Browsing by Author "Chan, SH"

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Activation of p-type GaN in a pure oxygen ambient
(2001-05-15)
Wen, TC
;
Lee, SC
;
Lee, WI
;
Chen, TY
;
Chan, SH
In this study, we activated p-type GaN in a pure oxygen ambient by rapid thermal annealing. The sheet resistance of p-type GaN was greatly reduced from > 10(7) Omega/square to 7.06 x 10(4) Omega/square after annealing in oxygen ambient at 500 degreesC, The photoluminescence intensity of blue emission increased by one order of magnitude compared to the as-grown sample. Moreover, the sheet resistance of p-type GaN annealed in pure oxygen ambient is lower than that of p-type GaN annealed in nitrogen ambient. The carrier concentrations of the samples annealed in oxygen ambient are higher than those annealed in nitrogen ambient. The better activation of p-type GaN in oxygen ambient is due to the higher activity of oxygen than that of nitrogen. Oxygen would remove hydrogen that passivates Ma atoms by forming H2O at a lower temperature.
Direct focusing modifications of elliptical Gaussian beam by non-circular apertures
(1998-11-01)
Chan, SH
;
Shiue, SG
;
Lu, MH
;
光電工程研究所
;
Institute of EO Enginerring
For focusing the elliptical Gaussian beam directly, the effects of a non-circular aperture on the focusing properties are studied. The focusing properties for different shapes of apertures, which include a circle, an ellipse and a rectangle, are calculated and compared. Moreover, for different elliptical Gaussian beams, an empirical aperture selection rule that can be used to circularize the focusing spot is proposed. The energy transmission ratios are also considered in this paper.
Direct focusing modifications of elliptical Gaussian beam by non-circular apertures
(1998-11-01)
Chan, SH
;
Shiue, SG
;
Lu, MH
;
光電工程學系
;
Department of Photonics
For focusing the elliptical Gaussian beam directly, the effects of a non-circular aperture on the focusing properties are studied. The focusing properties for different shapes of apertures, which include a circle, an ellipse and a rectangle, are calculated and compared. Moreover, for different elliptical Gaussian beams, an empirical aperture selection rule that can be used to circularize the focusing spot is proposed. The energy transmission ratios are also considered in this paper.
Effects of O-2 plasma treatment on the electric and dielectric characteristics of Ba0.7Sr0.3TiO3 thin films
(2000-04-01)
Leu, CC
;
Chan, SH
;
Chen, HY
;
Horng, RH
;
Wuu, DS
The effects of the O-2 plasma treatment on the electric and dielectric characteristics of Ba0.7Sr0.3TiO3 (BST) thin films were investigated. As a result of the exposure of the as-deposited or the annealed BST films to the O-2 plasma, the leakage current density of the BST films can be improved. Typically, the leakage current density can decrease by three orders of magnitude as compared that of the non-plasma treated sample at an applied voltage of 1.5 V. It is found that the plasma treatment changes the surface morphology. The capacitance of the BST films was reduced by 10%similar to 30%. The improvement of the leakage current density and the reduction of a dielectric constant for the plasma treated samples could be attributed to the reduction of carbon contaminations of BST thin films. The 10 year life time of the time-dependent dielectric breakdown (TDDB) studies indicates that all the samples have a life time of over 10 years of operation at a voltage bias of 1 V. (C) 2000 Elsevier Science Ltd. Al rights reserved.
Effects of rapid thermal annealing on Si delta-doped GaInP grown by low pressure metalorganic chemical vapor deposition
(1995-12-01)
Wang, CJ
;
Feng, MS
;
Chan, SH
;
Wu, JW
;
Chang, CY
We have investigated the effects of rapid thermal annealing on the Si delta-doped GaInP. The spatial localization of carriers was derived and used to determine the diffusion coefficient of Si in GaInP by the capacitance-voltage measurement. We found an unusual mobility change of Si delta-doped GaInP after annealing from Hall-effect measurement. The compensation effect of Si amphoteric property could not be used to explain this behavior. From photoluminescence spectra, it is suggested that the ordered/disordered transformation is the dominate factor for mobility increase after annealing. On the contrary, the degradation of quantum confinement in delta-doped structure by dopant diffusion after annealing is responsible for the decrease of mobility. Therefore, the behavior of mobility could be considered as a competition result of these two mechanisms.
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 electrical characterization of Si delta-doped GaInP by low pressure metalorganic chemical vapor deposition
(1996-05-15)
Wang, CJ
;
Feng, MS
;
Chan, SH
;
Chang, CY
;
Wu, JH
The growth and electrical characterization of Si delta-doped GaInP grown by low-pressure metalorganic chemical vapor deposition are reported in this article. It was found that the sheet carrier density saturated as a function of doping time or flow rate. Because of the limitations of Hall-effect measurements, the saturation was explained as the result of electron population in satellite L valley. The mobility enhancement was observed for the delta-doped structure with an enhancement factor of 2-3. A sharp capacitance-voltage profile with a full width at half-maximum of 30 Angstrom was obtained. Depletion-mode Si delta-doped GaInP field-effect transistors with a gate length of 2 mu m and gate width of 50 mu m were fabricated and showed good device pinch-off characteristics. The extrinsic maximum transconductance of 92 mS/mm was obtained and a broad plateau transconductance profile was observed to confirm the electron confinement in the V-shape potential well of a delta-doped GaInP layer. (C) 1996 American Institute of Physics.
Growth and electrical characterization of Si delta-doped GaInP by low pressure metalorganic chemical vapor deposition
(1996-05-15)
Wang, CJ
;
Feng, MS
;
Chan, SH
;
Chang, CY
;
Wu, JH
The growth and electrical characterization of Si delta-doped GaInP grown by low-pressure metalorganic chemical vapor deposition are reported in this article. It was found that the sheet carrier density saturated as a function of doping time or flow rate. Because of the limitations of Hall-effect measurements, the saturation was explained as the result of electron population in satellite L valley. The mobility enhancement was observed for the delta-doped structure with an enhancement factor of 2-3. A sharp capacitance-voltage profile with a full width at half-maximum of 30 Angstrom was obtained. Depletion-mode Si delta-doped GaInP field-effect transistors with a gate length of 2 mu m and gate width of 50 mu m were fabricated and showed good device pinch-off characteristics. The extrinsic maximum transconductance of 92 mS/mm was obtained and a broad plateau transconductance profile was observed to confirm the electron confinement in the V-shape potential well of a delta-doped GaInP layer. (C) 1996 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.
Structure of high resistivity GaAs film grown by low-temperature metalorganic chemical vapor deposition
(1996-11-18)
Chen, WC
;
Chang, CS
;
Chan, SH
;
光電工程學系
;
Department of Photonics
The structure of a low-temperature GaAs layer grown by low-pressure metalorganic chemical vapor deposition with precursors of triethylgallium and arsine is reported. Dense particles containing Ga clusters are found in a high resistivity GaAs film grown at 420 degrees C, The size and concentration of particles are about 800-1000 nm and 7X10(11) cm(-3), respectively. (C) 1996 American Institute of Physics.