Semiconductor device and method of manufacturing the device
In a manufacturing method of a semiconductor device, first, a first semiconductor layer, a second semiconductor layer, and a p-type third semiconductor layer are sequentially epitaxially grown on a substrate. After that, the third semiconductor layer is selectively removed. Then, a fourth semiconductor layer is epitaxially grown on the second semiconductor layer. Then, a gate electrode is formed on the third semiconductor layer.
1. A nitride semiconductor device comprising:
a substrate;
a first semiconductor layer formed on the substrate;
a second semiconductor layer formed on the first semiconductor layer, and having greater bandgap energy than the first semiconductor layer;
a p-type third semiconductor layer selectively formed on the second semiconductor layer;
a fourth semiconductor layer formed on the second semiconductor layer; and
a gate electrode formed on the third semiconductor layer, wherein:
the third semiconductor layer does not cover the fourth semiconductor layer,
the third semiconductor layer is made of Al y Ga 1-y N, where 0≦y<1,
the fourth semiconductor layer is made of Al z Ga 1-z N, where 0<z<1, z≠y,
a composition of the fourth semiconductor layer changes continuously or gradually, and
at least a part of the fourth semiconductor layer has greater bandgap energy than the second semiconductor layer.
2. The nitride semiconductor device of claim 1 , wherein
a part of the fourth semiconductor layer which is in contact with the second semiconductor layer is lattice matched with the second semiconductor layer.
3. The nitride semiconductor device of claim 1 , wherein
the fourth semiconductor layer is a multilayer formed by stacking a plurality of layers having different compositions.
4. A nitride semiconductor device comprising:
a substrate;
a first semiconductor layer formed on the substrate;
a second semiconductor layer formed on the first semiconductor layer, and having greater bandgap energy than the first semiconductor layer;
a p-type third semiconductor layer selectively formed on the second semiconductor layer;
a fourth semiconductor layer formed on the second semiconductor layer; and
a gate electrode formed on the third semiconductor layer, wherein:
the third semiconductor layer does not cover the fourth semiconductor layer,
the third semiconductor layer is made of Al y Ga 1-y N, where 0≦y<1,
the fourth semiconductor layer is made of Al z Ga 1-z N, where 0<z<1, z≠y, and
a top surface of the third semiconductor layer is partly covered by the fourth semiconductor layer.
5. A nitride semiconductor device comprising:
a substrate;
a first semiconductor layer formed on the substrate;
a second semiconductor layer formed on the first semiconductor layer, and having greater bandgap energy than the first semiconductor layer;
a p-type third semiconductor layer selectively formed on the second semiconductor layer;
a fourth semiconductor layer formed on the second semiconductor layer; and
a gate electrode formed on the third semiconductor layer, wherein:
the third semiconductor layer does not cover the fourth semiconductor layer,
the third semiconductor layer is made of Al y Ga 1-y N, where 0≦y<1,
the fourth semiconductor layer is made of Al z Ga 1-z N, where 0<z<1, z≠y, and
a top surface of the third semiconductor layer is located higher than a highest part of a top surface of the fourth semiconductor layer measured from a surface of the substrate.
6. A nitride semiconductor device comprising:
a substrate;
a first semiconductor layer formed on the substrate;
a second semiconductor layer formed on the first semiconductor layer, and having greater bandgap energy than the first semiconductor layer;
a p-type third semiconductor layer formed on the second semiconductor layer;
a fourth semiconductor layer formed on the second semiconductor layer; and
a gate electrode formed on the third semiconductor layer, wherein:
the third semiconductor layer does not cover the fourth semiconductor layer,
the third semiconductor layer is made of Al y Ga 1-y N, where 0≦y<1,
the fourth semiconductor layer is made of Al z Ga 1-z N, where 0<z<1, z≠y, and
a bandgap energy of the fourth semiconductor layer is greater than a bandgap energy of the third semiconductor layer.
7. The nitride semiconductor device of claim 6 , wherein
the first semiconductor layer is made of GaN, and
the second semiconductor layer is made of Al x Ga 1-x N, where 0<x≦1.
8. The nitride semiconductor device of claim 6 , wherein
the nitride semiconductor device is a normally-off transistor.
9. The nitride semiconductor device of claim 6 , wherein
the second semiconductor layer and the fourth semiconductor layer are not formed in-situ.
10. The nitride semiconductor device of claim 6 , wherein
the third semiconductor layer is made of GaN.