Browsing by Author "Tzou, An-Jye"

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AlN Surface Passivation of GaN-Based High Electron Mobility Transistors by Plasma-Enhanced Atomic Layer Deposition
(2017-04-27)
Tzou, An-Jye
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Chu, Kuo-Hsiung
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Lin, I-Feng
;
Ostreng, Erik
;
Fang, Yung-Sheng
We report a low current collapse GaN-based high electron mobility transistor (HEMT) with an excellent thermal stability at 150 degrees C. The AlN was grown by N-2-based plasma enhanced atomic layer deposition (PEALD) and shown a refractive index of 1.94 at 633 nm of wavelength. Prior to deposit AlN on III-nitrides, the H-2/NH3 plasma pretreatment led to remove the native gallium oxide. The X-ray photoelectron spectroscopy (XPS) spectroscopy confirmed that the native oxide can be effectively decomposed by hydrogen plasma. Following the in situ ALD-AlN passivation, the surface traps can be eliminated and corresponding to a 22.1% of current collapse with quiescent drain bias (V-DSQ) at 40 V. Furthermore, the high temperature measurement exhibited a shift-free threshold voltage (V-th), corresponding to a 40.2% of current collapse at 150 degrees C. The thermal stable HEMT enabled a breakdown voltage (BV) to 687 V at high temperature, promising a good thermal reliability under high power operation.
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
;
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.
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.
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)
Efficiency improvement of GaN-based ultraviolet light-emitting diodes with reactive plasma deposited AlN nucleation layer on patterned sapphire substrate
(2014-09-16)
Lee, Chia-Yu
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Tzou, An-Jye
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Lin, Bing-Cheng
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Lan, Yu-Pin
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Chiu, Ching-Hsueh
The flip chip ultraviolet light-emitting diodes (FC UV-LEDs) with a wavelength of 365 nm are developed with the ex situ reactive plasma deposited (RPD) AlN nucleation layer on patterned sapphire substrate (PSS) by an atmospheric pressure metal-organic chemical vapor deposition (AP MOCVD). The ex situ RPD AlN nucleation layer can significantly reduce dislocation density and thus improve the crystal quality of the GaN epitaxial layers. Utilizing high-resolution X-ray diffraction, the full width at half maximum of the rocking curve shows that the crystalline quality of the epitaxial layer with the (RPD) AlN nucleation layer is better than that with the low-temperature GaN (LT-GaN) nucleation layer. The threading dislocation density (TDD) is estimated by transmission electron microscopy (TEM), which shows the reduction from 6.8 x 10(7) cm(-2) to 2.6 x 10(7) cm(-2). Furthermore, the light output power (LOP) of the LEDs with the RPD AlN nucleation layer has been improved up to 30 % at a forward current of 350 mA compared to that of the LEDs grown on PSS with conventional LT-GaN nucleation layer.
Full-color monolithic hybrid quantum dot nanoring micro light-emitting diodes with improved efficiency using atomic layer deposition and nonradiative resonant energy transfer
(2019-04-01)
Chen, Sung-Wen Huang
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Shen, Chih-Chiang
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Wu, Tingzhu
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Liao, Zhen-You
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Chen, Lee-Feng
Full-color displays based on micro light-emitting diodes (mu LEDs) can be fabricated on monolithic epitaxial wafers. Nanoring (NR) structures were fabricated on a green LED epitaxial wafer; the color of NR-mu LEDs was tuned from green to blue through strain relaxation. An Al2O3 layer was deposited on the sidewall of NR-mu LEDs, which improved the photoluminescence intensity by 143.7%. Coupling with the exposed multiple quantum wells through nonradiative resonant energy transfer, red quantum dots were printed to NR-mu LEDs for a full-color display. To further improve the color purity of the red light, a distributed Bragg reflector is developed to reuse the excitation light. (C) 2019 Chinese Laser Press
Greatly Improved Carrier Injection in GaN-based VCSEL by Multiple Quantum Barrier Electron Blocking Layer
(2015)
Hsieh, Dan-Hua
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Tzou, An-Jye
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Lin, Da-Wei
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Kao, Tsung-Sheng
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Lin, Chien-Chung
In this report, the fabrication and characteristics of III-nitride based vertical-cavity surface-emitting laser (VCSEL) with bulk AlGaN and AlGaN/GaN superlattice electron blocking layer (EBL) are observed experimentally and theoretically. The results have been revealed that laser performance is improved by using superlattice EBL. The output power and the slope efficiency are enhanced by the improvement of carrier injection into active region. And the reduction of threshold current density from 10 to 8 kA/cm2 is also observed. Theoretical calculation results suggest that the improved carrier injection efficiency can be mainly attributed to the partial release of the strain at the interface of last quantum barrier and superlattice EBL and hence the increase of electrons and holes effective barrier height.
Greatly Improved Efficiency Droop for InGaN-Based Green Light Emitting Diodes by Quaternary Content Superlattice Electron Blocking Layer
(2015)
Lin, Da-Wei
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Tzou, An-Jye
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Huang, Jhih-Kai
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Lin, Bing-Cheng
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Chang, Chun-Yen
We presented a low efficiency droop behavior green light emitting diodes (LEDs) with a quaternary content InAlGaN/GaN superlattice electron blocking layer (SL-EBL). The light output power shows a 57% enhancement and only 30% efficiency droop, which is attributed to a smooth band bending with a uniform carrier distribution.
Growing GaN LEDs on amorphous SiC buffer with variable C/Si compositions
(2016-01-22)
Cheng, Chih-Hsien
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Tzou, An-Jye
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Chang, Jung-Hung
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Chi, Yu-Chieh
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Lin, Yung-Hsiang
The epitaxy of high-power gallium nitride (GaN) light-emitting diode (LED) on amorphous silicon carbide (a-SixC1-x) buffer is demonstrated. The a-SixC1-x buffers with different nonstoichiometric C/Si composition ratios are synthesized on SiO2/Si substrate by using a low-temperature plasma enhanced chemical vapor deposition. The GaN LEDs on different SixC1-x buffers exhibit different EL and C-V characteristics because of the extended strain induced interfacial defects. The EL power decays when increasing the Si content of SixC1-x buffer. The C-rich SixC1-x favors the GaN epitaxy and enables the strain relaxation to suppress the probability of Auger recombination. When the SixC1-x buffer changes from Si-rich to C-rich condition, the EL peak wavelengh shifts from 446 nm to 450 nm. Moreover, the uniform distribution contour of EL intensity spreads between the anode and the cathode because the traping density of the interfacial defect gradually reduces. In comparison with the GaN LED grown on Sirich SixC1-x buffer, the device deposited on C-rich SixC1-x buffer shows a lower turn-on voltage, a higher output power, an external quantum efficiency, and an efficiency droop of 2.48 V, 106 mW, 42.3%, and 7%, respectively.
Growth evolution and magneto-optical characteristics of self-assembled ZnTe/ZnMnSe quantum dots
(2013-09-01)
Lee, Ling
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Fan, Wen-Chung
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Chien, Kun-Feng
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Tzou, An-Jye
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Chou, Wu-Ching
The growth evolution and the magneto-optical characteristics of the self-assembled single-layer ZnTe/ZnMnSe quantum dots grown by molecular beam epitaxy were investigated. As the ZnTe coverage is above 2.0 monolayers, a Stranski-Krastanov growth process is observed with a significantly increased dot density on top of two-dimensional plateaus. As the coverage exceeds 2.7 monolayers, ripened dots dominate instead. Furthermore, a saturated degree of circular polarization of 76% at applied magnetic field of 4 T and the formation of magnetic polarons with a formation time of 7.4 ns were demonstrated. (c) 2012 Elsevier B.V. All rights reserved.
High-Efficiency InGaN/GaN Core-Shell Nanorod Light-Emitting Diodes With Low-Peak Blueshift and Efficiency Droop
(2017-03)
Tzou, An-Jye
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Hsieh, Dan-Hua
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Hong, Kuo-Bin
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Lin, Da-Wei
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Huang, Jhih-Kai
In this study, novel three-dimensional (3-D) nanoscale structures and methodology are demonstrated for application in high-efficiency core-shell nanorod (NR) light-emitting diodes (LEDs). The key to our successful growth of the structures is the introduction of passivation, which can be used to selectively grow active layers in desired structures. Through the fabrication methodology, core-shell NR green LEDs exhibiting large nonpolar active region and homogeneous indium distributions without a point tip shape were achieved. Stable light emission at a central wavelength of 518 nm was achieved as the injected current increased to more than 40 mA. The improved NR LEDs exhibited a stable luminescence emission wavelength (blueshift of 62 nm) and low-efficiency droop (18.1%) at 200 mA. Our scheme is scalable and compatible with current technologies, which provides a new perspective for developing high-performance, 3-D nanoscale optoelectronic devices.
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
Non-thermal alloyed ohmic contact process of GaN-based HEMTs by pulsed laser annealing
(2016-05)
Tzou, An-Jye
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Hsieh, Dan-Hua
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Chen, Szu-Hung
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Li, Zhen-Yu
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Chang, Chun-Yen
We have demonstrated Si implantation incorporation into GaN HEMTs with a non-alloyed ohmic contact process. We optimized the power density of pulsed laser annealing to activate implanted Si dopants without a thermal metallization process. The experimental results show that the GaN surface will be reformed under the high power density of the illumination conditions. It provides a smooth surface for following contact engineering and leads to comparable contact resistance. The transmission line model (TLM) measurement shows a lower contact resistance to 6.8. x. 10(-7) Omega . cm(2) via non-alloyed contact technology with significantly improved surface morphology of the contact metals. DC measurement of HEMTs shows better current and on-resistance. The on-resistance could be decreased from 2.18 to 1.74 m Omega-cm(2) as we produce a lower contact resistance. Pulsed laser annealing also results in lower gate leakage and smaller dispersion under a pulse I-V measurement, which implies that the density of the surface state is improved.
Optical and Magnetic Properties of Zn1-xMnxO Grown by Plasma-Assisted Molecular Beam Epitaxy
(2014-06-01)
Chou, Wu Ching
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Tzou, An-Jye
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Chen, Hsuan-Shao
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Chien, Kun-Feng
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Fan, Wen-Chung
Zn1-xMnxO films (0 <= x <= 0.070) were grown by plasma-assisted molecular beam epitaxy on Si substrates with AlN buffer layers. For low Mn concentration samples, x <= 0.02, photoluminescence spectra show strong near band edge emission. Strong phonon and exciton coupling-induced resonant Raman scattering was observed. Paramagnetic, antiferromagnetic, and ferromagnetic phases were observed. Room temperature ferromagnetism for all samples was attributed to the bound magnetic polaron effect.
Suppression of Current Collapse in Enhancement Mode GaN-Based HEMTs Using an AIGaN/GaN/AIGaN Double Heterostructure
(2017-04-01)
Ho, Shin-Yi
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Lee, Chun-Hsun
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Tzou, An-Jye
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Kuo, Hao-Chung
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Wu, Yuh-Renn
Current collapse is a phenomenon that increases the channel resistance during the switching process when the high gate and drain voltages are applied. The effect can be found from GaN-based high electron mobility transistors (HEMTs) and is an obstacle for their applications to power electronics. There have been numerous reports on suppressing current collapse using semiconductor process technologies. In this paper, an enhancement mode (E-mode) AIGaN/GaN/AIGaN double heterostructure was proposed. The current collapse phenomena were studied on devices of E-mode MIS and Schottky gate HEMTs. The results indicate the suppression of current collapse for devices with double heterostructure.
Wavelength tunable InGaN/GaN nano-ring LEDs via nano-sphere lithography
(2017-03-03)
Wang, Sheng-Wen
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Hong, Kuo-Bin
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Tsai, Yu-Lin
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Teng, Chu-Hsiang
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Tzou, An-Jye
In this research, nano-ring light-emitting diodes (NRLEDs) with different wall width (120 nm, 80 nm and 40 nm) were fabricated by specialized nano-sphere lithography technology. Through the thinned wall, the effective bandgaps of nano-ring LEDs can be precisely tuned by reducing the strain inside the active region. Photoluminescence (PL) and time-resolved PL measurements indicated the lattice-mismatch induced strain inside the active region was relaxed when the wall width is reduced. Through the simulation, we can understand the strain distribution of active region inside NRLEDs. The simulation results not only revealed the exact distribution of strain but also predicted the trend of wavelength-shifted behavior of NRLEDs. Finally, the NRLEDs devices with four-color emission on the same wafer were demonstrated.
Wavelength Tuning in InGaN/GaN Light-emitting Diodes with Strain-induced Through Nanosphere Lithography
(2017-01-01)
Chen, Sung-Wen Huang
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Wang, Sheng-Wen
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Hong, Kuo-Bin
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Tsai, Yu-Lin
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Tzou, An-Jye
Nano-ring light emitting diodes with different wall width shows that the effective bandgap can be tuned by reducing the strain. This research successful to make the devices with four colors emission on the same wafer.