Field-effect semiconductor device

A field-effect semiconductor device comprising semiconductor layers formed on a semiconductor substrate in the order listed below:

• a first semiconductor buffer layer;
• an undoped second semiconductor layer;
• a third semiconductor layer of a first conductivity type;
• and
• a fourth semiconductor layer of said first conductivity type;
• wherein
• the electron affinity of the second semiconductor layer at the interface with the First semiconductor buffer layer is greater than that of the first semiconductor buffer layer, the forbidden band gap of the second semiconductor layer increases in a graded manner from the first semiconductor buffer layer to the third semiconductor layer side, the electron affinity of the second semiconductor layer at the interface with the third semiconductor layer is not smaller than that of the third semiconductor layer, and the electron affinity of the fourth semiconductor layer is not greater than that of the third semiconductor layer.

A field-effect semiconductor device comprising semiconductor layers formed on a semiconductor substrate in the order listed below:

• a first semiconductor buffer layer;
• an undoped second semiconductor layer;
• an undoped third semiconductor layer;
• a fourth semiconductor layer of a first conductivity type;
• and
• an undoped fifth semiconductor layer;
• wherein
• the electron affinity of the second semiconductor layer is greater than that of the first semiconductor buffer layer, the electron affinity of the third semiconductor layer at the interface with the second semiconductor layer is not greater than that of the second semiconductor layer, the forbidden band gap of the third semiconductor layer increases in a graded manner from the second semiconductor layer to the fourth semiconductor layer side, the electron affinity of the third semiconductor layer at the interface with the fourth semiconductor layer is not smaller than that of the fourth semiconductor layer, and the electron affinity of the fifth semiconductor layer is not greater than that of the fourth semiconductor layer.

A field-effect semiconductor device comprising semiconductor layers formed on a semiconductor substrate in the order listed below:

• a first semiconductor buffer layer;
• an undoped second semiconductor layer;
• a third semiconductor layer of a first conductivity type;
• and
• an undoped fourth semiconductor layer;
• wherein
• the electron affinity of the second semiconductor layer at the interface with the first semiconductor buffer layer is greater than that of the first semiconductor buffer layer, the forbidden band gap of the second semiconductor layer increases in a graded manner from the first semiconductor buffer layer to the third semiconductor layer side, the electron affinity of the second semiconductor layer at, the interface with the third semiconductor layer is not smaller than that of the third semiconductor layer, and the electron affinity of the fourth semiconductor layer is not greater than that of the third semiconductor layer.

A field-effect transistor comprising:

• a semiconductor substrate;
• a first semiconductor buffer layer formed on the semiconductor substrate;
• an undoped second semiconductor layer formed on the first semiconductor buffer layer;
• an undoped third semiconductor layer formed on the second semiconductor layer;
• a fourth semiconductor layer of a first conductivity type formed on the third semiconductor layer;
• a fifth semiconductor layer of undoped type or said first conductivity type formed on the fourth semiconductor layer;
• a contact layer of said first conductivity type formed on the fifth semiconductor layer;
• a source electrode formed on the contact layer;
• a drain electrode formed on the contact layer;
• and
• a gate electrode formed on the fifth semiconductor layer;
• wherein
• the electron affinity of the second semiconductor layer is greater than that of the first semiconductor buffer layer, the electron affinity of the third semiconductor layer at the interface with the second semiconductor layer is not greater than that of the second semiconductor layer, the forbidden band gap of the third semiconductor layer increases in a graded manner from the second semiconductor layer to the fourth semiconductor layer side, the electron affinity of the third semiconductor layer at the interface with the fourth semiconductor layer is not smaller than that of the fourth semiconductor layer, and the electron affinity of the fifth semiconductor layer is not greater than that of the fourth semiconductor layer.

A field-effect transistor comprising:

• a semiconductor substrate;
• a first semiconductor buffer layer formed on the semiconductor substrate;
• an undoped second semiconductor layer formed on the first semiconductor buffer layer;
• a third semiconductor layer of a first conductivity type formed on the second semiconductor layer;
• a fourth semiconductor layer of undoped type or said first conductivity type formed on the third semiconductor layer;
• a contact layer of said first conductivity type formed on the fourth semiconductor layer;
• a source electrode formed on the contact layer;
• a drain electrode formed on the contact layer;
• and
• a gate electrode formed on the fourth semiconductor layer;
• wherein
• the electron affinity of the second semiconductor layer at the interface with the first semiconductor buffer layer is greater than that of the first semiconductor buffer layer, the forbidden band gap of the second semiconductor layer increases in a graded manner from the first semiconductor buffer layer to the third semiconductor layer side, the electron affinity of the second semiconductor layer at the interface with the third semiconductor layer is not smaller than that of the third semiconductor layer, and the electron affinity of the fourth semiconductor layer is not greater than that of the third, semiconductor layer.