced transparency indicates photon bleaching in the MQW. Apparently, free carrier dynamics strongly affects optical nonlinearity, while nonlinear absorption provides a small contribution to the limitations of current green LEDs. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)