The diode made by AIST has a diamond substrate and a material called ruthenium for the electrodes. This replaced gold and platinum electrodes from the old devices which are not so stable. Gold and platinum reacts with the substrate and peels off, making the diodes unusable. Besides this the devices needed to be cooled down to 250°C.
The new power device works at temperatures of 400°C for at least 1500 hours. But major problem at this moment is that the device can only handle 1A current.
With time, this technology will probably be optimized so this kind of devices could be used in hybrid cars without needing to be cooled down.