Nitride semiconductor device and manufacturing method therefor

A nitride semiconductor device comprising:

• a first nitride semiconductor layer that constitutes an electron transit layer;
• a second nitride semiconductor layer that is formed above the first nitride semiconductor layer, is greater in bandgap than the first nitride semiconductor layer, and constitutes an electron supply layer;
• a third nitride semiconductor layer that is formed selectively above the second nitride semiconductor layer, the third nitride semiconductor layer having a ridge portion of a ridge shape that contains an acceptor type impurity;
• a gate electrode that is formed above the ridge portion;
• a passivation film that is disposed on the second nitride semiconductor layer, the third nitride semiconductor layer, and the gate electrode and has a first opening portion and a second opening portion that are disposed across the ridge portion from each other;
• a source electrode that is in contact with the second nitride semiconductor layer via the first opening portion and with which a portion is formed above the passivation film;
• and
• a drain electrode that is in contact with the second nitride semiconductor layer via the second opening portion and with which a portion is formed above the passivation film such as to oppose the source electrode across the ridge portion;
• and
• wherein the third nitride semiconductor layer has, between the ridge portion side end of the first opening portion and the first opening portion side end of the ridge portion and/or between the ridge portion side end of the drain electrode and the second opening portion side end of the ridge portion, an extension portion that extends outward from a portion below a thickness intermediate position of at least one side surface of the ridge portion, and a separated portion that is not in contact with the ridge portion and the extension portion and is substantially equal in film thickness to the extension portion.

A nitride semiconductor device comprising:

• a first nitride semiconductor layer that constitutes an electron transit layer;
• a second nitride semiconductor layer that is formed above the first nitride semiconductor layer, is greater in bandgap than the first nitride semiconductor layer, and constitutes an electron supply layer;
• a third nitride semiconductor layer that is formed selectively above the second nitride semiconductor layer, the third nitride semiconductor layer having a ridge portion of a ridge shape that contains an acceptor type impurity;
• a gate electrode that is formed above the ridge portion;
• a passivation film that is disposed on the second nitride semiconductor layer, the third nitride semiconductor layer, and the gate electrode and has a first opening portion and a second opening portion that are disposed across the ridge portion from each other;
• a source electrode that is in contact with the second nitride semiconductor layer via the first opening portion and with which a portion is formed above the passivation film;
• and
• a drain electrode that is in contact with the second nitride semiconductor layer via the second opening portion and with which a portion is formed above the passivation film such as to oppose the source electrode across the ridge portion;
• and
• wherein the third nitride semiconductor layer has, between the ridge portion side end of the first opening portion and the first opening portion side end of the ridge portion and/or between the ridge portion side end of the drain electrode and the second opening portion side end of the ridge portion, an extension portion that extends outward from a portion below a thickness intermediate position of at least one side surface of the ridge portion, and
• wherein the third nitride semiconductor layer is constituted of at least a first semiconductor region and a second semiconductor region that differ in bandgap and the extension portion includes the first semiconductor region.