Origin of defect-insensitive emission probability in In-containing (Al,In,Ga)N alloy semiconductors


Group-III-nitride semiconductors have shown enormous potential as light sources for full-colour displays, optical storage and solid-state lighting. Remarkably, InGaN blue- and green-light-emitting diodes (LEDs) emit brilliant light although the threading dislocation density generated due to lattice mismatch is six orders of magnitude higher than that in conventional LEDs. Here we explain why In-containing (Al,In,Ga)N bulk films exhibit a defect-insensitive emission probability. From the extremely short positron diffusion lengths (<4 nm) and short radiative lifetimes of excitonic emissions, we conclude that localizing valence states associated with atomic condensates of In–N preferentially capture holes, which have a positive charge similar to positrons. The holes form localized excitons to emit the light, although some of the excitons recombine at non-radiative centres. The enterprising use of atomically inhomogeneous crystals is proposed for future innovation in light emitters even when using defective crystals.

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Figure 1: Schematic representation for polarizations and energy band profiles of strained In0.15Ga0.85N/GaN quantum wells.
Figure 2: Internal quantum efficiency ηint of the near-band-edge emission peaks in In-containing 3D (Al,In,Ga)N films.
Figure 3: Radiative and non-radiative lifetimes for the NBE emission in In-containing 3D (Al,In,Ga)N films.
Figure 4: Panchromatic CL mapping image and intensity line profile for the NBE CL peak in a-plane In0.1Ga0.9N/GaN MQW.
Figure 5: Schematic representations of trapped positrons in In-containing 3D (Al,In,Ga)N films.
Figure 6: Relations between effective non-radiative lifetime τNR,eff for the near-band-edge PL peak at 300 K and point defects in In-containing 3D (Al,In,Ga)N films.


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This work was supported in part by the 21st Century COE program ‘Promotion of Creative Interdisciplinary Materials Science for Novel Functions’ under MEXT, Japan.

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A.U. carried out the positron annihilation measurement; T.O., T.K. and T.S. carried out TRPL and CL measurements; B.A.H., A.C., P.T.F., S.K., S.P.D., J.S.S., U.K.M. and S.N. grew GaN, InGaN and AlGaN films and QWs; S.Y., S.K., H.A. and I.A. grew AlInN films; J.H. grew AlInGaN films; S.F.C. carried out several of the above measurements and analysis, and organized this research project.

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Correspondence to Shigefusa F. Chichibu.

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Chichibu, S., Uedono, A., Onuma, T. et al. Origin of defect-insensitive emission probability in In-containing (Al,In,Ga)N alloy semiconductors. Nature Mater 5, 810–816 (2006). https://doi.org/10.1038/nmat1726

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