Growth of high mobility GaN and AlGaN/GaN high electron mobility translator structures on 4H-SiC by ammonia molecular-beam epitaxy

Ammonia molecular-beam epitaxy has been used to grow high-quality epilayers of GaN and AlGaN/GaN heterostructure held-effect transistor (HFET) structu res on insulating 4H-SiC. The growth process, which used a magnetron sputte r epitaxy deposited buffer layer of AlN, has been described previously. Ex situ pretreatment of the SiC substrate was found to be unnecessary. For a s ingle 2.0 mum thick. silicon doped epilayer, a room temperature (RT) electr on mobility of 500 cm(2)/Vs was measured at a carrier density of 6.6 X 10(1 6) cm(-3). For the HFET structure, a room temperature mobility of 1300 cm(2 )/Vs at a sheet carrier density of 3.3 X 10(12) cm(-2) was observed, increa sing to 11 000 cm(2)/Vs at 77 K. The surface morphology of the layers indic ated a coalesced mesa structure similar to what we observed for growth on s apphire, but with a lower overall defect density and correspondingly larger grain size. The observation of well-resolved Shubnikov de Haas oscillation s at fields as low as 3 T indicated a relatively smooth interface. (C) 2001 American Institute of Physics.