Temperature and doping dependencies of electrical properties in Al-doped 4H-SiC epitaxial layers

The free hole concentration and the low-field transport properties of Al-doped 4H-SiC epilayers with several acceptor concentrations grown on semi-insulating substrates have been investigated in the temperature range from 100 to 500 K by Hall-effect measurements. Samples have been grown by cold-wall chemical vapor deposition (CVD) in the Al acceptor concentration range from 3x10(15) to 5.5x10(19) cm(-3). The dependencies of the acceptor ionization ratio at 300 K and the ionization energy on the acceptor concentration were estimated. Numerical calculations of the hole Hall mobility and the Hall scattering factor have been performed based on the low-field transport model using relaxation-time approximation. At the low acceptor concentrations, the acoustic phonon scattering dominates the hole mobility at 300 K. At the high acceptor concentrations, on the other hand, the neutral impurity scattering dominates the mobility. A Caughey-Thomas mobility model with temperature dependent parameters is used to describe the dependence of the hole mobilities on the acceptor concentration, and the physical meanings of the parameters are discussed.