One can go for MSc - Physics after BTech. You have to find a suitable college / university near your place.
What you can do is take Electronics or Mathematical Physics as your main subject. It will help you when you go for research in Physics. The particular interest you are showing can be met through the route of research only.
If you can afford you can try some foreign universities also as research prospects are better there.
There is one site which has a lot of information regarding such universities in abroad - www.hotcoursesabroad.com
You can search information there.
In India other than IITs there are many reputed colleges and universities for Physics and some of which are-
St. Stephen's College, Delhi
Hindu College, Delhi
Hans Raj College, Delhi
Miranda House (for Women), Delhi
Presidency University/ Presidency College, Kolkata
St. Xavier's College, Kolkata
Presidency College, Chennai
Madras Christian College, Chennai
Loyola College, Chennai
Vellore Institute of Technology, Vellore
St. Anns College for Women, Hyderabad
Christ University/ Christ College, Bengaluru
St. Xavier's College, Mumbai
Fergusson College, Pune
BITS Pilani, Pilani
Delhi University, Delhi
University of Pune, Pune
University of Hyderabad, Hyderabad
Jadavpur University, Kolkata
University of Calcutta, Kolkata
Panjab University, Punjab
Jamia Milia Islamia, Delhi
Gauhati University, Guwahati
Knowledge is power.