| 摘要 |
PROBLEM TO BE SOLVED: To relax rapid current drop at the time of the end of inverse recovery, and to reduce spike voltage. SOLUTION: A p type anode layer 2 and an n+ type cathode layer 3 are respectively formed at one edge and the other edge of a substrate constituted of an n type semiconductor whose density is extremely low, and an i layer 1 is formed between the p type anode layer 2 and the n+ type cathode layer 3 in this semiconductor element. An n type impurity layer 6 whose density is lower than that of the n type cathode layer 3 is formed between the i layer 1 and the n+ type cathode layer 3. A distance Wn of the n type impurity layer 6 is made sufficiently shorter than a distance Wi of the i layer 1. Also, the following formula is established by defining the maximum electric field intensity as Emax, and electric field intensity when the inclination of the electric field is changed due to the difference of density of the i layer 1 and the n type impurity layer 6 as Einf, and a distance from the distance Wi when the electric field is turned into 0 as Wn' (Wn'<Wn) for obtaining a design breakdown strength Vb of the semiconductor element. In this formula, Vb=(Emax+Einf)Wi/2+EinfWn'/2.
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