Selective MBE growth of nonalloyed ohmic contacts to 2D electron gas in high-electron-mobility transistors based on GaN/AlGaN heterojunctions

Specific features of how nonalloyed ohmic contacts to the 2D conducting channel of high-electron-mobility transistors based on AlGaN/(AlN)/GaN heterostructures are fabricated via deposition of heavily doped $n^+$-GaN through a SiO$_2$ mask by ammonia molecular-beam epitaxy have been studied. The technique developed makes it possible to obtain specific resistances of contacts to the 2D gas as low as 0.11 $\Omega$ mm on various types of Ga-face nitride heterostructures, which are several times lower than the resistance of conventional alloyed ohmic contacts.