Browsing by Author "Tsai, JY"

Now showing 1 - 20 of 21

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.
Comparisons of InP/InGaAlAs and InAlAs/InGaAlAs distributed Bragg reflectors grown by metalorganic chemical vapor deposition
(2004-02-25)
Lu, TC
;
Tsai, JY
;
Kuo, HC
;
Wang, SC
;
光電工程學系
Long wavelength vertical cavity surface emitting lasers (VCSELs) are considered the best candidates for the low cost reliable light emitters in fiber communications. The low refractive index contrast in the conventional InP-based lattice-matched distributed Bragg reflectors (DBRs), InP/InGaAsP, impeded the development of 1.3-1.5 mum VCSELs. However, the monolithic InP-based lattice-matched DBRs are still most attractive and desirable. The InP/InGaAlAs and InAlAs/InGaAlAs DBRs with larger refractive index contrast than the conventional InP/InGaAsP DBRs have been demonstrated recently. In this report, we compare these two material systems in terms of optical and electrical properties of DBRs. We found the InP/InGaAlAs DBRs have better electrical and optical properties, while the InAlAs/InGaAlAs DBRs have much lower growth complexity. (C) 2003 Elsevier B.V. All rights reserved.
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 gas ratio on electrical properties of electron-cyclotron-resonance nitride films grown at room temperature
(1996-06-01)
Chang, KM
;
Tsai, JY
;
Li, CH
;
Yeh, TH
;
Wang, SW
The effects on the electrical properties of electron-cyclotron-resonance (ECR) nitride films grown at room temperature with different SiH4/N-2 gas ratios from 7 sccm/43 seem to 2 sccm/48 seem are systematically investigated. Superior properties of the films with low bulk trap density 8X10(17) cm(-3), small trap cross section, high breakdown strength 12.12 MV/cm, and near-stoichiometric refractive index 2.0 are obtained when the gas ratio SiH4/N-2 is 5 sccm/45 sccm, the microwave power is 210 W, and the chamber pressure is 0.5 mTorr. With the microwave power, total gas flow rate, and total pressure unchanged, the decrease in SiH4/N-2 ratio lower than 5/45 results in larger trap density and some lower breakdown strength. On the other side, increasing SiH4/N-2 ratio results in higher hydrogen content, lower breakdown strength, and films which are easily degraded during consecutive voltage sweep. High microwave power will eliminate the weak bonds and strengthen the electrical stability of the high SiH4/N-2 ratio film. (C) 1996 American Institute of Physics.
Effects of gas ratio on electrical properties of electron-cyclotron-resonance nitride films grown at room temperature
(1996-06-01)
Chang, KM
;
Tsai, JY
;
Li, CH
;
Yeh, TH
;
Wang, SW
The effects on the electrical properties of electron-cyclotron-resonance (ECR) nitride films grown at room temperature with different SiH4/N-2 gas ratios from 7 sccm/43 seem to 2 sccm/48 seem are systematically investigated. Superior properties of the films with low bulk trap density 8X10(17) cm(-3), small trap cross section, high breakdown strength 12.12 MV/cm, and near-stoichiometric refractive index 2.0 are obtained when the gas ratio SiH4/N-2 is 5 sccm/45 sccm, the microwave power is 210 W, and the chamber pressure is 0.5 mTorr. With the microwave power, total gas flow rate, and total pressure unchanged, the decrease in SiH4/N-2 ratio lower than 5/45 results in larger trap density and some lower breakdown strength. On the other side, increasing SiH4/N-2 ratio results in higher hydrogen content, lower breakdown strength, and films which are easily degraded during consecutive voltage sweep. High microwave power will eliminate the weak bonds and strengthen the electrical stability of the high SiH4/N-2 ratio film. (C) 1996 American Institute of Physics.
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.
Electronic structure and transport properties of La0.7Ce0.3MnO3
(2005-10-01)
Chang, WJ
;
Tsai, JY
;
Jeng, HT
;
Lin, JY
;
Zhang, KYJ
X-ray absorption spectroscopy (XAS), optical reflectance spectroscopy, and the Hall effect measurements were used to investigate the electronic structure in La0.7Ce0.3MnO3 thin films (LCeMO). The XAS results are consistent with those obtained from LDA+U calculations. In that the doping of Ce has shifted up the Fermi level and resulted in marked shrinkage of hole pockets originally existing in La0.7Ca0.3MnO3 (LCaMO). The Hall measurements indicate that in LCeMO the carriers are still displaying the characteristics of holes as LDA+U calculations predict. Analyses of the optical reflectance spectra evidently disapprove the scenario that the present LCeMO might have been dominated by the La-deficient phases.
Enhanced light output in InGaN-based light-emitting diodes with onmidirectional one-dimensional photonic crystals
(2006-03-01)
Lin, CH
;
Tsai, JY
;
Kao, CC
;
Kuo, HC
;
Yu, CC
We have Successfully designed and fabricated GaN-based light-emitting diodes (LEDs) containing an omnidirectional one-dimensional photonic crystal (ID PC). The ID PC is composed of alternatively stacked TiO2 and SiO2 layers designed to possess a photonic band gap (PBG) within the blue regime of interest. With the same multiple quantum well (MQW) emission peak at approximately 450 nm and a driving Current of 20 mA, the light output powers of the LED with and without the ID PC are approximately 11.7 and 6.5 mW, respectively. The enhancement in light extraction of our LED with ID PC demonstrates that a property designed omnidirectional ID PC can have a higher reflectance and a wider reflection angle than a conventional distributed Bragg reflector (DBR). Our work shows promising potential for the enhancement of output powers of commercial light emitting devices.
Fabrication and performance of blue GaN-based vertical-cavity surface emitting laser employing AlN/GaN and Ta2O5/SiO2 distributed Bragg reflector
(2005-08-22)
Kao, CC
;
Peng, YC
;
Yao, HH
;
Tsai, JY
;
Chang, YH
GaN-based vertical-cavity surface emitting laser with 3 lambda cavity and hybrid mirrors, consisting of the 25 pairs AlN/GaN dielectric Bragg reflector and the 8 pairs Ta2O5/SiO2, was fabricated. The laser action was achieved under the optical pumping at room temperature with a threshold pumping energy density of about 53 mJ/cm(2). The laser emits 448 nm blue wavelength with a linewidth of 0.25 nm and the laser beam has a degree of polarization of about 84%. (c) 2005 American Institute of Physics.
Gallium nitride nanorods fabricated by inductively coupled plasma reactive ion etching
(2002-08-15)
Yu, CC
;
Chu, CF
;
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 reflectivity distributed Bragg reflectors for 1.55 mu m VCSELs using InP/airgap
(2003-10-01)
Tsai, JY
;
Lu, TC
;
Wang, SC
;
光電工程學系
;
Department of Photonics
A high reflecting InP/airgap distributed Bragg reflector (DBR) using InGaAs as sacrificial layers is demonstrated. The 3-pair InP/airgap DBR is formed by etching the InGaAs layers of the MOCVD grown InP/InGaAs structure using H2SO4 solution. A rigid and stable InP/airgap DBR with a peak reflectivity of 99.9% at 1.54 mum and a stopband width of about 200 nm is achieved. (C) 2003 Elsevier Ltd. All rights reserved.
InP/InGaAlAs distributed Bragg reflectors grown by low-pressure metal organic chemical vapor deposition
(2003-04-01)
Lu, TC
;
Tsai, JY
;
Chu, JT
;
Chang, YS
;
Wang, SC
Long-wavelength vertical cavity surface emitting lasers (VCSELs) are considered the best candidate for the future low-cost reliable light sources in fiber communications. However, the absence of high refractive index contrast in InP-lattice-matched materials impeded the development of 1.3-1.5 mum VCSELs. Although wafer fusions provided the alternative approaches to integrate the InP-based gain materials with the GaAs/AlAs materials for their inherent high refractive index contrast, the monolithic InP-based lattice-matched distributed Bragg reflectors (DBRs) are still highly attractive and desirable. In this report, we demonstrate InP/InGaAlAs DBRs with. larger refractive index contrast than InP/InGaAsP and InAlAs/InGaAlAs DBRs. The switching between InP and InGaAlAs layers and growth rate control have been done by careful growth interruption technique and accurate in situ optical monitoring in low-pressure metal organic chemical vapor deposition. A 35 pairs 1.55 mum centered InP/InGaAlAs DBRs has the stopband of more than 100 nut and the highest reflectivity of more than 99%. A VCSEL structure incorporating 3 5 pairs InP/InGaAlAs DBR as the bottom mirror combined with a 2lambda thick periodic gain cavity and 10 pairs SiO2/TiO2 top dielectric mirrors was fabricated. The VCSELs lased at 1.56 mum by optical pumping at room temperature with the threshold pumping power of 30 mW. (C) 2002 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.
Low-resistance ohmic contacts on p-type GaN using Ni/Pd/Au metallization
(2000-11-20)
Chu, CF
;
Yu, CC
;
Wang, YK
;
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].
Reactive ion etching of compound semiconductors grown by MOCVD technique with BCl3/SF6/Ar mixtures
(1995)
Chang, KM
;
Tsai, JY
;
Yeh, CB
;
Yeh, TH
;
Wang, SW
Reactive ion pretreatment technique to improve the ashing resistance of low dielectric constant high carbon content polymer
(2000-07-01)
Chang, KM
;
Yang, JY
;
Chang, YH
;
Tsai, JY
;
電子工程學系及電子研究所
The oxygen plasma via resist strip process causes significant damage to organic spin on polymer (Allied Signal X-720); thus its inter-level dielectric application is limited. A simple treatment technology, reactive glass stabilization (RGS), using reactive ion is proposed to reform the X-720 film surface. The reactive ion modification of the X-720 film can improve the resistance against oxygen plasma. The measurements of stress, thickness variation, scanning electron microscope (SEM) micrographs of gap filling and dielectric constant show that RGS can be practically used in the low dielectric material application with non-etch-back process. The measurements of fourier transform infrared (FTIR) spectroscopy, and auger electron spectroscopy (AES) show that RGS can effectively reform the surface of the X-720 film and increase the ashing resistance even in high carbon content spin on polymer.
Reduction of selectivity loss probability on dielectric surface during chemical vapor deposition of tungsten using fluorinated oxide and removing silanol units on dielectric surface
(1996-12-01)
Chang, KM
;
Wang, SW
;
Li, CH
;
Tsai, JY
;
Yeh, TH
Dielectric materials and surface pretreatment are important for the control of selectivity loss during the chemical vapor deposition (CVD) of W in SiH4/H-2/WF6 ambient. Water-related silanol (SiOH) units on an oxide surface, which come from a wet cleaning step and moisture in clean room air, are found to act as nucleation centers, resulting in selectivity loss. Removing these silanol units by in situ NF3 plasma pretreatment effectively inhibits the nucleation of W. Reduction of the dielectric constant, as well as doping of fluorine in oxide, was shown to suppress the selectivity loss. This is due to the high electronegativity of the FxSiOy film surface, which repels the WF6 molecules. The resistance to selectivity loss of W on FxSiOy is better than that on BPSG. From these results, nucleation of W is inferred to initiate from the adsorption of WF6 on the insulator surface in the WF6/SiH4/H-2 ambient. On the other hand, a novel method that uses FxSiOy as an intermetal dielectric (IMD) or that involves capping on a dielectric material (e.g., BPSG), was proposed to reduce the selectivity loss probability during selective growth processes.
Room-temperature operation of optically pumped blue-violet GaN-based vertical-cavity surface-emitting lasers fabricated by laser lift-off
(2006-04-01)
Chu, JT
;
Lu, TC
;
Yao, HH
;
Kao, CC
;
Liang, WD
Room-temperature optically pumped GaN-based vertical-cavity surface- emitting lasers (VCSELs) were demonstrated by laser lift-off. A VCSEL was fabricated by combining a GaN-based cavity with two dielectric distributed Bragg reflectors: SiO2/TiO2 and SiO2/Ta2O5. The Q factor of the VCSEL is 518 indicating a good interfacial layer quality of the structure. The laser emits blue-violet wavelength light at 414 nm under optical pumping at room temperature with a threshold pumping energy of 270 nJ. The laser emission has a narrow linewidth of 0.25 nm and a degree of polarization of 70%. The laser emission patterns clearly indicate a vertical lasing action of the VCSEL.
Study of dry etching for GaN and InGaN-based laser structure using inductively coupled plasma reactive ion etching
(2004-03-25)
Kao, CC
;
Huang, HW
;
Tsai, JY
;
Yu, CC
;
Lin, CF
Dry etching of undoped, n-GaN, p-GaN and InGaN laser structure was investigated by inductively coupled plasmas reactive ion etching (ICP-RIE) using Ni mask. As Cl-2/Ar gas flow rates were fixed at 10/25 sccm, the etched surface roughness has the lowest value of 0.2 nm at constant ICP/bias power = 300/100 W and 5 mTorr chamber pressure for undoped GaN. The highest etching rate of 12,000 Angstrom/min for n-GaN was achieved at 30 mTorr, 300 W ICP, 100 W bias power using low Cl-2 flow rate (Cl-2/Ar = 10/25 sccm) gas mixtures. The surface roughness was dependent of bias power and chamber pressure, and shows a low root mean square (rms) roughness value of about I nm at 50 W of bias power for n-GaN and p-GaN. For etching of InGaN laser structure using high O-2 flow rate (Cl-2/Ar = 50/20 sccm) and low chamber pressure 5 mTorr, a smooth mirror-like facet of InGaN laser diode structure was obtained. Using these etching parameters, mirror-like facets can be obtained which can be used for the fabrication of nitride-based laser diodes. Moreover, at the fixed Cl-2/Ar flow rate of 10/25 sccm, ICP/bias power of 200/100 W and chamber pressure of 30 mTorr, the InGaN-based materials nanorods were fabricated with a density of about 10(8) cm(-2) and dimension of 50-100 nm. (C) 2004 Elsevier B.V. All rights reserved.
The influence of precleaning process on the gate oxide film fabricated by electron cyclotron resonance plasma oxidation
(1997-01-01)
Chang, KM
;
Li, CH
;
Fahn, FJ
;
Tsai, JY
;
Yeh, TH
The influence of the precleaning process on the characteristics of SiO2 film grown by using electron cyclotron resonance (ECR) plasma oxidation at room temperature is presented in this work. We find that the growth rate, electrical properties, and reliability of the ECR plasma grown oxide is improved by this precleaning step. Two growth mechanisms are found which determine the electrical properties of the plasma grown oxide. The plasma damage is also discussed. We find that plasma oxidation produces little plasma damage in our experiments. Excellent ECR plasma grown silicon dioxide with good electrical properties and reliability characteristics are obtained by this precleaning technique.