Browsing by Author "Chu, CF"

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Atomic force microscope study of GaN films grown by hydride vapor phase epitaxy
(1999)
Fang, HM
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Wang, YK
;
Tsai, RY
;
Chu, CF
;
Wang, SC
We report the results of the investigation of the structural, surface morphological, and optical properties of GaN films grown by hydride vapor phase epitaxy. These films were grown on sapphire substrate with no intentional dopings. These as-grown GaN film samples with thickness ranging from 5.58 mu m to 14.9 mu m were investigated under room temperature conditions. The surface morphology of these films was investigated using an atomic force microscopy (AFM). The root mean square (RMS) values of surface roughness range from 0.281 nm to 0.133 nm. The thicker films show lower defect counts with a defect density of about 2 x 10(8) cm(-2). The structural property of these films was measured by double crystal X-ray diffraction (DC-XRD). The full width at half maximum (FWHM) of X-ray diffraction angle decreases as the film thickness increases with a lowest FWHM of about 265.5 arcsec. The optical properties of these films were investigated by photoluminescence (PL) measurement at room temperature. The results show a dominant near band-edge UV emission peak that increases with the film thickness with very weak yellow emission band.
Beryllium-implanted P-type GaN with high carrier concentration
(2001-05-01)
Yu, CC
;
Chu, CF
;
Tsai, JY
;
Lin, CF
;
Lan, WH
We report the results of beryllium implantation in Mg-doped GaN to obtain a high hole concentration and lower activation energy for Mg. The metal organic chemical vapor deposition (MOCVD)-grown Mg-doped GaN samples were implanted with Be ions at two different energies of 50 keV and 150 keV and a dose of 10(14) cm(-2). The implemented samples were subsequently annealed at 1100 degreesC for 60 s. The annealed samples showed an increase of hole concentration by three orders of magnitude from the non-implanted value of 5.5 x 10(16) to 8.1 x 10(19) cm(-3) as determined by Hall measurement. The activation energy of Mg dopants for the implanted annealed samples estimated from the temperature dependence of the photoluminescence data is about 170 meV, which is nearly 30% lower than that for the as-grown samples.
Brightness enhancement of ITO/GaN LEDs by self-aligned micro-net structures
(2005)
Chang, KM
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Chu, JY
;
Cheng, CC
;
Chu, CF
;
電子工程學系及電子研究所
Arrays of square and hexagonal holes of various dimensions were patterned on indium-tin-oxide (ITO)/GaN light-emitting diodes (LEDs) using the self-aligned method to increase the light extraction area and shorten the optical paths. The hole region was etched to give the sidewall of the active layer a sloped profile, and it was passivated by SiOxNy films to extract more light. The self-aligned micro-net LED is at least 10% brighter than the conventional structure in the normal direction without loss of operating voltage or leakage current. The ratio of luminescence to total output power is increased by 25% at a current density of 100 A/cm(2). Moreover, varying the hole dimensions and the designed density increased the peak external quantum efficiency by 5% at a current of 3 mA. The greater axial luminescence and the higher external quantum efficiency make LEDs self-aligned micro-net structures quite useful in surface-mounting and low-power-consuming devices, such as cellular phones. (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Characteristics of optical properties of the interrupt growth method on InGaN/GaN MQW structures
(2000)
Lin, CF
;
Shu, CK
;
Lee, WH
;
Wen, TC
;
Chu, CF
The growth method and material properties of InGaN/GaN multiple quantum well (MQW) structures were studied in this experiment. The InGaN/GaN-MQW structure were deposited above the 2 mum-thick high quality GaN layers (with background carrier concentration was about 3.2 x 10(16) cm(-3)) on Al2O3 substrates. The interrupt growth time was 10 sec between GaN barrier layer and InGaN well growth at 690 degreesC. The stronger intensity and sharper photoluminescence (PL) spectra was observed from the interrupt growth MQW structures. The mean deviation of the PL peak position was lower than 1% by using the interrupt growth MQW structures at difference growth temperature. The PL spectra was become broaden and weaker by reducing the interrupt time during InGaN/GaN growth. The thickness of one pair InGaN/GaN was also identified by DCX-ray measurement and the growth rate InGaN layer was also calculated in this experiment.
Comparison of p-side down and p-side up GaN light-emitting diodes fabricated by laser lift-off
(2003-02-15)
Chu, CF
;
Yu, CC
;
Cheng, HC
;
Lin, CF
;
Wang, SC
The performance characteristics of laser lift-off (LLO) freestanding InGaN/GaN multiple quantum well (MQW) light-emitting diodes (LEDs) mounted on a Cu substrate with p-side up, and p-side down configurations were determined and compared. The InGaN/GaN MQW LED structures, which were originally fabricated on a sapphire substrate, were transferred to a Cu substrate by the LLO process into two different configurations, namely p-side up and p-side down with the same Ni/Pd/Au p-contact metallizations. Both p-side down and p-side up LLO-LEDs showed a higher current operation capability up to 400 mA than the original LEDs on the sapphire substrate. The p-side down LLO-LEDs showed a nearly eightfold increase in the light output power compared to the p-side up LLO-LEDs. The p-side down LLO-LEDs also showed a more stable wavelength emission spectrum than the p-side up ones.
Effect of different n-electrode patterns on optical characteristics of large-area p-side down InGaN light-emitting diodes fabricated by laser lift-off
(2005)
Chu, JT
;
Liang, WD
;
Kao, CC
;
Huang, HW
;
Chu, CF
Large-area (1000x1000 gm) p-side down InGaN light-emitting diodes (LEDs) have been fabricated by laser lift-off (LLO) technique. The p-side down LEDs with different geometric patterns of n-electrode were fabricated to investigate electrode pattern-dependent optical characteristics. Current crowding effect was first observed in in the p-side down InGaN LLO-LEDs. The LEDs with well designed n-electrode shows a uniform distribution of light-emitting pattern and higher out put power due to uniform current spreading and minimization of thermal effect. The output power saturation induced by current crowding in the LEDs with simplest geometric n-electrode was demonstrated. In absent of transparent contact layer for current spreading, the n-electrode pattern has remarkable influence on the current distribution and consequently the light output power of the large-area p-side down LEDs.
Effect of rapid thermal annealing on beryllium implanted p-type GaN
(2004-03-25)
Huang, HW
;
Kao, CC
;
Tsai, JY
;
Yu, CC
;
Chu, CF
We report the results of rapid thermal annealing (RTA) effect on beryllium implanted in situ activated p-type GaN samples and investigate the ramping and isothermal annealing effect of RTA process for these samples. It is found that the optimum RTA condition is at the temperature of 1100 degreesC for 15 s. Furthermore, with equal total isothermal time of 60 s, we compared the multiple step annealing (MSA) at 1100 degreesC for four periods with single step annealing (SSA) for one period at the same annealing temperature of 1100 degreesC, and observed that the ramping effect with MSA could repair Be-related complex defect, and one time, long period isothermal annealing effect with SSA seems to induce much more defect. It seems that the multiple step annealing is more effective and induce less defect than single step annealing for Be-implanted in situ activated p-type GaN samples. (C) 2004 Elsevier B.V. All rights reserved.
Effects of different n-electrode patterns on optical characteristics of large-area p-side-down InGaN light-emitting diodes fabricated by laser lift-off
(2005-11-01)
Chu, JT
;
Kao, CC
;
Huang, HW
;
Liang, WD
;
Chu, CF
Large-area p-side-down InGaN light-emitting diodes (LEDs) 1000 x 1000 mu m(2) in size have been fabricated by laser lift-off (LLO). The p-side-down LEDs with different geometric patterns of n-electrodes were fabricated to investigate electrode pattern-dependent optical characteristics. The current crowding effect was observed in the large-area p-side-down InGaN LLO-LEDs. A LED with a well-designed n-electrode pattern shows a uniform distribution of light emission and a higher output power due to uniform current spreading. The output power saturation induced by the current crowding effect was investigated. In the absence of a transparent contact layer for current spreading, the n-electrode pattern has a marked influence on the current distribution and the consequent light output power of the large-area p-side-down LEDs.
Electrical and optical properties of beryllium-implanted Mg-doped GaN
(2002-08-15)
Yu, CC
;
Chu, CF
;
Tsai, JY
;
Lin, CF
;
Wang, SC
We investigated the electrical and optical characteristics of beryllium implanted Mg-doped GaN materials. The Mg-doped GaN samples were grown by metalorganic chemical vapor deposition system and implanted with Be ions at two different energies of 50 and 150 keV and two different doses of about 10(13) and 10(14) cm(-2). The implanted samples were subsequently rapidly thermal annealed at 900, 1000, and 1100 degreesC for various periods. The annealed samples showed an increase of hole concentration by three orders of magnitude from nonimplanted value of 5.5x10(16) to 8.1x10(19) cm(-3) as obtained by Hall measurement. The high hole concentration samples also showed low specific resistance ohmic contact of about 10(-3) Omega cm(2) and 10(-6) Omega cm(2) using Ni/Au and Ni/Pd/Au metallization, respectively, without any further annealing process. It is also found from the temperature dependent photoluminescence that the activation energy of Mg dopants of the Be implanted samples has an estimated value of about 170 meV, which is nearly 30% lower than the as-grown samples of about 250 meV. The crystal quality and surface morphology of the Be implanted samples measured by x-ray diffraction and atomic force microscopy show no obvious degradation in the crystal quality and surface morphology. (C) 2002 American Institute of Physics.
Fabrication of large-area GaN-based light-emitting diodes on Cu substrate
(2005-04-01)
Chu, JT
;
Huang, HW
;
Kao, CC
;
Liang, WD
;
Lai, FI
A large-area GaN-based light-emitting diode (LED) 1000 x 1000 mu m(2) in size with a p-side down configuration was fabricated using wafer bonding and laser lift-off (LLO) techniques. The thin GaN LED was transferred onto a copper substrate without p peeling or cracks. The large-area LEDs showed a uniform light-emission pattern over entire defined mesa area without a transparent contact layer on the p-type GaN. The operating current of the large-area LEDs can be driven up to 1000 mA with continuously increasing light output-power. The light output-power is 240 mW with a driving current of 1000 mA. Large-area emission and high current operation make the LLO-LEDs applicable to high-power LED applications.
Fabrication of p-side down GaN vertical ligbt emitting diodes on copper substrates by laser lift-off
(2004)
Chu, JT
;
Kuo, HC
;
Kao, CC
;
Huang, HW
;
Chu, CF
The fabrication process and performance characteristics of the laser lift-off (LLO) GaN light emitting diodes (LEDs) were investigated. The LLO-GaN LEDs with 300 x 300 mum(2) on Cu show a nearly 4-fold increase in the light output power over the regular LLO-LEDs on the sapphire substrate. High operation current for the LLO-LEDs on Cu was also demonstrated. The large area-emission of 1000 x 1000 Pm 2 of p-side down GaN LLO-LEDs on Cu were fabricated. Further improvement of max light output are achieved. The LLO process should be applicable to other GaN-based light emitting devices in particular for those high light output power and high operation current devices. (C) 2004 WILEY-VCH Verlag GmbH & Co, KGaA, Weinheim.
Gallium nitride nanorods fabricated by inductively coupled plasma reactive ion etching
(2002-08-15)
Yu, CC
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Chu, CF
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Tsai, JY
;
Huang, HW
;
Hsueh, TH
We report a novel method of fabricating gallium nitride (GaN) nanotods of controllable dimension and density from GaN epitaxial film using inductively coupled plasma reactive ion etching (ICP-RIE). The GaN epitaxial film was grown on a sapphire substrate by metal-organic chemical vapor deposition. Under the fixed Cl-2/Ar flow rate of 10/25 sccm and ICP/bias power of 200/200 W. the GaN nanorods and array were fabricated with a density of 10(8)-10(10) cm(-2) and dimension of 20-100 nm by varying the chamber pressure from 10 to 30 mTorr. The technique offers one-step, controllable method for the fabrication of GaN nanostructures and should be applicable for the fabrication of GaN-based nano-optoelectronic devices.
High etching rate of GaN films by KrF excimer laser
(2001-05-22)
Chu, CF
;
Lee, CK
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Yu, CC
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Wang, YK
;
Tasi, JY
A study of laser processing of gallium nitride (GaN) material is reported. A pulsed KrF excimer laser at 248 nm with 20-nsec pulse width and 1 Hz repetition rate is used to etch the GaN film. We establish the material etching parameters under different environmental conditions. By changing the pulsed energy at constant pulse numbers, ablation of GaN surface was observed at threshold laser fluence about 0.3 J cm(-2). Laser etching increase with reducing environment pressure. Al 1.0 J cm (-2) laser fluence, the etching fate is about 35 nm per pulse at atmosphere pressure and increases to 60 nm per pulse at low pressure. The etched depth also increases with increasing laser fluence. The surface morphology of the etched surface was also investigated. (C) 2001 Elsevier Science B.V. All rights reserved.
Investigation of beryllium implanted P-type GaN
(2001-05-22)
Yu, CC
;
Chu, CF
;
Tsai, JY
;
Wang, SC
;
光電工程學系
We report the preliminary results of beryllium implanted into P-type GaN and the effects on the characteristic of Mg-doped P-GaN. These samples were implanted with Be ions were implanted with two different energies of 50 and 150 keV at two different doses of similar to 10(13) and 10(14) cm(-2) at room temperature. Surface morphology and photoluminescence measurements are presented. (C) 2001 Elsevier Science B.V. All rights reserved.
Large emitting area GaN based light emitting diode fabricated on conducting copper substrates
(2004)
Chu, JT
;
Liang, WD
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Chu, CF
;
Kuo, HC
;
Wang, SC
Low-resistance ohmic contacts on p-type GaN using Ni/Pd/Au metallization
(2000-11-20)
Chu, CF
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Yu, CC
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Wang, YK
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Tsai, JY
;
Lai, FI
In this letter, a low-resistance ohmic contact on p-type GaN using an alloy of Ni/Pd/Au is reported. The Mg doped p-type GaN samples were grown by metalorganic chemical vapor deposition with a carrier concentration of 4.1x10(17) cm(-3). The as-grown Mg doped samples were deposited with Ni (20 nm)/Pd (20 nm)/Au (100 nm) and then annealed in air, nitrogen, and oxygen ambient conditions at different annealing temperatures ranging from 350 to 650 degreesC. Linear I-V ohmic characteristics were observed with specific resistance as low as 1.0x10(-4) Omega cm(2) for the samples annealed in oxygen atmosphere. Similar contact metal composition was also deposited on Be-implanted p-type GaN samples with a carrier density of 8.1x10(19) cm(-3). Without further annealing process, the samples show good ohmic contact with a lowest specific resistance of 4.5x10(-6) Omega cm(2). (C) 2000 American Institute of Physics. [S0003-6951(00)01847-7].
Study of GaN light-emitting diodes fabricated by laser lift-off technique
(2004-04-15)
Chu, CF
;
Lai, FI
;
Chu, JT
;
Yu, CC
;
Lin, CF
The fabrication process and performance characteristics of the laser lift-off (LLO) GaN light-emitting diodes (LEDs) were investigated. The LLO-GaN LEDs were fabricated by lifting off the GaN LED wafer structure grown on the original sapphire substrate by a KrF excimer laser at 248 nm wavelength with the laser fluence of 0.6 J/cm2 and transferring it onto a Cu substrate. The LLO-GaN LEDs on Cu show a nearly four-fold increase in the light output power over the regular LLO-LEDs on the sapphire substrate. High operation current up to 400 mA for the LLO-LEDs on Cu was also demonstrated. Based on the emission wavelength shift with the operating current data, the LLO-LEDs on Cu show an estimated improvement of heat dissipation capacities by nearly four times over the light-emitting devices on sapphire substrate. The LLO process should be applicable to other GaN-based LEDs in particular for those high light output power and high operation current devices. (C) 2004 American Institute of Physics.