Ohmic Contacts on p‐GaN

With the development of GaN‐based optoelectronic devices, the need for p‐GaN contacts with low resistivity, good thermal stability, and high transparency or reflectivity has become more pressing. Various contact schemes to satisfy these requirements have been investigated in the past two decades. In this progress report, the main developments of contacts on p‐GaN throughout these years are summarized. The primary focus is on the materials aspects of the contacts and the functional mechanisms related to their relevant properties. The important process of surface treatment is also discussed briefly at the end of the article.