It was recalled that B diffusion could be used to compensate the n-type layer of a p+nn+ 6H-type structure. Measurements which were performed under reverse-bias conditions, for currents ranging from 10 to 500A, showed that this process was very efficient at temperatures of about 300K: a voltage of 670V was found for a reverse current of 10A, instead of the 120V which was expected for a structure without diffused B. However, the breakdown voltage decreased rapidly as the temperature was increased. The use of capacitance measurements showed that the doping level in the n-type layer evolved in the same way as did the temperature (ranging from 1013 at 300K to 1017/cm3 at 500K). A high B concentration appeared to be responsible for this doping variation as a function of temperature. The results of admittance spectroscopy revealed the presence of D centers, at 0.62eV above the valence band, which were associated with B concentrations that were similar to, or greater than, the N concentration in the n-type layer. An increase in the doping level with temperature was suggested to be responsible for this decrease in breakdown voltage.

S.Ortolland, C.Raynaud, J.P.Chante, M.L.Locatelli, A.A.Lebedev, A.N.Andreev, N.S.Savkina, V.E.Chelnokov, M.G.Rastegaeva, A.L.Syrkin: Journal of Applied Physics, 1996, 80[9], 5464-8