your research should first be based upon your field of interest. Then you find a 'niche' area from within the field. Please remember, it is 'YOUR' research and should be based upon your interests and aptitude.
You also have to take decision about the type of health care-Primary or Secondary or Tertiary you want to address. Also depend upon your interest you can decide to work on public or private health care delivery system. Once this is clear than it would be easier for you to select an appropriate area of research.
Hi. First find out why r u interested in Healthcare management only. Then identify which side of healthcare service- demand or supply or both u r interested.