Hi Ashwini!

There are many colleges which offer direct PhD after BTech , you just need to qualify the entrance exams. Or other way is , you can do dual degree from any IIT : Mtech + PhD. The IITs which offer direct PhD are IIT Kanpur, IIT Gandhinagar, etc. IIMs also pffer direct PhD after Btech under the name of FPM (Fellow Program in Management).  It's a 4–5 year program after which you even have the chance to be recruited as a faculty member in IIMs itself.  The admission to this programme is done by GATE/ CAT/ GMAT and further followed by interview.

If you xcrack GATE exam and you have good CGPA in BTech , let it ne 8 or 9 out of 10, prepare a good SOP (Study of Purpose) and a good SOR (Statement of Research). Prepare well for interview calls from reputed instituted such as IITs, IISc, IIMs etc and qualify the interview. And you can join as a PhD candidate.

Thankyou!