Modeling of hole tunneling in polarization-based contacts to wurtzite p-type Gallium Nitride using thin indium Gallium Nitride caps

The paper presents hole transport calculations for contact resistances to p-type GaN with thin InGaN cap layers of 20 A or less thickness, taking explicitly into account three different kinds of holes with very different effective masses and mass anisotropies the split-off, heavy and light holes. It is shown that polarization discontinuity induces electric fields of several MV per cm that reduce the effective tunneling width for holes. The predominance of split-off holes in the tunneling flux is established despite their smaller Fermi-Dirac occupation factors, and a two order of magnitude improvement in contact resistance is demonstrated.The use of cap layers with large piezoelectric polarization can also be used to eliminate the need for extreme annealing treatments for contact resistance optimization.