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ABSTRACT: We investigated the carrier transient response of the nanopatterned silicon heterojunction photodiodes using ZnO as the n-type semiconductor. The results show that under the constant light illumination intensity, the planar structure has faster carrier response than the nanopatterned amorphous silicon (intrinsic) (a-Si(i)) diodes. It is attributed to a higher number of generated carriers in the nanostructure (due to the lower surface reflectivity) that increases the probability of collisions. On the other hand, the shortest response time of the device with nanopatterned p<sup>+</sup>-Si suggests that carriers can be effectively transported vertically and horizontally through the p-i(intrinsic)-n structure. Furthermore, the wavelength-dependent rise time is correlated to the different transport distance between electrons and holes at different excited wavelengths.
IEEE Photonics Technology Letters 12/2010; · 2.19 Impact Factor
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Cheng-Pin Chen,
Pei-Hsuan Lin,
Yen-Jen Hung,
Shao-Shun Hsu,
Liang-Yi Chen,
Yun-Wei Cheng,
Min-Yung Ke,
Ying-Yuan Huang,
Chun-Hsiang Chang,
Ching-Hua Chiu,
Hao-Chung Kuo,
JianJang Huang
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ABSTRACT: In this work, n-GZO/a:amorphous-Si(i:intrinsic)/p + -Si photodiodes are fabricated. We employed a nanosphere lithographic technique to obtain nanoscale patterns on either the a-Si(i) or p + -Si surface. As compared with the planar n-GZO/p + -Si diode, the devices with nanopatterned a-Si(i) and nanopatterned p + -Si substrates show a 32% and 36.2% enhancement of photoresponsivity. Furthermore, the acceptance angle measurement reveals that the nanostructured photodiodes have larger acceptance angles than the planar structure. It also shows that the device with the nanocone structure has a higher acceptance angle than that with the nanorod structure.
Nanotechnology 04/2010; 21(21):215201. · 3.98 Impact Factor
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ABSTRACT: We fabricated InGaN/GaN nanorod light emitting diode (LED) arrays using nanosphere lithography for nanorod formation, PECVD (plasma enhanced chemical vapor deposition) grown SiO(2) layer for sidewall passivation, and chemical mechanical polishing for uniform nanorod contact. The nano-device demonstrates a reverse current 4.77nA at -5V, an ideality factor 7.35, and an optical output intensity 6807mW/cm(2) at the injection current density 32A/cm(2) (20mA). Moreover, the investigation of the droop effect for such a nanorod LED array reveals that junction heating is responsible for the sharp decrease at the low current.
Optics Express 04/2010; 18(8):7664-9. · 3.59 Impact Factor
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ABSTRACT: In this work, GZO/ZnO/GaN diodes with the light emitting ZnO layer sandwiched between two SiO(2) thin films was fabricated and characterized. We observed a strong excitonic emission at the wavelength 377nm with the Mg(2+) deep level transition and oxygen vacancy induced recombination significantly suppressed. In comparison, light emission from the GZO/GaN device (without SiO(2) barriers) is mainly dominant by defect radiation. Furthermore, the device with confinement layers demonstrated a much higher UV intensity than the blue-green emission of the GZO/GaN p-n device.
Optics Express 12/2009; 17(25):22912-7. · 3.59 Impact Factor
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ABSTRACT: The polarization behavior of the light-emitting diodes (LEDs) with nanorods surrounding the p-mesa is investigated. The nanorods were fabricated using a natural nanosphere lithography and are intended to diffract laterally propagated light. In the horizontal direction, s-polarized light is dominated since the injected carriers choose to fill up the lowest energy state in a direction parallel to the quantum-well layers. The p/s-polarized ratio starts to increase with the increase of radiated angles and eventually saturates. Since the Bragg diffraction of laterally propagated p-polarized mode by nanorods is more efficient than the s-polarized light, the p/s-ratio of the device with nanorods is higher than that without rods. The p/s-ratio of the LED with nanorods is 1.96 at 90<sup>deg</sup>, and is 1.52 when the integrating intensity between 0<sup>deg</sup> and 90<sup>deg</sup> is considered.
IEEE Photonics Technology Letters 12/2009; · 2.19 Impact Factor
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ABSTRACT: We designed and fabricated GaN-based light emitting diodes encompassed with self-aligned nanorod arrays of three different distribution densities. The radiation profiles show that the device with less dense nanorod distribution has the highest optical power enhancement factor. By regarding the nanorod arrays as sidewall reflectors, the enhancement is due to the light diffraction of the laterally guided mode to radiative modes in the surface normal direction. As for the densest nanorods in our experiment, the radiation profile shows a better emission directionality as the guided modes are phase matched to the radiation modes. However, they show less optical output enhancement since some of the laterally propagated light is diffracted back to p-mesa by the first several columns of nanorods.
IEEE Electron Device Letters 11/2009; · 2.85 Impact Factor
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ABSTRACT: In this study, the process of nanosphere lithography was developed and applied to LED surface texturing and nanorod device fabrication. We observed a texture-size-dependent improvement of total light output. While the increase of output optical power from the textured LEDs can be attributed to surface roughening in the GaN-air surface and to the increase of internal quantum efficiency as the strain is relaxed with the surface texturing, the size-dependent device performance is related to the interaction of generated photons with the textured surface. We further etched through the p-GaN and quantum well region to form p-i-n nanorods on the sample. By inserting a spacer to prevent p-type contact from shorting the n-GaN, we successfully demonstrated nanorod LED arrays. For such a device, a narrower radiation profile was demonstrated from the nanorod LED array as compared with that from the planar LED. The result is associated with the vertical guiding effect along the nanorod cylinder and the Bragg scattering of photons extracted from the sidewall by the rest of the rods. Furthermore, the electroluminescence spectra showed a nearly constant peak wavelength of the nanorod LED arrays, which is due to the suppression of the effect of quantum confined Stark effect.
IEEE Journal of Selected Topics in Quantum Electronics 09/2009; · 3.78 Impact Factor
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ABSTRACT: We fabricate the nanorod arrays at the periphery of light-emitting mesa as the reflector. The nanorod arrays redirect the laterally propagated light. The output power is enhanced by 32.1% at 30 mA injection current.
Lasers and Electro-Optics, 2009 and 2009 Conference on Quantum electronics and Laser Science Conference. CLEO/QELS 2009. Conference on; 07/2009
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ABSTRACT: In this work, n-ZnO/p-Si photodiodes were fabricated and characterized to explore their potential applications in solar cells. With a coating of silica nanoparticles, we observed the enhancement of photoresponsivity and acceptance angle at a wavelength between 400 and 650 nm. The 17.6% increase of the photoresponsivity over the conventional device is due to the improved optical transmission toward the semiconductor through the silica nanoparticles. Furthermore, the acceptance angle of the nanoparticle coated device is dramatically increased, which is attributed to the effect of Bragg diffraction.
Nanotechnology 07/2009; 20(24):245204. · 3.98 Impact Factor
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ABSTRACT: We demonstrate a method of utilizing self-assembled nanorod array reflectors to collect the laterally propagating guided modes from a light emitting diode (LED). We measure an enhancement factor of 12.2% and 18.4%, respectively, from the sidewall emission of GaN-based LEDs encompassed with 10 and 20 microm thick nanorod array reflectors. Such enhancement is found to be omnidirectional due to a broken symmetry from a randomized distribution of the nanorod array placed along the periphery of the LED's mesa. These observations indicate that the use of nanorod reflectors can efficiently redirect the propagation of the laterally guided modes to the surface normal direction.
Nanotechnology 02/2009; 20(3):035202. · 3.98 Impact Factor
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ABSTRACT: In this study, the process of nanosphere lithography was developed and applied to LED surface texturing and nanorod device fabrication. We observed a texture-size-dependent improve-ment of total light output. While the increase of output optical power from the textured LEDs can be attributed to surface rough-ening in the GaN–air surface and to the increase of internal quan-tum efficiency as the strain is relaxed with the surface texturing, the size-dependent device performance is related to the interac-tion of generated photons with the textured surface. We further etched through the p-GaN and quantum well region to form p-i-n nanorods on the sample. By inserting a spacer to prevent p-type contact from shorting the n-GaN, we successfully demonstrated nanorod LED arrays. For such a device, a narrower radiation pro-file was demonstrated from the nanorod LED array as compared with that from the planar LED. The result is associated with the vertical guiding effect along the nanorod cylinder and the Bragg scattering of photons extracted from the sidewall by the rest of the rods. Furthermore, the electroluminescence spectra showed a nearly constant peak wavelength of the nanorod LED arrays, which is due to the suppression of the effect of quantum confined stark effect.
IEEE Journal of Selected Topics in Quantum Electronics 01/2009; 15. · 3.78 Impact Factor
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ABSTRACT: A low-junction-temperature light emitting diode (LED) by selectively ion-implantation in part of the p-type GaN layer is demonstrated. The junction temperature extracted from a forward voltage method of an ion-implanted LED is significantly lower than that of a conventional LED. Furthermore, the linearity of the luminescence–current curve of the device is improved without altering electrical properties.
Optics Communications - OPT COMMUN. 01/2009; 282(5):835-838.
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ABSTRACT: A practical process to fabricate InGaN/GaN multiple quantum well light emitting diodes (LEDs) with a self-organized nanorod structure is demonstrated. The nanorod array is realized by using nature lithography of surface patterned silica spheres followed by dry etching. A layer of spin-on-glass (SOG), which intervening the rod spacing, serves the purpose of electric isolation to each of the parallel nanorod LED units. The electroluminescence peak wavelengths of the nanorod LEDs nearly remain as constant for an injection current level between 25mA and 100mA, which indicates that the quantum confined stark effect is suppressed in the nanorod devices. Furthermore, from the Raman light scattering analysis we identify a strain relaxation mechanism for lattice mismatch layers in the nanostructure.
Optics Express 08/2008; 16(14):10549-56. · 3.59 Impact Factor
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Min Yann Hsieh,
Cheng Yin Wang,
Liang Yi Chen,
Tzu Pu Lin,
Min Yung Ke,
Yun Wei Cheng,
Yi Cheng Yu, Cheng Pin Chen,
Dong Ming Yeh,
Chih Feng Lu,
Chi Feng Huang,
C.C. Yang,
Jian Jang Huang
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ABSTRACT: A practical approach to fabricate textured GaN-based light-emitting diodes (LEDs) by nanosphere lithography is presented. By spin coating a monolayer of SiO<sub>2</sub> nanoparticles as the mask, textured LEDs can be fabricated. Both textured p-GaN and textured indium tin oxide LEDs show significant improvement over conventional LEDs without damaging the electrical characteristics. The results show that the method is promising for manufacturing low-cost high-efficient GaN-based LEDs.
IEEE Electron Device Letters 08/2008; · 2.85 Impact Factor
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ABSTRACT: The authors report on the 394 nm UV light emission from low-temperature sputtered n- Zn O / Si O <sub>2</sub> thin films on top of the p- Ga N heterostructure. They compare samples with and without a Si O <sub>2</sub> current blocking layer. With a Si O <sub>2</sub> layer, electroluminescence spectrum shows a sharp emission peak at 394 nm , which is attributed to the recombination of accumulated carriers between n- Zn O / Si O <sub>2</sub> and p- Ga N / Si O <sub>2</sub> junctions. As for the sample without a Si O <sub>2</sub> layer, a broadband ranging from 400 to 800 nm is observed, which is due to Mg <sup>+</sup> deep-level transition in the GaN along with defects in the ZnO layers.
Applied Physics Letters 09/2007; · 3.84 Impact Factor
