Bendable III-N Visible Light-Emitting Diodes beyond Mechanical Flexibility: Theoretical Study on Quantum Efficiency Improvement and Color Tunability by External Strain

Shervin, Shahab; Kim, Seunghwan; Asadirad, Mojtaba; Karpov, S. Yu.; Zimina, Daria; Ryou, Jae‐Hyun

doi:10.1021/acsphotonics.5b00745

Cited by 21 publications

(12 citation statements)

References 50 publications

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“…5 Shervin et al also suggested that controlled external bending can lead to improvements in internal quantum efficiency and emission wavelength tunability of light-emitting diodes (LEDs). 6,7 Furthermore, as opposed to an n-type two-dimensional electron gas (2DEG) channel in HEMTs, Wang et al demonstrated that the formation of a p-type two-dimensional hole gas (2DHG) channel is possible in flexible In x Al 1Àx N/GaN heterostructures by bending, possibly enabling high-hole-mobility transistors. 8 However, the aforementioned reports are only based on numerical modeling.…”

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confidence: 99%

Modulation of the two-dimensional electron gas channel in flexible AlGaN/GaN high-electron-mobility transistors by mechanical bending

Wang

Chen

Lundh

et al. 2020

Applied Physics Letters

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We investigate the effect of strain on the two-dimensional electron gas (2DEG) channel in a flexible Al 0.25 Ga 0.75 N/GaN high-electron-mobility transistor (HEMT) by mechanical bending to prove the concept of active polarization engineering to create multifunctional electronic and photonic devices made of flexible group III-nitride thin films. The flexible HEMTs are fabricated by a layer-transfer process and integrated with a 150-lm-thick Cu film. The strain values are estimated from high-resolution x-ray diffraction and Raman spectroscopy in 4-cm bend-down and À4-cm bend-up test conditions. The strain-induced piezoelectric polarization can alter the charge density of the 2DEG in the channel at the AlGaN/GaN interface and thus modify the output characteristics of the flexible HEMTs. Accordingly, output characteristics show an increase in output current by 3.4% in the bend-down condition and a decrease by 4.3% in the bend-up condition. Transfer characteristics show a shift of threshold voltage, which also supports the 2DEG channel modulation during bending. Computational simulation based on the same structure confirms the same current modulation effect and threshold voltage shift. Furthermore, the electrical characteristics of the flexible HEMTs show a repeatable dependence on the strain effect, which offers potential for electro-mechanical device applications.

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confidence: 99%

Modulation of the two-dimensional electron gas channel in flexible AlGaN/GaN high-electron-mobility transistors by mechanical bending

Wang

Chen

Lundh

et al. 2020

Applied Physics Letters

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“…This novel orientation avoids common problems observed in flexible LEDs, such as peak emission wavelength shifts and decreased light output during applied mechanical stress. [8][9][10][11] This degradation is mainly due to a strain-induced piezoelectric response affecting the active region of the LED. As bending increases, piezoelectric fields produced in the quantum wells create a measureable peak shift in the electroluminescence (EL) characteristics that affects spectral uniformity of the LEDs and degrades the performance of the light emitters for applications, such as solid-state lighting and next-generation displays.…”

Section: Introductionmentioning

confidence: 99%

Optically invariant InGaN nanowire light-emitting diodes on flexible substrates under mechanical manipulation

Asad

Wang

et al. 2019

npj Flex Electron

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The integration of GaN-based light-emitting diodes (LEDs) onto flexible platforms provides opportunities for conformal lighting, wearable electronics, and bendable displays. While this technology may enhance the functionality of the light source, the development of flexible GaN LEDs suffers from performance degradation, when mechanical bending is applied during operation. A unique approach to eliminate the degradation employs dot-in-wire structures, using cylindrical light-emitting heterostructures that protrude above the flexible platform, separating the active light-emitting region from the bending substrate. Here, we demonstrate the optical enhancement of nanowire light emitters by changing the geometric orientation within a 1 × 1 mm 2 array of nanowires on a flexible platform through bending of the substrate platform. The flexible structures were achieved by transferring GaN nanowire LEDs from sapphire substrates onto flexible polyethylene terephthalate (PET) using a "paste-and-cut" integration process. The I-V characteristics of the nanowire LEDs showed negligible change after integration onto the PET, with a turn-on voltage of 2.5 V and a forward current of 400 μA at 4 V. A significant advantage for the nanowire devices on PET was demonstrated by tilting the LEDs through substrate bending that increased the electroluminescence (EL) intensity, while the I-V characteristics and the EL peak position remained constant. Through finite-element analysis and three-dimensional finite-difference time-domain modeling, it was determined that tilting the protruding devices changed the effective distance between the structures, enhancing their electromagnetic coupling to increase light output without affecting the electrical properties or peak emission wavelength of the LEDs.

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“…Although these studies have beautifully revealed numerous possibilities of the applications on the flexible devices for the free-standing LEDs, few of them have deeply investigated the relation between the emission performance and their deformation states. Interestingly, a theoretical study recently reported by Shervin et al has unveiled the color tunability by external strain on InGaN/GaN quantum-well (QW) structure for the overall visible spectral range . Their study inspires us to utilize NM InGaN LEDs on the flexible substrates to study the emission wavelength tunability through the bending process.…”

Section: Introductionmentioning

confidence: 99%

Bendable InGaN Light-Emitting Nanomembranes with Tunable Emission Wavelength

Lin

et al. 2018

ACS Appl. Mater. Interfaces

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The integration of light-emitting diodes (LEDs) into the flexible devices has exhibited a great potential in the nextgeneration consumer electronics. In this study, we have demonstrated an exfoliated InGaN nanomembrane LED (NM-LED) separated from a GaN/sapphire substrate through an electrochemically wet etching process. The peak wavelengths blue-shifted phenomenon of the photoluminescence (PL) and the electroluminescence spectra were observed on the free-standing NM-LED compared to the nontreated LED with the same structure, which can be ascribed to the partial strain relaxation of the LED structure confirmed by the Raman spectra and the X-ray diffraction curves. A small divergent angle of the PL emission light has also been observed on the NM-LED. Moreover, the peak emission wavelength of this NM-LED can be even modulated from a red shift (521.7 nm) to a blue shift (500.4 nm) compared with that of the flat state (509.4 nm) while being curved convexly from top p-GaN:Mg side to bottom n-GaN:Si side. Our study provides an elegant way to develop a bendable light source with variable emission wavelengths through the mechanical deformation method.

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Bendable III-N Visible Light-Emitting Diodes beyond Mechanical Flexibility: Theoretical Study on Quantum Efficiency Improvement and Color Tunability by External Strain

Cited by 21 publications

References 50 publications

Modulation of the two-dimensional electron gas channel in flexible AlGaN/GaN high-electron-mobility transistors by mechanical bending

Modulation of the two-dimensional electron gas channel in flexible AlGaN/GaN high-electron-mobility transistors by mechanical bending

Optically invariant InGaN nanowire light-emitting diodes on flexible substrates under mechanical manipulation

Bendable InGaN Light-Emitting Nanomembranes with Tunable Emission Wavelength

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