Browsing by Author "Yang, H. C."

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Characteristics of efficiency droop in GaN-based light emitting diodes with an insertion layer between the multiple quantum wells and n-GaN layer
(2010-12-20)
Chang, S. P.
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Wang, C. H.
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Chiu, C. H.
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Li, J. C.
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Lu, Y. S.
We have studied the characteristics of efficiency droop in GaN-based light emitting diodes (LEDs) with different kinds of insertion layers (ILs) between the multiple quantum wells (MQWs) layer and n-GaN layer. By using low-temperature (LT) (780 degrees C) n-GaN as IL, the efficiency droop behavior can be alleviated from 54% in reference LED to 36% from the maximum value at low injection current to 200 mA, which is much smaller than that of 49% in LED with InGaN/GaN short-period superlattices layer. The polarization field in MQWs is found to be smallest in LED with InGaN/GaN SPS layer. However, the V-shape defect density, about 5.3 x 10(8) cm(-2), in its MQWs region is much higher than that value of 2.9 x 108 cm(-2) in LED with LT n-GaN layer, which will lead to higher defect-related tunneling leakage of carriers. Therefore, we can mainly assign this alleviation of efficiency droop to the reduction of dislocation density in MQWs region rather than the decrease of polarization field. (C) 2010 American Institute of Physics. [doi:10.1063/1.3531957]
Efficiency droop alleviation in InGaN/GaN light-emitting diodes by graded-thickness multiple quantum wells
(2010-11-01)
Wang, C. H.
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Chang, S. P.
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Chang, W. T.
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Li, J. C.
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Lu, Y. S.
InGaN/GaN light-emitting diodes (LEDs) with graded-thickness multiple quantum wells (GQW) was designed and grown by metal-organic chemical vapor deposition. The GQW structure, in which the well-thickness increases along [0001] direction, was found to have superior hole distribution as well as radiative recombination distribution by performing simulation modeling. Accordingly, the experimental investigation of electroluminescence spectrum reveals additional emission from the narrower wells within GQWs. Consequently, the efficiency droop can be alleviated to be about 16% from maximum at current density of 30 to 200 A/cm(2), which is much smaller than that for conventional LED (32%). Moreover, the light output power was enhanced from 18.0 to 24.3 mW at 20 A/cm(2). (C) 2010 American Institute of Physics. [doi:10.1063/1.3507891]
Hole injection and efficiency droop improvement in InGaN/GaN light-emitting diodes by band-engineered electron blocking layer
(2010-12-27)
Wang, C. H.
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Ke, C. C.
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Lee, C. Y.
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Chang, S. P.
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Chang, W. T.
A graded-composition electron blocking layer (GEBL) with aluminum composition increasing along the [0001] direction was designed for c-plane InGaN/GaN light-emitting diodes (LEDs) by employing the band-engineering. The simulation results demonstrated that such GEBL can effectively enhance the capability of hole transportation across the EBL as well as the electron confinement. Consequently, the LED with GEBL grown by metal-organic chemical vapor deposition exhibited lower forward voltage and series resistance and much higher output power at high current density as compared to conventional LED. Meanwhile, the efficiency droop was reduced from 34% in conventional LED to only 4% from the maximum value at low injection current to 200 A/cm(2). (C) 2010 American Institute of Physics. [doi:10.1063/1.3531753]
Hole transport improvement in InGaN/GaN light-emitting diodes by graded-composition multiple quantum barriers
(2011-10-24)
Wang, C. H.
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Chang, S. P.
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Ku, P. H.
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Li, J. C.
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Lan, Y. P.
Graded-composition multiple quantum barriers (GQB) were designed and incorporated in c-plane InGaN/GaN light-emitting diodes (LEDs) grown on c-plane sapphire substrate to improve hole transport and efficiency droop. The simulation of GQB LED design predicts enhancement of the hole transport in the active region at both low and high current densities. The fabricated LED with GQB structure exhibits lower series resistance and substantially reduced droop behavior of only 6% in comparison with 34% for conventional LED, supporting the improvement of hole transport in our design. (C) 2011 American Institute of Physics. [doi:10.1063/1.3655903]