High electron mobility transistor structure and method of fabricating the same
A high electron mobility transistor includes a substrate. A first III-V compound layer is disposed on the substrate. A second III-V compound layer is embedded within the first III-V compound layer. A P-type gallium nitride gate is embedded within the second Ill-V compound layer. A gate electrode is disposed on the second III-V compound layer and contacts the P-type gallium nitride gate. A source electrode is disposed at one side of the gate electrode. A drain electrode is disposed at another side of the gate electrode.
1. A fabricating method of a high electron mobility transistor structure, comprising:
forming a normally-off transistor, wherein steps of fabricating the normally-off transistor comprises:
providing a substrate and a first III-V compound layer disposed on the substrate;
etching the first III-V compound layer to form a first trench;
performing a first epitaxial process to form a second III-V compound layer filling up the first trench;
etching the second III-V compound layer to form a second trench;
performing a second epitaxial process to form a P-type gallium nitride gate filling up the second trench;
forming a first gate electrode, wherein the first gate electrode is disposed on the second III-V compound layer and contacts the P-type gallium nitride gate; and
forming a first source electrode and a first drain electrode, wherein the first source electrode and the first drain electrode are respectively disposed at two sides of the first gate electrode, both of the first source electrode and the first drain electrode are on the second III-V compound layer and contact the second III-V compound layer and the first III-V compound layer.
2. The fabricating method of a high electron mobility transistor structure of claim 1 , wherein an obtuse angle is defined between a bottom of the first trench and a sidewall of the first trench.
3. The fabricating method of a high electron mobility transistor structure of claim 1 , wherein the P-type gallium nitride gate does not contact the first III-V compound layer.
4. The fabricating method of a high electron mobility transistor structure of claim 1 , wherein a distance is between a bottom of the P-type gallium nitride gate and the first III-V compound layer, the distance is perpendicular to a top surface of the substrate, and the distance is between 10 and 20 nanometers.
5. The fabricating method of a high electron mobility transistor structure of claim 1 , wherein the first III-V compound layer surrounds the second III-V compound layer, and the second III-V compound layer surrounds the P-type gallium nitride gate.
6. The fabricating method of a high electron mobility transistor structure of claim 1 , a top surface of the second III-V compound layer, a top surface of the first III-V compound layer and a top surface of the P-type gallium nitride gate are aligned.
7. The fabricating method of a high electron mobility transistor structure of claim 1 , further comprising before performing the first epitaxial process, forming an aluminum nitride layer covering the first trench.
8. The fabricating method of a high electron mobility transistor structure of claim 1 , wherein the substrate comprises a normally-off transistor region and a normally-on transistor, and the normally-off transistor is disposed within the normally-off transistor region.
9. The fabricating method of a high electron mobility transistor structure of claim 8 , further comprising a normally-on transistor disposed within the normally-on transistor region, wherein steps of fabricating the normally-on transistor comprise:
etching the first III-V compound layer to form a third trench in the normally-on transistor region while etching the first III-V compound layer to form the first trench;
performing the first epitaxial process to form two of the second III-V compound layers respectively filling up the first trench and the third trench;
after forming a mask covering the normally-on transistor region, etching the second III-V compound layer within the normally-off transistor region to form the second trench;
after forming the P-type gallium nitride gate, removing the mask;
after removing the mask, forming a second gate electrode on the second III-V compound layer within the normally-on transistor region; and
after removing the mask, forming a second source electrode and a second drain electrode within the normally-on transistor region while forming the first source electrode and the first drain electrode, wherein the second source electrode and the second drain electrode are respectively disposed at two sides of the second gate electrode, both of the second source electrode and the second drain electrode are on the second III-V compound layer and contact the second III-V compound layer and the first III-V compound layer.
10. The fabricating method of a high electron mobility transistor structure of claim 1 , wherein when seeing from a top view, the P-type gallium nitride gate is deviated from a center of the second III-V compound layer.