ZnO is a direct wide-band-gap(3.37 eV)semiconductor.It has attracted considerable attention as a potential candidate material for gas sensors

transparent electrode and surface acoustic wave deices

especially for ultraviolet light-emitting diodes(LEDs)and laser diodes(LDs).However

for ultimately fabricating ZnO-based optoelectronic devices

the performance of the contacts to ZnO is attracting more and more attention.This is because a good ohmic contact allows lower operating voltage and minimizes dissipation of power

while a poor ohmic property leads to poor device performance and eventually device failure.Compared with that to n-type ZnO

the fabrication of ohmic contacts to p-type ZnO is more difficult since the work function of p-type ZnO is higher than that of single metal.The contact properties of Au

In

Ni/Au to N-doped p-type ZnO films grown by MBE method were reported.The zinc(Zn)source was supplied by evaporating metal zinc with 99.999 9% through a Knudsen effusion cell.NO gas activated by an Oxford Applied Research r.f.(13.56 MHz)plasma source with a power of 300 W was used as both N and O source.Compared with Au and In contacts

Ni/Au contact is more suitable to form stable ohmic contact to p-type ZnO.The contacts behavior of Ni/Au after annealing under N

2

and O

2

ambient were given.It was found Ni/Au contact gave a degenerative behavior after rapid thermal annealing(RTA)under O

2

ambient at the temperature of 300℃ for 150 s

while an improved contact behavior was obtained after RTA under N

2

in the same temperature for 150 s.The dependence of Ni/Au contact on the annealing temperature under N

2

gas ambient was investigated.With the increase of the annealing temperature

the resistances of Ni/Au contacts decrease firstly and then increase.In this experiment

after RTA at 400℃ under N

2

for 150 s

the Ni/Au contact gives a better ohmic characteristic

and the contact resistivity is about 0.8 Ω·cm

2

.