GaN-GaN junctions with ultrathin AlN interlayers: Expanding heterojunction design

The formation of a two-dimensional electron gas (2DEG) was observed at GaN-GaN junctions, when an AlN layer of a thickness greater than or equal to 0.5 nm was inserted, and the GaN cap layer was modulation-doped with silicon. No 2DEG was found for undoped samples. When the AlN interlayer thickness was increased from 0.5 to 1 nm, the electron mobility increased from 720 to 1250 cm2/Vs at 300 K and from 6400 to 12 000 cm2/Vs at 77 K. The electron mobility was also affected by the Si-spike doping concentration with the highest electron mobility of 13 800 cm2/Vs at 77 K measured for a doping of 5x10(12) cm(-2). The formation of the 2DEG was attributed to the polarization-induced discontinuity in the conduction band caused by the extremely strong polarization fields in the pseudomorphically strained AlN interlayers. (C) 2002 American Institute of Physics.