JPS5513990A - Semiconductor device - Google Patents

Abstract

PURPOSE: To improve the breakdown characteristic by forming the pn-junction serving as the gardring against the reverse bias operated abalanche photo diode.

CONSTITUTION: On a n⁺-type substrate 11 formed is a n⁺-type layer 12, on which a n⁺-type layer 13 having a mesaform layer 13' is formed. Further on the layer 13 formed is a n-type layer 14, in which a p-type layer 16 is formed to provide a pnjunction plane 17. Since a depletion layer is spread into the mesaform layer 13' by applying the reverse bias on the junction plane 17, the breakdown voltage at the circumference of the pn-junction where the forbidden band width of the layer 14 burying the mesaform layer 13' is larger than that of the layer 13' becomes higher than the breakedown voltage at the pn-junction above the mesaform layer 13'. Furthermore, since the impurities concentration in the layer 14 is lower than that in the layer 13, the internal maximum electric field is formed at the pn-junction 17 above the layer 13' rather than at the circumference of the pn-junction 17 upon applying the constant reverse bias and the uniform breakdown will be caused in the former. Thus, the breakdown characteristic can be improved through the gardring structure.

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