Browsing by Author "Tsang, JS"

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Activation of p-type GaN in a pure oxygen ambient
(2001-05-15)
Wen, TC
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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.
Compositional disordering of InGaAs/GaAs heterostructures by low-temperature-grown GaAs layers
(1996-01-15)
Tsang, JS
;
Lee, CP
;
Lee, SH
;
Tsai, KL
;
Tsai, CM
Compositional disordering of InGaAs/GaAs superlattices using a low-temperature-grown GaAs cap layer (LT-GaAs) by molecular beam epitaxy has been studied. The disordering of the superlattice was verified by photoluminescence and double-crystal x-ray rocking curve measurements. The Ga-vacancy-enhanced interdiffusion due to the presence of LT-GaAs was found to be the disordering mechanism. Diffusion equations and the Schrodinger's equation were solved numerically to obtain the composition profile and the transition energies in the disordered quantum well, respectively. The simulated energy shifts for samples under different annealing conditions agreed very well with the experimental results. The calculated effective diffusivity for the In-Ga interdiffusion has an activation energy of 1.63 eV, which is smaller than the activation energy 1.93 eV, for intrinsic interdiffusion. The diffusivity for the enhanced In-Ga interdiffusion due to the presence of LT-GaAs is about two orders of magnitude larger than the intrinsic In-Ga diffusivity. (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.
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.
Optical and structural properties of epitaxially lifted-off GaAs films
(1998-01-01)
Fan, JC
;
Lee, CP
;
Tsai, CM
;
Wang, SY
;
Tsang, JS
The influence of the layer thickness on the optical and structural properties of the epitaxially lifted-off (ELO) thin films has been studied. The ELO films bonded to Si, InP, and GaAs substrates have also been compared. The structure was characterized by high-resolution double-crystal x-ray diffraction and the optical properties were measured by the temperature-dependent photoluminescence spectroscopy. A biaxial compressive strain was observed for the samples bonded to Si with a buffer layer thinner than 1000 nm. Due to different thermal expansion coefficient between the grafted thin film and the host substrate, the emission spectra of the quantum wells of the lifted-off thin films are redshifted compared to the as-grown sample. The amount of the redshift is larger for thinner films. (C) 1998 American Institute of Physics.
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.
The effect of barrier structure on the performance of double barrier quantum well infra-red photodetectors
(1996-02-01)
Tsai, KL
;
Lee, CP
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Chen, PC
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Tsang, JS
;
Tsai, CM
The effects of the inner and outer barriers on the performance of mid-wavelength (3-5 mu m) GaAs/AlGaAs double barrier quantum well infra-red photodetectors (DBQWIPs) have been studied. It was found that the peak response wavelength had a significant red shift when the thickness of the AlAs inner barriers was below 10 Angstrom. This is attributed to the lowering of the upper state energy in the quantum wells. The responsivity of DBQWIPs decreases with the inner barrier thickness. This is because the optical gain decreases faster than the increasing rate of the quantum efficiency when the inner barrier thickness increases. The responsivities for devices with different Al compositions (0.35 and 0.24) in the outer barriers are in the same range, but the dark currents for devices with Al(0.35)G(0.65)As outer barriers are much lower than those with Al0.24Ga0.76As outer barriers. Nearly two orders of magnitude improvement in detectivity was observed when the Al composition in the outer barriers was changed from 0.24 to 0.35. A high detectivity of 1 x 10(11) cm Hz(1/2) W-1 at 77 K was obtained for a device with 12 Angstrom AlAs inner barriers and 300 Angstrom Al0.35Ga0.65As outer barriers.
Thermal annealing of Pd/InAlAs Schottky contacts for transistor buried-gate technologies
(1998-01-01)
Chuang, HF
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Lee, CP
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Tsai, CM
;
Liu, DC
;
Tsang, JS
We studied the thermal reaction of Pd/In0.52Al0.48As contacts using capacitance-voltage (C-V), current-voltage, Auger electron spectroscopy, and x-ray diffraction analyses and compared the results to those for Pd/Al0.25Ga0.75As and Pd/In0.53Ga0.47As contacts. The thickness of InAlAs consumed by the reaction during annealing was calculated directly from the measured C-V profiles. Pd starts to react with InAlAs at a temperature of 100 degrees C, lower than it does with AlGaAs. For thermally annealed Pd/InAlAs and Pd/AlGaAs, both compositional and structural changes were found at the Pd/semiconductor interface. However, in heat-treated Pd/InGaAs samples, compositional changes but no structural changes were observed. (C) 1998 American Institute of Physics.
Thermal annealing of Pd/InAlAs Schottky contacts for transistor buried-gate technologies
(1998-01-01)
Chuang, HF
;
Lee, CP
;
Tsai, CM
;
Liu, DC
;
Tsang, JS
We studied the thermal reaction of Pd/In0.52Al0.48As contacts using capacitance-voltage (C-V), current-voltage, Auger electron spectroscopy, and x-ray diffraction analyses and compared the results to those for Pd/Al0.25Ga0.75As and Pd/In0.53Ga0.47As contacts. The thickness of InAlAs consumed by the reaction during annealing was calculated directly from the measured C-V profiles. Pd starts to react with InAlAs at a temperature of 100 degrees C, lower than it does with AlGaAs. For thermally annealed Pd/InAlAs and Pd/AlGaAs, both compositional and structural changes were found at the Pd/semiconductor interface. However, in heat-treated Pd/InGaAs samples, compositional changes but no structural changes were observed. (C) 1998 American Institute of Physics.
Thermal reactions of Pd/AlxGa1-xAs contacts
(1996-09-01)
Chuang, HF
;
Lee, CP
;
Tsang, JS
;
Fan, JC
;
電子工程學系及電子研究所
Pd/AlxGa1-xAs Schottky contacts and their thermal reactions are studied by capacitance-voltage measurements, current-voltage measurements, and x-ray diffraction. The thickness of AlxGa1-xAs consumed by the Pd/AlxGa1-xAs reaction during annealing was calculated. For annealing temperatures below 300 degrees C the Schottky characteristics of the diodes were good but the electrical junction moves into AlxGa1-xAs after annealing. The amount of junction movement was calculated directly from our measurements. The diffusion coefficients of Pd in AlxGa1-xAs and the activation energy were estimated. The activation energy was found to be larger for higher Al concentration. PdAl, PdAs2, PdGa5, and Pd5Ga2 were detected in the compounds formed by the Pd/AlxGa1-xAs reaction after annealing. (C) 1996 American Institute of Physics.
Thermal reactions of Pd/AlxGa1-xAs contacts
(1996-09-01)
Chuang, HF
;
Lee, CP
;
Tsang, JS
;
Fan, JC
;
電子工程學系及電子研究所
Pd/AlxGa1-xAs Schottky contacts and their thermal reactions are studied by capacitance-voltage measurements, current-voltage measurements, and x-ray diffraction. The thickness of AlxGa1-xAs consumed by the Pd/AlxGa1-xAs reaction during annealing was calculated. For annealing temperatures below 300 degrees C the Schottky characteristics of the diodes were good but the electrical junction moves into AlxGa1-xAs after annealing. The amount of junction movement was calculated directly from our measurements. The diffusion coefficients of Pd in AlxGa1-xAs and the activation energy were estimated. The activation energy was found to be larger for higher Al concentration. PdAl, PdAs2, PdGa5, and Pd5Ga2 were detected in the compounds formed by the Pd/AlxGa1-xAs reaction after annealing. (C) 1996 American Institute of Physics.