Reduction of the Specific Contact Resistance in p-type GaN-based Devices via Polarization Doping.

The power efficiency of GaN-based devices is sensitive to energy loss at p-type semiconductor contacts. Low resistance contacts to p-type GaN are difficult to achieve due to limitations in extrinsic acceptor doping. These limitations can be avoided via polarization doping. Au/Ni contacts deposited on a 2nm thick strained In$_{x}$Ga$_{1-x}$N capping layer atop a p-type GaN layer exhibited three orders of magnitude reduction in the specific contact resistance versus the single layer p-type GaN control. Increased band bending near the interface due to the polar field resulted in a reduced tunneling barrier width and a decrease in the specific contact resistance. At a minimum critical capping layer thickness, a two-dimensional hole gas (2DHG) forms in the In$_{x}$Ga$_{1-x}$N layer. The effect of the composition and thickness of the capping layer on the specific contact resistance and the hole concentration in a 2DHG has been determined using self-consistent solutions to the Schr\"{o}dinger and Poisson equations and will be reported in the presentation. The results of these simulations will also be compared with data from electrical measurements on actual In$_{x}$Ga$_{1-x}$N/GaN heterostructures.