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Photoluminescence studies of GaN films of different buffer layer and doping concentration
(1998-02-01)
Shen, CC
;
Shu, CK
;
Lin, HC
;
Ou, J
;
Chen, WK
Photoluminescence (PL) measurements of GaN films with various buffer thicknesses and Si-doping concentrations have been carried out. PL response of one specific sample was studied for temperature dependence. The results showed that the band gap energy reduction is linearly proportional to the temperature increase with a slope of similar to-4 x 10(-4) eV.K-1 and that the activation energies for donor-bound and acceptor-bound exciton transitions are 15 and 18 meV, respectively. In Si-doped GaN films, the PL data indicated that the reduced gap depends on the third power of carrier concentration as n(1/3). We also obtained a concentration coefficient of 2.34 x 10(-4) eV.cm and a band gap energy of 3.426 eV in the undoped GaN film.
Raman and X-ray studies of InN films grown at different temperatures by metalorganic vapor phase epitaxy
(1998-09-01)
Chen, WK
;
Lin, HC
;
Pan, YC
;
Ou, J
;
Shu, CK
We used Raman scattering and X-ray diffraction (XRD) methods to investigate the properties of InN films deposited at temperatures ranging from 325 to 600 degrees C by metalorganic vapor phase epitaxy (MOVPE). Significant line broadening, softening and intensity evolution were observed from films at growth temperatures between 375 and 450 degrees C. This can be attributed to the formation of mixed hexagonal and cubic structures and related dislocation defects. As the growth temperature was further increased, the hexagonal phase tvas found to be dominant in the deposited InN film.
A high-temperature thermodynamic model for metalorganic vapor phase epitaxial growth of InGaN
(1999-09-01)
Ou, J
;
Pan, YC
;
Lee, WH
;
Shu, CK
;
Lin, HC
A thermodynamic analysis tailored with a high-temperature parameter was performed for metalorganic vapor phase epitaxial (MOVPE) growth of InxGa1-xN alloys. Accordingly, a series of InGaN samples were prepared under various input In flow rates and growth temperatures. Theoretical results indicate that the In solid concentration tends to increase with increasing In flow rate and with decreasing temperature, whereas the metal droplets form more easily on the surface at lower growth temperatures and higher In fluxes, which are in good agreement with our experimental data.
Optical and electrical investigations of isoelectronic In-doped GaN films
(2000)
Shu, CK
;
Lee, WH
;
Pan, YC
;
Chen, CC
;
Lin, HC
The optical and electrical properties of isoelectronic In-doped GaN films grown by metalorganic vapor phase epitaxy (MOVPE) were investigated by X-ray, photoluminescence (PL), Hall and Raman measurements. As a result, adequate In-doping quantity causes not only a reduction of yellow luminescence and unintentional background concentration, but an enhanced mobility and decrease in the widths. The improved crystalline and optical qualities of GaN films may be attributed to the decrease in defects. (C) 2000 Elsevier Science Ltd. All rights reserved.
On-wafer electrooptic probing using rotational deformation modulation
(2000-09-01)
Chen, WH
;
Kuo, WK
;
Huang, SL
;
Huang, YT
;
電子工程學系及電子研究所
On-wafer electrooptic probing of two-dimensional electric-field vector (E-vector) is demonstrated by using one laser beam and one electrooptic prober. This technique utilizes both compressed-stretched deformation and rotational deformation on the index ellipsoid of the electrooptic crystal. Both experiment and simulation were performed to map the E-vector on a circuit hoard, and the measurement error is within 2.2%.
Two-dimensional electric-field vector measurement by a LiTaO3 electro-optic probe tip
(2000-09-20)
Kuo, WK
;
Chen, WH
;
Huang, YT
;
Huang, SL
;
電子工程學系及電子研究所
An electro-optic probe tip that is made from LiTaO crystal to make tangentially two-dimensional electric-field (E-field) vector measurements is presented. We combine a new electro-optic modulation technique and a conventional one to resolve the two E-tield components. The new modulation effect on the optical probing beam is caused by rotation of the principal axis the electro-optic crystal, which is proportional to the E-field. Inasmuch as there is no free charge involved in the axis rotation, rotation modulation of the axis can be as fast as conventional modulation. The principles are carefully derived, and an experimental system constructed, to measure two-dimensional E-field vectors on a test pattern. The results are in good agreement with those obtained with commercial software for electromagnetic simulation. The sensitivities of two tangential E-field components are 76 (mV/cm)/root Hz and 0.8 (V/cm)root Hz, respectively. The root-mean-square error of an E-field directional measurement is 1.5 degrees. (C) 2000 Optical Society of America OCIS codes: 120.5410, 230.2090, 230.4110, 130.6010.
Isoelectronic As doping effects on the optical characteristics of GaN films grown by metalorganic chemical-vapor deposition
(2000-10-30)
Huang, HY
;
Lin, WC
;
Lee, WH
;
Shu, CK
;
Liao, KC
We have studied the As doping effects on the optical characteristics of GaN films by time-integrated photoluminescence and time-resolved photoluminescence. When As is incorporated into the film, the localized defect levels and donor-acceptor pair transition become less resolved. The recombination lifetime of neutral-donor-bound exciton (I-2) transition in undoped GaN increases with temperature as T-1.5. However, the I-2 recombination lifetime in As-doped GaN first decreases exponentially from 98 to 41 ps between 12 and 75 K, then increases gradually to 72 ps at 250 K. Such a difference is related to the isoelectronic As impurities in GaN, which generate nearby shallow levels that dominate the recombination process. (C) 2000 American Institute of Physics. [S0003-6951(00)01941-0].
Structure study of GaN : Mg films by X-ray absorption near-edge structure spectroscopy
(2001)
Pan, YC
;
Wang, SF
;
Lee, WH
;
Lin, WC
;
Chiang, CI
X-ray absorption near-edge fine structure (XANES) spectroscopy from N K-edge measurement was employed to examine the crystal structure of metallorganic vapor phase epitaxy (MOVPE) grown Mg-doped GaN (GaN:Mg) films. The result showed that Mg doping induced crystal stacking faults to occur at the film surface causing a fraction of hexagonal phase to transform into cubic phase. As a consequence of this, XANES spectra of the films were found to vary with the dopant concentration and to lose pure hexagonal character when examined with the incident angle theta of the X-ray beam. Spectral characteristic variation between the two phases allows us to estimate the phase composition of the samples. The trend of increasing cubic phase component in dopant concentration is consistent with the observed Normaski optical micrograph. (C) 2001 Published by Elsevier Science Ltd.
Gallium K-edge x-ray absorption study on Mg-doped GaN
(2001-01-01)
Pan, YC
;
Wang, SF
;
Lee, WH
;
Lee, MC
;
Chen, WK
Ga K-edge x-ray absorption measurements were employed to investigate Mg-doping effects in GaN samples. Strong polarization-dependent x-ray absorption near-edge structures become less pronounced with increasing doping concentration, indicating the formation of a mixing-phase structure of cubic and hexagonal phases. Analysis of the extended x-ray absorption region of the spectra revealed doping-related defects such as vacancies, substitutions, and interstitial occupations. They were formed anisotropically in the crystal c axis direction and its perpendiculars. Disorderliness arising from phase mix and defects is believed to have lowered the Debye temperature of the doped GaN films and caused the destructive interference of the absorption fine-structure oscillation functions. These effects were taken into account for the observed large coordination number reductions in our samples. (C) 2001 American Institute of Physics.
Effects of thermal annealing on Ni/Ta/n-GaN Schottky diodes
(2001-03-15)
Chen, GL
;
Chang, FC
;
Chung, WC
;
Huang, BR
;
Chen, WH
The thermal effects of Ni/Ta/n-GaN Schottky diodes have been investigated for the first time using current-voltage, X-ray photoemission spectroscopy and Auger electron spectroscopy (AES) methods. Their barrier height is found to increase monotonously with increasing annealing temperature up to 800 degreesC. Preliminary results indicate that when a Th intermediate layer is added into the Ni/GaN diodes, it can prevent the metal-semiconductor interdiffusion and Ni accumulation adjacent to GaN substrate to a large extent so that a more thermally stable device can be obtained.

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