I am trying to contact core-multishell GaN nanowires with a n-doped core and a p-doped multishell radial around the core via E-Beam lithopraphy. To characterize them I tried to realize ohmic contacts with Ni/Au to the p-doped GaN-shell. Because of the geometry of the wires I need to vapor deposit 30nm Nickel/300nm Gold to make sure, that the contact path doesn't ripp off the wire after the evaporation. Does anyone have experience with contacting p-GaN nanowires with Ni/Au and the formation of ohmic contacts? I tried several temperature steps in the RTA without any big impact on the results (up to 590°C). Thank you very much
Hi Jan, have you tried to go up with the temp.? Usually on GaN for to have ohmic contact you need a temperature arond 800 C by RTA. (60 sec should be enough).
Hi Giovanni,
During my research I found out that the best temperatures for p-doped GaN and Ni/Au is around 550°C. If you go much higher in temperatur your contact resistivity becomes worse. This also works for n-GaN and Ti/Au. The maximum temperatur I tested was 700°C, but without any noticable success.
Did you make the heating temp by RTA or what? can you send me the time of heating?
So I compare the heating time with my parameters.
The behaviour of the contact is like rectifying contact or has it some strange trend?
I tried RTA and Hotplate. I tried 1 minute, 5 minutes and additional heating after the first heating! There are no remarkable differences. It seems that for nanowires an annealing under air (hotplate) doesn't improve the contact resistivity like it does with layers. The trend of the I-V-characteristics are different. some are rectifying but most of them show some back-to-back diode behaviour (like two shottky contacts)
For semipolar surfaces the c-plane recipies did not work. The same may be due for the m-plane sidewalls, although m-plane is generally believed to behave more c-like for p-contact. It all depends on the actual p-doping of the shells, which might be very hard to access.
The p-doping of the shell cant be measured because of the geometry of the wires. What do you mean by "m-plane is generally believed to behave more c-like for p-contact"? Are there polarisation fields on the m-plane with a contact to the p-shell?
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