Two-dimensional electron-gas density in AlXGa1−XN/GaN heterostructure field-effect transistors

We have calculated maximum two-dimensional electron-gas densities in AlXGa1−XN/GaN heterostructure field-effect transistors with wurtzite crystal structures in (0001) orientation, by self-consistently solving Schrödinger’s and Poisson’s equations, taking the piezoelectric effect into account. In order to obtain a guideline for increasing electron densities in the devices, we have examined dependences of the maximum electron densities on both Al compositions of AlXGa1−XN layers and lattice relaxations at the heterointerfaces. The maximum electron density was found to depend more strongly on the lattice relaxation than on the Al composition, which determines the conduction-band discontinuity. Controlling the lattice relaxation is shown to be crucial for obtaining high electron densities in the devices.