Parasitic Hole Channels in AlGaN/GaN Heterojunction Structures

The formation of free holes in multi-junctioned cation-faced AlGaN/GaN structures for use as heterojunction field-effect transistors (HFETs) is investigated theoretically. The model is based on a self-consistent solution of a multi-band k · p Hamiltonian, the Poisson, and charge balance equations and includes the electron and hole-induced exchange-correlation potentials via density functional theory. The piezoelectric and spontaneous polarizations are taken into account. Realistic surface boundary conditions are incorporated by imposing a sheet layer of surface donors populated according to Fermi–Dirac statistics. For cation-faced structures, the calculations show that a two-dimensional hole gas (2DHG) may form at each GaN on AlGaN interface, depending on the structural geometry.