Browsing by Author "Chi, GC"

Now showing 1 - 17 of 17

A bilayer Ti/Ag ohmic contact for highly doped n-type GaN films
(1996-01-08)
Guo, JD
;
Lin, CI
;
Feng, MS
;
Pan, FM
;
Chi, GC
Ohmic contacts with low resistance are fabricated on n-type GaN films using Ti/Ag bilayer metallization. The GaN films are grown by low pressure metalorganic chemical vapor deposition (LP-MOCVD) with Si as the dopant. Ohmic characteristics are studied for films with carrier concentration range from 1.5 x 10(17) to 1.7 x 10(19) cm(-3). The lowest value for the specific contact resistivity of 6.5 x 10(-5) Ohm cm(2) is obtained without annealing. The barrier height of Ti on GaN is calculated to be 0.067 eV. (C) 1996 American Institute of Physics.
Characterization of GaN epitaxial layers on SiC substrates with AlxGa1-xN buffer layers
(1997-12-18)
Lin, CF
;
Cheng, HC
;
Feng, MS
;
Chi, GC
;
材料科學與工程學系
High quality GaN epitaxial layers were obtained with AlxGa1-xN buffer layers on 6H-SiC substrates. The low-pressure metalorganic chemical vapor deposition (LP-MOCVD) method was used. The 500 Angstrom thick buffer layers of AlxGa1-xN (0 less than or equal to x less than or equal to 1) were deposited on SiC substrates at 1025 degrees C. The FWHM of GaN (0004) X-ray curves are 2-3 arcmin, which vary with the Al content in AlxGa1-xN buffer layers. An optimum Al content is found to be 0.18. The best GaN epitaxial film has the mobility and carrier concentration about 564 cm(2) V-1 s(-1) and 1.6 x 10(17) cm(-3) at 300 K. The splitting diffraction angle between GaN and AlxGa1-xN were also analyzed from X-ray diffraction curves. (C) 1997 Elsevier Science S.A.
Characterization of p-type InxGa1-xN grown by metalorganic chemical vapor deposition
(2001-03-01)
Wen, TC
;
Lee, WI
;
Sheu, JK
;
Chi, GC
;
友訊交大聯合研發中心
This study investigates the electrical and optical characteristics of Mg-doped InxGa1-xN grown by metalorganic chemical vapor deposition. All the Mg-doped InxGa1-xN layers show p-type conduction after thermal annealing. Room temperature (RT) carrier concentration increases exponentially with an In mole fraction increase. The highest hole concentration of bull; Mg-doped InxGa1-xN is 1.65 x 10(19) cm(-3). Also, the RT photoluminescence (PL) spectra of Mg related emissions in InxGa1-xN are displayed. However, the PL peak intensity becomes weak after the post-annealing process on Mg-doped InxGa1-xN. This degradation might be created by the surface dissociation during the post-annealing process. (C) 2001 Elsevier Science Ltd. All rights reserved.
Growth and characterizations of GaN on SiC substrates with buffer layers
(1997-09-01)
Lin, CF
;
Cheng, HC
;
Chi, GC
;
Feng, MS
;
Guo, JD
High quality GaN epitaxial layers were grown on 6H-SiC substrates by using low-pressure metalorganic chemical vapor deposition method, Samples employing a three-period GaN/Al0.08Ga0.92N (100 Angstrom/100 Angstrom) as a buffer layer produce a good quality GaN epitaxial layer, with mobility and carrier concentration of 612 cm(2)/V.s and 1.3x10(17) cm(-3) (at 300 K), respectively, The enhanced electron mobility in the Al0.08Ga0.92N/GaN heterostructures is also observed, By using the van der Pauw method of Hall measurement, the sheet carrier density and mobility at 4.2 K for the Al0.08Ga0.92N/GaN heterostructure are 5.8x10(12) cm(-2) and 5300 cm(2)/V.s, respectively. Strong SdH (Shubnikov-de Haas) oscillations were observed to confirm the two-dimensional electron gas (2DEG) phenomenon at the AlGaN/GaN top heterointerface. In addition, an extra SdH oscillation also resulted from the high-duality 2DEG channel of the GaN/AlGaN bottom heterointerface. (C) 1997 American Institute of Physics.
Growth and characterizations of GaN on SiC substrates with buffer layers
(1997-09-01)
Lin, CF
;
Cheng, HC
;
Chi, GC
;
Feng, MS
;
Guo, JD
High quality GaN epitaxial layers were grown on 6H-SiC substrates by using low-pressure metalorganic chemical vapor deposition method, Samples employing a three-period GaN/Al0.08Ga0.92N (100 Angstrom/100 Angstrom) as a buffer layer produce a good quality GaN epitaxial layer, with mobility and carrier concentration of 612 cm(2)/V.s and 1.3x10(17) cm(-3) (at 300 K), respectively, The enhanced electron mobility in the Al0.08Ga0.92N/GaN heterostructures is also observed, By using the van der Pauw method of Hall measurement, the sheet carrier density and mobility at 4.2 K for the Al0.08Ga0.92N/GaN heterostructure are 5.8x10(12) cm(-2) and 5300 cm(2)/V.s, respectively. Strong SdH (Shubnikov-de Haas) oscillations were observed to confirm the two-dimensional electron gas (2DEG) phenomenon at the AlGaN/GaN top heterointerface. In addition, an extra SdH oscillation also resulted from the high-duality 2DEG channel of the GaN/AlGaN bottom heterointerface. (C) 1997 American Institute of Physics.
Improved contact performance of GaN film using Si diffusion
(2000-04-03)
Lin, CF
;
Cheng, HC
;
Chi, GC
;
Bu, CJ
;
Feng, MS
In this letter, we investigate a metalization process for reducing the contact resistance on undoped GaN layers. The Si metal source was diffused successfully into the GaN films by using SiOx/Si/GaN/Al2O3 structures. By using a high-temperature annealing process, we diffused and activated the Si atoms into the GaN film. This caused a heavy doped n-type GaN layer to be formed near the GaN surface. Under high temperatures, such as a diffusion process at 1000 degrees C, the as-deposited Ni/Al/Ti contact had good ohmic properties and a low specific contact resistivity (rho(c)) of 1.6 x 10(-3) Ohm cm(2). Rapid thermal annealing the contact at 800 degrees C for 30 s caused the rho(c) to decrease rapidly to 5.6 x 10(-7) Ohm cm(2). The Ni/Al/Ti contact characteristics on the GaN films diffused at various temperatures are also discussed. (C) 2000 American Institute of Physics. [S0003-6951(00)02114-8].
Improvement of near-ultraviolet InGaN/GaN light-emitting diodes by inserting an in situ rough SiN(x) interlayer in n-GaN layers
(2003-10-27)
Tu, RC
;
Chuo, CC
;
Pan, SM
;
Fan, YM
;
Tsai, CE
Near-ultraviolet 400-nm InGaN/GaN multiple-quantum-well light-emitting diodes (LEDs) with and without an in situ rough SiN(x) interlayer inserted into the n-GaN underlying layer were grown on c-face sapphire substrates by metalorganic vapor phase epitaxy. Inserting the SiN(x) interlayer into the n-GaN underlying layer slightly reduced leakage current induced by reducing the defect density. Additionally, an enhancement of light extraction for the LED with a SiN(x) interlayer is expected because of the increased intensity of light scattered on the SiN(x) nanomask, changing the directions of propagation of light. Consequently, the emission efficiency of an LED with an in situ rough SiN(x) interlayer doubles that without a SiN(x) interlayer. (C) 2003 American Institute of Physics.
Improvement of near-ultraviolet InGaN/GaN light-emitting diodes by inserting an in situ rough SiNx interlayer in n-GaN layers
(2003-10-27)
Tu, RC
;
Chuo, CC
;
Pan, SM
;
Fan, YM
;
Tsai, CE
Near-ultraviolet 400-nm InGaN/GaN multiple-quantum-well light-emitting diodes (LEDs) with and without an in situ rough SiNx interlayer inserted into the n-GaN underlying layer were grown on c-face sapphire substrates by metalorganic vapor phase epitaxy. Inserting the SiNx interlayer into the n-GaN underlying layer slightly reduced leakage current induced by reducing the defect density. Additionally, an enhancement of light extraction for the LED with a SiNx interlayer is expected because of the increased intensity of light scattered on the SiNx nanomask, changing the directions of propagation of light. Consequently, the emission efficiency of an LED with an in situ rough SiNx interlayer doubles that without a SiNx interlayer. (C) 2003 American Institute of Physics.
Mobility enhancements in AlGaN/GaN/SiC with stair-step and graded heterostructures
(1997-05-12)
Lin, CF
;
Cheng, HC
;
Huang, JA
;
Feng, MS
;
Guo, JD
In this letter, we report the observation of the enhanced electron mobility in three different Al0.08Ga0.92N/GaN heterostructures. These structures were deposited on (0001) 6H-SiC substrates by using the low-pressure metalorganic chemical vapor deposition method. The structure was composed of 500 Angstrom AlGaN compositional stair-step layer deposited onto 1.3 mu m GaN epitaxial layer. There is a 100 Angstrom GaN Cap layer on top of the AlGaN layer to prevent the oxidation of the AlGaN layer. By using the van der Pauw method of Hall measurement, the sheet carrier density and mobility for Al0.08Ga0.92N/GaN heterostructure are 6.6x10(12) cm(-2) and 5413 cm(2)/Vs at 77 K, respectively. This high value of mobility is, to the best of our knowledge, the first observed two-dimensional electron gas (2DEG) at the AlGaN/GaN stair-step type of heterostructure. Other interface structures such as graded composition and bulk composition structures were also prepared and 2DEG properties were observed. (C) 1997 American Institute of Physics.
Mobility enhancements in AlGaN/GaN/SiC with stair-step and graded heterostructures
(1997-05-12)
Lin, CF
;
Cheng, HC
;
Huang, JA
;
Feng, MS
;
Guo, JD
In this letter, we report the observation of the enhanced electron mobility in three different Al0.08Ga0.92N/GaN heterostructures. These structures were deposited on (0001) 6H-SiC substrates by using the low-pressure metalorganic chemical vapor deposition method. The structure was composed of 500 Angstrom AlGaN compositional stair-step layer deposited onto 1.3 mu m GaN epitaxial layer. There is a 100 Angstrom GaN Cap layer on top of the AlGaN layer to prevent the oxidation of the AlGaN layer. By using the van der Pauw method of Hall measurement, the sheet carrier density and mobility for Al0.08Ga0.92N/GaN heterostructure are 6.6x10(12) cm(-2) and 5413 cm(2)/Vs at 77 K, respectively. This high value of mobility is, to the best of our knowledge, the first observed two-dimensional electron gas (2DEG) at the AlGaN/GaN stair-step type of heterostructure. Other interface structures such as graded composition and bulk composition structures were also prepared and 2DEG properties were observed. (C) 1997 American Institute of Physics.
Observation of dislocation etch pits in epitaxial lateral overgrowth GaN by wet etching
(2002-04-01)
Wen, TC
;
Lee, WI
;
Sheu, JK
;
Chi, GC
;
電子物理學系
This work investigates dislocation etch pits in epitaxial lateral overgrowth (ELO) GaN by wet etching. A mixture of H2SO4 and H3PO4 was used as an etching solution. SEM and AFM were employed to observe the surface topography. For the as-grown sample, SEM images show the flat, smooth surface without any pits or hillocks. After the chemical etching, hexagonal shaped etch pits were observed at the edge of ELO GaN. AFM observation of etched ELO GaN displayed high densities of etch pits clustered in the "window" region and the coalescent line of two growing fronts. In contrast, the overgrowth region was nearly free of etch pits. Moreover, we observed that different sizes of etch pits dominated in "window" region and coalescent region. This implied different types dislocations dominated in these regions. (C) 2002 Elsevier Science Ltd. All rights reserved.
Properties of Mg activation in thermally treated GaN : Mg films
(2000-12-01)
Lin, CF
;
Cheng, HC
;
Chang, CC
;
Chi, GC
;
電子工程學系及電子研究所
The Mg accepters of GaN films are activated as p-type GaN with rapid thermal annealing (RTA) and furnace treatments. The GaN:Mg films are activated successfully by using the RTA system below 1000 degreesC for 1 min. After the RTA treatment, we observed a sharper linewidth and stronger emission intensities from donor to acceptor peaks in the photoluminescence spectra. By comparing the electrical properties of GaN:Mg films at optimum conditions made with RTA (800 degreesC) and furnace (700 degreesC) treatments, we find similar activated hole concentration and a higher hole mobility for GaN:Mg films with RTA treatment at 800 degreesC. A higher bulk resistivity caused by increasing nitrogen vacancies is found at higher temperature and longer time RTA treatments. Faster treatment times and lower temperatures for the GaN:Mg films were achieved with the RTA activation process. (C) 2000 American Institute of Physics. [S0021-8979(00)04120-7].
The dependence of the electrical characteristics of the GaN epitaxial layer on the thermal treatment of the GaN buffer layer
(1996-06-24)
Lin, CF
;
Chi, GC
;
Feng, MS
;
Guo, JD
;
Tsang, JS
The GaN buffer layer was grown on the sapphire substrate by low-pressure metalorganic chemical vapor deposition (LP-MOCVD) at 525 degrees C. The following 1.3 mu m epitaxial GaN growth was carried out at 1025 degrees C. We varied the ramping rate from 12.5 to 100 degrees C/min to study the quality of the epitaxial GaN. It has been found that the x-ray peak width, photoluminescence (PL) linewidth, Hall mobilities, and carrier concentrations of GaN epitaxial layer strongly depend on the in situ thermal ramping rate. An optimum thermal ramping rate was found to be of 20 degrees C/min. The maximum mobility is 435 cm(2)/V s at carrier concentration of 1.7 x 10(17) cm(-3). The minimum full width at half maximum (FWHM) of x ray and PL were 5.5 min and 12 meV occur at a ramping rate of 20 degrees C/min. The decrease of the mobility at high and low ramping rate can be attributed to the thermal stress and the reevaporation of the GaN buffer layer. (C) 1996 American Institute of Physics.
Thermal annealing effects on the optical gain of InGaN/GaN quantum well structures
(2003-03-01)
Chen, CC
;
Hsueh, TH
;
Ting, YS
;
Chi, GC
;
Chang, CA
In this work, the variation of the optical gain in the InGaN/GaN quantum well after thermal annealing is simulated. The potential profile change of the quantum well resulting from the interdiffusion of Ga and In atoms across the interface of the well and the barrier during the thermal treatments is assumed to follow Fick's law. The results show that the thermal annealing can induce an increase of the optical gain in the InGaN/GaN quantum well. The maximum optical gain can be obtained at a diffusion length of 0.4 nm of In and Ga atoms. However, an excessive annealing may result in decreasing the optical gain. There is a good agreement between the experimental data in literature and the optimized diffusion length studied in this work. (C) 2002 Elsevier Science Ltd. All rights reserved.
Ultra-high-density InGaN quantum dots grown by metalorganic chemical vapor deposition
(2004-02-15)
Tu, RC
;
Tun, CJ
;
Chuo, CC
;
Lee, BC
;
Tsai, CE
This study examined how the duration of SiNx treatment on an underlying GaN layer affects the optical property, surface morphology and density of following InGaN quantum dots (QDs). InGaN QDs with extremely high density of near 3 x 10(11) cm(-2) exhibited strong photoluminescence (PL) emission at room temperature (RT). Increasing the duration of the SiN, treatment of the underlying GaN layer, the RT-PL peak of the following InGaN nano-islands and QDs was found to be red-shifted from the violet to the greenish region, and the spectrum was broadened. Additionally, the average height of InGaN nano-islands and QDs increased with the duration of SiNs treatment, explaining the redshift of the RT-PL peak.
W ohmic contact for highly doped n-type GaN films
(2000-04-01)
Lin, CF
;
Cheng, HC
;
Chi, GC
;
電子工程學系及電子研究所
;
奈米中心
Ohmic contacts with low resistance and low barrier height were fabricated on n-type GaN films using W metallization. The n-type GaN films were grown by low pressure metalorganic chemical vapor deposition (LPMOCVD) with Si as the dopant. Ohmic characteristics were studied for GaN films with Si carrier concentration varying from 1.4 x 10(17) to 1.8 x 10(19) cm(-3). The specific contact resistivity were reduced with increasing Si-doping concentration on as-deposited W/GaN films, and the lowest value was 3.6 x 10(-4) Ohm cm(2) on n-type GaN with a concentration of 1.8 x 10(19) cm(-3). After rapid thermal annealing (RTA) treatment on W/GaN films at 1000 degrees C for 30 s, the specific contact resistivity were reduced to 1 x 10(-4) Ohm cm(2). The W metal on n-type GaN films, show that good thermal stability varied the annealing temperatures. The barrier height of as-deposited W metal on GaN is calculated to be 0.058 eV. (C) 2000 Elsevier Science Ltd. All rights reserved.
X-ray crystallographic study of GaN epitaxial films on Al2O3(0001) substrates with GaN buffer layers
(1996-06-10)
Lee, CH
;
Chi, GC
;
Lin, CF
;
Feng, MS
;
Guo, JD
Samples of GnN(0001) epitaxial films on sapphire Al2O3(0001) with different thicknesses of GaN buffer layers were characterized by x-ray diffraction method in both in-plane and plane-normal directions. The results show that all the epitaxial films Me of good quality with the GaN[<10(1)over bar 0>] parallel to Al2O3[<11(2)over bar 0>] and GaN[<1(2)over bar 10>]parallel to Al2O3[<1(1)over bar 00>]. This arrangement of crystal orientation can be attributed to the chemical potential overriding the lattice spacing mismatch. The x-my results also indicate that the crystal coherence lengths; in the in-plane direction are smaller than those measured in the plane-normal direction, i.e., a columnar-like structure normal to the film is observed; The rocking curve widths in the in-plane direction are also larger than those measured in the plane-normal direction. In-plane measurement of rocking curve and coherence length are essential physical quantities directly related to the electron mobility which was measured predominantly in the in-plane direction. The best epitaxial structure is the one grown with 10 nm buffer layer. (C) 1996 American Institute of Physics.