Group III nitride semiconductor device, production method therefor, power converter
Provided is an HEMT exhibiting a normally-off characteristic and low on-state resistance, which includes a first carrier transport layer; two separate second carrier transport layers formed of undoped GaN and provided on two separate regions of the first carrier transport layer; and carrier supply layers formed of AlGaN and respectively provided on the two separate second carrier transport layers. The second carrier transport layers and the carrier supply layers are respectively formed through crystal growth on the first carrier transport layer. The heterojunction interface between the second carrier transport layer and the carrier supply layer exhibits high flatness, and virtually no growth-associated impurities are incorporated in the vicinity of the heterojunction interface. Therefore, reduction in mobility of 2DEG is prevented, and on-state resistance is reduced.
1. A semiconductor device comprising:
a first carrier transport layer formed of a Group III nitride semiconductor;
a second carrier transport layer which is formed through selective re-growth of a Group III nitride semiconductor and is provided on a region of the first carrier transport layer; and
a carrier supply layer formed through selective growth of a Group III nitride semiconductor having a bandgap larger than that of the Group III nitride semiconductor of the second carrier transport layer, the carrier supply layer being provided on the second carrier transport layer,
wherein laminate structures comprising the second carrier transport layer and the carrier supply layer are formed on two separate regions of a surface of the first carrier transport layer, and
wherein the semiconductor device further comprises:
a first electrode which is provided on the carrier supply layer of one of the two separate regions and which is electrically connected to the second carrier transport layer of the same region;
a second electrode which is provided on the carrier supply layer of the other region and which is electrically connected to the second carrier transport layer of the same region;
an insulating film which is provided on a region of the first carrier transport layer sandwiched between the two separate regions and also on the mutually facing lateral end surfaces of the two separate laminate structures; and
a control electrode formed on the insulating film.
2. A semiconductor device according to claim 1 , wherein the insulating film has a thickness smaller than that of the second carrier transport layer.
3. A semiconductor device according to claim 1 , wherein each of the first electrode and the second electrode is in ohmic contact with the corresponding second carrier transport layer.
4. A semiconductor device according to claim 1 , wherein one of the first electrode and the second electrode is electrically connected to the control electrode.
5. A semiconductor device according to claim 1 , wherein the carrier supply layer comprises a plurality of layers.
6. A semiconductor device according to claim 1 , the semiconductor device further comprising:
on the carrier supply layer, one or more layer pairs,
each pair comprising an under layer formed through selective growth of a Group III nitride semiconductor, and an upper layer formed through selective growth of a Group III nitride semiconductor having a bandgap larger than that of the Group III nitride semiconductor of the under layer,
wherein an under layer which contacts with the carrier supply layer has a bandgap smaller than that of the Group III nitride semiconductor of the carrier supply layer.
7. A semiconductor device according to claim 1 , wherein lateral end surfaces of the second carrier transport layer and the carrier supply layer are inclined such that the area of a horizontal cross section of the second carrier transport layer and the carrier supply layer parallel to the main surface of the device is reduced with increasing distance between the cross section and the first carrier transport layer.
8. A power converter comprising the semiconductor device according to claim 1 .
9. A semiconductor device according claim 1 , wherein the insulating film is provided also on the top surfaces of the carrier supply layers, and the control electrode extends, via the insulating film, onto the carrier supply layers.
10. A semiconductor device according to claim 9 , wherein a portion or the entirety of the insulating film comprises a plurality of layers.
11. A semiconductor device according to claim 9 , wherein a portion of the insulating film provided on the first carrier transport layer exhibits a property different from that of a portion of the insulating film provided on the carrier supply layer.
12. A semiconductor device according to claim 1 , wherein the semiconductor device further comprises a layer for preventing transport of carriers in a region away from the second carrier transport layer, and the first carrier transport layer is provided on the carrier transport preventing layer.
13. A semiconductor device according to claim 12 , wherein the carrier transport preventing layer is formed of a Group III nitride semiconductor having a conduction type different from that of the Group III nitride semiconductor of the first carrier transport layer.
14. A semiconductor device according claim 12 , wherein the carrier transport preventing layer comprises a Group III nitride semiconductor having a bandgap larger than that of the Group III nitride semiconductor of the first carrier transport layer.
15. A semiconductor device according to the claim 12 , wherein the carrier transport preventing layer is provided on a layer formed of a Group III nitride semiconductor having a bandgap larger than that of the Group III nitride semiconductor of the carrier transport preventing layer.