The realization of ohimic contact to n-GaN is usually achieved by using Ti/Al bilayer electrodes with high temperature annealing. Nevertheless

the process of high temperature annealing may destruct the electronic structure of devices

such as quantum well and superlattice structure. The ultimate objective of this research work is to obtain low resistance ohimic contact to n-GaN without high temperature annealing

thus avoiding the destruction of electronic structure effectively. In the research both nonalloyed condition and low temperature annealing are applied. Under nonalloyed condition

we firstly use alloyed TiAl

3

as contact electrode material directly on n-GaN with carrier concentration of 2×10

18

cm

-3

. Compared with conventional Ti/Al bilayer structure

alloyed TiAl

3

structure facilitates the realization of nonalloyed n-type ohmic contact. However

with annealing at 500℃

the contact behavior of Ti/Al bilayer is improved rapidly and achieves ohmic

which is lower than the temperature assumed in some papers. After applying RIE process

both Ti/Al bilayer and TiAl

3

alloyed electrodes behave ohmic

which indicates that the surface of GaN is cleaning

thus intimate contact of Ti and GaN is vital to achieve ohmic contact to n-GaN. In the further experiment

Ti/TiAl

3

bilayer structure is introduced to compare with TiAl

3

alloyed structure. Both of the two structures behave ohmic with RIE process

yet TiAl

3

alloyed shows lower contact resistance

and excess Ti has no obvious effect to contact behavior under nonalloyed condition. After annealing with different temperature

Ti/TiAl

3

bilayer structure tends to form an ohmic contact with lower contact resistance. It proves that excess Ti is activated to form ohmic contact at high temperature annealing. Further analysis implies both of the nitrogen vacancies and TiAl

3

mechanisms play a critical role to form a low contact resistance ohmic contact to n-GaN

under the condition of nonalloyed or low annealing temperature. Accordingly

based on alloyed TiAl

3

structure

Ti/TiAl

3

/Ni/Au structure is designed

which decreases the contact resistance significantly

and the specific contact resistance of 3×10

-5

Ω·cm

2

is obtained with CTLM measurement.The introduction of TiAl

3

alloyed material can make a role as high temperature annealing in the aspect of forming TiAl

3

at the interface. With a certain thickness ratio

Ti/TiAl

3

can achieved low ohmic contact with low temperature annealing. Therefore

TiAl

3

alloyed will be promising in the application field of photoelectron and micro-electron devices that require strict temperature conditions.