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 a coustic phonons is calculated as a function of areal density taking into ac count 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 max imum 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 st ructure considered the mobility at 300 K goes through a weak maximum at abo ut 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 t emperatures 77 and 600 K are also obtained. The contribution made by interf ace-roughness scattering is also discussed.