Characterization of the carrier confinement for InGaN/GaN light emitting diode with multiquantum barriers
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Characterization of the carrier confinement for InGaN/GaN light emitting diode with multiquantum barriers Jen-Cheng Wang1, Chung-Han Lin1, Ray-Ming Lin1, Tzer-En Nee1, a), Bor-Ren Fang2, and Ruey-Yu Wang2 1 Department of Electronic Engineering, Chang Gung University, 259 Wen-Hwa 1st Road, Kwei-Shan, Tao-Yuan, Taiwan, Republic of China. 2
Nan Ya Photonics Incorporation,
55 Wei-Wang Street, Shu-Lin, Taipei, Taiwan, Republic of China. Electronic mail: [email protected]
a)
ABSTRACT Electroluminescence (EL) of InGaN/GaN multiquantum wells (MQW) in blue light-emitting diodes (LED) with multiquantum barriers (MQB) has been investigated. It was found that a device with an MQB structure exhibited better performance in carrier confinement, as well as higher temperature insensitivity, compared with the conventional MQW LEDs. The total cross sections ware obtained for those devices with and without MQBs, by fitting to the measurement of the spectral intensity. Not only the cross sections, but also the carrier lifetimes depending on temperature can therefore be mainly attributed to changes in Boltzmann population. All the detailed calculations are also agreement with the observations. INTRODUCTION Recently, there have been extensive studies on improving the characteristics of nitride-based optoelectronic devices, which are potentially very important for a variety of applications [1,2]. There are several approaches to the realization of high brightness blue and green light-emitting diodes (LEDs) [3-5]. However, since exctions within the active region determine the heterostructural optical response, little work has been carried out thus far regarding the introduction of a multiquantum barrier (MQB) structure in order to suppress the carrier leakage, improve the quantum efficiency and increase the number of electrons and holes that are recombined inside the active region. Electroluminescence (EL) cross sections, that determine the electron and the photon relaxation processes in the MQW heterostructures, were obtained by measuring the device efficiency by looking at the response of a spectral line to the carrier injection excitation. For this work, we investigated in depth the abnormal temperature dependent characteristics of InGaN/GaN MQW blue LEDs, with and without MQBs, via an examination of the cross section temperature evolution. Particular EL intensity behaviors were discussed, using a rate equation model analysis and a wide temperature range, from 20 to 300 K. The results
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indicate that an MQB structure can significantly suppress carrier leakage, which not only increases the carrier confinement, but also improves the quantum efficiency. EXPERIMENTS The LED samples were both grown by metal organic vapor phase epitaxy on c-plane sapphire substrates with a 20-nm-thick GaN buffer layer. The wafer consisted of a 3-µm-thick n-type GaN layer, with 5 period 2-nm-thick unintentionally doped InxGa1-xN (0.15 < x < 0.18) quantum wells, and a 150-nm-thick p-type GaN on top. For comparison, we also arranged two d
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