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Micro and nano analysis of 0.2 mm
Ti/Al/Ni/Au ohmic contact to
AlGaN/GaN
A. Fontsere`,1,a) A. Pe´rez-Toma´s,1 M. Placidi,1 J. Llobet,1 N.
Baron,2,3 S. Chenot,2
Y. Cordier,2 J. C. Moreno,2 P. M. Gammon,4 M. R. Jennings,4 M.
Porti,5 A. Bayerl,5
M. Lanza,5 and M. Nafrı´a5
APPLIED PHYSICS LETTERS 99, 213504 (2011)
報告者: W.C.Jian
Outline
• Introduction
• Experiment
• Conclusion
Introduction
 As GaN technology continues to gain popularity, it
is necessary to control the ohmic contact properties and to
improve device consistency across the whole wafer.
 In this paper, we use a range of submicron
characterization tools to understand the conduction
mechanisms through the AlGaN/GaN ohmic contact.
 Our results suggest that there is a direct path for electron
flow between the two dimensional electron gas and the
contact pad. The estimated area of these highly
conductive pillars is around 5% of the total contact area.
Experiment
• I-V curve, TLM, 接觸電阻結果
(a) Typical I-V-T
measurement
and
(b) and (c) shows
the RT, Rsh, and
Rc evolution with
temperature.
Experiment
• SEM & FIB 量測結果
TLM SEM cross
section images of
the Ti/Al/Ni/Au
ohmic contact
annealed at 750 C
for 30 s. (a) View of
the FIB machined
lamella still
anchored,
(b) detailed view of
the different layers,
and (c) an enlarged
image of
the ohmic contact
area.
Experiment
• EDX data
EDX analyses at five distinct ohmic contact regions
named C1, C2, C3, C4, and C5 (depicted in Fig. 2(c)). EDX relative composition
for Ti, Al, Ni, and Au is included in the table on the right.
Experiment
• TEM data
Cross sectional TEM images of the (a) Ti/Al/Ti/Au contact annealed
at 750 C for 30 s and (b) detailed image of region C5.
Experiment
• AFM & SEM data
(a) Topography and (b) current map of TLM surface
taken with the cAFM for the 1.0 0.5 lm2 scan. (c) SEM image of FIB partial
etch on TLM surface.
Experiment
• AFM & SEM data
(a) Topography and
(b) current map of
lamella
crosssection
taken with the
cAFM for the 0.55
0.55 lm2 scan.
Conclusion
 The submicron features of a typical Ti/Al/Ni/Au ohmic
contact to AlGaN/GaN, with reduced Rc of 0.2X mm, have
been investigated in detail.
 This included TLM vs T, in the temperature range of 25
C–300 C and a range of physical analysis tools like SEM,
FIB, TEM, and cAFM.
 The results suggest that the preferential contact
Mechanism is a direct electron path between the electrons
of the 2DEG and the metal stack, though only a small part
of the contact is actually conducting.
Thanks for your attention