Mechatronics Engineering

Yes you can choose mechatronics after your Diploma in electronics as it is combination of both electronics and mechanical. It is a very good field. Also one can change the field of study after Diploma.

Modern production equipment consists of mechatronic modules that are integrated according to a control architecture. The most known architectures involve hierarchy, polyarchy, heterarchy, and hybrid. The scope is limited as of now but its growth would be tremendous. An industrial robot is a prime example of a mechatronics system; it includes aspects of electronics, mechanics, and computing to do its day-to-day jobs. With this specialization you can have good scope outside India, specially in a country like Japan.

Robotics and Mechatronics are specialist fields. Most engineering colleges that offer these fields at UG level in India don't have adequate facilities. So, after joining, students are left in a fix and stuck due to lack of opportunities and narrow scope.
Rather than opting for Mechatronics or Robotics, you must opt for Mechanical Engineering. There are few engineering colleges abroad which have good infrastructure for Robotics. Eg. - UIUC, UCLA, Cornell etc.