Study of Dopant Activation and Ionization for Phosphorus in 4H-SiC

Ion implantation is the most useful technology for doping of 4H silicon carbide to fabricate power devices. Semiconductor properties depend on implanted doping activation and ionization, and these properties are critical for the proper design and modeling of SiC power devices. In 4H-SiC, during activation annealing, the atomic diffusion rate is low, and thus full dopant activation is not readily achieved. Also, dopants in 4H-SiC are observed to have very deep energy levels. The temperature behavior of the electrical characteristics depends on the ionization energy level, and these values are not adequately characterized in 4H-SiC over all doping levels. To improve device modeling accuracy and device design predictive capabilities as a function of temperature and doping levels, further study of the behavior of dopants in SiC is crucial. Due to its demonstrated usefulness in epitaxial n-type SiC growth, nitrogen is the element most frequently employed in device manufacturing for n-type doping. However, phosphorus can serve as an alternative, with ionization energies expected to be close to nitrogen. In this work, electrical characterization of phosphorus-implanted 4H-SiC is examined as a function of doping and temperature. For this purpose, four-point van der Pauw probes are prepared, and resistivity and Hall measurements are carried out. Resistivity values are observed to decrease as temperature and doping concentration increase. Concerning Hall mobility, at low temperatures, the Hall mobility decreases due to increased impurity scattering, while at very high temperatures, it decreases because of increased phonon scattering. The increase in carrier concentration with the increase in temperature indicates incomplete ionization and relatively deep ionization energies. From the obtained data, a two-level charge neutrality equation is used to extract and compare the activation percentage and ionization energies for dopants in hexagonal and cubic sites. For a doping level of ~ 3.2 × 10¹⁸ cm⁻³, dopant ionization energy levels of 82 meV and 40 meV are found for the cubic and hexagonal sites, respectively, and these are observed to be a function of doping concentration. The extracted activation rate and ionization energies are useful for improving the predictive capability of SiC device modeling.