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Self-Powered, Self-Healed, and Shape-Adaptive Ultraviolet Photodetectors
(2020-02-26)
Tsai, Meng-Shian
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Shen, Tien-Lin
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Wu, Hsing-Mei
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Liao, Yu-Ming
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Liao, Yu-Kuang
The emergence of self-healing devices in recent years has drawn a great amount of attention in both academics and industry. Self-healed devices can autonomically restore a rupture as unexpected destruction occurs, which can efficiently prolong the life span of the devices; hence, they have an enhanced durability and decreased replacement cost. As a result, integration of wearable devices with self-healed electronics has become an indispensable issue in smart wearable devices. In this study, we present the first self-powered, self-healed, and wearable ultraviolet (UV) photodetector based on the integration of agarose/poly(vinyl alcohol) (PVA) double network (DN) hydrogels, which have the advantages of good mechanical strength, self-healing ability, and tolerability of multiple types of damage. With the integration of a DN hydrogel substrate, the photodetector enables 90% of the initial efficiency to be restored after five healing cycles, and each rapid healing time is suppressed to only 10 s. The proposed device has several merits, including having an all spray coating, self-sustainability, biocompatibility, good sensitivity, mechanical flexibility, and an outstanding healing ability, which are all essential to build smart electronic systems. The unprecedented self-healed photodetector expands the future scope of electronic skin design, and it also offers a new platform for the development of next-generation wearable electronics.
Seeing pressure in color based on integration o highly sensitive pressure sensor and emission tunable light emitting diode
(2019-11-25)
Shen, Tien-Lin
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Chen, Chien-Tung
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Liao, Yu-Kuang
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Su, Teng-Yu
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Liu, Che-Yu
We demonstrate a highly sensitive, low-cost, environmental-friendly pressure sensor derived from a wool-based pressure sensor with wide pressure sensing range using wool bricks embedded with a Ag nano-wires. The easy fabrication and light weight allow portable and wearable device applications. Wth the integration of a light-emitting diode possessing multi-wavelength emission, we illustrate a hybrid multi-functional LED-integrated pressure sensor that is able to convert different applied pressures to light emission with different wavelengths. Due to the high sensitivity of the pressure sensor, the demonstration of acoustic signal detection has also been presented using sound of a metronome and a speaker playing a song. This multi-functional pressure sensor can be implemented to technologies such as smart lighting, health care, visible light communication (VLC), and other internet of things (IoT) applications. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
Ultrahigh-Performance Self-Powered Flexible Photodetector Driven from Photogating, Piezo-Phototronic, and Ferroelectric Effects
(1970-01-01)
Shen, Tien-Lin
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Chu, Yu-Wei
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Liao, Yu-Kuang
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Lee, Wen-Ya
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Kuo, Hao-Chung
Owing to the need for dynamic, real-time, and on-site data collection in internet of things applications, the realization of ultra-sensitive sensing networks with self-powered, flexible, and lightweight devices has become an important issue for the development of sensor systems. In this work, a novel, high-performance, self-powered photodetector is achieved through the combination of photogating, piezo-phototronic, and ferroelectric effect by incorporating a ferroelectric thin film of poly(vinylidene fluoride-co-trifluoroethylene) in a rationally designed device structure with suitable band alignment, which can modulate carrier transport behavior at the interface due to the internal electric field produced by light illumination, external strain, or voltage-poled dipole. This enables photocurrent and overall device performance to improve significantly. The unprecedented photodetector presented in this study has several merits, including mechanical flexibility and light weight that allow it to adapt to arbitrary surface topology; additionally, its self-powering capability and high reliability are urgently needed for the demanding functionality of devices for the development of next-generation optoelectronic devices, spanning from wearable communication to unattended harsh environments with a human-friendly interface.
Breakthrough to Non-Vacuum Deposition of Single-Crystal, Ultra-Thin, Homogeneous Nanoparticle Layers: A Better Alternative to Chemical Bath Deposition and Atomic Layer Deposition
(2017-04-01)
Liao, Yu-Kuang
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Liu, Yung-Tsung
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Hsieh, Dan-Hua
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Shen, Tien-Lin
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Hsieh, Ming-Yang
Most thin-film techniques require a multiple vacuum process, and cannot produce high-coverage continuous thin filmswith the thickness of a fewnanometers on rough surfaces. We present a new "paradigm shift" non-vacuum process to deposit high-quality, ultra-thin, single-crystal layers of coalesced sulfide nanoparticles (NPs) with controllable thickness down to a few nanometers, based on thermal decomposition. This provides high-coverage, homogeneous thickness, and large-area deposition over a rough surface, with little material loss or liquid chemical waste, and deposition rates of 10 nm/min. This technique can potentially replace conventional thin-film deposition methods, such as atomic layer deposition (ALD) and chemical bath deposition (CBD) as used by the Cu(In, Ga) Se2 (CIGS) thin-film solar cell industry for decades. We demonstrate 32% improvement of CIGS thin-film solar cell efficiency in comparison to reference devices prepared by conventional CBD deposition method by depositing the ZnS NPs buffer layer using the new process. The new ZnS NPs layer allows reduction of an intrinsic ZnO layer, which can lead to severe shunt leakage in case of a CBD buffer layer. This leads to a 65% relative efficiency increase.
High-performance InGaN-based green light-emitting diodes with quaternary InAlGaN/GaN superlattice electron blocking layer
(2016-05-30)
Tzou, An-Jye
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Lin, Da-Wei
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Yu, Chien-Rong
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Li, Zhen-Yu
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Liao, Yu-Kuang
In this study, high-performance InGaN-based green light-emitting diodes (LEDs) with a quaternary InAlGaN/GaN superlattice electron blocking layer (QSL-EBL) have been demonstrated. The band structural simulation was employed to investigate the electrostatic field and carriers distribution, show that the efficiency and droop behavior can be intensively improved by using a QSL-EBL in LEDs. The QSL-EBL structure can reduce the polarization-related electrostatic fields in the multiple quantum wells (MQWs), leading to a smoother band diagram and a more uniform carriers distribution among the quantum wells under forward bias. In comparison with green LEDs with conventional bulk-EBL structure, the light output power of LEDs with QSL-EBL was greatly enhanced by 53%. The efficiency droop shows only 30% at 100 A/cm(2) comparing to its peak value, suggesting that the QSL-EBL LED is promising for future white lighting with high performance. (C) 2016 Optical Society of America
An Investigation of Carbon-Doping-Induced Current Collapse in GaN-on-Si High Electron Mobility Transistors
(2016-06-01)
Tzou, An-Jye
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Hsieh, Dan-Hua
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Chen, Szu-Hung
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Liao, Yu-Kuang
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Li, Zhen-Yu
This paper reports the successful fabrication of a GaN-on-Si high electron mobility transistor (HEMT) with a 1702 V breakdown voltage (BV) and low current collapse. The strain and threading dislocation density were well-controlled by 100 pairs of AlN/GaN superlattice buffer layers. Relative to the carbon-doped GaN spacer layer, we grew the AlGaN back barrier layer at a high temperature, resulting in a low carbon-doping concentration. The high-bandgap AlGaN provided an effective barrier for blocking leakage from the channel to substrate, leading to a BV comparable to the ordinary carbon-doped GaN HEMTs. In addition, the AlGaN back barrier showed a low dispersion of transiently pulsed I-D under substrate bias, implying that the buffer traps were effectively suppressed. Therefore, we obtained a low-dynamic on-resistance with this AlGaN back barrier. These two approaches of high BV with low current collapse improved the device performance, yielding a device that is reliable in power device applications.
Efficiency droop behavior improvement through barrier thickness modification for GaN-on-silicon light-emitting diodes
(2015-03-05)
Tzou, An-Jye
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Lin, Bing-Cheng
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Lee, Chia-Yu
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Lin, Da-Wei
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Liao, Yu-Kuang
Crack-free GaN-based light-emitting diodes (LEDs) were grown on 150-mm-diameter Si substrates by using low-pressure metal-organic chemical vapor deposition. The relationship between the LED devices and the thickness of quantum barriers (QBs) was investigated. The crystal quality and surface cracking of GaN-on-Si were greatly improved by an AlxGa1-xN buffer layer composed of graded Al. The threading dislocation density of the GaN-on-Si LEDs was reduced to < 7 x 10(8) cm(-2), yielding LEDs with high internal quantum efficiency. Simulation results indicated that reducing the QB thickness improved the carrier injection rate and distribution, thereby improving the droop behavior of the LEDs. LEDs featuring 6-nm-thick QBs exhibited the lowest droop behavior. However, the experimental results showed an unanticipated phenomenon, namely that the peak external quantum efficiency (EQE) and light output power (LOP) gradually decreased with a decreasing QB thickness. In other words, the GaN-on-Si LEDs with 8-nm-thick QBs exhibited low droop behavior and yielded a good peak EQE and LOP, achieving a 22.9% efficiency droop and 54.6% EQE. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)
Observation of unusual optical transitions in thin-film Cu(In,Ga)Se-2 solar cells
(2012-11-05)
Liao, Yu-Kuang
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Kuo, Shou-Yi
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Lin, Woei-Tyng
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Lai, Fang-I
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Hsieh, Dan-Hua
In this paper, we examine photoluminescence spectra of Cu(In,Ga)Se-2 (CIGS) via temperature-dependent and power-dependent photoluminescence (PL). Donor-acceptor pair (DAP) transition, near-bandedge transition were identified by their activation energies. S-shaped displacement of peak position was observed and was attributed to carrier confinement caused by potential fluctuation. This coincides well with the obtained activation energy at low temperature. We also present a model for transition from V-Se to V-In and to V-Cu which illustrates competing mechanisms between DAPs recombinations. (C) 2012 Optical Society of America
Large Scale Single-Crystal Cu(In,Ga)Se-2 Nanotip Arrays For High Efficiency Solar Cell
(2011-10-01)
Liu, Chin-Hung
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Chen, Chia-Hsiang
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Chen, Szu-Ying
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Yen, Yu-Ting
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Kuo, Wei-Chen
In this paper, we demonstrated direct formation of large area Cu(In,Ga)Se-2, nanotip arrays (GIGS NTRs) by using one step Ar+ milling process without template. By controlling milling time and incident angles, the length of CIGS NTRs with adjustable tilting orientations can be precisely controlled. Formation criteria of these CIGS NTRs have been discussed in terms of surface curvature, multiple components, and crystal quality, resulting in a highly anisotropic milling effect. The CIGS NTRs have very low reflectance <0.1% at incident wavelengths between 300 to 1200 nm. Open circuit voltage and short circuit current of CIGS NTRs solar cell were measured to be similar to 390 mV and similar to 22.56 mA/cm(2), yielding the filling factor and the efficiency of 59 and 5.2%, respectively. In contrast to CIGS thin film solar cell with efficiency of 3.2%, the nanostructured CIGS NTRs can have efficiency enhancement of similar to 160% due to the higher light absorption ability because of the nanostructure. The merits of current approach include the latest way via template-free direct creating process of nanostructured CIGS NTRs with controllable dimensionality and large scale production without postselenization process.
Photon management of GaN-based optoelectronic devices via nanoscaled phenomena
(2016-09)
Tsai, Yu-Lin
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Lai, Kun-Yu
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Lee, Ming-Jui
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Liao, Yu-Kuang
;
Ooi, Boon S.
Photon management is essential in improving the performances of optoelectronic devices including light emitting diodes, solar cells and photo detectors. Beyond the advances in material growth and device structure design, photon management via nanoscaled phenomena have also been demonstrated as a promising way for further modifying/improving the device performance. The accomplishments achieved by photon management via nanoscaled phenomena include strain-induced polarization field management, crystal quality improvement, light extraction/harvesting enhancement, radiation pattern control, and spectrum management. In this review, we summarize recent development, challenges and underlying physics of photon management in GaN-based light emitting diodes and solar cells. (C) 2016 Elsevier Ltd. All rights reserved.

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