Browsing by Author "Uen, Wu-Yih"

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Annealing effects on the p-type ZnO films fabricated on GaAs substrate by atmospheric pressure metal organic chemical vapor deposition
(2011-02-03)
Huang, Yen-Chin
;
Weng, Li-Wei
;
Uen, Wu-Yih
;
Lan, Shan-Ming
;
Li, Zhen-Yu
The effects of post-annealing conducted at 500-650 degrees C on structural, electrical and optical properties of ZnO film fabricated on GaAs (1 0 0) substrate by atmospheric pressure metal-organic chemical vapor deposition are investigated. X-ray diffraction analyses show that the Zn(3)As(2) and ZnGa(2)O(4) phases are produced for the specimens post-annealed at 500 degrees C and above. Hall measurements indicate that stable p-type ZnO films with hole concentration ranging from 4.7 x 10(18) to 8.7 x 10(19) cm(-3) can be obtained by modulating the annealing temperature from 500 to 600 degrees C. In particular, room-temperature photoluminescence (PL) measurements indicate that the superior-quality p-type film could be achieved by a post-annealing treatment at 600 degrees C. Moreover, low temperature PL spectra at 10 K are dominated by the acceptor-related luminescence mechanisms for the films post-annealed at 550 degrees C and above. The ionization energy of acceptor was calculated to be 133-146 meV, which is in good agreement with that theoretically predicted for the As(Zn)-2V(Zn), complex in ZnO. The interdiffused arsenic atoms in the film post-annealed at 600 inverted perpendicular C are suggested to form the As(Zn)-2V(Zn) complex quite effectively, resulting in the most enhanced p-type conductivity and improved material quality. (C) 2010 Elsevier B.V. All rights reserved.
Back-Contacted Thin-Film GaAs Solar Cells
(2016-01-01)
Hong, Chung-Yu
;
Lin, Yu-Chen
;
Ho, Kuan-Ying
;
Tsai, Jia-Ling
;
Chien, Zhan-Tien
In this work, we present a thin-film GaAs solar cell employing via contacts for forming a back-contacted solar cell to eliminate light blocking effects and enhance photon recycling at the same time. The fabrication procedure and the characterization of the fabricated devices are discussed in this paper. From our measurement, a conversion efficiency of 6.5%, open circuit voltage of 0.95 V, and a current density of 8.6mA/cm(2) under one-sun illumination were obtained in a 5x5 mm cell.
Characterizations of Ga-doped ZnO films on Si (111) prepared by atmospheric pressure metal-organic chemical vapor deposition
(2009-11-01)
Huang, Yen-Chin
;
Li, Zhen-Yu
;
Weng, Li-Wei
;
Uen, Wu-Yih
;
Lan, Shan-Ming
Gallium-doped ZnO films were grown on p-Si(111) substrates by atmospheric pressure metal-organic chemical vapor deposition (AP-MOCVD) using diethylzinc and water as reactant gases and triethyl gallium (TEG) as a n-type dopant gas. The structural, electrical, and optical properties of ZnO:Ga films obtained by varying the flow rate of TEG from 0.56 to 3.35 mu mol/min were examined. X-ray diffraction patterns and scanning electron microscopy images indicated that Ga doping plays a role in forming microstructures in ZnO films. A flat surface with a predominant orientation (101) was obtained for the ZnO:Ga film fabricated at a flow rate of TEG = 2.79 mu mol/min. This film also revealed a lowest resistivity of 4.54 x 10(-4) Omega cm, as measured using the van der Pauw method. Moreover, low temperature photoluminescence (PL) emission recorded at 12 K demonstrated the Burstein Moss shift of PL line from 3.365 to 3.403 eV and a line broadening from 100 to 165 meV as the TEG flow rate varied from 0.56 to 2.79 mu mol/min. This blueshift behavior of PL spectra from ZnO: Ga films features the degeneracy of semiconductor, which helps to recognize the enhancing of transparency and conductivity of ZnO films fabricated by AP-MOCVD using Ga-doping technique. (C) 2009 American Vacuum Society. [DOI: 10.1116/1.3212895]
Characterizations of gallium-doped ZnO films on glass substrate prepared by atmospheric pressure metal-organic chemical vapor deposition
(2009-07-31)
Huang, Yen-Chin
;
Li, Zhen-Yu
;
Chen, Hung-hsin
;
Uen, Wu-Yih
;
Lan, Shan-Ming
Ga-doped zinc oxide (ZnO:Ga) films were grown on glass substrate by atmospheric pressure metal-organic chemical vapor deposition (AP-MOCVD) using diethylzinc and water as reactant gases and triethyl gallium (TEG) as an n-type dopant gas. The structural, electrical and optical properties of ZnO:Ga films obtained at various flow rates of TEG ranging from 1.5 to 10 sccm were investigated. X-ray diffraction patterns and scanning electron microscopy images indicated that Ga-doping plays an important role in forming microstructures in ZnO films. A smooth surface with a predominant orientation of (101) was obtained for the ZnO:Ga film grown at a flow rate of TEG=7.5 sccm. Moreover, a lowest resistivity of 3.6 x 10(-4) Omega cm and a highest mobility of 30.4 cm(2) V(-1) s(-1) were presented by the same sample, as evaluated by Hall measurement. Otherwise. as the flow rate of TEG was increased, the average transmittance of ZnO:Ga films increased from 75% to more than 85% in the wavelength range of 400-800 nm, simultaneously with a blue-shift in the absorption edge. The results obtained suggest that low-resistivity and high-transparency ZnO films can be obtained by AP-MOCVD using Ga-doping sufficiently to make the films grow degenerate and effect the Burstein-Moss shift to raise the band-gap energy from 3.26 to 3.71 eV. (C) 2009 Elsevier B.V. All rights reserved.
Enhancing the Emission Efficiency of In(0.2)Ga(0.8)N/GaN MQW Blue LED by Using Appropriately Misoriented Sapphire Substrates
(2009-01-01)
Li, Zhen-Yu
;
Uen, Wu-Yih
;
Lo, Ming-Hua
;
Chiu, Ching-Hua
;
Lin, Po-Chun
In this paper, we report the fabrication of an In(0.2)Ga(0.8)N/GaN multiple-quantum-well (MQW) structure on vicinal sapphire substrates with a very small offset angle of 0-1 degrees by low-pressure metallorganic chemical vapor deposition. Our study demonstrates that the quality of the In(0.2)Ga(0.8)N/GaN MQW structure is very sensitive to the offset angle of the vicinal substrate. High-resolution X-ray diffraction analyses demonstrated high-order satellite peaks and clear fringes between them for all MQW structures fabricated, from which the interface roughness (IRN) was estimated. The IRN of the In(0.2)Ga(0.8)N/GaN MQW structure fabricated on 0.2 degrees off sapphire substrate was determined as 1.36% of the quantum well layer period. Besides, reciprocal lattice mapping was employed to examine the strain status of the MQW. The lattice relaxation of the same specimen mentioned above was estimated to be 7.4x10(-5). It is therefore manifested that an In(0.2)Ga(0.8)N/GaN MQW structure with abrupt interfaces and good layer periodicity was grown. From it, a shortest radiative lifetime of 14.2 ns and a lowest fluctuation of 5.6 meV in the emission energy of micro-photoluminescence mapping were achieved. In addition, superior material qualities of the whole film fabricated on 0.2 degrees off substrate were recognized by cross-sectional transmission electron microscopy. Based on the results mentioned above, a high-quality In(0.2)Ga(0.8)N/GaN MQW blue light, emitting diode (LED) has been fabricated on 0.2 degrees off substrate, which demonstrated a strong room-temperature electroluminescence emission at the wavelength of 465 nm and with the full width at half maximum of only 19 nm. The same device also showed an output power of 13.4 mW and an external quantum efficiency of 19.2%. Both these characteristics are improved drastically compared with the devices fabricated on the substrates with other offset angles. Conclusively, the use of an appropriately misoriented sapphire substrate is suggested to be effective for elevating the emission efficiency of In(0.2)Ga(0.8)N/GaN MQW blue LED fabricated thereon.
Enhancing the Emission Efficiency of In0.2Ga0.8N/GaN MQW Blue LED by Using Appropriately Misoriented Sapphire Substrates
(2009-01-01)
Li, Zhen-Yu
;
Uen, Wu-Yih
;
Lo, Ming-Hua
;
Chiu, Ching-Hua
;
Lin, Po-Chun
In this paper, we report the fabrication of an In0.2Ga0.8N/GaN multiple-quantum-well (MQW) structure on vicinal sapphire substrates with a very small offset angle of 0-1 degrees by low-pressure metallorganic chemical vapor deposition. Our study demonstrates that the quality of the In0.2Ga0.8N/GaN MQW structure is very sensitive to the offset angle of the vicinal substrate. High-resolution X-ray diffraction analyses demonstrated high-order satellite peaks and clear fringes between them for all MQW structures fabricated, from which the interface roughness (IRN) was estimated. The IRN of the In0.2Ga0.8N/GaN MQW structure fabricated on 0.2 degrees off sapphire substrate was determined as 1.36% of the quantum well layer period. Besides, reciprocal lattice mapping was employed to examine the strain status of the MQW. The lattice relaxation of the same specimen mentioned above was estimated to be 7.4x10(-5). It is therefore manifested that an In0.2Ga0.8N/GaN MQW structure with abrupt interfaces and good layer periodicity was grown. From it, a shortest radiative lifetime of 14.2 ns and a lowest fluctuation of 5.6 meV in the emission energy of micro-photoluminescence mapping were achieved. In addition, superior material qualities of the whole film fabricated on 0.2 degrees off substrate were recognized by cross-sectional transmission electron microscopy. Based on the results mentioned above, a high-quality In0.2Ga0.8N/GaN MQW blue light, emitting diode (LED) has been fabricated on 0.2 degrees off substrate, which demonstrated a strong room-temperature electroluminescence emission at the wavelength of 465 nm and with the full width at half maximum of only 19 nm. The same device also showed an output power of 13.4 mW and an external quantum efficiency of 19.2%. Both these characteristics are improved drastically compared with the devices fabricated on the substrates with other offset angles. Conclusively, the use of an appropriately misoriented sapphire substrate is suggested to be effective for elevating the emission efficiency of In0.2Ga0.8N/GaN MQW blue LED fabricated thereon.
Fabrication of whitely luminescent silicon-rich nitride films by atmospheric pressure chemical vapor deposition
(2008-06-01)
Lin, Chia-Hung
;
Uen, Wu-Yih
;
Huang, Yen-Chin
;
Li, Zhen-Yu
;
Liao, Sen-Mao
Silicon-rich nitride (SRN) films that can exhibit an intense white-light emission were fabricated by atmospheric pressure chemical vapor deposition. SRN films were deposited on Si substrates using gaseous SiH(2)Cl(2) (DCS) and NH(3) as the source materials for Si and N, respectively. The deposition temperature was kept at 850 degrees C, and H(2) was used as the carrier gas with its flow rate modulated to maintain chamber pressure at 1 atm during the deposition. The optical properties of films obtained at various deposition times from 15 to 60 min were examined by photoluminescence (PL) measurement. An intense luminescence band (1.5-3.5 eV) was observed by the naked eye for all as-deposited samples. Besides, time-resolved PL exhibited a short radiative lifetime of about 1 ns for SRN films. Moreover, high resolution plan-view transmission electron microscopy demonstrated the existence of Si dots in SRN films with the dot sizes ranging from 2 to 6 nm and a dot density of about 4 x 10(12)/cm(2). On the basis of the results obtained, we considered that the related luminescence mechanism for SRN films is connected to crystalline Si dots produced therein.
Growth of gamma-In2Se3 films on Si substrates by metal-organic chemical vapor deposition with different temperatures
(2008-04-01)
Huang, Yen-Chin
;
Li, Zhen-Yu
;
Uen, Wu-Yih
;
Lan, Shan-Ming
;
Chang, K. J.
In2Se3 films were deposited on the p(+)-Si(1 1 1) substrates by metal-organic chemical vapor deposition (MOCVD) for the first time at temperatures higher than 500 degrees C. Trimethyl indium (TMI) and H2Se were used as the source reactants with the flow ratio of [H2Se]/[TMI] being maintained at 6.7. The growth temperature was varied from 350 to 650 degrees C. Powder X-ray diffraction analyses revealed that the In2Se3 film grown is polycrystalline and has a wurtzite structure when the growth temperature is below 450 degrees C. Instead, a rhombohedral structure began to appear when the growth temperature is above 450 degrees C. Besides, SEM observations indicated a surface morphology of columnar structure for all films grown. Optical properties were examined by photoluminescence (PL) measurements. It was found that by conducting the growth at 550 degrees C a strong PL emission at around 2.14 eV was observed at 20 K. The luminescence mechanism was found to be dominated by the free excitons based on the temperature-dependent PL spectra from 20 to 120 K. However, bound exciton emissions were also observed or even became the dominant band when the films were grown at temperatures lower than 500 degrees C. Otherwise, the intensity of the 2.14 eV peak reduced greatly when the growth temperature was higher than 5 50 degrees C. Power-dependent PL measurements with excitation power varying from 0.1 to 100 mW confirm the luminescent mechanism and the material quality of the film grown at 550 degrees C. It is concluded that single-phase gamma-In2Se3 films can be achieved at temperatures lower than 450 degrees C; however, good-quality In2Se3 films with the simultaneous appearance of gamma- and beta-phase structures can be grown at around 550 degrees C. (C) 2007 Elsevier B.V. All rights reserved.
Growth of InN on Si (111) by atmospheric-pressure metal-organic chemical vapor deposition using InN/AlN double-buffer layers
(2008-07-01)
Li, Zhen-Yu
;
Lan, Shan-Ming
;
Uen, Wu-Yih
;
Chen, Ying-Ru
;
Chen, Meng-Chu
Indium nitride (InN) epilayers have been successfully grown on Si (111) substrates with low-temperature (450 degrees C) grown InN and high-temperature (1050 degrees C) grown AlN (InN/AlN) double-buffer layers by atmospheric-pressure metal-organic chemical vapor deposition (AP-MOCVD). X-ray diffraction characterizations indicated that highly (0001)-oriented hexagonal InN was grown on Si (111) substrate. Photoluminescence (PL) analyses performed at room temperature showed a strong emission at 0.72 eV with a full width at half maximum of 121 meV. Excitation intensity dependent measurements demonstrated the PL mechanism to be the band-to-band transition. Time-resolved PL could be fitted by a single exponential exhibiting an ordered film and a recombination lifetime of around 0.85 ns. In particular, transmission electron microscopy characterizations indicated that the use of AlN first buffer is very important to achieve a structurally uniform (0001)-oriented InN epilayer on Si (111) by AP-MOCVD. (C) 2008 American Vacuum Society.
High-Efficiency and Crack-Free InGaN-Based LEDs on a 6-inch Si (111) Substrate With a Composite Buffer Layer Structure and Quaternary Superlattices Electron-Blocking Layers
(2014-05-01)
Li, Zhen-Yu
;
Lee, Chia-Yu
;
Lin, Da-Wei
;
Lin, Bing-Cheng
;
Shen, Kun-Ching
In this paper, a composite buffer layer structure (CBLS) with multiple AlGaN layers and grading of Al composition/u-GaN1/(AlN/GaN) superlattices/u-GaN2 and InAlGaN/AlGaN quaternary superlattices electron-blocking layers (QSLs-EBLs) are introduced into the epitaxial growth of InGaN-based light-emitting diodes (LEDs) on 6-inch Si (111) substrates to suppress cracking and improve the crystalline quality and emission efficiency. The effect of CBLS and QSLs-EBL on the crystalline quality and emission efficiency of InGaN-based LEDs on Si substrates was studied in detail. Optical microscopic images revealed the absence of cracks and Ga melt-back etching. The atomic force microscopy images exhibited that the root-meansquare value of the surface morphology was only 0.82 nm. The full widths at half maxima of the (0002) and (1012) reflections in the double crystal X-ray rocking curve were similar to 330 and 450 arcs, respectively. The total threading dislocation density, revealed by transmission electron microscopy, was <6 x 10(8) cm(-2). From the material characterizations, described above, blue and white LEDs emitters were fabricated using the epiwafers of InGaNbased LEDs on 6-inch Si substrates. The blue LEDs emitter that comprised blue LEDs chip and clear lenses had an emission power of 490 mW at 350 mA, a wall-plug efficiency of 45% at 350 mA, and an efficiency droop of 80%. The white LEDs emitter that comprised blue LEDs chip and yellow phosphor had an emission efficiency of similar to 110 lm/W at 350 mA and an efficiency droop of 78%. These results imply that the use of a CBLS and QSLs-EBL was found to be very simple and effective in fabricating high-efficiency InGaN-based LEDs on Si for solid-state lighting applications.
Improved Output Power of InGaN-Based Ultraviolet LEDs Using a Heavily Si-Doped GaN Insertion Layer Technique
(2012-02-01)
Chiu, Ching-Hsueh
;
Lin, Chien-Chung
;
Tu, Po-Min
;
Huang, Shih-Cheng
;
Tu, Chia-Cheng
In this paper, a high quality ultraviolet lightemitting diodes (UV-LEDs) at 375 nm was developed using a heavy Si-doping technique with metal organic chemical vapor deposition. By using high-resolution X-ray diffraction, the full width at half-maximum of the rocking curve shows that the GaN film inserting a heavily Si-doped GaN layer (Si-HDL) had high crystalline quality. From the transmission electron microscopy image, the threading dislocation density was decreased after inserting a Si-HDL between undoped and n-doped GaN layers by nanoscale epitaxial lateral overgrowth. As a result, a much smaller reverse current and a higher light output were achieved. The improvement of light output at an injection current of 20 mA was enhanced by 40%. Therefore, we can use an in-situ nano pattern without complex photolithography and etching process and improve the internal quantum efficiency of UV-LEDs.
Intrinsic p-type ZnO films fabricated by atmospheric pressure metal organic chemical vapor deposition
(2010-11-01)
Huang, Yen-Chin
;
Li, Zhen-Yu
;
Weng, Li-Wei
;
Uen, Wu-Yih
;
Lan, Shan-Ming
The structural, electrical, and optical properties of ZnO films fabricated by atmospheric pressure metal organic chemical vapor deposition (AP-MOCVD) under various gas flow ratios of [H(2)O]/[DEZn] (VI/II ratio) ranging from 0.55 to 2.74 were systematically examined. Hall effect measurements exhibited an evident effect of the VI/II ratio on the conduction type of the intrinsic films. An n-type film was fabricated at the VI/II ratio=0.55; however, p-type ZnO films with the hole concentration of the order of 10(17) cm(-3) could be achieved at VI/II ratios higher than 1.0. In particular, the highest mobility of 91.6 cm(2)/V s and the lowest resistivity of 0.369 Omega cm have been achieved for the specimen fabricated at the VI/II ratio=1.10. Moreover, room-temperature photoluminescence (PL) measurements demonstrated an interstitial Zn (Zn(i)) donor defect related emission at 2.9 eV for the n-type film, while a Zn vacancy (V(Zn)) acceptor defect related one at 3.09 eV for the p-type films. The existence of material intrinsic defects was further confirmed by low temperature PL measurements conducted at 10 K. Conclusively, the conduction type of undoped ZnO films deposited by AP-MOCVD is resolved by the VI/II ratio used, which causes the formation of various kinds of intrinsic defects, Zn(i) otherwise VZn. p-type ZnO films with the hole concentration in the range of (1.5-3.3) x 10(17) cm(-3) can be achieved with good reproducibility by modulating a VI/II ratio the range 1.0-2.2 for the AP-MOCVD process. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3484138]
Luminescence mechanisms of silicon-rich nitride films fabricated by atmospheric pressure chemical vapor deposition in N(2) and H(2) atmospheres
(2009-03-01)
Lin, Chia-Hung
;
Uen, Wu-Yih
;
Lan, Shan-Ming
;
Huang, Yen-Chin
;
Liao, Sen-Mao
This work examines possible luminescence mechanisms of silicon-rich nitride (SRN) films that were fabricated by atmospheric pressure chemical vapor deposition (APCVD). Under an ambient gas of either H(2) or N(2), two SRN films were deposited using the same precursors of Si and N. While photoluminescence (PL) measurements of both as-deposited specimens revealed an intense luminescence band (1.8-3.8 eV), which was observable by the naked eye, a detailed examination of the high energy band of the PL spectra over 2.8 eV yielded different results for those samples that were fabricated in different ambiences. To determine the reason for these differences, Fourier-transform infrared spectroscopy and x-ray photoelectron spectroscopy were conducted, suggesting unique chemical bonds and elemental ratio of nitrogen to silicon in SRN films. Further analysis involving plan-view high-resolution transmission electron microscopic observations of SRN films demonstrated the embedding of Si quantum dots (Si QDs), but with some differences depending on the deposition environment. Analyses of the results obtained suggest that the emission from SRN films that were deposited by APCVD is not only dominated by the quantum confinement effect of Si QDs, but also subordinately affected by the surface states around these Si QDs.
Luminescence mechanisms of silicon-rich nitride films fabricated by atmospheric pressure chemical vapor deposition in N-2 and H-2 atmospheres
(2009-03-01)
Lin, Chia-Hung
;
Uen, Wu-Yih
;
Lan, Shan-Ming
;
Huang, Yen-Chin
;
Liao, Sen-Mao
This work examines possible luminescence mechanisms of silicon-rich nitride (SRN) films that were fabricated by atmospheric pressure chemical vapor deposition (APCVD). Under an ambient gas of either H-2 or N-2, two SRN films were deposited using the same precursors of Si and N. While photoluminescence (PL) measurements of both as-deposited specimens revealed an intense luminescence band (1.8-3.8 eV), which was observable by the naked eye, a detailed examination of the high energy band of the PL spectra over 2.8 eV yielded different results for those samples that were fabricated in different ambiences. To determine the reason for these differences, Fourier-transform infrared spectroscopy and x-ray photoelectron spectroscopy were conducted, suggesting unique chemical bonds and elemental ratio of nitrogen to silicon in SRN films. Further analysis involving plan-view high-resolution transmission electron microscopic observations of SRN films demonstrated the embedding of Si quantum dots (Si QDs), but with some differences depending on the deposition environment. Analyses of the results obtained suggest that the emission from SRN films that were deposited by APCVD is not only dominated by the quantum confinement effect of Si QDs, but also subordinately affected by the surface states around these Si QDs.