High electron-mobility transistor
A nitride semiconductor device is disclosed. The semiconductor device provides the GaN channel layer, the InAlN barrier layer on the GaN channel layer, and the n-type AlGaN layer on the InAlN barrier layer. The source and drain electrodes are formed on the n-type AlGaN layer, while, the gate electrode is formed directly on the InAlN barrier layer. The n-type AlGaN layer has the aluminum (Al) composition greater than 20% at the interface against the InAlN barrier layer, which is greater than the aluminum (Al) composition at the interface against the source electrode.
1. A nitride semiconductor device, comprising:
a channel layer made of gallium nitride (GaN);
a barrier layer made of indium aluminum nitride (InAlN) that is formed on the channel layer;
an n-type layer made of aluminum gallium nitride (AlGaN) that is formed on the barrier layer, the n-type layer being doped with n-type impurities, the n-type layer having an aluminum composition greater than 20% at an interface against the barrier layer, the aluminum composition of the n-type layer at the interface being greater than the aluminum composition at a surface opposite to the interface; and
a source electrode, a drain electrode, and a gate electrode, the source electrode and the drain electrode being provided on the n-type layer, and the gate electrode being in direct contact with the barrier layer.
2. The nitride semiconductor device of claim 1 , wherein the n-type layer has a thickness greater than 50 nm but smaller than 100 nm.
3. The nitride semiconductor device of claim 2 , wherein the n-type layer includes a first layer including the interface and a second layer including the surface, the first layer having the aluminum composition greater than 20% and greater than an aluminum composition of the second layer.
4. The nitride semiconductor device of claim 3 , wherein the first layer and the second layer have respective thicknesses greater than 40 nm.
5. The nitride semiconductor device of claim 1 , wherein the aluminum composition of the n-type layer monotonically decreases from the interface to the surface.
6. The nitride semiconductor device of claim 1 , wherein the barrier layer has a thickness greater than 9 nm but less than 12 nm.
7. The nitride semiconductor device of claim 1 , wherein the n-type layer has an opening that exposes a surface of the barrier layer, the gate electrode being formed within the opening.
8. The nitride semiconductor device of claim 7 , further including an insulating film that covers the barrier layer exposed within the opening and the gate electrode provided within the opening.
9. The nitride semiconductor device of claim 1 , wherein the barrier layer has an indium composition greater than 15% but smaller than 20%.
10. The nitride semiconductor device of claim 9 , wherein the barrier layer has a lattice constant substantially matching with a lattice constant of the channel layer.
11. The nitride semiconductor device of claim 9 , wherein the n-type layer has a lattice constant miss-matched with a lattice constant of the barrier layer.
12. The nitride semiconductor device of claim 1 , wherein the n-type layer has a doping density of the n-type impurities from 1×10 18 cm −3 to 5×10 18 cm −3 .
13. The nitride semiconductor device of claim 12 , wherein the n-type impurities are silicon (Si).