NTT demonstrated an aluminum nitride (AlN) transistor featuring a large breakdown field. The innovation is seen as a promising semiconductor material for achieving low-loss, high-voltage power devices. NTT produced the high-quality AlN by using metalorganic chemical vapor deposition (MOCVD)4 and also developed formation methods of ohmic and Schottky contacts.
NTT said that by using a wide bandgap semiconductor with a large breakdown field, it is possible to reduce the loss and increase the breakdown voltage. Therefore, wide bandgap semiconductors such as silicon carbide (SiC) and gallium nitride (GaN) are being developed for power devices. UWBG semiconductors with a breakdown field larger than that of SiC or GaN further improve the performance of power devices. UWBG semiconductors include AlN, diamond, and gallium oxide (Ga2O3) (Table I). For AlN power devices, the power loss is theoretically expected to be only 5% of Si, 35% of SiC, and 50% of GaN.
In 2002, NTT succeeded in fabricating semiconducting AlN for the first time in the world, thus opening up new avenues in semiconductor device applications. Among UWBG semiconductors, AlN is advantageous in that devices can be fabricated on large-scale wafers and various device structures can be obtained by heterojunction formation with other nitride semiconductors such as GaN. However, there have been few reports on power device fabrications in this vein, and their characteristics need to be improved.
