Doped absorption for enhanced responsivity for high speed photodiodes
View Patent ↗A photodiode with a semiconductor intrinsic light absorption layer has at least one p-doped light absorption layer or an n-doped light absorption layer, and preferably both. The diode also has a cathode electrode and an anode electrode electrically coupled with the p-doped light absorption layer or the n-doped light absorption layer.
1. A method of generating an electrical current in response to light comprising the steps of:
(a) absorbing light by a light-absorption intrinsic semiconductor layer having a thickness ti, a doping concentration below 5e14 cm −3 , and producing, in response to light absorbed by said light-absorption intrinsic semiconductor layer, electrical carriers that are transported therethrough;
(b) absorbing light by a first light absorption doped semiconductor layer doped with one of p- and n-conductivity type-determining impurities, having a thickness td1, and a first doping concentration dc 1 between 1e17 and 2e18 cm −3 , said first light absorption doped semiconductor layer having a first surface thereof abutting a first surface of said light absorption intrinsic semiconductor layer, and producing, in response to light absorbed by said first light absorption doped semiconductor layer, electrical carriers that are transported therethrough, and wherein td1/ti is greater than or equal to 0.17; and
(c) extracting electrical current comprised of said carriers produced by and transported through said light-absorption intrinsic semiconductor layer and said first light absorption doped semiconductor layer, by means of a first electrode electrically coupled to said first light absorption doped semiconductor layer, and a second electrode electrically coupled to said light absorption intrinsic semiconductor layer, wherein
step (b) further comprises absorbing light by a second light absorption doped semiconductor layer doped with the other of said p- and n-conductivity type-determining impurities, having a thickness td2, and a second doping concentration dc 2 between 1e17 and 2e18 cm −3 , said second light absorption doped semiconductor layer having a first surface thereof abutting a second surface of said light absorption intrinsic semiconductor layer that is spaced apart from said first surface of said light absorption intrinsic semiconductor layer by material of said light absorption intrinsic semiconductor layer therebetween, and producing, in response to light absorbed by said second light absorption doped semiconductor layer, electrical carriers that are transported therethrough, and wherein (td1+td2)/ti is greater than or equal to 0.17, and
step (c) comprises extracting said electrical current, comprised of said carriers produced by and transported through said light-absorption intrinsic semiconductor layer and said first and second light absorption doped semiconductor layers, by means of said first electrode electrically coupled to said first light absorption doped semiconductor layer, and said second electrode electrically coupled to said second light absorption doped semiconductor layer.
2. The method according to claim 1 , wherein said first light absorption doped semiconductor layer comprises a light absorption p-doped semiconductor layer and said second light absorption doped semiconductor layer comprises a light absorption n-doped semiconductor layer, and wherein
step (c) comprises extracting said electrical current by means of a p-doped anode electrode electrically coupled to a second surface of said light absorption p-doped semiconductor layer, and an n-doped cathode electrode electrically coupled to a second surface of said light absorption n-doped semiconductor layer.
3. The method according to claim 1 , wherein the total thickness td1+td2+ti of said first and second light absorption semiconductor layers and said light absorption intrinsic semiconductor layer is greater than v/(2f 3-db ) by 20% or more, where v is the saturation drift velocity of either an electron or a hole, whichever is smaller, in said light absorption intrinsic semiconductor layer, and wherein f 3-dB is the frequency at which the amplitude of responsivity of said method is reduced to 1/√{square root over (2)} of its DC low-frequency value.
4. The method according to claim 1 , wherein, for a 3-dB bandwidth frequency of 40 GHz or higher, said first and second light absorption doped semiconductor layers and said light absorption intrinsic semiconductor layer are InGaAs lattice-matched to InP, and the total thickness (td1+td2+ti) of said first and second light absorption doped semiconductor layer and said light absorption intrinsic semiconductor layer is greater than 0.60 microns.
5. The method according to claim 1 , wherein, for a 3-dB bandwidth frequency of 40 GHz or higher, said first and second light absorption doped semiconductor layers and said light absorption intrinsic semiconductor layer are InGaAs lattice-matched to InP, and the total thickness (td1+td2+ti) of said first and second light absorption doped semiconductor layer and said light absorption intrinsic semiconductor layer is greater than 0.65 microns.
6. The method according to claim 1 , wherein, for a 3-dB bandwidth frequency of 40 GHz or higher, said first and second light absorption doped semiconductor layers and said light absorption intrinsic semiconductor layer are InGaAs lattice-matched to InP, and the total thickness (td1+td2+ti) of said first and second light absorption doped semiconductor layer and said light absorption intrinsic semiconductor layer is greater than 0.70 microns.