Luminescence Spectra Of Superbright Blue and Green InGaN/AlGaN/GaN Light-Emitting Diodes
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Internet Journal o f
Nitride S emiconductor Research
Volume 1, Article 11
Luminescence Spectra Of Superbright Blue and Green InGaN/AlGaN/GaN Light-Emitting Diodes K. G. Zolina, V. E. Kudryashov, A. N. Turkin, A. E. Yunovich Moscow State Lomonosov University Shuji Nakamura Nichia Chemical Industries This article was received on May 25, 1996 and accepted on September 20, 1996.
Abstract Electroluminescence spectra of superbright blue and green LEDs based on epitaxial Inx Ga1-xN/Aly Ga 1-yN/GaN heterostructures with thin quantum well active layers [1] were studied at currents J = 0.01-20 mA. Spectral maxima of blue and green LEDs are ω max = 2.58-2.75 eV and ω max = 2.38-2.45 eV, dependent on the active layer In content. The low energy tails of the spectra are exponential with the parameter E0 = 42-50 meV almost independent of the temperature. The high energy tails of the spectra are exponential with a temperature dependent parameter E1 = 20-40 meV. Both parameters (E0, E1) are current independent at J > 0.5 mA. The spectral band can be described by taking into account quantum size effects, impurities and electron-phonon interactions in active layers. A structure in the spectra was detected which can be described by the influence of light interference in the GaN layer on the sapphire substrate. Light intensity was a linear function of the drive current over the interval J = 1-20 mA, and was slightly temperature dependent. In the blue LEDs, the efficiency fall off at low currents (J < 0.7 mA) had a I ~ J4-5 dependence at room temperature. The green LEDs showed no such dependence. The influence of tunnel effects on the efficiency at low currents is discussed. Tunnel radiation spectra with maxima moving with the voltage were detected at low currents in III-N structures.
1. Introduction The development of electroluminescent heterostructures based on GaN and III-N ternary compounds has been quite successful over the past three years ( [2] and references therein). The best short wavelength (violet, blue, bluish-green) light-emitting diodes (LEDs) were MOVPE-grown InGaN/AlGaN/GaN multilayers with a thin (25-30 Å) In 1-xGax N active layer. External quantum efficiencies in the 4-9 % range have been achieved [1] [2]. The electroluminescence (EL) spectra of InGaN/AlGaN/GaN heterostructures were studied in [1], and in the earlier publications of the same group [3] [4] [5]. In this paper, we report the spectra of the multilayered structures InGaN/AlGaN/GaN with a thin active InGaN layer at currents J=0.01-20mA at temperatures T=200-300K. A model of the radiative recombination in two dimensional (2D) structures which takes into account potential fluctuations [6] was previously applied to describe photoluminescence spectra of GaAs/AlGaAs multiple quantum wells [7], and is used here to analyze the spectra of GaN 2D LED structures. Optical interference can occur in multilayered structures and we have detected the influence of interference on the spectra of blue-green LEDs. In addition, the spectra of tunnel radiation were detected
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