Tailoring of internal fields in AlGaN/GaN and InGaN/GaN heterostructure devices

A study of the internal electric field distributions in ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}/\mathrm{G}\mathrm{a}\mathrm{N}$ and ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}/\mathrm{G}\mathrm{a}\mathrm{N}$ heterostructures grown on (0001) GaN is presented. The fields are deduced taking into account the device structure, background doping, and the difference in the total (spontaneous and piezoelectric) polarization of the layers. Two basic structures, a multiple quantum well in the depletion region of a $p-n$ junction and the heterojunction field effect transistor, are analyzed. The cases where the field distribution can be approximated analytically are discussed. When charge accumulation is present at the interfaces, a self-consistent solution of the Schrödinger and Poisson equations is obtained. By comparing with available experimental data, the polarization field in ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}/\mathrm{G}\mathrm{a}\mathrm{N}$ heterostructures has been estimated for two Al contents.