Browsing by Author "Huang, Gen-Sheng"

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CW lasing of current injection blue GaN-based vertical cavity surface emitting laser
(2008-04-07)
Lu, Tien-Chang
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Kao, Chih-Chiang
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Kuo, Hao-Chung
;
Huang, Gen-Sheng
;
Wang, Shing-Chung
Here, we report the cw laser operation of electrically pumped GaN-based vertical cavity surface emitting laser (VCSEL). The GaN-based VCSEL has a ten-pair InGaN/GaN multiple quantum well active layer embedded in a GaN hybrid microcavity of 5 lambda optical thickness with two high reflectivity mirrors provided by an epitaxially grown AlN/GaN distributed Bragg reflector (DBR) and a Ta(2)O(5)/SiO(2) dielectric DBR. cw laser action was achieved at a threshold injection current of 1.4 mA at 77 K. The laser emitted a blue wavelength at 462 nm with a narrow linewidth of about 0.15 nm. The laser beam has a divergence angle of about 11.7 degrees with a polarization ratio of 80%. A very strong spontaneous coupling efficiency of 7.5x10(-2) was measured. (C) 2008 American Institute of Physics.
Infrared reflectance of optical phonon modes in AlGaN epitaxial layers grown on sapphire substrates - art. no. 68941U
(2008)
Chen, Jun-Rong
;
Lu, Tien-Chang
;
Huang, Gen-Sheng
;
Ko, Tsung-Shine
;
Kuo, Hao-Chung
We reported the systematical study of optical properties of hexagonal AlxGa1-xN epitaxial films grown on c-sapphire substrate using metal-organic chemical vapor deposition. By performing Fourier transform infrared spectroscopy measurements, the high-frequency dielectric constants and phonon frequencies can be obtained by theoretically fitting the experimental infrared reflectance spectra using a four-phase layered model. The high-frequency dielectric constant of AlxGa1-xN varies between 4.98 and 4.52 for epsilon(infinity,perpendicular to) (polarization perpendicular to the optical axis) and between 4.95 and 4.50 for epsilon(infinity,//) (polarization parallel to the optical axis) respectively when the aluminum composition changes from 0.15 to 0.24. Furthermore, from experimental infrared reflectance spectra of AlxGa1-xN films, a specific absorption dip at 785 cm-1 was observed when the aluminum composition is larger than 0.24. The dip intensity increases and the dip frequency shifts from 785 to 812 cm(-1) as aluminum composition increases from 0.24 to 0.58. According to the reciprocal space map of x-ray diffraction measurements, the emergence of this dip could be resulted from the effects of strain relaxation in AlGaN epitaxial layers due to the large lattice mismatch between GaN and AlGaN epitaxial film.
Optically pumped GaN-based vertical cavity surface emitting lasers: Technology and characteristics
(2007-08-01)
Wang, Shing-Chung
;
Lu, Tien-Chang
;
Kao, Chih-Chiang
;
Chu, Jong-Tang
;
Huang, Gen-Sheng
We review the fabrication technology and performance characteristics of optically pumped GaN-based vertical cavity surface emitting lasers (VCSELs). Two types of VCSELs with different microcavity structures are described. First type of VCSEL has a hybrid microcavity structure that consists of an epitaxially grown AIN/GaN distributed Bragg reflector (DBR), a GaN active layer with InGaN/GaN multiple quantum wells (MQWs), and a Ta2O5/SiO2 dielectric DBR. Second type of VCSEL has a dielectric DBR microcavity structure that has a similar InGaN/GaN MQWs active layer sandwiched in two dielectric DBRs formed bv Ta2O5/SiO and TiO2/SiO2. Both types of VCSELs achieved laser action under optical pumping at room temperature with emission wavelength of 448 and 414 nm for hybrid DBR VCSEL and dielectric DBR VCSEL, respectively. Both lasers showed narrow emission linewidth with high degree of polarization and large spontaneous emission coupling factors of about 10-2. In addition, a high characteristic temperature of over 240K was measured, and a distinct spatially inhomooeneous emission pattern was observed.