Improved Performance of GaN-Based Blue LEDs With the InGaN Insertion Layer Between the MQW Active Layer and the n-GaN Cladding Layer

Jang, C. H.; Sheu, Jinn-Kong; Tsai, Cheng-Mu; Chang, Shoou‐Jinn; Lai, Wei–Chih; Lee, Ming-Lun; Ko, T.K.; Shen, C.F.; Shei, Shih–Chang

doi:10.1109/jqe.2009.2036269

Cited by 34 publications

(22 citation statements)

References 11 publications

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“…However, it is not clear if electron cooler is still effective for a typical MQW stack with thick GaN barriers of 12 nm. Also different from the previous works [14,15] where the improved current spreading effect is assigned as the reason of the efficiency improvement by using InGaN insertion layer, here it is found that the improved device performance is actually owing to the promoted hole transport into the MQWs by reducing the valance band barrier height of MQWs. Thus, in this work, we studied InGaN/GaN MQW LEDs with the InGaN intermediate layer below the MQW region as the EC layer both experimentally and theoretically.…”

Section: Introductioncontrasting

confidence: 99%

“…Another solution is to grow InGaN intermediate layer before MQWs, which proves effective in improving the InGaN/GaN LED external quantum efficiency (EQE) and optical output power [11][12][13][14][15]. The reasons of the effectiveness of InGaN intermediate layer were tentatively attributed to either the improved current spreading effect promoted by the InGaN intermediate layer [14,15], or the electron cooler (EC) effect [11][12][13] that the hot electrons are thermalized by interacting with longitudinal optical (LO) phonons [16]. However, the exact mechanisms of the InGaN EC contributing to the reduction of electron overflow and the efficiency improvement have still remained unclear thus far.…”

Section: Introductionmentioning

confidence: 99%

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On the mechanisms of InGaN electron cooler in InGaN/GaN light-emitting diodes

et al. 2014

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Electron overflow limits the quantum efficiency of InGaN/GaN light-emitting diodes. InGaN electron cooler (EC) can be inserted before growing InGaN/GaN multiple quantum wells (MQWs) to reduce electron overflow. However, detailed mechanisms of how the InGaN EC contributes to the efficiency improvement have remained unclear so far. In this work, we theoretically propose and experimentally demonstrate an electron meanfree-path model, which reveals the InGaN EC reduces the electron mean free path in MQWs, increases the electron capture rate and also reduces the valence band barrier heights of the MQWs, in turn promoting the hole transport into MQWs.

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Section: Introductioncontrasting

confidence: 99%

Section: Introductionmentioning

confidence: 99%

On the mechanisms of InGaN electron cooler in InGaN/GaN light-emitting diodes

et al. 2014

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“…For reference, InGaN/GaN LED without SRL were also grown. All the LED structures were consisted of a 30-nm-thick GaN nucleation layer grown at 550°C, followed by a 2-μm-thick undoped GaN layer grown at 1050°C, a 4-μm-thick Si doped n-type GaN layer with a carrier concentration of 5 × 10 18 Fig. 1(d).…”

Section: Methodsmentioning

confidence: 99%

“…Although nanostructures have been approved to be effective in strain relaxation, complicated processes need to improve the compatibility in LED production. One of the practical approaches is to introduce an additional layer such as InGaN/GaN short period superlattices (SPS) [14][15][16], InGaN layer and InGaN/GaN MQW layer [17,18], or low-temperature (LT) n-GaN layer [19], between the n-type GaN and the InGaN/GaN active layer. Studies have revealed that such insertion layers can be regarded as the lattice-mismatch buffer between the underlying n-GaN and overlying QWs, which can release the residual strain in MQWs layer, reduce the Vpits density in MQWs, improve the crystal quality of InGaN/GaN MQWs, enhance electron capture rate of the active layer and improve the current spreading in LED.…”

Section: Introductionmentioning

confidence: 99%

Performance improvement of GaN-based LEDs with step stage InGaN/GaN strain relief layers in GaN-based blue LEDs

Jia¹,

Yu²,

Lu³

et al. 2013

Opt. Express

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The performance of nitride-based LEDs was improved by inserting dual stage and step stage InGaN/GaN strain relief layer (SRL) between the active layer and n-GaN template. The influences of step stage InGaN/GaN SRL on the structure, electrical and optical characteristics of GaN-based LEDs were investigated. The analysis of strain effect on recombination rate based k·p method indicated 12.5% reduction of strain in InGaN/GaN MQWs by inserting SRL with step stage InGaN/GaN structures. The surface morphology was improved and a smaller blue shift in the electroluminescence (EL) spectral with increasing injection current was observed for LEDs with step stage SRL compared with conventional LEDs. The output power of LEDs operating at 20 mA was about 15.3 mW, increased by more than 108% by using step stage InGaN/GaN SRL, which shows great potential of such InGaN/GaN SRL in modulating InGaN/GaN MQWs optical properties based on its strain relief function.

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“…Currently, several research groups are working on improving current spreading. These methods include the use of transparent conducting layer (TCL) or current spreading layers (CSLs) [18][19], patterned structures, electron blocking layer (EBL) [17], InAlN/InGaN insertion layer between the n-GaN layer and MQWs [20], use of quaternary alloys etc. [21] Nevertheless, at higher current-level, the current crowding effect is still severe.…”

Section: Introductionmentioning

confidence: 99%