Patent ID: 6870239
Filing Date: 2005-03-22
Classification: H01L

Abstract:
1. An avalanche photodiode having an extrinsic absorption region and comprising: an absorption region having first and second opposed sides between which photon energy is absorbed in the generation of primary electron-hole pairs each of which primary electron-hole pairs comprises a primary electron and a primary hole, the absorption region being fabricated from a p-doped first material constituting a diode anode adapted for reverse-bias, electrically conductive engagement with the positive-charge-attracting cathode of an external energy source and having a first conduction band potential and a first valence band potential; a charge-carrier multiplication region joined through a junction to the absorption region, the charge-carrier multiplication region being fabricated from a second material having a second conduction band potential and a second valence band potential and being adapted to facilitate the generation of secondary electron-hole pairs through impact ionization, each secondary electron-hole pair including a secondary electron and a secondary hole, wherein the introduction of primary electrons from the absorption region into the multiplication region for impact ionization is preferred over the introduction of primary holes from the absorption region into the multiplication region for impact ionization; and an n-doped diode cathode adapted for reverse-bias, electrically conductive engagement with the negative-charge-attracting anode of the external energy source and situated with respect to the multiplication region such that, when the avalanche photodiode is reverse biased, the p-doped absorption region assumes a negative charge, the n-doped diode cathode assumes a positive charge and an electric field is present across the multiplication region between the absorption region and the diode cathode, wherein, at the junction, one of (i) the first conduction band potential of the first material from which the absorption region is fabricated is, relative to an electron, one of (a) equal to and (b) higher than the second conduction band potential of the second material from which the multiplication region is fabricated such that the introduction of primary electrons from the absorption region into the multiplication through thermal diffusion is facilitated by the absence of a conduction-band-dependent potential barrier and (ii) the first conduction band potential is lower than the second conduction band potential such that there exists a conduction-band-dependent potential barrier opposing the movement of a primary electron from the absorption region into the multiplication region, but wherein the relative values of the first and second conduction band potentials are selected such that the probability of migration by a primary electron from the absorption region into the multiplication region is not below a predetermined minimum primary-electron-migration probability.