JianJang Huang

National Taiwan University, T’ai-pei, Taipei, Taiwan

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Publications (49)74.95 Total impact

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    ABSTRACT: Using light-emitting diodes(LEDs) for visible light communication has become an alternative choice of radio source due to channel crowding of the radio-frequency (RF) signal. The modulation bandwidth of LEDs is usually limited by the spontaneous carrier lifetime in multiple quantum wells. Here, sub-GHz modulation of GaN-based LED employing photonic crystal(PhC) nanostructure is demonstrated. The guided photonic modes of the LEDs are modulated by the RF signal. Both carrier lifetime of lower- and higher-order modes are studied in time-resolved photoluminescence(TRPL) at room temperature. The f-3dB-J curve of the PhCLED exhibits a higher bandwidth than the typical LED structure. At 11.41 kA/cm2, the optical −3-dB bandwidth (f-3dB) up to 234 MHz of the PhCLED (PhCLED) is achieved. Our studies on TRPL at different wavelengths and frequency response at different injection current densities conclude that the higher operation speed is attributed to faster radiative carrier recombination of extracted guided modes from the PhC nanostructure.
    Preview · Article · Jan 2016 · Journal of Applied Physics
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    ABSTRACT: Despite the rapid progress of GaN light-emitting diodes, the quest for better epistructure quality with less defects and relaxed strains to achieve higher internal quantum efficiency has been a popular topic. Here, we propose an AlN nanorod template grown on the sapphire substrate using vapor-liquid-solid method. The corresponding material quality, including voids near nanorods, Raman spectra, and transmission electron microscopy images, indicates significant improvement.
    No preview · Article · May 2015 · IEEE Journal of Quantum Electronics
  • Finella Lee · Liang-Yu Su · Chih-Hao Wang · Yuh-Renn Wu · Jianjang Huang
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    ABSTRACT: For conventional GaN-based high electron mobility transistors (HEMTs), the work function of gate metal is critical to electrical parameters, such as OFF-state leakage current, forward operating current, and threshold voltage. A high work function is thus required to maintain Schottky gate contact. In this letter, an enhancement-mode HEMT composed of p-type GaN/AlGaN/GaN was fabricated. Unlike typical HEMTs that the Schottky barrier height is determined by the energy difference between gate metal work function and semiconductor (AlGaN, or GaN) conduction band, the insertion of the p-GaN relieves the constraint of gate metal. In addition, the gate Schottky barrier now correlates to the valence band of the semiconductor. Here we compare the HEMT performance of different gate metals-Ni/Au, Ti/Au, and Mo/Ti/Au. The results reveal that a tradeoff between VTH and output drain current.
    No preview · Article · Mar 2015 · IEEE Electron Device Letters
  • Chih-Hao Wang · Shin-Yi Ho · JianJang Huang
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    ABSTRACT: The phenomenon of current collapse was investigated on p-GaN/AlGaN/GaN enhancement-mode high electron mobility transistors. Contrary to our original thought of carrier depletion on the p-GaN/AlGaN/GaN layers so that less carrier traps, current collapse was observed from such a device without surface passivation. The results were compared with the device passivated with SiO2 dielectric, which showed much less severe current collapse within the gate bias of −15 V. To understand the mechanism of dielectric passivation, the capacitance–voltage measurement was performed. Our results show that the donor-like dislocations in the SiO2/GaN interface help to deplete carriers on the device surface and within the p-GaN, thus maintaining channel carriers and mitigating current collapse.
    No preview · Article · Jan 2015 · IEEE Electron Device Letters
  • Liang-Yu Su · JianJang Huang
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    ABSTRACT: The relatively high-mobility metal-oxide thin-film transistors (TFTs) have the potential to realize radio-frequency (RF) circuits operating in the megahertz regime. Here, we investigate the RF performance of amorphous indium gallium zinc oxide (a-IGZO) TFTs on the glass substrate with the sputtered channel layer. The device exhibits a high current density of 22.6 mA/mm by employing thin bi-layer Al2O3/SiO2 gate dielectrics. The 1.5 μm gate length device achieves a current gain cutoff frequency fT of 384 MHz and a maximum frequency of oscillation fmax of 1.06 GHz. The record high RF response among the amorphous oxide channels makes it possible to explore new large-area electronics applications, such as low-cost radio frequency identification (RFID) tags. Furthermore, the corresponding small signal parameters were extracted and the voltage dependences of RF response were studied.
    No preview · Article · Nov 2014 · Solid-State Electronics
  • Yu-Feng Yin · Yen-Chen Lin · Jianjang Huang
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    ABSTRACT: Negative refraction was demonstrated in the visible wavelength range by two-dimensional (2D) photonic crystals inscribed at the peripheral of a GaN-based light-emitting diode (LED). Self-collimated behaviors in TE polarization were observed in the far-field measurement.
    No preview · Conference Paper · Nov 2013
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    ABSTRACT: Typically, photonic crystal light-emitting diodes employ shallow nanostructures which only higher-order optical modes can be interacted with. Here, both the shallow photonic crystals and nanohole arrays (etched through active layers) are fabricated, which serve to diffract, respectively, higher and lower optical modes in the active layer. Our results indicate that the photon lifetime can be controlled by adjusting the geometry of shallow nanostructures and nanohole arrays. The angular emission profiles are thus determined by the dominance of higher- and lower-order mode quality factors in the band structure.
    No preview · Article · Oct 2013 · Journal of Applied Physics
  • Huang-Kai Lin · Liang-Yu Su · Chia-Chin Hung · JianJang Huang
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    ABSTRACT: In this work, we explore an indium gallium zinc oxide (IGZO) thin film transistor structure with a vacuum annealed IGZO thin film inserted between the dielectric and typical channel layers. The device demonstrates a better subthreshold swing and field-effect mobility due to the suppression of defects in the channel and the channel/dielectric interface. The hybrid channel structure also exhibits the flexibility of adjusting the threshold voltage. The superior carrier mobility was then verified from the transient response of the inverter circuit constructed by the devices.
    No preview · Article · Jul 2013 · Thin Solid Films
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    ABSTRACT: In recent years, researchers have demonstrated negative refraction theoretically and experimentally by pumping optical power into photonic crystal (PhC) or waveguide structures. The concept of negative refraction can be used to create a perfect lens that focuses an object smaller than the wavelength. By inserting two-dimensional PhCs into the peripheral of a semiconductor light emitting structure, this study presents an electroluminescent device with negative refraction in the visible wavelength range. This approach produces polarization dependent collimation behavior in far-field radiation patterns. The modal dispersion of negative refraction results in strong group velocity modulation, and self-focusing and -defocusing behaviors are apparent from light extraction. This study further verifies experimental results by using theoretic calculations based on equifrequency contours.
    No preview · Article · Jan 2013 · Optics Letters
  • Yu-Feng Yin · Yen-Chen Lin · JianJang Huang
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    ABSTRACT: Negative refraction was demonstrated in the visible wavelength range by two-dimensional (2D) photonic crystals inscribed at the peripheral of a GaN-based light-emitting diode (LED). Self-collimated behaviors in TE polarization were observed in the far-field measurement.
    No preview · Conference Paper · Jan 2013
  • Liang-Yu Su · Huang-Kai Lin · Chia-Chin Hung · JianJang Huang
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    ABSTRACT: High-κ dielectric is regarded as an effective material to reduce the operating voltage of the amorphous indium gallium zinc oxide (a-IGZO) thin film transistors (TFTs). However, the dielectric with high permittivity often has the drawbacks of inducing small conduction band offset energy and high interface trap density. Here a bilayer HfO2/SiO2 gate dielectric for thin-film transistors (TFTs) is employed to address the issues. Compare to the a-IGZO TFT with solely 15 nm-thick HfO2 gate dielectric, the TFT with the bilayer HfO2/SiO2 (10 nm/5 nm) gate dielectric improves the subthreshold swing (SS) from 0.22 to 0.12 V/decade, the mobility from 1.4 to 7 cm2/V ⋅ s and current on–off ratio from 9 x 106 to 1.3 x 109. Finally, Hooge's parameters (extracted from the low-frequency noise measurement) of a-IGZO TFTs were investigated to understand the defects near the channel/dielectrics interface so that the role of the thin SiO2 layer can be verified. The device with bilayer HfO2/SiO2 structure exhibits a value of 2 x 10-3, which is an order of magnitude lower than the one with a single HfO2 layer. The Hooge's parameter of our bilayer dielectric is the lowest among the reported metal–oxide based TFTs on the glass substrate.
    No preview · Article · Dec 2012 · Journal of Display Technology
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    ABSTRACT: Subthreshold swing (SS) is a key parameter in evalu- ating the power consumption and material properties of thin-film transistors (TFTs). In this letter, we report an amorphous indium gallium zinc oxide (a-IGZO) TFT with a high-κ SiO2/HfO2 gate insulator. The device shows a SS of 96 mV/decade and an on-to-off current ratio of 1.5 × 10 10 . The low SS was attributed to the fully depleted channel state, low interface defects, and efficient modula- tion of the device. With low defect states, the device demonstrates only 2.71% change of operating currents after 1.5 × 10 4 s stress. Index Terms—Amorphous InGaZnO, subthreshold swing (SS), thin-film transistors (TFTs).
    No preview · Article · Sep 2011 · IEEE Electron Device Letters
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    ABSTRACT: For InGaN/GaN based nanorod devices using top-down etching process, the optical output power is affected by non-radiative recombination due to sidewall defects (which decrease light output efficiency) and mitigated quantum confined Stark effect (QCSE) due to strain relaxation (which increases internal quantum efficiency). Therefore, the exploration of low-temperature optical behaviors of nanorod light emitting diodes (LEDs) will help identify the correlation between those two factors. In this work, low-temperature EL spectra of InGaN/GaN nanorod arrays was explored and compared with those of planar LEDs. The nanorod LED exhibits a much higher optical output percentage increase when the temperature decreases. The increase is mainly attributed to the increased carriers and a better spatial overlap of electrons and holes in the quantum wells for radiative recombination. Next, while the nanorod array shows nearly constant peak energy with increasing injection currents at the temperature of 300K, the blue shift has been observed at 190K. The results suggest that with more carriers in the quantum wells, carrier screening and band filling still prevail in the partially strain relaxed nanorods. Moreover, when the temperature drops to 77K, the blue shift of both nanorod and planar devices disappears and the optical output power decreases since there are few carriers in the quantum wells for radiative recombination.
    No preview · Article · Sep 2011 · Proceedings of SPIE - The International Society for Optical Engineering
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    ABSTRACT: Strain in the semiconductor light emitting layers has profound effect on the energy band structure and the optical properties of the light emitting diodes (LEDs). Here, we report the fabrication and characterization of GaN nanorod LED arrays. We found that the choice of nanorod passivation materials results in the variation of strain in the InGaN/GaN quantum wells, and thus the corresponding change of light emission properties. The results were further investigated by performing Raman measurement to understand the strain of nanorods with different passivation materials and by calculating the optical transition energy of the devices under the influence of strain-induced deformation potential and the piezoelectric polarization field.
    Full-text · Article · Jul 2011 · Optics Express
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    ABSTRACT: Traditional implementation of photonic crystals (PhCs) on LED light emission surfaces results in weak coupling of light with the PhCs. Here we introduce a GaN-based LED surrounded with a nanohole PhC structure along the mesa edges. The laterally guided modes in the epi-structure can be effectively coupled with the two-dimensional periodic structure. The proposed structure results in the improvement of LED light extraction and provides flexibility of radiation directionality control.
    No preview · Article · May 2011 · Optics Letters
  • Yun-Wei Cheng · Szu-Chieh Wang · Yu-Feng Yin · JianJang Huang
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    ABSTRACT: GaN-based light emitting diodes with proper-designed photonic crystal structures as surface texturing and sidewall reflectors are fabricated to improve the collection of laterally propagated light and the directionality of the device.
    No preview · Article · Apr 2011
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    ABSTRACT: Partial strain relaxation from the light-emitting diode (LED) with surface-textured p-GaN was observed. The textured device possesses less efficiency droop and a higher current level at the efficiency maximum, as compared with the planar one. The results suggest that surface roughening affects not only the external light extraction but also the internal quantum efficiency. Furthermore, the photoluminescent (PL) measurement at low temperature reveals that the percentage increment of the optical power of the textured LED over that of the planar LED becomes lower. In addition to the effect of frozen nonradiative defect states, the PL difference is related to the strain-correlated quantum-confined Stark effect.
    Full-text · Article · Mar 2011 · IEEE Electron Device Letters
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    ABSTRACT: For InGaN/GaN based nanorod devices using a top-down etching process, the optical output power is affected by non-radiative recombination due to sidewall defects (which decrease light output efficiency) and the mitigated quantum confined Stark effect (QCSE) due to strain relaxation (which increases internal quantum efficiency). Therefore, the exploration of low-temperature optical behaviors of nanorod light emitting diodes (LEDs) will help identify the correlation between these two factors. In this work, low-temperature electroluminescent (EL) spectra of InGaN/GaN nanorod arrays were explored and compared with those of planar LEDs. The nanorod LED exhibits a much higher optical output percentage increase when the temperature decreases. The increase is mainly attributed to the increased carriers in the quantum wells for radiative recombination. Also, due to a better spatial overlap of electrons and holes in the quantum wells, the increased number of carriers can be more efficiently recombined in the nanorod device. Next, while the nanorod array shows nearly constant peak energy in the EL spectra at various injection currents at the temperature of 300 K, a blue shift has been observed at 190 K. The results suggest that with less non-radiative recombination and thus more carriers in the quantum wells, carrier screening and band filling still prevail in the partially strain relaxed nanorods. Moreover, when the temperature drops to 77 K, the blue shift of both nanorod and planar devices disappears and the optical output power decreases since there are fewer carriers in the quantum wells for radiative recombination.
    Full-text · Article · Jan 2011 · Nanotechnology
  • Source
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    ABSTRACT: For InGaN/GaN based nanorod devices using top-down etching process, the optical output power is affected by non-radiative recombination due to sidewall defects (which decrease light output efficiency) and mitigated quantum confined Stark effect (QCSE) due to strain relaxation (which increases internal quantum efficiency). Therefore, the exploration of low-temperature optical behaviors of nanorod light emitting diodes (LEDs) will help identify the correlation between those two factors. In this work, low-temperature EL spectra of InGaN/GaN nanorod arrays was explored and compared with those of planar LEDs. The nanorod LED exhibits a much higher optical output percentage increase when the temperature decreases. The increase is mainly attributed to the increased carriers and a better spatial overlap of electrons and holes in the quantum wells for radiative recombination. Next, while the nanorod array shows nearly constant peak energy with increasing injection currents at the temperature of 300K, the blue shift has been observed at 190K. The results suggest that with more carriers in the quantum wells, carrier screening and band filling still prevail in the partially strain relaxed nanorods. Moreover, when the temperature drops to 77K, the blue shift of both nanorod and planar devices disappears and the optical output power decreases since there are few carriers in the quantum wells for radiative recombination.
    Full-text · Article · Jan 2011
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    ABSTRACT: INTRODUCTION ZnO based nanostructures have been explored for potential applications to light emitting devices. Vertically aligned ZnO nanowires can be synthesized with various low-temperature methods including electrodeposition[1], spray pyrolysis[2], vapor deposition method[3], and hydrothermal synthesis[4]. Recently, several researches have demonstrated nanowire LEDs consisting of a p-type GaN thin film and n-type ZnO vertical nanowire arrays[5-8]. However, in most works the defect band emission was observed in the electroluminescence spectra. Similar behavior can be observed from planar devices with the ZnO thin film on p-GaN[9], which is associated with the carrier overflow to the bulk semiconductor without radiatively recombining in the depletion region in the heterojunction[10]. To mitigate defect band emission, a high band gap MgO is proposed in this letter as the carrier blocking layer for ZnO nanowire LED arrays. In addition, the carrier tunneling process through the MgO layer enables us to investigate carrier transport and light emitting behaviors at low temperature. In this work, ZnO nanowire LEDs were fabricated and characterized with the presence of an MgO current blocking layer. The EL spectra at various temperatures were analyzed to reveal carrier transport properties in the heterostructure.
    Full-text · Article · Jan 2011