  We studied the diffusion coefficient of hot electrons of GaN crystals in
moderate electric (1...10 kV/cm) and magnetic (1...4 T) fields. Two
configurations, parallel and crossed fields, are analysed. The study was
carried out for compensated bulk-like GaN samples at different lattice
temperatures (30...300 K) and impurity concentrations (10^16..10^17 cm^{-3}).
We found that at low lattice temperatures and low impurity concentrations,
electric-field dependencies of the transverse-to-current components of the
diffusion tensor are non-monotonic for both configurations, while the diffusion
processes are greatly controlled by the magnetic field. With an increase of the
lattice temperature or the impurity concentration, the behaviour of the
diffusion tensor becomes more monotonous and less affected by the magnetic
field. We showed that such behaviour of the diffusion processes is due to the
distinct kinetics of the hot electrons in polar semiconductors with strong
electron-optical phonon coupling. We suggest that measurements of the diffusion
coefficient of the electrons subjected to electric and magnetic fields
facilitate the identification of features of different electron transport
regimes and the development of more efficient devices and practical
applications.
