Vertical GaN-based semiconductor device
A vertical semiconductor device in which pinch-off characteristics and breakdown voltage characteristics can be stably improved by fixing the electric potential of a p-type GaN barrier layer with certainty is provided. The semiconductor device includes a GaN-based stacked layer having an opening, a regrown layer including a channel located so as to cover a wall surface of the opening, an n + -type source layer that is in ohmic contact with the source electrode, a p-type GaN barrier layer, and a p + -type GaN-based supplementary layer located between the p-type GaN barrier layer and the n + -type source layer. The p + -type GaN-based supplementary layer and the n + -type source layer form a tunnel junction to fix the electric potential of the p-type GaN barrier layer at a source potential.
1. A vertical semiconductor device including a GaN-based stacked layer having an opening, the semiconductor device comprising:
a regrown layer including a channel located so as to cover a wall surface of the opening;
a p-type GaN-based semiconductor layer having an end face covered with the regrown layer at the wall surface of the opening;
an n + -type GaN-based semiconductor layer serving as a top layer of the GaN-based stacked layer;
a p + -type GaN-based supplementary layer containing a p-type impurity in a concentration higher than that of the p-type GaN-based semiconductor layer, the p + -type GaN-based supplementary layer being located between the p-type GaN-based semiconductor layer and the n + -type GaN-based semiconductor layer;
a gate electrode located on the regrown layer in the opening; and
a source electrode located on the GaN-based stacked layer around the opening so as to be in contact with the regrown layer and the n + -type GaN-based semiconductor layer,
wherein the regrown layer includes an electron drift layer and an electron source layer and the channel is formed of two-dimensional electron gas generated in the electron drift layer at a position near an interface between the electron drift layer and the electron source layer, and
the p + -type GaN-based supplementary layer is included in a structure that electrically connects the p-type GaN-based semiconductor layer and the source electrode to each other in order to fix an electric potential of the p-type GaN-based semiconductor layer at an electric potential of the source electrode, and
the n + -type GaN-based semiconductor layer and the p + -type GaN-based supplementary layer form a tunnel junction, and the source electrode and the p-type GaN-based semiconductor layer are electrically connected to each other through the tunnel junction.
2. The semiconductor device according to claim 1 , wherein the p + -type GaN-based supplementary layer has a p-type impurity concentration of 5×10 18 cm −3 or more and 5×10 20 cm −3 or less and the n + -type GaN-based semiconductor layer has a donor concentration of 1×10 18 cm −3 or more and 5×10 20 cm −3 or less.
3. The semiconductor device according to claim 1 , further comprising an extended electrode conductively connected to the p + -type GaN-based supplementary layer, wherein the extended electrode is electrically connected to the source electrode.
4. The semiconductor device according to claim 3 , wherein the source electrode extends so as to also serve as the extended electrode.
5. The semiconductor device according to claim 1 , wherein the thickness of the p + -type GaN-based supplementary layer is one fifth or less the thickness of the p-type GaN-based semiconductor layer.
6. The semiconductor device according to claim 1 , wherein the p + -type GaN-based supplementary layer has a thickness of 5 nm or more and 100 nm or less.
7. The semiconductor device according to claim 1 , wherein the p + -type GaN-based supplementary layer is disposed away from the wall surface of the opening.
8. The semiconductor device according to claim 1 , wherein an insulating layer is formed on the regrown layer and below the gate electrode.