Browsing by Author "Guo, JD"

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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.
Electrical properties of multiple high-dose Si implantation in p-GaN
(1999-07-15)
Lai, WC
;
Yokoyama, M
;
Tsai, CC
;
Chang, CS
;
Guo, JD
This work performs Si ion implantation the electrical conductive type of the p-GaN film from p-type to n-type. Multiple implantation method is also used to form a uniform Si implanted region in the p-type GaN epitaxial layer. Implant energies for the multiple implantation are 40, 100, and 200 KeV. The implant dose is 5 x 10(15) cm(-2) for each implant energy. After implantation, the samples are annealed in a N-2 ambient for different annealing temperatures and annealing times. The activation efficiency reaches as high as 20% when annealing the sample at 1000 degrees C. The carrier activation energy is about 720 meV. The low activation energy indicates that the hopping process mechanism is the dominant mechanism for the activation of the Si implantation in p-GaN. Moreover, the rectifying I-V characteristic of the p-n GaN diode is also examined.
Electrical properties of the Si implantation in Mg doped p-GaN
(1999-11-01)
Lai, WC
;
Yokoyama, M
;
Tsai, CC
;
Chang, CS
;
Guo, JD
This work performs Si ion implantation to activate and convert the electrical conduction of p-GaN films from p-type to n-type. Multiple implantation method is used to form a uniform Si implanted region in the p-type GaN epitaxial layer. Implantation energies for the multiple implantation are 10, 100, and 200 keV. The implantation dose is 5 x 10(15) cm(2) for each implantation energy. After implantation, the samples were annealed in an N-2 ambient for different annealing temperatures and annealing times. The activation efficiency reaches as high as 20% when annealing the sample at 1000 degrees C,. The carrier activation energy is about 720 meV. The low activation energy indicates that the hopping process mechanism is the dominant mechanism for the activation of the Si implant in p-GaN. In addition, the rectifying I-V characteristic of the p-n GaN diode is also examined.
Epitaxial growth of the GaN film by remote-plasma metalorganic chemical vapor deposition
(1998-10-01)
Lai, WC
;
Chang, CY
;
Yokoyama, M
;
Guo, JD
;
Tsang, JS
GaN films were successfully grown by the remote-plasma metalorganic chemical vapor deposition (RPMOCVD) system. The composition of the GaN films could be tuned from nitrogen-rich to stoichiometric growth by varying the mole flow rate of trimethylgallium (TMGa). A hypothesis concerning the collisions between excited nitrogen and TMGa was also brought up. The collision between excited nitrogen and TMGa influences the characteristics of surface morphology, composition, growth rate, and growth mechanism. The characteristics of the GaN film were optimized by changing the growth conditions. The narrowest FWHM of the double-crystal X-ray rocking curve is about 0.2 degrees. Under optimized conditions, the composition of the GaN film is almost the same as that of the reference GaN film grown by MOCVD.
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.
High-performance An/Ti/Ge/Pd ohmic contacts on n-Type In0.5Ga0.5P
(1996-04-01)
Chai, CY
;
Wu, JW
;
Guo, JD
;
Huang, JA
;
Lai, YL
High-performance Au/Ti/Ge/Pd ohmic contacts on n(+)-In0.5Ga0.5P have been fabricated for the first time. Using an n(+)-In0.5Ga0.5P epitaxial layer grown by low pressure metalorganic chemical vapor deposition (LP-MOCVD) with a Si dopant concentration of about 2 x 10(18) cm(-3), the minimum specific contact resistivity is as low as 1.2 x 10(-5) Ohm . cm(2), which is much lower than that of AuGeNi contacts after rapid thermal annealing at 400 degrees C for 60 s. The thermal stability of the Au/Ti/Ge/Pd system is significantly higher than that of conventional AuGeNi due to the introduction of the Ti barrier layer. Many holes and islands are observed on the surfaces of samples annealed at high temperature. The outdiffusion of P from the decomposed In0.5Ga0.5P substrate and agglomeration of Pd and Ge are the primary causes of contact degradation.
Investigation of the indium atom interdiffusion on the growth of GaN/InGaN heterostructures
(1997-03-01)
Tsang, JS
;
Guo, JD
;
Chan, SH
;
Feng, MS
;
Chang, CY
The influence of the growth procedure on the optical quality of InGaN grown on GaN has been investigated. The photoluminescence spectrum of the sample with a low-temperature-grown GaN cap layer or a graded-temperature-grown GaN cap layer has a shorter peak wavelength than that of the sample grown with a normal-temperature-grown GaN layer. The shift of the peak wavelength increases with the increase of the layer thickness for the sample with the low-temperature-gown GaN. This is because the defects contained in the low-temperature-grown GaN cap layer induce the outdiffusion of In atoms during the temperature-ramped procedure. The narrower linewidths and higher intensities of the PL spectra for InGaN after In outdiffusion may be due to the reduction of the strains, dislocations or defects. The Raman spectra and the Auger electron spectra also indicate that the low-temperature-grown GaN has a lot of defects which reduce the phonon peak intensity and induce the interdiffusion of In atom during the growth of GaN/InGaN heterostructures.
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.
Reactive ion etching of GaN with BCl3/SF6 plasmas
(1996-07-01)
Feng, MS
;
Guo, JD
;
Lu, YM
;
Chang, EY
;
材料科學與工程學系
Reactive ion etching (RIE) with BCl3/SF6 plasmas of high quality GaN films grown by low pressure metallorganic chemical vapor deposition (LP-MOCVD) is reported. A high etch rate of 2100 Angstrom min(-1) was achieved with BCl3/SF6 plasmas at gas pressure 40 mtorr, total gas flow rate 40 seem, and radio-frequency (RF) power 300 W. The parameters affecting the etch rates such as BCl3/SF6 flow ratio, total gas pressure, RF power and self-bias voltage have been studied. Results indicate that under high RF power (300 W) the radical concentration is an etch rate-limiting factor at lower BCl3/SF6 pressure (lower than 40 mtorr), while self-bias voltage (ion bombardment) is a rate-limiting factor at higher pressure (more than 40 mtorr). Under lower RF power (150 W), self-bias voltage becomes the dominant factor of etch rate. Scanning electron microscopy (SEM) shows that the etched profile is highly anisotropic, and the etched area has some columnar residues due to Al compound contamination from the Al cathode during RIE.
Reactive ion etching of GaN with BCl3/SF6 plasmas
(1996-07-01)
Feng, MS
;
Guo, JD
;
Lu, YM
;
Chang, EY
;
材料科學與工程學系
Reactive ion etching (RIE) with BCl3/SF6 plasmas of high quality GaN films grown by low pressure metallorganic chemical vapor deposition (LP-MOCVD) is reported. A high etch rate of 2100 Angstrom min(-1) was achieved with BCl3/SF6 plasmas at gas pressure 40 mtorr, total gas flow rate 40 seem, and radio-frequency (RF) power 300 W. The parameters affecting the etch rates such as BCl3/SF6 flow ratio, total gas pressure, RF power and self-bias voltage have been studied. Results indicate that under high RF power (300 W) the radical concentration is an etch rate-limiting factor at lower BCl3/SF6 pressure (lower than 40 mtorr), while self-bias voltage (ion bombardment) is a rate-limiting factor at higher pressure (more than 40 mtorr). Under lower RF power (150 W), self-bias voltage becomes the dominant factor of etch rate. Scanning electron microscopy (SEM) shows that the etched profile is highly anisotropic, and the etched area has some columnar residues due to Al compound contamination from the Al cathode during RIE.
Schottky contact and the thermal stability of Ni on n-type GaN
(1996-08-01)
Guo, JD
;
Pan, FM
;
Feng, MS
;
Guo, RJ
;
Chou, PF
The Schottky barrier height of Ni on n-GaN has been measured to be 0.56 and 0.66 eV by capacitance-voltage (C-V) and current-density-temperature (J-T) methods, respectively. Gallium nickel (Ga4Ni3) is formed as Ni is deposited on the GaN film, which affects the barrier height markedly. The thermal stability of Ni on GaN is also investigated by annealing these specimens at various temperatures. Specimen annealing at temperatures above 200 degrees C leads to the formation of nickel nitrides Ni3N and Ni4N at the interface of Ni and GaN. These interfacial compounds change the measured barrier height to 1.0 and 0.8 eV by C-V and J-T methods, respectively. Comparisons of Schottky characteristics of Ni with those of Pt, Pd, Au, and Ti are also discussed. (C) 1996 American Institute of Physics.
Study of a common deep level in GaN
(1999)
Wen, TC
;
Lee, SC
;
Lee, WI
;
Guo, JD
;
Feng, MS
A deep level with the activation energy around 0.45 similar to 0.6eV has persistently appeared in GaN samples grown by hydride vapor-phase epitaxy, organometallic vapor-phase epitaxy and molecular beam epitaxy. However, the origin of this deep level still remains unclear. In this study, we investigated this deep level trap E2 of GaN films by using deep level transient spectroscopy. The GaN films were grown by a conventional low pressure organometallic vapor-phase epitaxy technique with different V/III ratios. Frequency-dependent capacitance measurement was performed to determine the most proper frequency for capacitance measurements Capacitance-voltage measurements were then applied to obtain the carrier concentrations. The carrier concentration became higher as the flow rate of NH3 got lower. The deep level E2 is found in GaN samples grown with higher V/III ratios. The trap concentration of level E2 increased with increasing NH3 flow rate. Compared with the theoretical prediction of the nitrogen antisite level in GaN, the level E2 was believed to be related to nitrogen antisites.
Study of Schottky barriers on n-type GaN grown by LP-MOCVD
(1995)
Guo, JD
;
Feng, MS
;
Pan, FM
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
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.
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.