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Localized Excitons in InGaN

Published online by Cambridge University Press:  10 February 2011

S. ChichiBu ,
T. Deguchi ,
T. Sota ,
K. Wada  and
S. Nakamura
S. ChichiBu
Affiliation:
Materials Department, University of California, Santa Barbara, CA 93106, and also Faculty of Science and Technology, Science University of Tokyo, 2641 Yamazaki, Noda, Chiba 278, Japan
T. Deguchi
Affiliation:
Department of Electrical, Electronics, and Computer Engineering, Waseda University, 3–4–1– Ohkubo, Shinjuku, Tokyo 169, Japan
T. Sota
Affiliation:
Department of Electrical, Electronics, and Computer Engineering, Waseda University, 3–4–1– Ohkubo, Shinjuku, Tokyo 169, Japan
K. Wada
Affiliation:
Compound Semiconductor Materials Research, NTT” System Electronics Laboratories, 3–1 Morinosato-Wakamiya, Atsugi, Kanagawa 243–01, Japan
S. Nakamura
Affiliation:
Department of Research and Development, Nichia Chemical Industries Ltd., 491 Oka, Kaminaka, Anan, Tokushima 774, Japan
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Abstract

Emission mechanisms of the device-quality quantum well (QW) structure and bulk three dimensional (3D) InGaN materials grown on sapphire substrates without any epitaxial lateral overgrown GaN (ELOG) base layers were investigated. The InxGx1−xN layers showed various degree of spatial potential (bandgap) fluctuation, which is probably due to a compositional inhomogeneity or monolayer thickness fluctuation produced by some kinetic driving forces initiated by the threading dislocations (TDs) or growth steps during the growth. The degree of fluctuation changed remarkably around nominal InN molar fraction x=0.2, which changes to nearly 8–10 % for the strained InxGa1−xN. This potential fluctuation induces energy tail states both in QW and 3D InGaN, showing a large Stokes-like shift combined with the red shift due to quantum confined Stark effect (QCSE) induced by the piezoelectric field. The spontaneous emission from undoped InGaN single quantum well (SQW) light-emitting diodes (LED's), undoped 3D double heterostructure (DH) LED's, and multiple quantum well (MQW) laser diode (LD) wafers was assigned as being due to the recombination of excitons localized at the potential minima, whose area was determined by cathodoluminescence (CL) mapping to vary from less than 60 nm to 300 nm in lateral size in the case of QW's. The lasing mechanisms of the cw In0.15Gao.85N MQW LD's having small potential fluctuation, whose bandgap broadenings are less than about 50 meV, can be described by the well-known electron-hole-plasma (EIHP) picture with Coulomb enhancement. The inhomogenous MQW LD's are considered to lase by EHP in segmented QW's or Q-disks. It is desirable to use entire QW planes with small potential inhomogeneity as gain media for higher performance LD operation.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 482 , 1997 , 613
Copyright
Copyright © Materials Research Society 1998

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