Electrical measurements are very sensitive to doping. Start with Hall effect

Hi,

 Please go for Hall and also C-V measurements.

SIMS, electrical measurements

Hi,

You must have reliable Ohmic and/or Schottky contacts on your NWs before you conduct the measurement of C-V and/or Hall effect. Therefore, SIMS would be a  better choice.

Hi, 

I heard that SIMS is good for highly doped material, it doesn't give reliable data for less doped material. You should try SIMS once.

You did not specify with what metal you want to dope the GaN nanowires. If the metal is a shallow donor (such as Si and Mg), then Daniella's recommendation of Hall Effect measurements is the way to go. If the metal is not a dopant, then SIMS or XPS may be the solution. Dr. Zetian Mi at McGill, reported studies on nanowires and their doping.

Hi All, Thanks for your suggestions

@ Theodore, I will try with Mg and Ba 

One of the constrain that I am facing is making metal contacts on the single nanowire. So please advice some optical measurements where such contacts are not required. And also I could not understand how Hall measurements can be done on Nanowires that requires a specific geometry of the contacts.

1. If the nanowires are long (several mm) you can cut one on a flat insulating surface and paint four contacts with silver paint. Connect a battery and Ammeter in the two outer contacts and a high impedance voltmeter in the two inner ones. In this four probe method the Ohmicity of the contacts is not relevant.

2. An alternative method is to use a contactless microwave conductivity measurements. Find attached an old paper where this method was used to study photoconductivity of GaAs films

If you want qualitative information when changing doping along the nanowire you can use scanning capacitance microscopy. This requires a NW diameter larger than the depletion depth of course.

For very high doping concentrations you can look at the band gap PL, as it can broaden above 10^19 cm-3.

I would suggest to conduct Hall, then C-V  measurements to characterize concentration of the active carriers (holes in your case). Also it is a good idea to check the concentration of an incorporated dopand by SIMS.

I do not have any suggestions about contacts because we have never tried to make them to nanowires. Probably as a first step, you can check the resistance of your NW using multimeter. If the resistance is very high (about multimeter range), most likely the doping is poor.

Or you can also use Spectroscopic ellipsometry for thin films. There you getting the optical properties out of the ellipsometric data.

Best regards

Christian