Semiconductor device and method of manufacturing semiconductor device
A semiconductor device according to the present invention includes a substrate, a plurality of semiconductor layers to be overlaid on the substrate and a gate electrode, a drain electrode, and a source electrode provided on the plurality of semiconductor layers, wherein each of the plurality of semiconductor layers includes a channel layer made with GaN and a barrier layer provided in contact with an upper surface of the channel layer and made with Al x Ga 1-x N, and a carbon concentration of the channel layer included in an uppermost semiconductor layer among the plurality of semiconductor layers is lower than an average value of carbon concentration of the channel layer included in the at least one semiconductor layer other than the uppermost semiconductor layer among the plurality of semiconductor layers.
1 . A semiconductor device comprising:
a substrate;
a plurality of pairs of semiconductor layers on the substrate; and
a gate electrode, a drain electrode, and a source electrode provided on the plurality of pairs of semiconductor layers, wherein
each of the plurality of pairs of semiconductor layers includes a channel layer made with GaN and a barrier layer provided in contact with an upper surface of the channel layer and made with Al x Ga 1-xN ,
a carbon concentration of the channel layer included in an uppermost pair of semiconductor layers among the plurality of pairs of semiconductor layers is lower than an average value of carbon concentration of the channel layers included in the pairs of semiconductor layers other than the uppermost pair of semiconductor layers, and
the uppermost pair of semiconductor layers is an uppermost pair of channel and barrier layers in the semiconductor device.
2 . The semiconductor device according to claim 1 , wherein a two-dimensional electron gas is formed at an interface with the barrier layer in the channel layer in each of the plurality of pairs of semiconductor layers.
3 . The semiconductor device according to claim 1 , wherein the channel layer included in the uppermost pair of semiconductor layers is thinner than the channel layer included in one of the pairs of semiconductor layers other than the uppermost pair of semiconductor layers.
4 . The semiconductor device according to claim 1 , wherein the carbon concentration of the channel layer included in the uppermost pair of semiconductor layers is lower than the carbon concentration of the channel layer included in the pair of semiconductor layers immediately below the uppermost pair of semiconductor layers.
5 . The semiconductor device according to claim 1 , wherein the channel layer included in the uppermost pair of semiconductor layers and the barrier layer included in the pair of semiconductor layers immediately below the uppermost pair of semiconductor layers contact each other.
6 . The semiconductor device according to claim 1 , wherein a sum of respective film thicknesses of the channel layer included in the uppermost pair of semiconductor layers and the barrier layer included in the pair of semiconductor layers immediately below the uppermost pair of semiconductor layers is 20 nm or less.
7 . The semiconductor device according to claim 1 , wherein in each barrier layer included in each of the pairs of semiconductor layers other than the uppermost pair of semiconductor layers-layer, x is 0.2 or more.
8 . The semiconductor device according to claim 1 , wherein the carbon concentration of the channel layer included in the uppermost pair of semiconductor layers is 3×10 16 cm −3 or less.
9 . The semiconductor device according to claim 1 , wherein the average value of the carbon concentration of the channel layer included in each of the pairs of semiconductor layers other than the uppermost pair of semiconductor layers is 1×10 16 cm −3 or more.
10 . The semiconductor device according to claim 1 , wherein the channel layer included in an uppermost pair of semiconductor layers among the plurality of pairs of semiconductor layers includes carbon as an impurity.