Mosaic Structure and Si Doping Related Peculiarities of Charge Carrier Transport in III-V Nitrides

Abstract

Studies of the charge carrier transport in undoped, moderately and heavily Si doped GaN and AlxGa1—xN (x = 0.1 to 0.2) epilayers with different mosaic structure are presented. The epilayers were grown by low-pressure MOCVD on (0001) sapphire substrates. The mosaic (columnar) structure of the epilayers has been characterized by X-ray diffraction and AFM surface topography studies. Application of electrostatic force microscopy (EFM) permitted to reveal irregular potential barriers at the mosaic domain boundaries in undoped layers and their reduction in Si doped layers. For undoped GaN and AlGaN epilayers unconventional transport of electrons (dependence σ ∼ exp (—1/T)) and a low RT mobility (20 to 70 cm2 V—1 s—1) have been found. We relate the peculiarities in the electron transport in undoped samples with additional carrier scattering on the potential barriers at domain boundaries. Si doping reduces the potential barriers. Moderate Si doping causes a considerable increase of the electron RT mobility up to 600 cm2 V—1 s—1 and restores the dependence μ ∼ T3/2.