Browsing by Author "Fang, HM"

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Atomic force microscope study of GaN films grown by hydride vapor phase epitaxy
(1999)
Fang, HM
;
Wang, YK
;
Tsai, RY
;
Chu, CF
;
Wang, SC
We report the results of the investigation of the structural, surface morphological, and optical properties of GaN films grown by hydride vapor phase epitaxy. These films were grown on sapphire substrate with no intentional dopings. These as-grown GaN film samples with thickness ranging from 5.58 mu m to 14.9 mu m were investigated under room temperature conditions. The surface morphology of these films was investigated using an atomic force microscopy (AFM). The root mean square (RMS) values of surface roughness range from 0.281 nm to 0.133 nm. The thicker films show lower defect counts with a defect density of about 2 x 10(8) cm(-2). The structural property of these films was measured by double crystal X-ray diffraction (DC-XRD). The full width at half maximum (FWHM) of X-ray diffraction angle decreases as the film thickness increases with a lowest FWHM of about 265.5 arcsec. The optical properties of these films were investigated by photoluminescence (PL) measurement at room temperature. The results show a dominant near band-edge UV emission peak that increases with the film thickness with very weak yellow emission band.
Frequency stabilization of an external cavity diode laser to molecular iodine at 657.483 nm
(2006-05-01)
Fang, HM
;
Wang, SC
;
Shy, JT
;
光電工程學系
;
Department of Photonics
The saturation spectrum of the P(84) 5-5 transition of I-127(2) at 657.483 nm is obtained with the third-harmonic demodulation method using an external cavity diode laser. The laser frequency is modulated by modulating the diode current instead of modulating the cavity length with a piezoelectric transducer (PZT). Current modulation allows a modulation frequency that is higher than PZT modulation. The signal-to-noise ratio of 1000 is better than previous results presented in the literature. The laser is frequency stabilized to the hyperfine component o of the P(84) 5-5 transition with a frequency stability of better than 10 kHz (2.2 X 10(-11) relative stability). (c) 2006 Optical Society of America.
Measurement of hyperfine splitting of molecular iodine at 532 nm by double-passed acousto optic modulator frequency shifter
(2006-04-01)
Fang, HM
;
Wang, SC
;
Liu, LC
;
Cheng, WY
;
Wu, KY
The hyperfine splitting of molecular iodine R(56) 32-0 transition at 532 nm is measured using a double-passed acousto optic modulator frequency shifting apparatus. Preliminary results, compared with the values recommended by the Consultative Committee for Length, show that the accuracy of our method is better than 20 kHz, which can be easily improved in the future.
Pressure and power broadening of the a(10) component of R(56) 32-0 transition of molecular iodine at 532 mn
(2006-01-01)
Fang, HM
;
Wang, SC
;
Shy, JT
;
光電工程學系
;
Department of Photonics
We determine the linewidth of the hyperfine structure a(10) component of R(56) 32-0 transition of I-127(2) at 532 nm using the dependence of the peak amplitude of the third-derivative signal on the modulation width. We also use the same method to investigate pressure broadening and power broadening of the a(10) component. (c) 2005 Elsevier B.V. All rights reserved.