High-Electron-Mobility Transistor Having a Buried Field Plate

A high-electron-mobility field effect transistor, comprising:

• a buffer region having a stepped lateral profile, the stepped lateral profile comprising first, second and third cross-sections of the buffer region, the first cross-section being thicker than the third cross-section, the second cross-section interposed between the first and third cross-sections and forming oblique angles with the first and third cross-sections;
• a barrier region along the stepped lateral profile of the buffer region, wherein the buffer region comprises a first semiconductor material and the barrier region comprises a second semiconductor material, the first and second semiconductor materials having different band-gaps such that an electrically conductive channel comprising a two-dimensional charge carrier gas arises at an interface between the buffer and barrier regions due to piezoelectric effects;
• and
• a buried field plate within the buffer region,
• wherein the barrier region is separated from the buried field plate by a portion of the buffer region,
• wherein the buried field plate comprises either one of:
• (i) an epitaxial conductive layer of semiconductor material as part of the buffer region, wherein the buried field plate comprises a section of the conductive layer of semiconductor material;
• or
• (ii) an epitaxial layer of semiconductor material as part of the buffer region, wherein a buried trench is formed in the buffer region, wherein the buried trench is filled with an electrically conductive material, wherein the buried field plate comprises the electrically conductive material that is filled in the buried trench.