Dear Mustafe,

Under these operating voltages there is no appreciable field effect. I would suggest that you measure C-V curve of the the transistor. Also, you may measure the transfer curve ID= f F(VGS AT CERAIN VALUE PF VDS. Both are indicative of the control effect of the transistor. It is advisable to measure at positive and negative VGS values.

wish you success

Prof Abdelhalim Zekry, 

Thanks for your appreciated answer, I will try it.

Sorry but I can't open your files ".fig" and consequently, I can't help you!

Can you convert your file in jpg!

Dear Harnois, 

Here are an Tiff file 

Thanks for your tiff file,

It seems that you have only electrical contact between drain and source. Are your sure that your gate are well "plugged"? What about IGS?

It could be useful to test your devices between -50 to + 50 in order to confirm if there are no effect of gate ("no modulation").

Please let me know about those electrical measurements

Thanks for the helpful answer, I will take these measurements and let you know.

Prof Abdelhalim and Dr Harnois, 

I have taken Id versus Vgs measurements as you recommended, here are the results at drain-source voltage of -50 V, is this right? I mean is this an actual FET behavior? Thanks a lot for your precious help.

Dear Mustafa,

Hope you are well. For me it was not the more suitable representation of the characteristics. For me it was clear that your transistor structure needs investigation why it is not working as satisfactory FET transistor. It was clear for me that there is no clear transistor effect and therefore i asked you for the C-V measurement. Foe sure you still do not have a worKing FET transistor. 

Wish you success

Dear,

I'm totally agree with professeur Zekry, C-V curves and Igs must be measured.

You must qualify the quality of your insulator.

Good luck