Abstract: A method of forming a planar semiconductor device, such as an array of APDs, includes the steps of doping a substantially planar block of n type semiconductor material with a p type dopant in accordance with a selected pattern to form a plurality of n type wells in the block surrounded by a foundation of p type semiconductor material. Each n type well is disposed so as to respectively adjoin a first surface of the block and such that a respective p-n junction is formed between the n type material in the well and the p type material foundation. The n type semiconductor material in each well has a substantially constant concentration of n type dopant throughout the n type material; the concentration of p type dopant in the foundation has a positive gradient extending from the p-n junction towards the second surface such that the peak surface electric field of the p-n junction in each well is less than the bulk electric field of the same p-n junction.

Abstract: An overvoltage responsive triggering circuit for a main high power thyristor comprises a plurality of n auxiliary thyristors and electric energy storing means connected in series across said main thyristor. The auxiliary thyristors are poled to conduct forward current in the same direction as said main thyristor and have an aggregate forward breakdown voltage greater than a predetermined threshold magnitude. Said threshold magnitude is greater than the aggregate forward voltage of said n auxiliary thyristors minus the forward breakdown voltage of one of said auxiliary thyristors. Between the anode and another electrode of said one auxiliary thyristor there is connected secondary voltage breakdown means having a blocking voltage less than the forward breakdown voltage of said one auxiliary thyristor, whereby said triggering circuit becomes conductive in the breakdown mode at said threshold voltage magnitude.