Mobility of electrons in bulk GaN andAlxGa1−xN/GaNheterostructures

The room-temperature drift mobility of electrons in the channel of a ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}/\mathrm{G}\mathrm{a}\mathrm{N}$ field-effect transistor associated with scattering by optical and acoustic phonons is calculated as a function of areal density taking into account the two-mode nature of the alloy and half-space and interface modes. It is found that the two-dimensional (2D) mobility is significantly greater than the bulk mobility and this means that the mobility goes through a maximum as a function of density corresponding to a transition from bulk to 2D transport. A simple model is used to describe the transition from bulk to 2D transport as the electron density increased. It is shown that for the structure considered the mobility at 300 K goes through a weak maximum at about 2000 ${\mathrm{cm}}^2$/V s at a density of about $2\times {10}^{12}\hspace{0.5em}{\mathrm{cm}}^{\mathrm{-}2}$ dropping to about 1300 ${\mathrm{cm}}^2$/V s at ${10}^{13}\hspace{0.5em}{\mathrm{cm}}^{\mathrm{-}2}.$ Results for the Hall factor and for the temperatures 77 and 600 K are also obtained. The contribution made by interface-roughness scattering is also discussed.