Well, It is not necessary to do PhD after clearing GATE exam. If your scores are high then it depends upon you whether you want to pursue your studies in Mtech or PhD ( as the duration of both the courses are different ) through a good Government Institute.

Hello. Gate exam is given for doing their higher studies. So masters and then phd is the series you must follow.

If you have qualified with good Mark's and percentage,  then you can apply for PHD in the desired stream.

For PHD, you must have a lot of potential to vein out something productive from the previous scopes. This requires alot of study and research. So, if you posses all this qualities,  then you can go ahead .

Hope that helps!