Fabrication and characterization of heterojunction diodes with HVPE-Grown GaN on 4H-SiC

GaN/SiC heterojunctions can improve the performance considerably for BJTs a nd FETs. In this work, heterojunction diodes have been manufactured and cha racterized. The fabricated diodes have a GaN n-type cathode region on top o f a JH-SIC p-type epi layer. The GaN layer was grown with HVPE directly on off-axis SiC without a buffer layer. Mesa structures were formed and a Ti m etallization was used as cathode contact to GaN, and the anode contact was deposited on the backside using sputtered Al. Both current-voltage (I-V) an d capacitance-voltage (C-V) measurements were performed on the diode struct ures. The ideality factor of the measured diodes was 1.1 and was constant w ith temperature. A built in potential of 2.06 V was extracted from I-V-meas urements and agrees well with the built in potential from C-V-measurements. The conduction band offset was extracted to 1.1 eV and the heterojunction was of type II. The turn on voltage for the diodes is about 1 V lower than expected and a suggested mechanism for this effect is discussed.