How is Thapar University for doing a PhD?

Thapar University is not good for doing Ph.D. The Computer Science department is full of people who are self-involved. 

Except for a few faculty members, others are not good. They will not help you in your research work and due to which you could miss deadlines. 

Clearing GATE and then going for some decent college is the better option. Your thesis will be the real mirror of what you do during your entire Ph.D program. Work hard and get into one of the prestigious colleges in the country.

We can say that give your best shot in the GATE exam and get your seat reserved in some decent college, so that you gain some knowledge along with the hands-on industry training.