Browsing by Author "Huang, BR"

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Dependence of deep level concentrations on ammonia flow rate in n-type GaN films
(2002-08-01)
Lee, L
;
Chang, FC
;
Chung, HM
;
Lee, MC
;
Chen, WH
Deep level transient spectroscoppy was used to characterize the deep levels of GaN films grown with various V/III ratios using metalorganic vapor phase epitaxy. Two prominent defects, located at E(C)-0.569 +/- 0.003 and E(C)-1.013 +/- 0.091 eV, were detected in this study. When the NH(3) flow rate was increased, we observed a slight increase in trap concentration of the E(C)-0.569 eV defect and a significant increase at E(C)-1.013 eV. Although a high V/III seems necessary for obtaining good quality GaN film, our results indicate that, if the ammonia is in excessive supply, it may generate a large number of E(C)-1.013 eV deep level defects, which deteriorate the film quality - which should be avoided with special care.
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.
Electrical properties of the free-standing diamond film at high voltages
(2001-05-01)
Huang, BR
;
Ke, WC
;
Chen, WK
;
電子物理學系
;
Department of Electrophysics
Polycrystalline diamond films were deposited on P-type (100) silicon substrates by the microwave plasma chemical vapor deposition system. The free-standing diamond film was then obtained by etching the silicon substrate with a KOH I solution. It was found that more non-diamond components, i.e., SiC and amorphous carbon, existed on the bottom surface of the free-standing diamond film. Two different contact geometries, coplanar contact and sandwich contact geometries, were used to characterize the in-plane and transverse hi.-h-voltage electrical properties of the free-standing diamond film, respectively. The transverse electrical property of the free-standing diamond film showed the asymmetric current-voltage (1-V) characteristic and lower break-down voltage at -220 V and 850 V. However, the in-plane electrical property exhibited the symmetric I-V characteristic in the range of - 1100 V to 1100 V. The electrical properties were successfully represented by the Frenkel-Poole conduction mechanism at high voltages (> 200 V). The simulated results indicated that the breakdown field was strongly related to the Coulombic center density of the free-standing diamond film.
Growth of diamond films with bias during microwave plasma chemical vapor deposition
(2002-03-01)
Lu, CA
;
Chang, L
;
Huang, BR
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Diamond films on 3-inch diameter (100) silicon wafers were synthesized with bias during microwave plasma vapor deposition (MPCVD). The deposition parameters were as follows: 0.13% CH4 in H-2 pressure at 30 torr; deposition temperature at 768-869 degreesC, and a deposition time of 3-3.5 h. The bias voltage applied to the substrates during diamond growth varied from 0 to -450 V. The deposited films were characterized by Raman spectroscopy and electron microscopy. The results show that the film properties are uniform across the whole 3-inch diameter area. Raman spectra show that the ratio of sp(3) to sp(2) is increased with the bias voltage up to -350 V, while further increases in voltage resulted in a decreased ratio. It was found that column-shaped grains of diamond were directly grown from the substrate surface without grain coalescence in the lateral direction during growth. The nucleation density of diamond with biased growth was of the order of 10(9) cm(-2). (C) 2002 Elsevier Science B.V. All rights reserved.
Successive current-voltage measurements of a thick isolated diamond film
(2001-11-01)
Huang, BR
;
Ke, WC
;
Hsu, JF
;
Chen, WK
;
電子物理學系
Polycrystalline diamond films were deposited on p-type (100) silicon substrate using a methane/hydrogen gas mixture in a microwave plasma-assisted chemical vapor deposition system. After the back-etched process, the Al contacts were evaporated on both sides of a 150 mum thick isolated diamond film for consecutive high-voltage measurements. It was found that the current-voltage (I-V) characteristics of the Al/diamond/Al structure exhibited two Schottky barrier diodes in a back-to-back configuration. Since the top diamond surface possessed better diamond quality than the bottom surface, the top Schottky diode with a breakdown voltage of 897 V and a lower breakdown voltage of -515 V for the bottom Schottky diode was observed for the first I-V measurement. However, the breakdown voltage was decreased by 37 and 140 V for the top and bottom Schottky diodes after the consecutive sixth repeated measurements. It was found that the oxygenated phenomenon was more prominent; in addition, the quality of the isolated diamond film was also degraded after the consecutive high-voltage measurements. It was indicated that decrease of the breakdown voltage was due to the oxidation layer and the non-diamond components on both surfaces of the isolated diamond film. (C) 2001 Elsevier Science B.V. All rights reserved.