Method for fabrication of deep-diffused avalanche photodiode

A method of forming a planar deep-diffused semiconductor device, the method comprising the step of:

• doping a planar block of n type doped semiconductor material with a p type dopant in accordance with a deep doping pattern to form at least one n type wells in said block, each of said n type wells being disposed so as to respectively adjoin a first surface of said planar block and such that a respective p-n junction is formed between said n type doped semiconductor material and surrounding portions of said planar block doped with said p type dopant;
• the step of doping said planar block in accordance with said deep doping pattern further comprising doping said block of semiconductor material to form a positive gradient of said p type dopant between each respective p-n junction and a second surface of said planar block such that the concentration of said p type dopant increases away from said p-n junction so that the p type dopant concentration at said second surface is higher than at said p-n junction, said second surface being disposed substantially opposite said first surface of said planar block, so as to form said planar deep-diffused semiconductor device.