DRDO Advertises positions each year for various Scientist/Research Assistant/JRF Positions. You need to apply for the vacancy, might or might not be asked for your GATE Score, followed by shortlisting and Interview. You do have M.Sc. Physics Vacancies, though they are scarce when compared to Engineering Positions. Have patience and wait for the Advertisement, in the meanwhile keep your GATE/CSIR NET Score with you, try applying for Research Positions at various other Research Institutions like CSIR,BARC, ISRO, IITs, IISc all of which have great research scope and career prospects.