Mobility of electrons in bulk GaN and AlxGa1-xN/GaN heterostructures

The room-temperature drift mobility of electrons in the channel of a AlxGa1-xN/GaN 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 cm(2)/V a at a density of about 2 x 10(12) cm(-2) dropping to about 1300 cm(2)/V s at 10(13) cm(-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.