Effect of ultrathin AIN spacer on electronic properties of GaN/SiC heterojunction bipolar transistors

GaN/SiC heterojunction bipolar transistors (HBTs) with an ultrathin AIN spacer layer at the n-GaN/p-SiC emitter junction are proposed for the control of the electronic properties of GaN/SiC heterojunctions. The insertion of an AIN spacer is found to be promising in terms of improving electron injection efficiency owing to the reduced potential barrier (054 eV) to electron injection and reduced recombination via interface traps. We also investigated the effect of pre-irradiation of active nitrogen atoms (N*) prior to AIN growth for the control of the electronic properties of GaN/AIN/SiC heterojunctions. We found that the potential barrier was further reduced to 0.46 eV by N* pre-irradiation. The HBT structure was successfully fabricated using our newly developed process featuring ion implantation and Pd ohmic contacts to obtain a low contact resistivity to a p-SiC base at a temperature as low as 600 degrees C. A fabricated HBT without an AIN layer showed a low current gain (a similar to 0.001), whereas the GaN/AIN/SiC HBT showed improved current gains of 0.1 in the case of using a 1-nm-thick AIN spacer without N* pre-irradiation and 0.2 in the case of using a 2-nm-thick AIN spacer with N* pre-irradiation. 2014 The Japan Society of Applied Physics