Browsing by Author "Huang, CN"

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Microstructural investigation of oxidized Ni/Au ohmic contact to p-type GaN
(1999-01-01)
Chen, LC
;
Chen, FR
;
Kai, JJ
;
Chang, L
;
Ho, JK
The phase evolution of oxidized (10nm) Ni/(5nm) Au films on p-GaN was examined with a field emission gun transmission electron microscope in conjunction with composition analyses to explore the mechanism of formation of low resistance ohmic contact to p-GaN. The p-GaN/Ni/Au sample heat treated above 500 degreesC in air was mainly composed of a mixture of crystalline NiO, Au and amorphous Ni-Ga-O phases. Small voids adjacent to the p-GaN film were also found. Moreover, NiO partially contacts to p-GaN as well as Au islands and the amorphous Ni-Ga-O phases. The results suggest that the crystalline NiO and/or amorphous Ni-Ga-O phases may play a significant role in the formation of a low resistance ohmic contact to p-GaN.
Microstructural investigation of oxidized Ni/Au ohmic contact to p-type GaN
(1999)
Chen, LC
;
Chen, FR
;
Kai, JJ
;
Chang, L
;
Ho, JK
The microstructure of oxidized Ni/Au films on p-GaN was examined to elucidate the formation of a low resistance ohmic contact to p-GaN with a field-emission gun transmission electron microscope in conjunction with composition analyses. The p-GaN/Ni/Au samples were heat treated at 500 degrees C in air mainly composed of a mixture of crystalline NiO, Au, and amorphous Ni-Ga-O phases. Small voids adjacent to the p-GaN film were also observed. The as-deposited Au film converted into discontinuous islands containing small amounts of Ni that connect with p-GaN. NiO formed a continuous film at the surface that covers the Au islands and the amorphous Ni-Ga-O phases. Moreover, NiO partially contacts p-GaN as well as Au islands and the amorphous Ni-Ga-O phase. The orientation relationship of the crystalline NiO, Au-rich islands, and p-GaN film was identified as NiO(111)//Au(11 (1) over bar)//GaN(0002) and NiO[1 (1) over bar 0]//Au[1 (1) over bar 0]//GaN[11 (2) over bar 0]. The results suggested that Ni atoms diffuse through the Au layer onto the surface and react with oxygen to form NiO, whereas Au atoms diffuse towards the inside to form a Au-Ni alloy. The microstructural examination indicated that the crystalline NiO and/or the amorphous Ni-Ga-O phases may significantly affect the low resistance ohmic contact to p-GaN. (C) 1999 American Institute of Physics. [S0021-8979(99)05219-6].
The effect of heat treatment on Ni/Au ohmic contacts to p-type GaN
(1999-11-16)
Chen, LC
;
Ho, JK
;
Chen, FR
;
Kai, JJ
;
Chang, L
The effect of heat treatment temperature on the microstructure and specific contact resistance of oxidized Ni(5 nm)/Au(5 nm) contacts to p-type GaN was investigated.,The: minimum specific contact resistance (Q(c)) obtained was 4 x 10(-6) Omega cm(2) after heat treating at 500 degrees C in air for 10 min. The cross-sectional microstructure of heat treated Ni/Au films on p-type GaN was examined with transmission electron microscope (TEM) in conjunction with compositional analyses. The high value of Q(c) for samples heat treated at lower temperatures (< 400 degrees C) was attributed to the fact that Au islands and crystalline NiO detached from the p-type GaN. When the temperature increased to 500 degrees C, NiO films and Au islands epitaxially constructed on p-type GaN matrix. The crystalline NiO may play a crucial role in the formation of low-resistance ohmic contact to p-GaN. Increasing the temperature further to 600 degrees C, large voids adjacent to p-GaN were observed which resulted in the reduction of contacting area deteriorating the contact resistance.
Thermal stability study of Ni/Ta n-GaN Schottky contacts
(2002-01-28)
Chen, GL
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Chang, FC
;
Shen, KC
;
Ou, J
;
Chen, WH
The Schottky behavior of Ni/Ta and Ni contacts on n-GaN was investigated under various annealing conditions by current-voltage measurements. It is found that with the addition of Ta between the Ni layer and the GaN substrate the thermal stability properties of devices can be significantly improved. Experimental results indicate that a high quality Ni/Ta n-GaN Schottky diode with an ideality factor and barrier height of 1.16 and 1.24 eV, respectively, can be obtained under 1 h annealing, at 700 degreesC. (C) 2002 American Institute of Physics.