Browsing by Author "Lai, FI"

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1.3-mu m InAs-InGaAs quantum-dot vertical-cavity surface-emitting laser with fully doped DBRs grown by MBE
(2006-01-01)
Yu, HC
;
Wang, JS
;
Su, YK
;
Chang, SJ
;
Lai, FI
We report InAs-InGaAs quantum-dot vertical-cavity surface-emitting lasers (VCSELs) grown by molecular beam epitaxy with fully doped n- and p-doped AlGaAs distributed Bragg reflectors and including an AlAs layer to form a current and waveguiding aperture. The metal contacts are deposited on a topmost p(+) (GaAs)-Ga-. contact layer and on the bottom surface of the n(+)-GaAs substrate. This conventional selectively oxidized top-emitting device configuration avoids the added complexity of fabricating intracavity or coplanar ohmic contacts. The VCSELs operate continuous-wave at room temperature with peak output powers of 0.33 mW and differential slope efficiencies up to 0.23 W/A. The peak lasing wavelengths are near 1.275 mu m, with a sidemode suppression ratio of 28 dB.
10 Gb/s single-mode vertical-cavity surface-emitting laser with large aperture and oxygen implantation
(2004-08-01)
Lai, FI
;
Hsueh, TH
;
Chang, YH
;
Kuo, HC
;
Wang, SC
High-speed single transverse mode 850 nm vertical cavity surface emitting lasers (VCSELs) with large emission aperture with a diameter of 8 Am were fabricated. These VCSELs exhibit good performance with threshold currents of 1.5 mA, a single transverse mode emission within the full operational range and a maximum output power of 3.8 mW. The large aperture is advantageous to these VCSELs with a smaller dynamic resistance (60 Omega) than that of conventional single-mode VCSEL. These single-mode VCSELs also demonstrate superior high-speed performance up to 10 Gb s(-1).
Catalyst-free GaN nanorods grown by metalorganic molecular beam epitaxy
(2006-05-01)
Kuo, SY
;
Kei, CC
;
Hsiao, CN
;
Chao, CK
;
Lai, FI
High-density GaN nanorods with outstanding crystal quality were grown on c-sapphire substrates by radio-frequency plasma-assisted metalorganic molecular beam epitaxy under catalyst- and template-free growth condition. Morphological and structural characterization of the GaN nanorods was employed by X-ray diffraction, energy dispersive X-ray spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy (HRTEM). These results indicate that the rod number density can reach 1 x 10(10) cm(-2) and the nanorods are well-aligned with preferentially oriented in the c-axis direction. Meanwhile, no metallic (Ga) droplet was observed at the end of the rods, which is the intrinsic feature of vapor-liquid-solid method. Nanorods with no traces of any extended defects, as confirmed by TEM, were obtained as well. In addition, optical investigation was carried out by temperature- and power-dependent micro-photoluminescence (mu-PL). The PL peak energies are red-shifted with increasing excitation power, which is attributed to many-body effects of free carriers under high excitation intensity. The growth mechanism is discussed on the basis of the experimental results. Catalyst-free GaN nanorods presented here might have a high potential for applications in nanoscale photonic devices.
Effects of doping concentration and annealing temperature on properties of highly-oriented al-doped ZnO films
(2006-01-18)
Kuo, SY
;
Chen, WC
;
Lai, FI
;
Cheng, CP
;
Kuo, HC
Transparent and conductive high-preferential c-axis-oriented Al-doped zinc oxide (ZnO:Al, AZO) thin films have been prepared by the sol-gel route. Film deposition was performed by spin-coating technique on Si(1 0 0) and glass substrate. Structural, electrical and optical properties were performed by XRD, SEM, four-point probe, photoluminescence (PL) and UV-VIS spectrum measurements. The effects of annealing temperature and dopant concentration on the structural and optical properties are well discussed. It was found that both annealing temperature and doping concentration alter the microstructures of AZO films. Also, PL spectra show two main peaks centered at about 380 nm (UV) and 520 nm (green). The variation of UV-to-green band emission was greatly influenced by annealing temperatures and doping concentration. Reduction in intensity ratio of UV-to-green might possibly originate from the formation of Al-O bonds and localized Al-impurity states. The minimum sheet resistance of 10(4)ohm/rectangle was obtained for the film doped with 1.6mol% Al, annealed at 750 degrees C. Meanwhile, all AZO films deposited on glass are very transparent, between 80% and 95% transmittance, within the visible wavelength region. These results imply that the doping concentration did not have significant influence on transparent properties, but improve the electrical conductivity and diversify emission features. (c) 2005 Elsevier B.V. All rights reserved.
Enhancement of light-output of GaN-based light-emitting diodes by bias-assisted photoelectrochemical oxidation of p-GaN in H2O
(2005)
Lai, FI
;
Chen, WY
;
Kao, CC
;
Lin, CF
;
Kuo, HC
An enhancement of GaN-based LEDs light output using photoelectrochemical (PEC) oxidation method via H2O on the p-GaN surface was demonstrated. The output light was improved 37% after 45min PEC oxidation.
Fabrication and characteristics of high-speed oxide-confined VCSELs using InGaAsP-InGaP strain-compensated MQWs
(2004-12-01)
Chang, YH
;
Kuo, HC
;
Lai, FI
;
Chang, YA
;
Lu, CY
This paper presents the fabrication and characteristics of high-performance 850-mn InGaAsP-InGaP strain-compensated multiple-quantum-well (MQW) vertical-cavity surface-emitting lasers (VCSELs). The InGaAsP-InGaP MQW's composition was optimized through theoretical calculations, and the growth condition was optimized using photoluminescence. These VCSELs exhibit superior performance with characteristics threshold currents similar to0.4 mA and slope efficiencies similar to0.6 mW/mA. The threshold current change with temperature is less than 0.2 mA, and the slope efficiency drops less than similar to30% when the substrate temperature is raised from room temperature to 85degreesC. A high modulation bandwidth of 14.5 GHz and a modulation current efficiency factor of 11.6 GHz/(mA) (1/2) are demonstrated. The authors have accumulated life test data up to 1000 h at 70degreesC/8 mA.
Fabrication and micro-photoluminescence investigation of Mg-doped gallium nitride nanorods
(2005-04-01)
Chang, YH
;
Hsueh, TH
;
Lai, FI
;
Chang, CW
;
Yu, CC
High-density magnesium (Mg)-doped gallium nitride (GaN) nanorods were fabricated by inductively coupled plasma reactive ion etching from a GaN film and had a mean length of approximately 50nm. A large blue-shift was observed in the photoluminescence (PL) peak energy of Mg-doped GaN nanorods under HeCd laser (325 nm) excitation. The PL spectra of the nanorods show a typical donor-acceptor-pair (DAP) emission at approximately 3.0 eV with a large blue-shift compared to that of the Mg-doped GaN film. The blue-shift energy increases from 8 meV to 67 meV as the excitation intensity varies from 12 kW/cm(2) to 56 kW/cm(2). Possible reasons for the power dependence of the spectral shift in the PL emission energy are discussed.
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 magnesium-doped gallium nitride nanorods and microphotoluminescence characteristics
(2006-05-01)
Lai, FI
;
Kuo, SY
;
Chang, YH
;
Huang, HW
;
Chang, CW
High density magnesium (Mg)-doped gallium nitride (GaN) nanorods were fabricated by inductively coupled plasma reactive ion etching technique from the epitaxial film. Under the fixed Cl-2/Ar flow rate of 10/25 SCCM (SCCM denotes cubic centimeter per minute at STP) and inductively coupled plasma/bias power of 200/200 W, the nanorods 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. A large blueshift was observed in the photoluminescence (PL) peak energy of Mg-doped GaN nanorods under HeCd laser (325 nm) excitation. The PL spectra of nanorods show a typical donor-acceptor-pair emission around 3.0 eV with a large blueshift compared to the Mg-doped GaN film. The blueshift energy increases from 8 to 67 meV as the excitation intensity varies from 12 to 56 kW/cm(2). Possible reasons causing the power dependence of spectral shift in the PL emission energy are discussed. 2006 American Vacuum Society.
High performance 1.27 mu m InGaAs : Sb-GaAsP quantum wells vertical cavity surface emitting laser
(2004)
Kuo, HC
;
Chang, YH
;
Lai, FI
;
Lee, PT
;
Wang, SC
High performance 1.27 mum InGaAs:Sb-GaAsP vertical cavity surface emitting lasers (VCSELs) are demonstrated with superior performance and temperature stability. The threshold current changes between 1.8 and 1.1 mA and the slope efficiency drops less than similar to30% when the temperature raised from room temperature to 70degreesC. High modulation bandwidth of 10.1 (8.8) GHz at 25degreesC (70degreesC) and bias current 6 mA are demonstrated.
High speed (> 13 GHz) modulation of 850 nm vertical cavity surface emitting lasers (VCSELs) with tapered oxide confined layer
(2005-06-01)
Chang, YH
;
Kuo, HC
;
Lai, FI
;
Tzeng, KF
;
Yu, HC
Improved oxide-implanted VCSELs utilising the tapered oxide layer are presented. The VCSELs exhibited similar static performance, but superior modulation bandwidth up to 13.2 GHz, compared with conventional blunt oxide VCSELs. The damping rate was reduced two times in the tapered oxide VCSEL and therefore enhanced the maximal modulation bandwidth. A very clean eye was demonstrated from the improved VCSEL with a rising time of 26 ps, falling time of 40 ps and jitter of less than 20 ps, operating at 10 Gbit/s with 6 mA bias and 6 dB extinction ratio. A comprehensive small signal measurement and analysis was conducted. Based on the equivalent circuit model, the extrinsic bandwidth limitation of the tapered oxide VCSELs was determined.
High temperature stability 850-nm In0.15Al0.08Ga0.77As/Al0.3Ga0.7As vertical-cavity surface-emitting laser with single Al0.75Ga0.25As current blocking layer
(2005)
Chang, YA
;
Lai, FI
;
Yu, HC
;
Kuo, HC
;
Laih, LW
In this paper, we employed a high bandgap Al0.75Ga0.25As layer acting as an electronic blocking layer in the upper In0.15Al0.08Ga0.77As/Al0.3Ga0.7As active region before the growth of p-type layers of 850-nm vertical-cavity surface-emitting lasers (VCSELs). A threshold current of 1.33mA and slope efficiency of 0.53W/A at 25 degrees C were obtained, and the temperature dependent light output and voltage versus current (L-I-V) characteristics showed that the VCSELs with a high bandgap Al0.75Ga0.25As layer were more stable when the substrate temperature was in a range of 25-95 degrees C. The threshold current increased with temperature up to 95 degrees C was less than 21% and the slope efficiency dropped only 24.5%.
High-speed (> 10 Gbps) 850 nm oxide-confined vertical cavity surface emitting lasers (VCSELs) with a planar process and reduced parasitic capacitance
(2004-07-01)
Chang, YH
;
Lai, FI
;
Lu, CY
;
Kuo, HC
;
Yu, HC
This study reports the high-speed performance of 850 nm oxide-confined vertical cavity surface emitting lasers (VCSELs) with a planar process and reduced parasitic capacitance. The parasitic capacitance of VCSELs was reduced using additional proton implantation. The small signal modulation bandwidth which was restricted by electric parasitic capacitance expanded from 2.3 GHz to 9 GHz after proton implantation. The reflection coefficient showed that the electric parasitic pole exceeded 20 GHz. An eye diagram of VCSEL with reduced parasitic capacitance operating at 10 Gps with 6 mA bias and 6 dB extinction ratio showed a very clean eye with a jitter of less than 20 ps.
High-speed characteristics of large-area single-transverse-mode vertical-cavity surface-emitting lasers
(2003-10-16)
Hsueh, TH
;
Kuo, HC
;
Lai, FI
;
Laih, LH
;
Wang, SC
The single transverse mode operation of VCSELs with low threshold current (I-th) of 1.5 mA, slope efficiencies about 0.35 W/A, high optical output power of 3.8 mW and speed performance of 10 Gbit/s is reported. The laser has continuous-wave operation and employs oxygen implantation, MOCVD regrowth and selective oxidation on semi-insulating GaAs substrate.
High-speed modulation of InGaAs : Sb-GaAs-GaAsP quantum-well vertical-cavity surface-emitting lasers with 1.27-mu m emission wavelength
(2005-03-01)
Kuo, HC
;
Chang, YH
;
Yao, HH
;
Chang, YA
;
Lai, FI
1.27-mum InGaAs: Sb-GaAs-GaAsP vertical-cavity surface-emitting lasers (VCSELs) were grown by metal-organic chemical vapor deposition and exhibited excellent performance and temperature stability. The threshold current changes from 1.8 to 1.1 mA and the slope efficiency falls less than similar to35% as the temperature raised from room temperature to 70 degreesC. With a bias current of only 5 mA, the 3-dB modulation frequency response was measured to be 8.36 GHz, which is appropriate for 10-Gb/s operation. The maximal bandwidth is measured,to be 10.7 GHz with modulation current efficiency factor (MCEF) of similar to5.25 GHz/(mA)(1/2). These VCSELs also demonstrate high-speed modulation up to 10 Gb/s from 25 degreesC to 70 degreesC.
Improvement of high speed performance for 10-Gb/s 850-nm VCSELs using InGaAsP/InGaP strain-compensated MQWs
(2004)
Chang, YS
;
Kuo, HC
;
Lai, FI
;
Chang, YA
;
Laih, LH
We present in this paper the MOCVD growth and characterization of high performance 850nm InGaAsP/InGaP strain-compensated MQWs vertical-cavity surface-emitting lasers (VCSELs). These VCSELs exhibit superior characteristics, with threshold currents similar to0.4 mA, and slope efficiencies similar to 0.6 mW/mA. The threshold current change is less than 0.2 mA and the slope efficiency drops by less than similar to30% when the substrate temperature is raised from room temperature to 85degreesC. These VCSELs also demonstrate high speed modulation bandwidth up to 12.5Gbit/s from 25degreesC to 85degreesC.
Improvement of kink characteristic of proton implanted VCSEL with ITO overcoating
(2004)
Lai, FI
;
Chang, YH
;
Laih, LH
;
Kuo, HC
;
Wang, SC
Proton implanted VCSEL has been demonstrated with good reliability and decent modulation speed up to 1.25 Gb/s. However, kinks in current vs light output (L-I) has been always an issue in the gain-guided proton implant VCSEL. The kink related jitter and noise performance made it difficult to meet 2.5 Gb/s (OC-48) requirement. The kinks in L-I curve can be attributed to non-uniform carrier distribution induced non-uniform gain distribution within emission area. In this paper, the effects of a Ti/TO transparent over-coating on the proton-implanted AlGaAs/GaAs VCSELs (15um diameter aperture) are investigated. The kinks distribution in L-I characteristics from a 2 inch wafer is greatly improved compared to conventional process. These VCSELs exhibit nearly kink-free L-I output performance with threshold currents similar to3 mA, and the slope efficiencies similar to 0.25 W/A. The near-field emission patterns suggest the Ti/ITO over-coating facilitates the current spreading and uniform carrier distribution of the top VCSEL contact thus enhancing the laser performance. Finally, we performed high speed modulation measurement. The eye diagram of proton-implanted VCSELs with Ti/ITO transparent over-coating operating at 2.125 Gb/s with 10mA bias and 9dB extinction ratio shows very clean eye with jitter less than 35 ps.
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].
Performance of 850 nm AlGaAs/GaAs implanted VCSELs utilizing silicon implantation induced disordering
(2003-10-01)
Lai, FI
;
Hsueh, TH
;
Chang, YH
;
Shu, WC
;
Lai, LH
In this paper, we report a novel implanted vertical surface emitting lasers (VCSELs) utilizing silicon implantation induced disordering. The VCSELs exhibit kink-free current-light Output performance with threshold currents similar to2.4 mA, and the slope efficiencies similar to0.45 W/A. The threshold current change with temperature is minimal and the slope efficiency drops less than similar to30% when the substrate temperature is raised to 90 degreesC. The eye diagram of VCSEL operating at 2.125 Gb/s with 7 mA bias and 10 dB extinction ratio shows very clean eye with jitter less than 30 ps. We have accumulated life test data up to 5000 It at 100 degreesC/20 mA with exceptional reliability and the WHTOL (high temperature and high humidity 85 degreesC/85 operating lifetime) biased at 8 mA has passed over 2000 h. (C) 2003 Elsevier Ltd. All rights reserved.
Photoluminescence from In0.3Ga0.7N/GaN multiple-quantum-well nanorods
(2005-04-01)
Hsueh, TH
;
Huang, HW
;
Lai, FI
;
Sheu, JK
;
Chang, YH
The fabrication of ln(0.3)Ga(0.7)N/GaN multiple-quantum-well nanorods with diameters of 60-100 nm and their optical characteristics performed by micro-photoluminescence measurements are presented. The nanorods were fabricated by inductively coupled plasma dry etching from a light-emitting diode wafer. The structure and surface properties of fabricated nanorods were verified by the field emission scanning electron microscopy and the transmission electron microscopy. The photoluminescence (PL) spectra with sharp linewidths of typically 1.5 nm were observed at 4 K. The excitation-power-dependent spectra show that no energy shift was observed for these sharp peaks. Moreover, increasing the excitation power instead leads to an occurrence of new, sharp PL peaks at the higher energy tail of the PL spectra, which suggest that excitons are strongly confined in quantum-dot-like regions or localization centres.