Ni based OHMIC contact on p-type GaN
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Date
2005-10
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Abstract
A new metallization scheme of Nil Ag on p-type GaN was studied to obtain reliable ohmic
contact. Silver (Ag) was selected as capping layer due to its characteristics as the best
metallic reflectors at visible wavelengths as an approach to employ the flip-chip
configuration. The contacts were first fabricated using the conventional photolithography
method. Then, the Ni/Ag metals were coated onto the p-GaN wafer through D.C. Sputter
equipment. Circular TLM structures were fabricated to extract the specific contact
resistivity of the contacts. The contacts were then annealed in rapid thermal process (RTP)
machine. In order to acquire lower resistance metal semiconductor interface; different
Nickel thickness, annealing duration (30 seconds, 1 minute and 2 minutes), as well as 2
different annealing ambient were applied on this contacts. The contacts exhibited ohmic
behavior at the annealing temperature of 600°C and 700°C. The contact which produces
the lowest specific contact resistivity is the sample that underwent annealing at 600°C in
vacuum ambient for 1 minute (Pc = 3.14 X 10.2 Ocm2
). In terms of surface morphology,
annealing in vacuum ambient has definitely produced contacts which resulted in a lot lower
surface roughness compared to those contacts annealed in nitrogen ambient. The
characterization of surface morphology was conducted using the scanning electron
microscopy (SEM) and the atomic force microscopy (AFM). X-ray diffraction (XRD) and
energy dispersive spectroscopy (EDS) were utilized to determine the microstructural
condition of the contacts. The electrical properties of the contacts were carried out using
the current-voltage (I-V) system. Fabrication of the Ni/Ag contacts on p-type GaN were
successfully fabricated and characterized.
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A new metallization scheme of Nil Ag on p-type GaN , was studied to obtain reliable ohmic contact