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Frontiers of Optoelectronics

Front Optoelec    2013, Vol. 6 Issue (4) : 429-434     DOI: 10.1007/s12200-013-0342-x
RESEARCH ARTICLE |
Improvement of blue InGaN light-emitting diodes with gradually increased barrier heights from n- to p-layers
Wu TIAN, Xiong HUI(), Yang LI, Jiangnan DAI, Yanyan FANG, Zhihao WU, Changqing CHEN
Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074, China
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Abstract

The advantages of blue InGaN light-emitting diodes (LED) with the active region of gradually increased barrier heights from n- to p-layers are studied. The energy band diagram, hole concentration, electrostatic field near the electron blocking layer (EBL), and the internal quantum efficiency (IQE) are investigated by Crosslight simulation program. The simulation results show that the structure with gradually increased barrier heights has better performance over the equal one, which can be attributed to the mitigated polarization effect near the interface of the last barrier/EBL due to less interface polarization charges. Moreover, reduced barrier height toward the n-layers is beneficial for holes injection and transportation in the active region. As a result, holes are injected into the active region more efficiently and distributed uniformly in the quantum wells, with which both the IQE and the total lighting power are increased. Although it can lead to the broadening of the spontaneous emission spectrum, the increase is slight such that it has little effect on the application in solid-state lighting.

Keywords InGaN      light-emitting diodes (LED)      polarization effect      gradual barrier height     
Corresponding Authors: HUI Xiong,Email:hsiung.hust@gmail.com   
Issue Date: 05 December 2013
 Cite this article:   
Wu TIAN,Xiong HUI,Yang LI, et al. Improvement of blue InGaN light-emitting diodes with gradually increased barrier heights from n- to p-layers[J]. Front Optoelec, 2013, 6(4): 429-434.
 URL:  
http://journal.hep.com.cn/foe/EN/10.1007/s12200-013-0342-x
http://journal.hep.com.cn/foe/EN/Y2013/V6/I4/429
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Wu TIAN
Xiong HUI
Yang LI
Jiangnan DAI
Yanyan FANG
Zhihao WU
Changqing CHEN
Fig.1  Schematic diagrams of structures A and B. In structure A the three pairs of InGaN/GaN quantum wells are of uniform composition, while in structure B barrier heights are gradually increased toward p-AlGaN layer
parametersGaNAlNInN
a/?3.1893.1123.545
c/?5.1854.9825.703
me0.20.320.07
me0.20.30.07
C13/GPa10610892
C33/GPa398373224
e13/(C?m-2)-0.35-0.5-0.57
e3/(C?m-2)1.271.790.97
PSP/(C?m-2)-0.034-0.09-0.042
Tab.1  Important parameters of AlN, GaN and InN used in the programs
Interfacesurface charge density/m-2
i-In0. 1Ga0.9N/i-GaN-3.4 × 1016
i-In0.21Ga0.79N/i-In0.1Ga0.9N-4.4 × 1016
i-In0.05Ga0.95N/i-In0.21Ga0.79N6.1 × 1016
i-In0.21Ga0.79N/i-In0.05Ga0.95N-6.1 × 1016
i-GaN/i-In0.21Ga0.79N7.8 × 1016
i-In0.21Ga0.79N/i-GaN-7.8 × 1016
i-Al0.05Ga0.95N/i-In0.21Ga0.79N8.6 × 1016
p-Al0.15Ga0.85N/i-Al0.05Ga0.95N1.7 × 1016
p-GaN/p-Al0.15Ga0.85N-2.5 × 1016
Tab.2  Surface fixed charge densities at interfaces of structure B
Fig.2  (a) Energy band diagram of structure A at forward voltage of 3.4 V. The red dash lines indicate the quasi-Fermi levels; (b) distribution of hole concentration in structure A at 3.4 V forward voltage in log scale
Fig.3  (a) Energy band diagram of structure B at forward voltage of 3.4 V. The red dash lines indicate the quasi-Fermi levels; (b) distribution of hole concentration in structure B at forward voltage of 3.4 V in log scale
Fig.4  Electrostatic field in structure A (black dash line) and structure B (red solid line) near the EBL at forward voltage of 3.4 V
Fig.5  Total light power and IQE as function of current for structure A (black dash line) and structure B (red solid line)
Fig.6  Total spontaneous emission rate for structure A (black dash line) and structure B (red solid line)
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