Excellent DC characteristics of HEMTs on semi-insulating silicon carbide substrate

The epitaxial layers of Al/sub 0.26/Ga/sub 0.74/N/GaN were grown by MOCVD with a good uniformity and carrier mobility of 1281 cm/sup 2//Vs at room temperature. High electron mobility transistor (HEMT) have been fabricated using AlGaN/GaN heterostructure on semi-insulating silicon carbide substrate. The fabricated 2.2 μm gate length Al/sub 0.26/Ga/sub 0.74/N/GaN HEMTs exhibited high transconductance 287 mS/mm with high drain current density 857 mA/mm. This is the first report with highest transconductance so far achieved for 2.2 μm gate length AlGaN/GaN HEMTs. Good I/sub DS/-V/sub DS/ characteristics of a 2.2 μm gate length and 15 μm gate width HEMT, yielding a maximum current density of 867 mA/mm and a record extrinsic transconductance of 287 mS/mm for the gate voltage of 0.2 V. From the transfer characteristics, the observed maximum drain-source current density is 1100 mA/mm for the gate and drain voltage of 3.8 and 10 V. The I-V characteristic is noteworthy for its minimal current decrease at large dissipation levels due to self-heating. Owing to the excellent thermal conductivity of the SiC substrate, the current density decreases during the sweep (857 mA/mm to 833 mA/mm) by only 2.8% when the drain bias is increases to 20 V. The self-heating effect is high for sapphire based device structures.