Ion Implantation Effects of Nitrogen, Boron, and Aluminum in Hexagonal Silicon Carbide

The effects of the implantation of ¹⁴N^{+ 11}B⁺, and ²⁷A1⁺ ions in hexagonal crystals were studied through optical and microanalytical methods. The optical data taken for 60 keV ¹⁴N ⁺ implants indicate that little damage occurs up to a fluence of 10¹⁴ cm⁻². For fluences between 10¹⁴ cm⁻² and , there is a rapid increase of the optical absorption below ∼3 eV with a broad absorption tail extending into the near infrared. For larger fluences, the optical absorption close to the band edge actually decreases. The band edge shifts to lower energies with increasing fluence. The radiation damage begins to anneal at low temperatures but is not completely removed until annealing at 1400° C. Boron and aluminum behave similarly to nitrogen as far as the general behavior of the damage in the implanted regions is concerned. Boron implanted crystals with peak concentrations in the 10²⁰ cm⁻³ range show weak yellow "boron" luminescence in the implanted areas after annealing. Qualitative thermoelectric power measurements indicate that boron implants up to this level do not result in conversion of n‐type layers to p‐type layers. For the aluminum implants conversion from n‐type to p‐type was observed for the highest fluence used, . The impurity profiles measured before and after annealing for crystals irradiated with different fluences show that the distribution of the impurities is broader than predicted by the LSS theory and changes with fluence. Upon annealing the impurities migrate toward the surface.