Electrical properties of MBE-grown AlGaN/GaN HEMT structures by using 4H-SiC (0001) vicinal substrates

摘要

AlGaN/GaN high electron mobility transistor (HEMT) structures were grown on 4H-SiC (0001) vicinal substrates with vicinal angles of 0.4°, 1° and 2° inclined toward < 1010 >, as well as 0° (just substrate) by radio-frequency plasma-assisted molecular beam epitaxy (rf-MBE). It was found that the mobility was enhanced by increasing the vicinal angle, particularly, the mobility in the sample grown on a 2°-off substrate exhibited 8600 cm~2/V s in contrast to that grown on a just sample (3310 cm~2/V s) at 30 K. In addition, the anisotropic two-dimensional electron gas (2DEG) mobility of the vicinal samples was clearly found, where the mobility at 30 K along the < 1120 > direction (parallel to the macro step) and that along < 1010 > direction (perpendicular to the macro step) were 5490 and 1600 cm~2/V s, respectively, for the 1 °-off sample. The enhancement of the 2DEG mobility is considered to be due to the improvement of film qualities by using vicinal substrates.