Wide band gap semiconductor device including junction field effect transistor

A wide band gap semiconductor device comprising:

• a semiconductor substrate having a transistor cell region, a diode forming region, an electric field relaxation region located between the transistor cell region and the diode forming region, and an outer peripheral region surrounding the transistor cell region, diode forming region, and the electric field relaxation region, the semiconductor substrate in the transistor cell region including a substrate, a first semiconductor layer disposed on the substrate, a second semiconductor layer disposed on the first semiconductor layer, and a third semiconductor layer disposed on the second semiconductor layer, the substrate made of a wide band gap semiconductor of a first conductivity type, the first semiconductor layer made of a wide band gap semiconductor of the first conductivity type and having an impurity concentration lower than an impurity concentration of the substrate, the second semiconductor layer made of a wide band gap semiconductor of a second conductivity type, the third semiconductor layer made of a wide band gap semiconductor of the first conductivity type and having an impurity concentration higher than the impurity concentration of the first semiconductor layer, the semiconductor substrate in the electric field relaxation region including the substrate, the first semiconductor layer disposed on the substrate, and the second semiconductor layer disposed on the first semiconductor layer;
• a junction field effect transistor (JFET) disposed in the transistor cell region, the JFET including a first trench penetrating the third semiconductor layer and the second semiconductor layer to the first semiconductor layer, a first gate region provided by the second semiconductor layer located on a side surface of the first trench, a source region provided by the third semiconductor layer located on the side surface of the first trench, a channel layer disposed on an inner wall of the first trench and made of a wide band gap semiconductor of the first conductivity type, a second gate region disposed on a surface of the channel layer so as to fill the first trench and made of a wide band gap semiconductor of the second conductivity type, a source electrode electrically coupled with the source region, and a drain electrode electrically coupled with the substrate;
• a diode disposed in the diode forming region and including a first-surface electrode and a second-surface electrode, the second-surface electrode provided by the drain electrode and operating as an anode, the first-surface electrode disposed on an opposite side of the semiconductor substrate from the second-surface electrode and operating as a cathode;
• an outer peripheral withstand-voltage part disposed in the outer peripheral region;
• and
• an isolating part disposed in the electric field relaxation region, the isolating part including a second trench penetrating the second semiconductor layer to the first semiconductor layer so as to divide the transistor cell region and the diode forming region, a first conductivity-type layer disposed on an inner wall of the second trench and made of a wide band gap semiconductor of the first conductivity type, and a second conductivity-type layer disposed on a surface of the first conductivity-type layer so as to fill the second trench and made of a wide gap semiconductor of the second conductivity type, the first conductivity-type layer and the second conductivity-type layer providing a PN junction.