| CPC H10D 64/411 (2025.01) [H10D 30/015 (2025.01); H10D 30/475 (2025.01); H10D 62/8503 (2025.01); H10D 64/01 (2025.01)] | 19 Claims |

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1. A semiconductor device, comprising:
a first nitride-based semiconductor layer;
a second nitride-based semiconductor layer disposed over the first nitride-based semiconductor layer, wherein the second nitride-based semiconductor layer has a bandgap greater than that of the first nitride-based semiconductor layer; and
a gate structure disposed over the first nitride-based semiconductor layer, wherein the gate structure comprises:
an outer spacer disposed over the second nitride-based semiconductor layer and having at least two opposite inner sidewalls to define a gate trench;
an inner spacer disposed over the first nitride-based semiconductor layer and within the gate trench; and
a gate electrode disposed in the gate trench and covered by the inner spacer, wherein the at least inner spacer and the gate electrode extend downward to collaboratively form a bottom portion of the gate structure with a first width greater than a second width of a bottom surface of the gate electrode,
wherein the semiconductor device further comprises a doped nitride-based semiconductor layer at least abutting against the outer spacer, wherein an entirety of a bottom surface of the doped nitride-based semiconductor layer is in a position under the inner spacer.
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