1. Start from the research, not the university
Your PhD years are spent inside one research group, so the group's topic and the advisor's working style decide your experience far more than the institution's name.
Write down three to five specific topics you would happily read about for four years — 'solar cell stability' rather than 'renewable energy'. Then search the directory for researchers publishing on exactly those topics.
2. Check that they are still active on the topic
A professor may be famous for work published fifteen years ago and have moved on since. Look at their most recent publications and the years attached to them.
On each researcher profile you can see works count, citations, h-index and their most-cited publications, which gives you a quick read on whether the topic is still live for them.
3. Confirm there is funding before you invest time
In much of Europe a PhD is a salaried job attached to a specific project, so funding exists or it does not. In the US and UK, funding often comes through the department or a scholarship.
Filter for supervisors marked as recruiting or with funding available, and cross-check the open positions listed for their group.
4. Write a short, specific first email
Six to ten lines is enough: who you are, your degree, the one paper of theirs you read and what you would want to build on, and a one-line note on funding or scholarships you are eligible for.
Attach a CV and a transcript. Do not send the same message to twenty people — advisors recognise a template instantly.
5. Ask their current students
Before you accept, email one or two current or former doctoral researchers from the group. Ask how often they meet the advisor, how feedback is given, and how long people take to finish.
Their answers tell you more than any webpage will.
Put this into practice
Search supervisors by country, university and research area, or let the PhD Finder rank funded positions against your profile.