III-nitride transistor with trench gate

A method of fabricating a transistor comprising:

• forming a drain contact layer;
• forming a channel layer on the drain contact layer;
• forming a p− layer on the channel layer;
• forming a source contact layer on the p− layer;
• forming a source electrode on the source contact layer;
• forming a drain electrode on the drain contact layer;
• forming a trench extending through the source contact layer and the p− layer, the trench having a vertical sidewall;
• and
• forming a gate structure in the trench comprising:
• forming an AlN layer on the sidewall of the trench;
• forming an insulating cap layer on the AlN layer;
• and
• forming a gate electrode on the insulator cap layer and covering the sidewall of the trench;
• wherein a bottom of the AlN layer does not extend below a bottom of the p− layer.

A transistor comprising:

• a source electrode;
• a drain electrode;
• a drain contact layer comprising n+ GaN, the drain contact layer in contact with the drain electrode;
• a channel layer of n− GaN on the drain contact layer;
• a p− layer of AlGaN or GaN on the channel layer;
• and
• a source contact layer of n+ GaN on the p− layer, the source contact layer in contact with the source electrode;
• a trench extending through the source contact layer and the p− layer, the trench having a vertical sidewall;
• and
• a gate structure formed in the trench comprising:
• an AlN layer formed on the sidewall of the trench;
• an insulating cap layer formed on the AlN layer;
• and
• a gate electrode formed on the insulator cap layer and covering the sidewall of the trench;
• wherein a bottom of the AlN layer does not extend below a bottom of the p− layer.