Formal cover letter, resume, degree certificate and recommendation letter are all necessary. Other materials that can prove the applicant's qualification, such as research and teaching experience, papers published in professional journals, reports made at professional conferences, honors and awards won, experiences in evaluating other people's scientific research achievements, patents owned, etc. , can increase the competitiveness of the applicant. In addition, documents that can prove your English ability are also very important. For more questions about the postdoctoral application in the United States, you can go to the postdoctoral section of the Cornerstone Forum for Studying in Jin Dongfang. I believe it will be of great help to you: