Ohmic contact technology in III-V nitrides using polarization effects in cap layers

A novel technology for low-resistance ohmic contacts to III-V nitrides is presented. The contacts employ polarization-induced electric fields in strained cap layers grown on lattice-mismatched III-V nitride buffer layers. With appropriate choice of the cap layer, the electric field in the cap layer reduces the thickness of the tunnel barrier at the metal contact/semiconductor interface. Design rules for polarization-enhanced contacts are presented giving guidance for composition and thickness of the cap layer for different III-V nitride buffer layers. Experimental results for ohmic contacts with p-type InGaN and GaN cap layers are markedly different from samples without a polarized cap layer thus confirming the effectiveness of polarization-enhanced ohmic contacts.