Bendable InGaN light-emitting nano-membranes with tunable

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Surfaces, Interfaces, and Applications

Bendable InGaN light-emitting nanomembranes with tunable emission wavelength Chia-Feng Lin, Chun-Lung Su, Han-Ming Wu, Yi-Yun Chen, Bo-Song Huang, Kuan-Lin Huang, Bing-Cheng Shieh, Heng-Jui Liu, and Jung Han ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b14506 • Publication Date (Web): 02 Oct 2018 Downloaded from http://pubs.acs.org on October 8, 2018

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ACS Applied Materials & Interfaces

Bendable InGaN light-emitting nano-membranes with tunable emission wavelength Chia-Feng Lin*,†, Chun-Lung Su†, Han-Ming Wu†, Yi-Yun Chen†, Bo-Song Huang†, Kuan-Lin Huang†, Bing-Cheng Shieh†, Heng-Jui Liu† , and Jung Han*,‡ †

Department of Materials Science and Engineering, National Chung Hsing University, 145

Xingda Rd., South Dist., Taichung, 402, Taiwan ‡

Department of Electrical Engineering, Yale University, 15 Prospect St, New Haven, CT, 06511,

United States

* Corresponding author. E-mail: [email protected] (Chia-Feng Lin) [email protected] (Jung Han)

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ABSTRACT The integration of light emitting diodes (LEDs) into the flexible devices has exhibited a great potential in the next-generation consumer electronics. In this study, we have demonstrated an exfoliated InGaN nano-membrane 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 (EL) spectra were observed on the free-standing NM-LED compared to the non-treated 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 (521.7nm) to a blue shift (500.4nm) compared with that of the flat state (509.4nm) 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. KEYWORDS Nano-membranes, InGaN, light emitting diodes, electrochemical etching process, bendable devices


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1. INTRODUCTION Gallium nitride (GaN) materials have wide applications on optoelectronic devices such as lightemitting diodes (LEDs), laser diodes (LD)1, and power devices.2,3 GaN-based membranes separated from the Al2O3 and Si substrates have potential applications for the flexible and stretchable optoelectronic devices. The membrane separation processes have been widely utilized, for example, the InGaN LED layers has been separated from the Al2O3 substrates through the laser lift-off process4,5, the chemical lift-off process6-8, and chemical-free transfer process.9 The InGaN-based LEDs grown on Si substrates has been lifted-off through the dry etching process10 and the wet etching process11,12,13,14 on Si substrates. The device structures separated from gallium arsenide (GaAs) substrates has been reported through the surface tensionassisted epitaxial lift-off process.15 The GaN16,17, InGaN18,19, and AlGaN/GaN20 nano-membrane structure, less than 0.5µm, had also been reported. 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 S. Shervin et al. has unveiled the color tunability by external strain on InGaN/GaN quantum-well (QW) structure for the overall visible spectral range.21 Their study inspires us to utilized nano-membranes InGaN LEDs on the flexible substrates to study the emission wavelength tunability through the bending process. In this work, high quality 0.3µm-thick nano-membrane InGaN LEDs (NM-LED) were fabricated and then separated from the GaN/sapphire substrate through the doping-selective electrochemically (EC) etching process. The tunable emission wavelengths of both photoluminescence (PL) spectra and electroluminescence (EL) spectra have been experimentally


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observed from bending test of the free-standing NM-LED. Our results have successfully demonstrated a variable light source for future bendable optoelectronics.

2. EXPERIMENTAL DETAILS

InGaN LED structures were grown on a 2 in. optical-grade c-face (0001) sapphire substrate using a metal organic chemical vapor deposition system. Trimethylgallium (TMGa), trimethylindium (TMIn), and ammonia (NH3) were used as precursors of gallium (Ga), indium (In), and nitrogen (N) sources material, respectively. Silane (SiH4) and biscyclopentadienyl magnesium (CP2Mg) were used as the n-type doping and p-type doping sources, respectively. The LED epitaxial layer consisted of a 50-nm-thick GaN buffer layer grown at 530oC, a 3.0-µmthick unintentionally doped GaN layer (u-GaN, 1050oC, 5×1016cm-3), a 200nm-thick n+-GaN:Si layer (1050oC, 2×1019cm-3), a 50nm-thick u-GaN layer (1050oC), a 150nm-thick n-GaN:Si layer (1050oC, 1×1018cm-3), three pairs of In0.2GaN/GaN (30Å/139Å) multiple-quantum wells (MQWs, 760oC), and a 50nm-thick p-GaN:Mg layer (950oC, 1×1018 cm-3). Then, a 100-nm-thick indium tin oxide (ITO) film was deposited on the p-type GaN:Mg layer acted as a transparent conductive layer. The patterned photoresist (PR) was prepared as the mask for the ITO wet etching process and the ICP dry etching process to define the mesa region. The ITO layer on the p-type GaN:Mg layer was annealed in furnace at 600oC for 30 min in order to improve the ohmic contact property. Then, the patterned Ti/Al (50nm/200nm) metal layers were deposited as the bottom n-GaN:Si conductive layer for the n-type contact metal layer. The wet etching channels on the LED structures were defined through a laser scribing (LS) process with a 0.5µm etched depth to reach the n+-GaN:Si sacrificial layer by using a 355nm pulse laser. The surface morphologies of the LED structures were observed using optical microscopy (OM) and a fieldemission scanning electron microscope (FE-SEM, JEOL 6700F). Light output power and farACS Paragon Plus Environment

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field radiation patterns were measured on non-encapsulated LEDs in chip form. The light reflectance spectra, the photoluminescence (PL) spectra, and the electroluminescence (EL) spectra were measured by using monochromators (JOBIN YVON iHR550) with a TE-cooled charge-coupled device (CCD) detector. The normal scan of X-ray diffraction (XRD) were collected at beamline BL-17B1 at the National Synchrotron Radiation Research Center (NSRRC) in Hsinchu, Taiwan. The incident beam was monochromated at 10 keV with a Si(111) double crystal mirror and then focused by a toroidal focusing mirror to get a higher intensity beam. All curves were plotted in the reciprocal lattice unit that is normalized to the sapphire substrate (1 r.l.u. = 2π/csapphire). The Raman spectra of the LED samples were measured by using the 632.8 nm HeNe laser as an excited laser source at room temperature.

3. RESULTS AND DISCUSSION

Figures 1 is the schematic that describe the architecture of LED sample under the overall lateral wet etching process. Before the etching process (Figure 1a), the LED epitaxial layer, consisted of an unintentionally doped GaN layer (u-GaN), a n-type Si-doped GaN (n-GaN:Si) layer, three pairs of In0.2GaN/GaN MQW layers, a p-GaN:Mg layer, and a transparent top electrode of indium tin oxide (ITO) in a sequential stacking, was deposited on the n+-GaN:Si sacrificial layer/u-GaN/sapphire substrate, which is termed as the standard LED (ST-LED). The function of the photoresist (PR) layer is used to protect the ITO layer during the EC wet etching process. During the etching process in Figure 1b, the n+-GaN:Si layer was removed through the doping-selective electrochemically (EC) etching process in a 0.5M nitride acid solution at positive 8V external bias voltage at room temperature.22 A 50nm-thick unintentionally doped GaN layer was inserted between top NM-LED and bottom n+-GaN:Si sacrificial layer to prevent the wet etching process at the normal direction of the samples. The u-GaN layer didn’t be etched ACS Paragon Plus Environment

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during the doping-selective EC wet etching process. Thin LED membrane can be prevented from etching by adding this thin u-GaN layer. In the EC etching process, the InGaN-based LED samples were immersed in the nitride acid solution at room temperature. The slightly curved-up LED film, caused by release of the substrate clamping effect at the edge of the substrate, at initial stage of the etching process can increase the lateral etching rate and effectively exfoliate the LED membrane from the underlying n+-GaN:Si sacrificial layer. The lifted-off free-standing InGaN-LED membrane with total thickness of 300 nm, with PIN can be obtained and defined as the nano-membrane LED (NM-LED) as shown in Figure 1c. The two step laser scribing process forms a 40µm grid with depth of 0.3µm. From the SEM micrograph as shown in Figure 1d, the free-standing NM-LED shows a very uniform thickness and flat surfaces on both side, indicating that the membrane can maintain its high quality without the obvious etching defects. The light reflectance spectra of the ST-LED and the NM-LED placed on the glass substrate were measured as shown in Figure 1e. The thicknesses of the total LED epitaxial layers can be estimated as 3.5µm for the ST-LED and 300nm for the NM-LED, respectively, from the light interference curves. The clear light interference phenomenon observed in the free-standing NM-LED structure also confirms that the bottom etched interface must be uniform and smooth after removing the n+-GaN:Si sacrificial layer. The micro-PL (µ-PL) spectra of the ST-LED and the NM-LED were measured to investigate the substrate clamping effect. As shown in Figure 2a and 2b, both samples show the peak wavelength blue-shift effect by increasing the 405nm laser excited power from 5mW to 50mW which was caused by the band-filling effect in the InGaN well layers. At 50mW laser excited power (with a 20µm laser spot size, 16kW/cm2 laser power density), the PL peak wavelengths are measured at 514.8 nm for the ST-LED and at 509.4 nm for the NM-LED, respectively. The short PL wavelength for the NM-LED is due to the partial strain relaxation in ACS Paragon Plus Environment

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the InGaN active layer, which has been evidenced by Raman and high-resolution X-ray diffraction techniques. In Figure 2c, the typical E2 (high) peak of the GaN layer, referred to the in-plane biaxial strain14, is at 573.1 cm-1 for the ST-LED and at 568.6 cm-1 for the NM-LED, respectively. Therefore, the GaN peak of the NM-LED has a 4.5 cm-1 shift to the short wavenumber compared to the ST-LED structure, indicating the internal in-plane compressive strain in GaN layer was partially released in the NM-LED structure. The similar result can be also obtained from the relative X-ray diffraction curves of the ST-LED and the NM-LED in Figure 2d which characterized by synchrotron based X-ray diffraction techniques. For the ST-LED, the regular satellite peaks of InGaN/GaN MQW layer as well as the diffraction peak of GaN have been found to distribute around the (0 0 0 10) reflection of the sapphire substrate, implying high crystal epitaxy and periodicity. On the other hand, for NM-LED, only diffraction peak of GaN and satellite peaks of InGaN/GaN MQW are left in the XRD curve, confirming that this lifted-off process can completely remove the sapphire substrate. It is noteworthy that in both cases the thickness of the InGaN/GaN MQW layer is much smaller than the total thickness of GaN films, and the c-axis lattice constants for all layers are very close. Therefore, we can expect that the main peak position of the InGaN/GaN MQW layer would overlap with the diffraction peaks of GaN films and is difficult to be identified. Although the mean c-axis lattice of the InGaN/GaN MQW layer cannot be directly obtained from diffraction main peak in XRD curves, we can still use the satellite peaks to realize the relative lattice variation. From the average interval between two neighboring satellite peaks, we can further calculate the corresponding modulation length (Λ = csapphire / ∆L) as around 169 Å, which is consistent with the designed pair-thickness of the InGaN/GaN MQW active layer. Interestingly, through the same calculation, the modulation thickness of the InGaN/GaN MQW layer for NM-LED is now reduced to 164 Å. Because the ACS Paragon Plus Environment

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MQW layers in ST-LED and NM-LED were prepared at the central region of the same epitaxial wafer, the slight decrease (~ 3%) in modulation length implies that the mean c-axis lattice of InGaN/GaN sublayer in ST-LED become smaller in NM-LED when the substrate clamping effect is released. According to the Poisson effect in most solid matters, the shrinkage of out-ofplane lattice indicates the expansion of in-plane lattices at the same time. Hence, the XRD result also confirms that the internal in-plane compressive strain of the InGaN/GaN active layers in the free-standing NM-LED membranes can be partially released through the EC lift-off process. For the angle-resolved photoluminescence measurements23, the angle dependent PL spectra maps were obtained by illuminating the backside of the samples with a 405nm excitation laser, which can transmit through the sapphire and the glass substrate. The PL spectra were detected at the front-side of the LED wafer and the flat NM-LED membrane without the device fabrication process. In Figure 2e, the Fabry–Pérot (FP) interference line-patterns is observed in the ST-LED structure caused by the PL light interference between the top GaN:Mg/Air interface and the bottom GaN/Al2O3 interface. In the Figure 2f, no clear FP interference can be observed in the NM-LED because the thickness of the NM-LED becomes much thinner than that of ST-LED. The central PL peak wavelengths are identified at 540.7nm for the ST-LED and at 534.5nm for the NM-LED which the laser power density of the 405nm laser was 2.5W/cm2 (20mW with a 1mm laser spot size). Here the longer peak wavelengths of both samples observed in the angledependent PL maps are due to available laser power density that is lower than it used in the µ-PL measurement as shown in Figure 2a and 2b. However, we can still acquire the same tendency, of which the NM-LED has a shorter wavelength than the ST-LED. Moreover, at 90o detected angle, the PL emission intensity of the NM-LED shows a elongated tail extending toward longer wavelength region (560~620nm), which is possibly caused by the surface states emission, the yellow band emission, from the etched GaN surface after removed the n+-GaN:Si sacrificial ACS Paragon Plus Environment

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layer. For more clear comparison between these two samples, the normalized PL far-field radiation pattern is reorganized in Figure 2g. By using this plot, we can easily define the divergent angle which is the detected angles at 50% of the peak intensity compared to the intensity at normal direction (90o). Obviously, the divergent angle of the NM-LED (106o) is smaller than that of ST-LED (120o). Besides, for the NM-LED, the high PL emission intensities are more concentrated on the detected region between 80o to 100o. These results indicate the NM-LED has larger advantage of more anisotropic and higher light extraction efficiency along the normal emission direction. For further practical application, the EL emission operated at 0.1mA operating current for the ST-LED and the NM-LED were performed as shown in the Figure 3a and 3b, respectively. The chip size of the LEDs was 50µm×50µm in size. The NM-LED structure was placed on the Al-coated glass substrate. The electrical probes were contacted on the ITO layer of the NM-LED and the Al/glass substrate that the electric current flowed in the vertical direction. Both samples can exhibit a strong green light emission. It also indicates that the NM-LED can be well operated even after the EC separation process. We then placed this NM-LED on a metal rod with the pGaN:Mg side convexly (here the condition is designated as P-NM-LED) for the EL measurement. Figures 3c-e show the real experimental setup through the optical microscopy (OM) images with the different magnifications and regions. The curvature of the P-NM-LED can be defined by the radius of the 16mm-diameter metal rod. The P-NM-LED membrane on an 8mm-diameter/1mm-thick glass tube was shown in Figure 3f. The dimension of the P-NM-LED film was 6mm×4mm in size. The incident 405nm laser light was coupled into the 1mm-thick glass tube from the right side. Then, the weak PL emission light can be observed from the PNM-LED film that excited by the 405nm laser light coupled from the glass tube into the membrane. ACS Paragon Plus Environment

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The µ-PL spectra of the P-NM-LED and the N-NM-LED were measured as shown in Figure 4a and 4b, respectively, by varying the 405nm laser excited power from 5mW to 50mW. At 50mW laser excited power (with a 20µm laser spot size), the PL peak wavelengths have been found at 521.7 nm for the P-NM-LED and at 500.4 nm for the N-NM-LED, respectively. The corresponding peak wavelength and the line-width of the PL spectra with different laser excited powers are shown in Figure 4c and 4d. The peak wavelength blue-shifted and the line-width broadened phenomena of the PL spectra were observed in all LED samples when raising the laser power. This phenomenon results from the band-filling effect in the band-tilted InGaN well layer. Recall that in the conventional InGaN/GaN MQW active layer, the lattice constants of the thin InGaN well layer is larger than the thick GaN barrier layer, implying that the InGaN well layer should suffer the internal in-plane compressive strain. The strain induced piezoelectric electrical field can further lead to the band-tilted phenomenon in the InGaN well layer. When the laser illuminates the sample, more photo-excited electrons would be transited into the tilted conduction band and then cause a large band gap that is responsible for the blueshifted phenomenon and the broadened linewidth. The wavelength blueshifted phenomena in all the LED structure indicated that the compressive in the InGaN active layer can be tunable through the different bended conditions. More interestingly, when the NM-LED is curved convexly with different side, its PL peak wavelength varies oppositely. It shows a red shift for P-NM-LED, whereas a blue shift for N-NM-LED, compared to the NM-LED and ST-LED under all laser powers. Such peak shifts can be mainly considered as the strain effect on the InGaN MQW layers in the NM-LED. In the separated NM-LED structure, the InGaN active layer still has the compressive strain due to the lattice mismatch between the InGaN well layer and the GaN barrier layer in the MQW structure. The compressive strain in the InGaN active can be tuned at the bend-up/bend-down ACS Paragon Plus Environment

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conditions. Because the thickness of both the p-GaN:Mg layer or MQW is 50nm, and the total thickness of the whole NM-LED is around 300 nm, we can expect that MQW would partial increase the external in-plane tensile and compressive strains when the sample is curved convexly with p-GaN:Mg side and n-GaN:Si side, respectively. These results perfectly match the theoretic prediction proposed by S. Shervin et al.19, where a red/blue shift occurs at the bendup/bend-down conditions (corresponding to our P-NM-LED/N-NM-LED). The EL emission measurement also exhibits similar results with the µ-PL spectra. The peak emission wavelengths of the ST-LED, NM-LED, and P-NM-LED are shown in Figure 5a-c, respectively. The relative emission intensities and the peak wavelengths are then plotted and compared in Figure 5d. The LED mesa region was 50µm×50µm in size for the EL measurement. At 0.3mA injection current (12 A/cm2 current density), the EL emission intensity of the NM-LED has a 37% enhancement compared to that of the ST-LED. The EL emission wavelength of the NM-LED simultaneously shows a blue shift compared to the ST-LED, consistent with the observation of µ-PL measurement as shown in Figure 2a and 2b. The EL emission wavelength of the free-standing NM-LED (512.3nm) had the blueshift phenomenon compared to the ST-LED (532.5nm) on the sapphire substrate. This is indicated that the compressive strain in InGaN active layer was partially released after separated from the GaN/sapphire substrate. In the P-NM-LED placed on the metal rod, the EL peak wavelength had a red-shift phenomenon from 532.5nm for the ST-LED to 546.2nm for the P-NM-LED. The compressive strain in the InGaN active layer is enlarged on the bended P-NM-LED structure. The external in-plane tensile strain applied on the P-NM-LED would cause more band tilt in InGaN active layer, and then decrease the electron-hole recombination efficiency. Therefore, lower EL intensity and longer peak wavelength are obtained in the P-NM-LED than both for STLED and NM-LED. However, the partially released internal compressive strain on InGaN active ACS Paragon Plus Environment

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layer in NM-LED can lead to high EL emission intensity and short emission wavelength.

4. CONCLUSION

In conclusions, we have successfully demonstrated tunable optoelectronic properties through the mechanical deformation process using the free-standing LED membrane structures. The internal in-plane compressive strain of MQW active layer in the NM-LED is partially released, and thus a band filling effect can result in a blueshift of emission wavelength and more anisotropic light emission property. Moreover, when this NM-LED is bended convexly with different sides, N-NM-LED or P-NM-LED, the emission peak wavelength simultaneously show a blue or red shift, respectively. Such phenomenon can be attributed to the different band tilting degree in the InGaN active layer induced by bending strain condition. Hence, this work provides an elegant method to achieve the purpose of the tunable and bendable light sources for practical use in the future.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] / [email protected]

ACKNOWLEDGMENT The authors gratefully acknowledge the financial support for this research by the Ministry of Science and Technology of Taiwan under grant No. 105-2221-E-005-012-MY2. We also acknowledge the measurement technical support from the EverBeing Int'l corp. This work is also supported in part by the Ministry of Education, Taiwan under the Higher Education Sprout Project. ACS Paragon Plus Environment

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Li, Y.; Feng, L.; Su, X.; Li, Q.; Yun, F.; Yuan, G.; Han, J. Whispering Gallery Mode Lasing from InGaN/GaN Quantum Well Microtube. Opt. Express 2017, 25 (15), 18072.

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Chang, T. H.; Xiong, K.; Park, S. H.; Yuan, G.; Ma, Z.; Han, J. Strain Balanced AlGaN/GaN/AlGaN Nanomembrane HEMTs. Sci. Rep. 2017, 7 (1), 6360.

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Shervin, S.; Kim, S. H.; Asadirad, M.; Karpov, S. Y.; Zimina, D.; Ryou, J. H. Bendable III-N Visible Light-Emitting Diodes beyond Mechanical Flexibility: Theoretical Study on Quantum Efficiency Improvement and Color Tunability by External Strain. ACS Photonics 2016, 3 (3), 486–493.

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Lin, C. F.; Dai, J. J.; Lin, M. S.; Chen, K. T.; Huang, W. C.; Lin, C. M.; Jiang, R. H.; Huang, Y. C. An AlN Sacrificial Buffer Layer Inserted into the GaN/Patterned Sapphire Substrate for a Chemical Lift-Off Process. Appl. Phys. Express 2010, 3 (3), 031001.

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David, A.; Fujii, T.; Moran, B.; Nakamura, S.; DenBaars, S. P.; Weisbuch, C.; Benisty, H. Photonic Crystal Laser Lift-off GaN Light-Emitting Diodes. Appl. Phys. Lett. 2006, 88 (13), 133514.


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FIGURE CAPTIONS

Figure 1 The NM separation processes consisted of (a) deposited the ITO and the photoresist (PR) on the InGaN-LED epitaxial layer, (b) the selective EC wet etching process on the n+-GaN:Si sacrificial layer, and (c). the free-standing InGaN-LED nano-membrane without top PR layer. (d). The SEM micrograph of the NM-LED structure. (e) The light reflectance spectra of the ST-LED on sapphire substrate and the NM-LED on glass substrate.

Figure 2 Power dependent PL spectra of the (a). ST-LED on sapphire substrate and (b) the NMLED on the glass substrate by varying laser excited powers at room temperature. (c). The Raman spectra of the ST-LED and the NM-LED structures. (d). The X-ray diffraction curves of the ST-LED and the NM-LED structures. The angle-dependent PL far field radiation spectra of (e) the ST-LED and (f) the NM-LED structures were observed by using the 405nm diode laser as an excited laser source at room temperature. (g) The normalized PL far field radiation patterns of the ST-LED and the NM-LED structures were observed.

Figure 3 (a). The EL emission image of the ST-LED on sapphire substrate, (b). The EL emission image of NM-LED on flat Al-coated glass substrate, (c). The EL emission image of the P-NM-LED on a metal rod. (d) The lower magnification image of the P-NM-LED on the probe station. (e) OM image of the P-NM-LED and the metal cutting surface observed on the metal rod. (f) The picture of P-NM-LED film placed on the glass tube and excited by the 405nm laser. ACS Paragon Plus Environment

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Figure 4 Power dependent PL spectra of (a) the N-NM-LED on a metal rod and (b). the P-NMLED on metal rod by varying laser excited powers at room temperature. (c). The peak wavelength and (d) the line-width of the PL spectra measured by varying the excitation power of the 405nm diode laser.

Figure 5 The EL emission spectra of (a) the ST-LED, (b) the flat NM-LED on Al-coated glass substrate, and (c). P-NM-LED on metal rod measured by varying the injection current. (d). The EL light output power and the emission wavelength of the LED samples were measured at room temperature.


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Figure 1


19


(a) 18000

ST-LED

(b) 18000

NM-LED

PL Intensity (a.u.)

15000

514.8nm 12000 9000

50mW

6000

5mW 3000

450

500

(c)12000

550

600

ST-LED NM-LED

-1

573.1 cm

9000

6000

-1

568.6 cm 3000

0 400

450

500

550

600

650

50mW 9000 6000

5mW

3000

450

(d)

Wavelength (nm)

509.4nm

12000

X-ray Intensity (arb. unit)

PL Intensity (a.u.)

15000

Raman Intensity (arb. unit)

700

500

600

4

10

ST-LED on C-Sapphire NM-LED on glass C-sapphire GaN

3

10

2

10

1

Λ≈169Å

10

GaN

0

10

-1

10

-2

10

Λ≈164Å

-3

10

-4

10

9.6

9.8

-1

10.0

10.2

10.4

00L (r.l.u.)sapph.

620

ST-LED

(f)

620

NM-LED 600

580

580

Wavelength (nm)

600

560 540 520 500

560 540 520 500

480

480 0

20

40

60

80

100

120

140

160

180

0

20

Angle (degree)

(g)

Normalized PL Intensity (%)

(e)

550

Wavelength (nm)

Wave number (cm )

Wavelength (nm)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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60

80

100

120

140

160

180

Angle (degree)

NM-LED ST-LED

120

40

90

120

60

100 80 30

150

60 40 20

0

180

0

Figure 2 ACS Paragon Plus Environment

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Figure 3


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Figure 4


22

(b) 25000

20000

15000

10000

0.3mA

0.01mA

5000

450

(c) 5000

500

550

600

Wavelength (nm)

4000 3500 3000

0.3mA

2500 2000

20000

0.3mA 15000

0.01mA

10000

5000

450

500

0.01mA

1500

550

600

Wavelength (nm)

(d)

P-NM-LED

4500

NM-LED

560

550

540

EL Intensity NM-LED ST-LED P-NM-LED

Wavelength 530 P-NM-LED ST-LED NM-LED 520

EL wavelength (nm)

ST-LED

EL Intensity (arb. unit)


(a) 25000


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


EL intensity (arb. unit)

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1000 500 450

500

550

600

0.00

0.05

0.10

0.15

0.20

0.25

510 0.30

Current (mA)

Wavelength (nm)

Figure 5


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Table of Contents (TOC)


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Bendable InGaN light-emitting nano-membranes with tunable

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