Browsing by Author "Lan, WH"

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AuBe Ohmic contacts to p-type ZnTe
(1998-12-10)
Lan, WH
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Lin, WJ
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Cheng, YC
;
Tai, K
;
Tasi, CM
Ohmic contacts of AuBe to p-ZnTe show a minimum specific contact resistance of 3.0 x 10(-6) Ohm cm(2) for a p-doping level of 1.6 x 10(19) cm(-3) and at an annealing temperature of 200 degrees C. The beryllium is very effective at improving the electrical properties of p-type contacts to ZnTe.
Beryllium-implanted P-type GaN with high carrier concentration
(2001-05-01)
Yu, CC
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Chu, CF
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Tsai, JY
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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.
Characteristics of nonalloyed pseudomorphic high electron mobility transistors using InAs/InxGa1-xAs (x=-> 0) AlyGa1-yAs (y=0 -> 0.3) contact structures
(1997-06-01)
Chen, SS
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Lin, CC
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Lan, WH
;
Tu, SL
;
Peng, CK
A molecular beam epitaxy InAs/InxGa1-xAs (x = 1 --> 0)/AlyGa1-yAs (y = 0 --> 0.3) heterojunction was used as an ohmic contact structure to the GaAs-based pseudomorphic high electron mobility transistors (PHEMTs). This nonalloyed PHEMT had a specific contact resistance r(c) of 1.05 x 10(-7) Omega . cm(2) and an extrinsic transconductance g(me) of 272 mS/mm for devices with 1 mu m gate-length, microwave measurements shelved a current gain cut-off frequency f(t) of 22 GHz and a maximum oscillation frequency f(max) of 43 GHz. These results are comparable to our best conventional PHEMTs' alloyed at 450 degrees C and 2 min duration. Meanwhile, a small-signal equivalent circuit model of the nonalloyed PHEMT has also been demonstrated.
Characteristics of nonalloyed pseudomorphic high electron mobility transistors using InAs/InxGa1-xAs (x=-> 0) AlyGa1-yAs (y=0 -> 0.3) contact structures
(1997-06-01)
Chen, SS
;
Lin, CC
;
Lan, WH
;
Tu, SL
;
Peng, CK
A molecular beam epitaxy InAs/InxGa1-xAs (x = 1 --> 0)/AlyGa1-yAs (y = 0 --> 0.3) heterojunction was used as an ohmic contact structure to the GaAs-based pseudomorphic high electron mobility transistors (PHEMTs). This nonalloyed PHEMT had a specific contact resistance r(c) of 1.05 x 10(-7) Omega . cm(2) and an extrinsic transconductance g(me) of 272 mS/mm for devices with 1 mu m gate-length, microwave measurements shelved a current gain cut-off frequency f(t) of 22 GHz and a maximum oscillation frequency f(max) of 43 GHz. These results are comparable to our best conventional PHEMTs' alloyed at 450 degrees C and 2 min duration. Meanwhile, a small-signal equivalent circuit model of the nonalloyed PHEMT has also been demonstrated.
Effect of thermal annealing of Ni/Au ohmic contact on the leakage current of GaN based light emitting diodes
(2003-09-22)
Hsu, CY
;
Lan, WH
;
Wu, YS
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材料科學與工程學系
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Department of Materials Science and Engineering
The effect of thermal annealing on current-voltage properties of GaN light emitting diodes (LEDs) has been studied. At annealing temperatures above 700 degreesC, the p-n junction of the diodes became very leaky and Ga-contained metallic bubbles were observed on the surface of Ni/Au p-ohmic contact. Transmission electron microscopy and energy dispersive x-ray spectrometer studies revealed that these metallic bubbles resided directly on top of the threading dislocations in GaN and both Ni and Au were indiffused into the LED structure along the cores of the TDs. The conducting paths formed by the metal containing dislocation cores are believed to be the cause for the observed short circuit behavior of p-n junctions at high annealing temperatures. (C) 2003 American Institute of Physics.
GaN-based light-emitting diodes with Ni/AuBe transparent conductive layer
(2003-10-01)
Chen, LC
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Hsu, CY
;
Lan, WH
;
Teng, SY
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材料科學與工程學系
Ni/AuBe as p-type ohmic contact to p-GaN in the heat treatment process are reported. By selection of an optimum condition, the best construction of Ni/AuBe bi-layers is 5 nm/5 nm thick. The light-transmission is about 75% for 470 nm blue light and the lowest specific contact resistance obtained is 2 x 10(-3) Omega cm(2) examined by transmission line model after heat treatment process at 500 degreesC alloying temperature during 10 min in nitrogen ambient. The Be atom may plays an important role in the formation of good ohmic contacts. On the other hand, Ni/AuBe bi-layers are also applied to GaN-based light-emitting diodes (LEDs) as p-type ohmic contact electrode. The typical I-V characteristics of the GaN-based LEDs with 5 nm/5 nm-thick Ni/AuBe TCL exhibit a forward-bias voltage of 3.41 V at injection Current of 20 mA. (C) 2003 Elsevier Ltd. All rights reserved.
High performance non-alloyed pseudomorphic high electron mobility transistors
(1996-07-01)
Peng, CK
;
Lan, WH
;
Tu, SL
;
Yang, SJ
;
Chen, SS
We have studied the InAs/GaAs strained layer superlattice (SLS) structures as non-alloyed contacts applied to pseudomorphic high electron mobility transistors (PHEMTs) grown by the molecular beam epitaxy (MBE) system. Transmission line measurements with four point configurations showed that specific contact resistances between 6.6 x 10(-7) and 2.6 x 10(-6) Omega cm(2) were obtained for the as-grown devices, with a linear correlation coefficient of 0.997. D.c. measurements of the as-grown PHEMT with 1 mu m gate showed a transconductance of 240 ms mm(-1). Microwave measurements on the same device showed a cut-off frequency of 19 GHz and a maximum power gain frequency of 42 GHz. These results are comparable with those of devices with the conventional contact scheme. Meanwhile, since the non-alloying process maintains excellent surface morphology and sharp metal pad edges, AuGeNi type metals can be used in small dimension devices. In contrast, the conventionally alloyed devices showed rough surface morphology and zigzag edges, which may affect device processing and limit the usefulness of AuGeNi metal as the ohmic contact in small dimension devices.
Optical properties of Zn1-xCdxSe epilayers grown on (100)GaAs by molecular beam epitaxy
(2004-08-01)
Kuo, MC
;
Chiu, KC
;
Shih, TH
;
Lai, YJ
;
Yang, CS
Zn1-xCdxSe epilayers were grown on (100) GaAs substrates by molecular beam epitaxy. Lattice constants of the epilayers were measured by (004) rocking curve X-ray diffraction. A full width at half maximum of 475 to 2100 arcsec was obtained. The dependence of the energy gap on temperature, measured by the photoluminescence (PL) spectra, was fitted by Varshni's [Y. P. Varshni: Physica 34 149 (1967)] and O'Donnell's [R. P. O'Donnell and X. Chen: Appl. Phys. Lett. 58 2924 (1991)] models. The fitting parameters beta (161 K to 368K) and (hv) (13 meV to 24 meV), related to phonon energy, were obtained from Varshni and O'Donnell fits, respectively. The activation energies calculated from the integrated PL intensity versus inverse temperature decrease as the Cd content increases. The broadening of the PL linewidth with temperature was fitted by Gamma(T) = Gamma(0) + Gamma(a)T + Gamma(LOI)/[exp(homega(LOI)/kT) - 1] + Gamma(LO2)/[exp(homega(LO2)/kT) - 1] + Gamma(i)exp(-/kT). The impurity binding energy, (E-b), was found to decrease as the Cd composition increases.
The influences of contact interfaces between the indium tin oxide-based contact layer and GaN-based LEDs
(2006)
Hsu, CY
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Lan, WH
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Wu, YCS
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材料科學與工程學系
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Department of Materials Science and Engineering
We have fabricated GaN-based light-emitting diodes (LEDs) using transparent indium tin oxide-based (ITO-based) p contacts. The current-voltage characteristics and life tests of GaN-based LEDs have been studied. LED life tests showed that a pure ITO contact layer had poor reliability at high current stress. We also found that the GaN-based LED could achieve good reliability with a NiO/ITO contact layer. Using transmission electron microscopy and energy-dispersive X-ray spectrometer analyses, we observed In-contained metallic interface between the p-GaN layer and the pure ITO contact layer after annealing at 600 degrees C. It revealed that ITO would react at interface or indiffuse near the interface at 600 C. The LED was degraded with unstable interfaces after life tests (stressed by a 50-mA current injection). To improve the reliability of GaN-based LEDs with the ITO contact layer, we suggest that the NiO layer be used to prevent the reaction and block the leakage pathway. (c) 2006 The Electrochemical Society.
Thermal annealing effect of indium tin oxide contact to GaN light-emitting diodes
(2005-10-01)
Hsu, CY
;
Lan, WH
;
Wu, YCS
;
材料科學與工程學系
;
Department of Materials Science and Engineering
We have fabricated GaN-based light-emitting diodes (LEDs) using transparent indium tin oxide (ITO) for p-type contacts. The current-voltage (I-V) characteristics of the devices have been studied. When annealed at 700 degrees C, the p-n junction of the diodes became very leaky, and even electrical short circuits have been observed. According to scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometer analyses (EDS), it was found that indium (In) diffused into the LED structure with defects such as threading dislocations (TDs) or V-pits. The defects provide leakage paths to cause short circuits in p-n junctions at high annealing temperatures.