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Analysis of Quality Factor Enhancement in the Monolithic InGaN/GaN Nanorod Array
(2019-04-01)
Huang, Chia-Yen
;
Tai, Tzu-Ying
;
Hong, Kuo-Bin
;
Kuo, Hao-Chung
;
Lu, Tien-Chang
Whispering gallery mode (WGM) lasers and resonators are key building blocks for photonic integrated circuits. The quality factor and resonant wavelength are strong functions of the cavity size. Nanoscale WGM cavities suffer from a low-quality factor due to prominent scattering loss. However, the quality factor could be enhanced by forming an optically-coupled rod array or photonic molecules. Through simulations, we revealed how rod-to-rod optical coupling influenced the threshold pumping level and dominant mode selection, where the trend showed good agreement with the experimental observation. According to the simulation, the quality factor could be enhanced by up to eight times by forming a six-rod photonic molecule. The quality factor and effective mode were both superior to the single rods with the same wafer device footprint.
Design and Fabrication of the Reliable GaN Based Vertical-Cavity Surface-Emitting Laser via Tunnel Junction
(2019-04-01)
Shen, Chih-Chiang
;
Lu, Yun-Ting
;
Yeh, Yen-Wei
;
Chen, Cheng-Yuan
;
Chen, Yu-Tzu
In this study, we theoretically designed and experimentally fabricated an InGaN vertical-cavity surface-emitting laser (VCSEL) with a tunnel junction (TJ) structure. From numerical simulation results, the optical loss of the device can be reduced by a TJ structure. Additionally, the leakage current of the VCSEL with TJ structure was much smaller than that of the VCSEL with an Indium-Tin-Oxide (ITO) layer. We have been demonstrated that laser output performance is improved by using the TJ structure when compared to the typical VCSEL structure of the ITO layer. The output power obtained at 2.1 mW was enhanced by a factor of 3.5 by the successful reduction of threshold current density (J(th)) from 12 to 8.5 kA/cm(2), and the enlarged slope efficiency was due to less absorption in VCSEL with a TJ structure. Finally, the samples passed the high temperature (70 degrees C) and high operation current (1.5 x J(th)) test for over 500 h.
Quantum dot vertical-cavity surface-emitting lasers covering the 'green gap'
(2017-01-01)
Mei, Yang
;
Weng, Guo-En
;
Zhang, Bao-Ping
;
Liu, Jian-Ping
;
Hofmann, Werner
Semiconductor vertical-cavity surface-emitting lasers (VCSELs) with wavelengths from 491.8 to 565.7 nm, covering most of the 'green gap', are demonstrated. For these lasers, the same quantum dot (QD) active region was used, whereas the wavelength was controlled by adjusting the cavity length, which is difficult for edge-emitting lasers. Compared with reports in the literature for green VCSELs, our lasers have set a few world records for the lowest threshold, longest wavelength and continuous-wave (CW) lasing at room temperature. The nanoscale QDs contribute dominantly to the low threshold. The emitting wavelength depends on the electron-photon interaction or the coupling between the active layer and the optical field, which is modulated by the cavity length. The green VCSELs exhibit a low-thermal resistance of 915 kW(-1), which benefits the CW lasing. Such VCSELs are important for small-size, low power consumption full-color displays and projectors.
Mode-Hopping Phenomena in the InGaN-Based Core-Shell Nanorod Array Collective Lasing
(2018-07-01)
Huang, Chia-Yen
;
Tai, Tzu-Ying
;
Lin, Jing-Jie
;
Chang, Tsu-Chi
;
Liu, Che-Yu
A two-dimensional monolithic InGaN-based core-shell it array was excited under a varying temperature. We observed an abrupt dominant mode hopping from 3.29 to 141 eV in the collective lasing as the temperature decreased from T = 240 to 225 K, Photoluminescence under a near-threshold pumping density revealed the splitting of spontaneous emission. between the core and the shell with a decreasing temperature. The bandgap evolution of GaN and InGaN showed opposite trends due to the interaction of temperature effects and bandgap renormalization effects. Theoretical simulation revealed the differences of gain spectra evolution between room lire and to temperature due to the difference the carrier dynamics, In the optically coupled nanorod array, the dominant lasing;mode was not only determined by it structure, but also strongly influenced by external operating conditions. Rattier than singular microcavity lasers the coupled nanorod array demonstrated a broader parameter space for on-chip wavelength manipulation.
Collective Lasing Behavior of Monolithic GaN-InGaN Core-Shell Nanorod Lattice under Room Temperature
(2017-10-01)
Huang, Chia-Yen
;
Lin, Jing-Jie
;
Chang, Tsu-Chi
;
Liu, Che-Yu
;
Tai, Tzu-Ying
We demonstrated a monolithic GaN-InGaN core-shell nanorod lattice lasing under room temperature. The threshold pumping density was as low as 140 kW/cm(2) with a quality factor as high as 1940. The narrow mode spacing between lasing peaks suggested a strong coupling between adjacent whisper gallery modes (WGM), which was confirmed with the far field patterns. Excitation area dependent photoluminescence revealed that the long-wavelength lasing modes dominated the collective lasing behavior under a large excitation area. The excitation-area-dependent lasing behavior resulted from the prominent optical coupling among rods. According to the optical mode simulations and truncated-rod experiments, we confirmed that the fine-splitting of lasing peaks originated from the coupled supermodes existing in the periodic nanorod lattices. With wavelength-tunable active materials and a wafer-level scalable processing, patterning optically coupled GaN-InGaN core-shell nanorods is a highly practical approach for building various on-chip optical components including emitters and coupled resonator waveguides in visible and ultraviolet spectral range.
Quantum dot vertical-cavity surface-emitting lasers covering the \'green gap\'
(2017-01)
Mei, Yang
;
Weng, Guo-En
;
Zhang, Bao-Ping
;
Liu, Jian-Ping
;
Hofmann, Werner
Semiconductor vertical-cavity surface-emitting lasers (VCSELs) with wavelengths from 491.8 to 565.7 nm, covering most of the \'green gap\', are demonstrated. For these lasers, the same quantum dot (QD) active region was used, whereas the wavelength was controlled by adjusting the cavity length, which is difficult for edge-emitting lasers. Compared with reports in the literature for green VCSELs, our lasers have set a few world records for the lowest threshold, longest wavelength and continuous-wave (CW) lasing at room temperature. The nanoscale QDs contribute dominantly to the low threshold. The emitting wavelength depends on the electron-photon interaction or the coupling between the active layer and the optical field, which is modulated by the cavity length. The green VCSELs exhibit a low-thermal resistance of 915 kW(-1), which benefits the CW lasing. Such VCSELs are important for small-size, low power consumption full-color displays and projectors.
Lasing Behavior, Gain Property, and Strong Coupling Effects in GaN-Based Vertical-Cavity Surface-Emitting Lasers
(2008-08-01)
Lu, Tien-Chang
;
Chu, Jung-Tang
;
Chen, Shih-Wei
;
Cheng, Bo-Siao
;
Kuo, Hao-Chung
The optical properties of a GaN-based vertical-cavity surface-emitting laser (VCSEL) with two dielectric distributed Bragg reflectors were investigated under optically pumped operation. The laser emits blue-violet light at a wavelength of 414 nm at room temperature with a high spontaneous emission coupling factor (beta-factor) of 2 x 10(-2) and a linewidth of 0.25 nm. The optical gain was determined by the Hakki-Paoli method by measuring the photoluminescence spectra below threshold conditions. At room temperature, an optical gain of 2900 cm(-1) was obtained under threshold condition. The linewidth enhancement factor (alpha-factor) is estimated front the ratio of the wavelength and gain derivation with respect to the carrier density, and the alpha-factor at room temperature is estimated to be 2.8. Strong exciton-photon coupling in the microcavity was observed at room temperature. A 9 meV Rabi splitting with 60% peak-to-valley contrast was determined from the photoluminescence measurements. Emission spectra showing the evolution of anticrossing behavior were also observed.
Numerical Study of In0.15Ga0.85N/GaN MQW Solar Cells with varying well band structure
(2013)
Wang, Hsun-Wen
;
Hsieh, Chi-Chang
;
Lai, Fang-I
;
Lin, Shiuan-Huei
;
Kuo, Hao-Chung
The photovoltaic properties of 14 pairs In0.15Ga0.85N/GaN multiple quantum well solar cells with varying indium composition of QW are investigated numerically. The simulation results show that smooth well structure of energy band can be reduce carrier confinement and the recombination to enhance photo-current generation. This helpful design is easy to improve carrier transport to collection. And the optimal In0.15Ga0.85N/GaN MQW solar cell had V-oc of 2.37V, J(sc) of 0.73, and the efficiency of 0.79%, which the efficiencies is enhanced 69.2 % to reference cell.
Numerical Study of (0001) Face GaN/InGaN p-i-n Solar Cell With Compositional Grading Configuration
(2012-06-15)
Kuo, Yen-Kuang
;
Lin, Bing-Cheng
;
Chang, Jih-Yuan
;
Chen, Fang-Ming
;
Kuo, Hao-Chung
The advantages of a (0001) face GaN/InGaN p-i-n solar cell with compositional grading configuration between i-InGaN/p-GaN layers are studied numerically. With the use of the grading layer, the conversion efficiency is markedly promoted due to the reduction of potential barrier height for holes and due to the decrease of polarization. Optimized conversion efficiency is obtained when the thickness of the grading layer increases to a critical value. This critical thickness is strongly influenced by the polarization charges and doping concentration of the grading layer. When the density of the polarization charges is high or the doping concentration is low, a thick grading layer is required to achieve high efficiency.
Effects of built-in polarization and carrier overflow on InGaN quantum-well lasers with electronic blocking layers
(2008-01-01)
Chen, Jun-Rong
;
Lee, Chung-Hsien
;
Ko, Tsung-Shine
;
Chang, Yi-An
;
Lu, Tien-Chang
Effects of built-in polarization and carrier overflow on InGaN quantum-well lasers with a ternary AlGaN or a quaternary AlInGaN electronic blocking layer (EBL) have been numerically investigated by employing an advanced device-simulation program. The simulation results indicate that the characteristics of InGaN quantum-well lasers can be improved by using the quaternary AlInGaN EBL. When the aluminum and indium compositions in the AlInGaN EBL are appropriately designed, the built-in charge density at the interface between the InGaN barrier and the AlInGaN EBL can be reduced. Under this circumstance, the electron leakage current and the laser threshold current can obviously be decreased as compared with the laser structure with a conventional AlGaN EBL when the built-in polarization is taken into account in the calculation. Furthermore, the AlInGaN EBL also gives a higher refractive index than the AlGaN EBL, which is a benefit for a higher quantum-well optical confinement factor in laser operations.

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