Method of forming a high electron mobility transistor

A method of fabricating a high electron mobility transistor (HEMT) comprising:

• epitaxially growing a second III-V compound layer on a first III-V compound layer, wherein the second III-V compound layer includes a different composition than the first III-V compound layer;
• depositing a dielectric layer over the second III-V compound layer, wherein the dielectric layer has an interface with the second III-V compound layer;
• forming a first opening and a second opening in the dielectric layer exposing the second III-V compound layer;
• forming a source feature and a drain feature disposed on the second III-V compound layer in the first and second openings respectively;
• and
• after forming the source feature and the drain feature, depositing a protection layer over the source feature, the drain feature, and the dielectric layer, wherein the protection layer extends a distance between the source feature and the drain feature.

A method of fabricating a high electron mobility transistor (HEMT) comprising:

• growing a gallium nitride (GaN) layer on a substrate;
• growing an aluminum nitride (AIN) layer on the GaN layer;
• depositing a cap layer of dielectric material over the AlN layer;
• forming a first opening in the cap layer, and depositing a metal layer in the first opening in the cap layer;
• depositing a conformal protective layer over the metal layer;
• and
• after depositing the conformal protective layer, etching a second opening in the conformal protective layer;
• and
• forming a gate structure in the second opening.