Question

27. explain in detail working principle of rapd. Why is it called reach through apd

Answer 1

i. To ensure carrier multiplication without excess noise for a specific thickness of multiplication region within the APD it is necessary to reduce the ratio of the ionization coefficients for electrons and holes k.

ii. Hence for minimum noise, the electric field at avalanche breakdown must be as low as possible and the impact ionization should be initiated by electrons.

iii. To this end a ‘reach through ‘structure has been implemented with the silicon APD.Hence called reach through APD.