In inhomogeneity and emission characteristics of InGaN

Yoichi Kawakami, Kunimichi Omae, Akio Kaneta, Koichi Okamoto, Yukio Narukawa, Takashi Mukai, Shigeo Fujita

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31 Citations (Scopus)

Abstract

Recombination dynamics of spontaneous and stimulated emissions have been assessed in InGaN-based light emitting diodes (LEDs) and laser diodes (LDs), by employing time-resolved photoluminescence and pump and probe spectroscopy. As for an In0.02Ga0.98N ultraviolet LED, excitons are weakly localized by 15 meV at low temperature, but they become almost free at room temperature (RT). It was found that addition of a small amount of In results in the reduction of nonradiative recombination centres originating from point defects. The internal electric field does exist in InGaN active layers, and induces a large modification of excitonic transitions. However, it alone does not explain the feature of spontaneous emission observed in an In0.3Ga0.7N blue LED such as an anomalous temperature dependence of peak energy, almost temperature independence of radiative lifetimes and mobility-edge type behaviour, indicating an important role of exciton localization. The lasing mechanism was investigated for In0.1Ga0.9N near ultraviolet (390 nm), In0.2Ga0.8N violet-blue (420 nm) and In0.3Ga0.7N blue (440 nm) LDs. The optical gain was contributed from the nearly delocalized states (the lowest quantized levels (LQLs) within quantum wells) in the violet LD, while it was from highly localized levels with respect to the LQL by 250 meV for the violet-blue LD, and by 500 meV for the blue LD. It was found that the photo-generated carriers rapidly (less than 1 ps) transferred to the LQL, and then relaxed to the localized tail within the timescale of a few ps, giving rise to the optical gain. Such gain spectra were saturated and other bands appeared in the vicinity of the LQL under higher photo-excitation.

Original languageEnglish
Pages (from-to)6993-7010
Number of pages18
JournalJournal of Physics Condensed Matter
Volume13
Issue number32
DOIs
Publication statusPublished - Aug 13 2001

All Science Journal Classification (ASJC) codes

  • Materials Science(all)
  • Condensed Matter Physics

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