學術出版;;Publications

Permanent URI for this communityhdl:11536/1

收集所有交通大學研究人員與學生個人或團體所發表之各項學術著作，涵蓋期刊論文、教師專書、學位論文等項。;;Collections of Publications of NCTU Researchers and Students Like Journal Papers and Thesis.

Browse

🏛️國立陽明交通大學機構典藏

Search Results

Now showing 1 - 10 of 101

High Output Power GaN-Based Green Resonant-Cavity Light-Emitting Diodes With Trapezoidal Quantum Wells
(2020-09-01)
Wu, Haocheng
;
Li, Heng
;
Kuo, Shiou-Yi
;
Chen, Bo-Yan
;
Lu, Tien-Chang
Green resonant-cavity light-emitting diode (RCLED) has great potential in optical communication but suffers low efficiency. In this study, GaN-based flip-chip green RCLED incorporated with nitrogen face-oriented inclination asymmetric trapezoidal quantum wells (NOAT-QWs) is proposed to enhance the light-output power (LOP). Samples with NOAT-QWs and normal symmetric square quantum wells (SS-QWs) were fabricated and characterized. Although their electrical characteristics and emission spectra are similar, the LOP and emission efficiency are significantly improved. At a driving current of 450 mA, the improvement of LOP for RCLED with NOAT-QWs can be as high as 1.44 times in comparison to the sample with SS-QWs. The unprecedented high output power of 115 mW and the narrow full-width-at-half-maximum (FWHM) of 6.4 nm in the emission spectrum give great potential in optical communication. The inherent mechanism was investigated by the finite element analysis, from which the simulation results match well with the experimental measurements. The simulation results reveal that the NOAT-QWs are beneficial in alleviating the quantum confined stark effect and facilitating easier hole carriers' flow across the barriers, leading to more electron-hole wave function overlaps and higher radiative recombination rate.
GaN-based vertical-cavity surface-emitting laser incorporating a TiO2 high-index-contrast grating
(2020-01-01)
Chang, Tsu-Chi
;
Hashemi, Ehsan
;
Bengtsson, Jorgen
;
Gustavsson, Johan
;
Haglund, Asa
We demonstrate the first electrically injected GaN-based VCSEL with a TiO2 high-contrast grating (HCG) as the top mirror. The TiO2-HCG rested directly on the n-GaN without an airgap for mechanical stability. A VCSEL with an aperture diameter of 10 mu m had a threshold current of 25 mA under pulsed operation at room temperature. Multiple longitudinal modes coexist around 400 nm, each TM-polarized with a linewidth of 0.5 nm (spectral resolution limited). This first demonstration of a TiO2-HCG VCSEL offers a new route to achieve polarization pinning and could also allow additional benefits such as post-growth setting of resonance wavelength.
Study of Charge Trapping Effects on AlGaN/GaN HEMTs Under UV Illumination With Pulsed I-V Measurement
(2020-06-01)
Nagarajan, Venkatesan
;
Chen, Kun-Ming
;
Chen, Bo-Yuan
;
Huang, Guo-Wei
;
Chuang, Chia-Wei
The charge trapping effects on AlGaN/GaN HEMTs under UV illumination are investigated using the pulsed current-voltage (I-V) measurement method. The test samples are unpassivated Schottky-gate HEMTs and metal-insulator-semiconductor HEMTs (MIS-HEMTs) with SiN gate dielectric. For HEMTs, the dominant charge trapping sources are the surface trap states, whereas, for MIS-HEMTs, they are trap states in the SiN gate dielectric and GaN buffer. When these devices are shined with the UV light, the drain current increases apparently in both samples owing to the generated photocurrent. By combining the UV illumination and pulsed I-V measurement, we find out the UV light has less effect on the surface charge trapping in the unpassivated HEMTs. Moreover, in MIS-HEMTs, we observe the charge trapping in the SiN gate dielectric becomes more serious under UV illumination, whereas the charge trapping in the GaN buffer is suppressed significantly. These findings are important for designing a GaN-based HEMT for photonic applications. In addition, the different responses of the surface-, buffer-, and gate-dielectric-related charge trapping to the UV light suggest that it would be easier to distinguish the trap types by introducing the UV illumination during the pulse measurement.
Effect of Strains and V-Shaped Pit Structures on the Performance of GaN-Based Light-Emitting Diodes
(2020-04-01)
Chen, Shuo-Wei
;
Chang, Chia-Jui
;
Lu, Tien-Chang
;
光電工程學系
;
Department of Photonics
Strains and V-shaped pits are essential factors for determining the efficiency of GaN-based light-emitting diodes (LEDs). In this study, we systematically analyzed GaN LED structures on patterned sapphire substrates (PSSs) with two types of growth temperature employed for prestrained layers and three different thickness of n-type GaN layers by using cathodoluminescence (CL), microphotoluminescence (PL), and depth-resolved confocal Raman spectroscopy. The results indicated that V-pits formation situation can be analyzed using CL. From the emission peak intensity ratio of prestrained layers and multiple quantum wells (MQWs) in the CL spectrum, information regarding strain relaxation between prestrained layers and MQWs was determined. Furthermore, micro-PL and depth-resolved confocal Raman spectroscopy were employed to validate the results obtained from CL measurements. The growth conditions of prestrained layers played a dominant role in the determination of LED performance. The benefit of the thick layer of n-GaN was the strain reduction, which was counteracted by an increase in light absorption in thick n-type doped layers. Consequently, the most satisfactory LED performance was observed in a structure with relatively lower growth temperature of prestrained layers that exhibited larger V-pits, leading to higher strain relaxation and thinner n-type GaN layers, which prevent light absorption caused by n-type GaN layers.
Low-Frequency Noise Characterization of AlGaN & x002F;GaN HEMTs and MIS-HEMTs Under UV Illumination
(2020-01-01)
Nagarajan, Venkatesan
;
Chen, Kun-Ming
;
Lin, Hsin-Yi
;
Hu, Hsin-Hui
;
Huang, Guo-Wei
The low-frequency noise characteristics of AlGaN & x002F;GaN HEMTs and MIS-HEMTs are investigated in the dark condition and under UV illumination. The test devices with a 3-& x03BC;m-thick GaN buffer and a 25-nm-thick Al_0.22Ga_0.78N barrier layer were fabricated on the silicon wafer. For MIS-HEMTs, a 25-nm-thick SiN layer was deposited as a gate dielectric. The measured low-frequency noises show a 1 & x002F;f spectrum and can be described by the carrier number fluctuation model. Different noise responses to the UV light between HEMTs and MIS-HEMTs were observed. By comparing the noise data in dark and under UV illumination, the noise sources under the gate and in the ungated gate-drain access region have been identified. From these results, we can find a design guideline to improve the noise and reliability of GaN-based devices for optoelectronic applications.
Investigation of Recessed Gate AlGaN/GaN MIS-HEMTs with Double AlGaN Barrier Designs toward an Enhancement-Mode Characteristic
(2020-02-01)
Wu, Tian-Li
;
Tang, Shun-Wei
;
Jiang, Hong-Jia
;
國際半導體學院
;
International College of Semiconductor Technology
In this work, recessed gate AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) with double AlGaN barrier designs are fabricated and investigated. Two different recessed depths are designed, leading to a 5 nm and a 3 nm remaining bottom AlGaN barrier under the gate region, and two different Al% (15% and 20%) in the bottom AlGaN barriers are designed. First of all, a double hump trans-conductance (g(m))-gate voltage (V-G) characteristic is observed in a recessed gate AlGaN/GaN MIS-HEMT with a 5 nm remaining bottom Al0.2Ga0.8N barrier under the gate region. Secondly, a physical model is proposed to explain this double channel characteristic by means of a formation of a top channel below the gate dielectric under a positive V-G. Finally, the impacts of Al% content (15% and 20%) in the bottom AlGaN barrier and 5 nm/3 nm remaining bottom AlGaN barriers under the gate region are studied in detail, indicating that lowering Al% content in the bottom can increase the threshold voltage (V-TH) toward an enhancement-mode characteristic.
Electrically Injected GaN-Based Vertical-Cavity Surface-Emitting Lasers with TiO2 High-Index-Contrast Grating Reflectors
(2020-04-15)
Chang, Tsu-Chi
;
Hashemi, Ehsan
;
Hong, Kuo-Bin
;
Bengtsson, Jorgen
;
Gustaysson, Johan
We demonstrate the first electrically injected GaNbased vertical-cavity surface-emitting lasers (VCSELs) with a TiO2 high-index-contrast grating (HCG) as the top mirror. Replacing the top distributed Bragg reflector (DBR) with an HCG offers substantial thickness reduction, polarization-pinning, and setting of the resonance wavelength by the grating parameters. Conventional HCGs are usually suspended in the low refractive index material, such as air, in order to create the largest refractive index contrast. However, the mechanical stability of such structures can be questioned and creating free-hanging GaN-membrane on top of GaN is problematic. We have therefore fabricated TiO2-HCGs resting directly on GaN without an air-gap. No DBR layers are used below the HCG to boost the reflectivity. A VCSEL with an aperture diameter of 10 mu m shows a threshold current of 25 mA under pulsed operation at room temperature. The lasing modes locate around 400 nm and are transversely electrically -polarized with a line width of 0.5 nm. The full-width half-maximum beam divergence is 10 degrees. This demonstration of a TiO2-HCG VCSEL offers a new route to achieve polarization pinning and could also allow additional benefits such as postgrowth setting of the resonance wavelength.
A Temperature Compensated 61-W Class-E Soft-Switching GaN-Based Active Diode Rectifier for Wireless Power Transfer Applications
(2019-01-01)
Yang, Shang-Hsien
;
Chen, Ke-Horng
;
Lin, Ying-Hsi
;
Lin, Shian-Ru
;
Tsai, Tsung-Yen
The proposed 6.78-MHz Class-E receiver features a soft-switching and temperature-compensated GaN-based active diode (GAD) rectifier design. Using the temperature dependence of the relationship between the driving voltage and the on-resistance of the switch, the gate-source control voltage of GaN can be adjusted to mitigate efficiency variations based on temperature effects. Moreover, a phase shift comparator activation controller is based on the direct relationship between the phase delay on the gate drive signals and the output power. The temperature dependency voltage offset of the comparator is alleviated with auto-zeroing. GAD rectifier ensures energy transfer up to 61 W and 6.8 A, high efficiency of 92%, and low harmonic distortion of 2.1%.
Demonstration of Annealing-free Metal-Insulator-Semiconductor (MIS) Ohmic Contacts on a GaN Substrate using Low Work-function Metal Ytterbium (Yb) and Al2O3 Interfacial Layer
(2019-01-01)
Wu, Tian-Li
;
Tseng, Yang-Yan
;
Huang, Chih-Fang
;
Chen, Zih-Sin
;
Lin, Chih-Chien
In this letter, the Metal-Insulator-Semiconductor (MIS) contacts are fabricated on the GaN substrates and compared to the Metal-Semiconductor (MS) contacts. To alleviate the Fermi level pinning effect at the Metal-Semiconductor interface, an Al2O3 interfacial layer (IL) (1 similar to 3 nm) is used to form the MIS contacts. By comparing the electrical characteristics, the contact with Onm Al2O3 layer, i.e., MS contact, shows a lowest current compared to the contacts with an Al2O3 IL, i.e., MIS contact. Furthermore, the current at 0.5V in the fabricated Transmission Line Measurement (TLM) device with lnm Al2O3 IL is 10(3) times higher the one without an Al2O3 IL. This proves that inserting an Al2O3 IL could mitigate the Fermi level pinning, resulting in a low Schottky barrier height. Finally, based on the TLM analysis, the resistivity of 5.1x10(-4) Omega.cm(2) is demonstrated in the MIS contact with lnm Al2O3 IL.
High-Uniformity Planar Mini-Chip-Scale Packaged LEDs with Quantum Dot Converter for White Light Source
(2019-05-29)
Chen, Lung-Chien
;
Tien, Ching-Ho
;
Chen, De-Fu
;
Ye, Zhi-Ting
;
Kuo, Hao-Chung
This study proposes a novel direct-lit mini-chip-scale packaged light-emitting diode (mini-CSPLED) backlight unit (BLU) that used quantum dot (QD) film, diffusion plate, and two prism films to improve brightness uniformity. Three different luminous intensity units, 120 degrees mini-CSPLED, 150 degrees mini-CSPLED, and 180 degrees mini-CSPLED with different emission angle structures were fabricated using a CSP process. In terms of component characteristics, although the 180 degrees mini-CSPLED light output power is about loss 4% (at 10mA) compared with 150 degrees mini-CSPLED, it has a large emission angle that forms a planar light source that contributes to improving the BLU brightness uniformity and reduced quantity of LEDs at the same area. In terms of BLU analysis, the blue mini-CSPLEDs with different emission angles excite the different QD film thicknesses; the chromaticity coordinates conversion to the white light region. The BLU brightness increases as the QD film thickness increases from 60, 90, and 150m. This result can achieve a brightness uniformity of 86% in a 180 degrees mini-CSPLED BLU + 150-m-thick QD films as compared to the 120 degrees mini-CSPLED BLU and 150 degrees mini-CSPLED BLU.

學術出版;;Publications

Browse

Filters

Settings

Sort By

Results per page

🏛️國立陽明交通大學機構典藏

Search Results