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Frontiers of Optoelectronics

Front Optoelec    2012, Vol. 5 Issue (3) : 284-291     DOI: 10.1007/s12200-012-0275-9
Temperature effects on output characteristics of quantum dot white light emitting diode
Faculty of Engineering, Islamic Azad University, Hamedan Branch, Hamedan 65138, Iran
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In this paper, we proposed quantum dot (QD) based structure for implementation of white light emitting diode (WLED) based on InGaN/GaN. The proposed structure included three layers of InGaN QD with box shapes and GaN barriers. By using of single band effective mass method and considering strain effect, piezoelectric and spontaneous polarizations internal fields, then solving Schr?dinger and Poisson equations self consistently, we obtained electron and hole eigen energies and wave functions. By evaluating dipole moment matrix elements for interband transitions, the output intensity was calculated due to the interband transition between two energy levels with highest emission probability. We adjusted QDs dimensions and material compositions so that the output light can be close to the ideal white light in chromaticity diagrams. Finally, effects of temperature variations on output spectrum and chromaticity coordinates were studied. We demonstrated that temperature variations in the range of 100 to 400 K decrease output intensity, broaden output spectral profile and cause a red shift in three main colors spectrums. This temperature variation deviates (x, y) are coordinated in the chromaticity diagram, but the output color still remains close to white.

Keywords quantum dot (QD)      InGaN      optical intensity spectrum      white light emitting diode (WLED)      chromaticity coordinate     
Corresponding Authors: RANJBARAN Amin,   
Issue Date: 05 September 2012
 Cite this article:   
Amin RANJBARAN. Temperature effects on output characteristics of quantum dot white light emitting diode[J]. Front Optoelec, 2012, 5(3): 284-291.
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Fig.1  (a) Schematic of the MQD-WLED containing three emitters grown vertically, spacing between adjacent single QDs in the laterally and vertically direction is adjusted to minimize overlaps of corresponding wave functions; (b) proposed cubic shaped InGaN QD within a large GaN QD. , and are quantum box dimensions
Fig.2  Wave functions corresponding to the first conduction band, (a) without internal field and strain effects, (b) with internal field and strain effects, and heavy hole band, (c) without internal field and strain effects, (d) with internal field and strain effects, for the blue color emitter. Deviation from dot center is obvious. Deviation of electron and hole wave functions from QD center, which decrease overlap between the electron and hole wave functions
colorLx = Ly /nmLz/nmbarrier/dotEc1Ehh1Eg,eff
red103.1GaN/In0.33Ga0.67N1.5518 eV-0.46952.0213
green103.2GaN/In0.26Ga0.74N1.8795 eV-0.43762.3171
blue103.5GaN/In0.17Ga0.83N2.2918 eV-0.39652.6883
Tab.1  QD dimensions and material compositions for red, green and blue emission colors
lattice constant a/?3.543.193.11
Tab.2  Wurtzite GaN-family QD parameters, which are used in our calculations
Fig.3  Output intensity for three light emitting layers of blue, green and red QDs at temperature = 300 K
Fig.4  QD-WLED output white light coordinate in standard chromaticity diagram
Fig.5  Temperature increasing effects from 100 to 400 K for emitter of (a) red, (b) green, (c) blue
Fig.6  Normalized output power spectral density for different values of temperature
Fig.7  Effects of temperature variation on normalized optical output power
Fig.8  Effects of temperature variation from 100 to 400 K on chromaticity coordinates for proposed structure
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