Browsing by Author "Lan, Wen-How"

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Annealing of defect states in reactive ion etched GaN
(2008-02-01)
Lan, Wen-How
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Huang, Kuo-Chin
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Huang, Kai Feng
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Lin, Jia-Ching
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Cheng, Yi-Cheng
The Al0.11Ga0.89N-based photodiodes fabricated under different annealing ambient after inductively Coupled plasma reactive ion etching process were studied. The dark current and photocurrent with different illuminated wavelengths were characterized. Higher photocurrent for the diode annealing in H-2 ambient can be observed and attributed to the defect-assisted photocurrent. This photocurrent shows a strong annealing ambient dependence and causes the shift of cutoff wavelength in the responsivity spectrum. The Surface state was characterized by the capacitance analysis with Schottky contact. (C) 2007 Elsevier Ltd. All rights reserved.
Conductivity study of nitrogen-doped calcium zinc oxide prepared by spray pyrolysis
(2016-01-15)
Hsu, Yu-Ting
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Lan, Wen-How
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Huang, Kai-Feng
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Lin, Jia-Ching
;
Chang, Kuo-Jen
In this study, the spray pyrolysis method was used to prepare unintentionally doped and nitrogen-doped calcium zinc oxide films by using zinc acetate, calcium nitrate precursor, and ammonium acetate precursor. Morphological and structural analyses were conducted using scanning electron microscopy and X-ray diffraction. The results indicated that film grain size decreased as the nitrogen doping was increased. Both calcium oxide and zinc oxide structures were identified in the unintentionally doped calcium zinc oxide. When nitrogen doping was introduced, the film mainly exhibited a zinc oxide structure with preferred (002) and (101) orientations. The concentration and mobility were investigated using a Hall measurement system. P-type films with a mobility and concentration of 10.6 cm(2) V-1 s(-1) and 2.8 x 10(17) cm(-3), respectively, were obtained. Moreover, according to a temperature-dependent conductivity analysis, an acceptor state with activation energy 0.266 eV dominated the p-type conduction for the unintentionally doped calcium zinc oxide. By contrast, a grain boundary with a barrier height of 0.274-0.292 eV dominated the hole conduction for the nitrogen-doped calcium zinc oxide films. (C) 2015 Elsevier B.V. All rights reserved.
Effects of Doping Ratio and Thermal Annealing on Structural and Electrical Properties of Boron-Doped ZnO Thin Films by Spray Pyrolysis
(2013-06-01)
Yu, Cheng-Chang
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Hsu, Yu-Ting
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Lee, Shao-Yi
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Lan, Wen-How
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Kuo, Hsin-Hui
Boron-doped zinc oxide (BZO) thin films have been fabricated by spray pyrolysis on a glass substrate. The morphology and electrical properties of the thin films were investigated. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses were performed. It was found that [B]/[Zn] ratio altered both the microstructure and concentration of the BZO thin films. The film grain size was reduced by increasing the [B]/[Zn] ratio. The highest Hall mobility was 3.65 cm(2)V(-1)s(-1) for the undoped ZnO thin film, and the highest carrier concentration of 1.0 x 10(19) cm(-3) was achieved for the as-deposited BZO thin film with [B]/[Zn] = 1.5 at. %. Conductivity was determined at different measurement temperatures and shallow donors provided the dominate conduction mechanism for the as-deposited BZO thin films. After 600 degrees C annealing, shallow level reduction and donors with a high activation energy of 129 +/- 6 meV in the BZO thin films were characterized, and the shallow donors that dominate the carrier concentration for the as-deposited spray-pyrolized BZO thin film were eliminated. (C) 2013 The Japan Society of Applied Physics
Effects of UV illumination on oxygen detection for ZnO film prepared by thermally oxidized Zn on sapphire substrate
(2014)
Yu, Cheng-Chang
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Hsu, Yu-Ting
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Lan, Wen-How
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Shih, Ming-Chang
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Hong, Jin-Hua
The ZnO thin film prepared after the 600 degrees C oxidation of thermally-evaporated Zn thin film on sapphire substrate was studied. A nano structured surface morphology was observed by scanning electron microscope. With following Ti/Au metallization, the metal-semiconductor-metal (MSM) device was formed. With ultra violate (UV) light illumination come from the mercury lamp with a short pass filter, the device resistance variation under oxygen atmosphere was investigated. The reduction of detection response time and recovery time for this device with UV light illumination were observed also. After discussion based on the grain boundary connected model, the observed resistance variation controlled by the nano texture was realized. The UV light illumination technology shows an effective method to enhance the gas detection response time for this ZnO MSM gas sensor. Keywords: ZnO, MSM,
Enhancement of light output power of InGaN/GaN multiple quantum well light-emitting diodes by titanium dioxide texturing
(2008-07-01)
Huang, Kuo-Chin
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Lan, Wen-How
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Huang, Kai Feng
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電子物理學系
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Department of Electrophysics
The enhancement of external quantum efficiency in InGaN/GaN multiple quantum well (MQW) light-emitting diodes (LEDs) with a titanium dioxide (TiO(2)) textured film has been observed. The output power values of conventional and TiO(2) textured LEDs Lit an injection Current of 20 mA are 6.25 and 8 mW, respectively. The external quantum efficiencies of the conventional and TiO(2) textured LEDs at an injection Current of 20 mA are 11.5 and 14.8%, respectively. The external quantum efficiency of the TiO(2) textured LEDs Lit an injection current of 20 mA is 28% higher than that of the conventional LEDs. A higher-output-power InGaN/GaN MQW LED has been obtained by coating with a TiO(2) textured film.
ICP-induced defects in GaN characterized by capacitance analysis
(2006-11-01)
Lan, Wen-How
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Huang, Kuo-Chin
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Huang, Kai Feng
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電子物理學系
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Department of Electrophysics
The defects induced by inductively coupled plasma reactive ion etching (ICP-RIE) on a Si-doped gallium nitride (GaN:Si) surface have been analyzed. According to the capacitance analysis, the interfacial states density after the ICP-etching process may be higher than 5.4 x 10(12) eV(-1) cm(-2), compared to around 1.5 x 10(11) eV(-1) cm(-2) of non-ICP-treated samples. After the ICP-etching process, three kinds of interfacial states density are observed and characterized at different annealing parameters. After the annealing process, the ICP-induced defects could be reduced more than one order of magnitude in both N-2 and H-2 ambient. The H-2 ambient shows a better behavior in removing ICP-induced defects at a temperature around 500 degrees C, and the interfacial states density around 2.2 x 10(11) eV(-1) cm(-2) can be achieved. At a temperature higher than 600 degrees C, the N-2 ambient provides a much more stable interfacial states behavior than the H-2 ambient. (c) 2006 Elsevier Ltd. All rights reserved.
Improved Output Power of Nitride-Based Light-Emitting Diodes With Convex-Patterned Sapphire Substrates
(2012-10-01)
Hsu, Yu-Ting
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Yu, Cheng-Chang
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Huang, Kai-Feng
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Lan, Wen-How
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Huang, Jing-En
Nitride-based light-emitting diodes (LEDs) grown on different convex-patterned sapphire substrates are proposed and fabricated. The electrical and optical properties of these LEDs are discussed in detail. It is found that the LED with a ball-shape patterned sapphire substrate has the best crystalline quality and I-V characteristic. On the other hand, on reducing total internal reflection, the LED with hexagonal-shape patterned sapphire substrate (HPSS) has the best performance on output power and external quantum efficiency. In comparison to the LED without patterned substrate, the LED with HPSS has 175% and 165% enhancement on output power and external quantum efficiency, respectively.
Indium-Nitrogen Codoped Zinc Oxide Thin Film Deposited by Ultrasonic Spray Pyrolysis on n-(111) Si Substrate: The Effect of Film Thickness
(2014)
Yu, Cheng-Chang
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Lan, Wen-How
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Huang, Kai-Feng
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電子物理學系
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Department of Electrophysics
Indium-nitrogen codoped zinc oxide (INZO) thin films were fabricated by spray pyrolysis deposition technique on n-(111) Si substrate with different film thicknesses at 450 degrees C using a precursor containing zinc acetate, ammonium acetate, and indium nitrate with 1 : 3 : 0.05 at.% concentration. The morphology and structure studies were carried out by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The grain size of the films increased when increasing the film thickness. From XRD spectra, polycrystalline ZnO structure can be observed and the preferred orientation behavior varied from(002) to (101) as the film thickness increased. The concentration and mobility were investigated by Hall effect measurement. the p-type films with a hole mobility around 3 cm(2)V(-1)s(-1) and hole concentration around 3 x 10(19) cm(-3) can be achieved with film thickness less than 385 nm. The n-type conduction with concentration 1 x 10(20) cm(-3) is observed for film with thickness 1089 nm. The defect states were characterized by photoluminescence. With temperature-dependent conductivity analysis, acceptor state with activation energy 0.139 eV dominate the p type conduction for thin INZO film. And the Zn-related shallow donors with activation energy 0.029 eV dominate the n-type conduction for the thick INZO film.
Investigation of the (Cu, Ga) InSe2 thin film with different pairs of CuGa/In sputtered layers
(2012)
Hsu, Yu-Ting
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Huang, Kai-Feng
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Tsai, Shang-I
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Lan, Wen-How
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Yueh, Ming
Thin film samples of (Cu,Ga) InSe2 (CIGS) were prepared by DC magnetron sputtering and the selenisation process onto soda lime glass substrates. All samples had the same deposition conditions, and the optimal sputtering thickness of samples with one CuGa/In pair and two CuGa/In pairs are also the same. After sample deposition, X-ray diffraction (XRD), scanning electron microscope (SEM) and Hall effect measurements were used to characterize the properties of these samples. From XRD measurement results, excepting an extra small CuSe peak existing in the samples with two CuGa/In pairs, the XRD peaks of all samples are perfectly matched with the phase diagram of CuGa0.3In0.7Se2 material. It was also found that the grain sizes of the samples with one CuGa/In pair are larger than those with two CuGa/In pairs from SEM images. All these observations on samples with two CuGa/In pairs can be attributed to the fact that the less In incorporation in CIGS films, which it has been proven that the sample with low In-to-CuGa ratio has stronger CuSe peak from XRD result. Furthermore, the p-type carrier characteristics can be observed for all samples from Hall measurement results. The carrier mobility and concentration of the samples with one CuGa/In pair can be achieved as high as 15.28 cm(2)/Vs and as low as 1.50x10(16) cm(-3), respectively, while the carrier mobility and concentration of the ones with two CuGa/In pairs can be achieved as 6.4 cm(2)/Vs and 6.27x10(17) cm(-3), respectively. The results of superior electrical properties of samples with one CuGa/In pair agree well with the observations form XRD and SEM results. In the final, the optimal value of In-to-CuGa ratio during CuGa/In layers deposition in this study is 0.625.
On the Nitrogen Doping in Erbium and Nitrogen Codoped Magnesium Zinc Oxide Diode by Spray Pyrolysis
(2020-01-01)
Chen, Chun-An
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Hsu, Yu-Ting
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Lan, Wen-How
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Huang, Kai-Feng
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Chang, Kuo-Jen
Diodes with an erbium and nitrogen codoped magnesium zinc oxide (MgZnO:Er,N) active layer were fabricated by spray pyrolysis on Si substrate with aqueous solutions including magnesium nitrate, zinc acetate, erbium acetate, ammonium acetate, and indium nitrate precursors. Diodes with different nitrogen content in their precursor were prepared and their properties were investigated. With scanning electron microscopy, film surface with mixed hexagonal flakes and tiny blocks was characterized for all samples. Certain morphologies varied for samples with different N contents. In the photoluminescence analyses, the intensity of the oxygen-related defects peak increased with the increasing of nitrogen content. The diodes were fabricated with an Au and In deposition on the top and backside. The diode current-voltage as well as capacitance-voltage characteristics were examined. An ununiformed n-type concentration distribution with high concentration near the interface in the MgZnO:Er,N layer was characterized for all samples. Diodes with high nitrogen content exhibit reduced breakdown voltage and higher interface concentration characteristics. Under reversed bias conditions with an injection current of 50 mA, a light spectrum with two distinct green emissions around wavelengths 532 and 553 nm was observed. A small spectrum variation was characterized for diodes prepared from different nitrogen content. The diode luminescence characteristics were examined and the diode prepared from N/Zn=1 in the precursor showed an optimal injection current-to-luminescence property. The current and luminescence properties of the diode were characterized and discussed.
Photocatalytic study of Zinc Oxide with bismuth doping prepared by spray pyrolysis
(2015-09-01)
Lin, Tzu-Yang
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Hsu, Yu -Ting
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Lan, Wen-How
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Huang, Chien-Jung
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Chen, Lung-Chien
The unintentionally doped and bismuth (Bi) doped zinc oxide (ZnO) films were prepared by spray pyrolysis at 450 degrees C with zinc acetate and bismuth nitrate precursor. The n-type conduction with concentration 6.13 x10(16)cm(-3) can be observed for the unintentionally doped ZnO. With the increasing of bismuth nitrate concentration in precursor, the p-type conduction can be observed. The p-type concentration 4.44x10(17)cm(-3) can be achieved for the film with the Bi/Zn atomic ratio 5% in the precursor. The photoluminescence spectroscopy with HeCd laser light source was studied for films with different Bi doping. The photocatalytic activity for the unintentionally doped and Bi-doped ZnO films was studied through the photodegradation of Congo red under UV light illumination. The effects of different Bi contents on photocatalytic activity are studied and discussed. Results show that appropriate Bi doping in ZnO can increase photocatalytic activity.
Thermal annealing effect between Ni film and Mg-doped GaN layer
(2006-08-01)
Hsu, Chin-Yuan
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Lan, Wen-How
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Wu, YewChung Sermon
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材料科學與工程學系
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Department of Materials Science and Engineering
The effects of thermal annealing between Ni film and a p-type GaN layer have been investigated. The electrical and optical properties were measured by Hall effect, capacitance-voltage (C-V) and photoluminescence (PL) measurements. The samples activated with Ni film obtained higher effective carrier concentrations than those activated without Ni film. Effective carrier concentrations of 5 x 10(15) and 1 x 10(17) cm(-3) We're achieved at an activating temperature of 400 degrees C without and with Ni film. The Ni film may act as a catalyst for the activation of Mg-doped GaN at a temperature less than 500 degrees C. At a temperature higher than 600 degrees C, the Ni film may react with the Mg-doped GaN. X-ray diffraction (XRD) analyses indicated that Ni film on Mg-doped GaN transforms to nickel oxide (NiO) and nickel nitride (Ni3N) during thermal annealing in air. The peaks of the PL spectra at 15 K of the samples activated at 600 degrees C with and without Ni film were observed at approximately 3.2 and 2.9 eV. We suggest that Ni atoms not only enhance hydrogen desorption but also diffuse into the Mg-doped GaN layers to form Ni-compound materials. At a high annealing temperature, impurities such as Ni nitride, nitrogen vacancies or other defects may reduce the carrier mobility and provide an increase in the effective carrier concentrations in the surface region.
Thickness Study of Er-Doped Magnesium Zinc Oxide Diode by Spray Pyrolysis
(2018-12-01)
Hsu, Yu-Ting
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Lee, Che-Chi
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Lan, Wen-How
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Huang, Kai-Feng
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Chang, Kuo-Jen
Erbium-doped magnesium zinc oxides were prepared through spray pyrolysis deposition at 450 degrees C with an aqueous solution containing magnesium nitrate, zinc acetate, erbium acetate, and indium nitrate precursors. Diodes with different erbium-doped magnesium zinc oxide thicknesses were fabricated. The effect of erbium-doped magnesium zinc oxide was investigated. The crystalline structure and surface morphology were analyzed using X-ray diffraction and scanning electron microscopy. The films exhibited a zinc oxide structure, with (002), (101), and (102) planes and tiny rods in a mixed hexagonal flakes surface morphology. With the photoluminescence analyses, defect states were identified. The diodes were fabricated via a metallization process in which the top contact was Au and the bottom contact was In. The current-voltage characteristics of these diodes were characterized. The structure resistance increased with the increase in erbium-doped magnesium zinc oxide thickness. With a reverse bias in excess of 8 V, the light spectrum, with two distinct green light emissions at wavelengths of 532 nm and 553 nm, was observed. The light intensity that resulted when using a different operation current of the diodes was investigated. The diode with an erbium-doped magnesium zinc oxide thickness of 230 nm shows high light intensity with an operational current of 80 mA. The emission spectrum with different injection currents for the diodes was characterized and the mechanism is discussed.
UV Enhanced Oxygen Response Resistance Ratio of ZnO Prepared by Thermally Oxidized Zn on Sapphire Substrate
(2013)
Yu, Cheng-Chang
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Hsu, Yu-Ting
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Lan, Wen-How
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Shih, Ming-Chang
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Hong, Jin-Hua
ZnO thin film was fabricated by thermally oxidized Zn at 600 degrees C for 1 h. A surface containing nanostructured dumbbell and lines was observed by scanning electron microscope (SEM). The ZnO resistor device was formed after the following Ti/Aumetallization. The device resistance was characterized at different oxygen pressure environment in the dark and under ultraviolet (UV) light illumination coming from the mercury lamp with a short pass filter. The resistance increases with the increase of oxygen pressure. The resistance decreases and response increases with the increase of light intensity. Models considering the barrier height variation caused by the adsorbed oxygen related species were used to explain these results. The UV light illumination technology shows an effective method to enhance the detection response for this ZnO resistor oxygen sensor.