Germanium silicon heterostructure photodetectors
A horizontal germanium silicon heterostructure photodetector comprising a horizontal germanium p-i-n diode disposed over a horizontal parasitic silicon p-i-n diode uses silicon contacts for electrically coupling to the germanium p-i-n through the p-type doped and n-type doped regions in the silicon p-i-n without requiring direct physical contact to germanium material. The current invention may be optically coupled to on-chip and/or off-chip optical waveguide through end-fire or evanescent coupling. In some cases, the doping of the germanium p-type doped and/or n-type doped region may be accomplished based on out-diffusion of dopants in the doped silicon material of the underlying parasitic silicon p-i-n during high temperature steps in the fabrication process such as, the germanium deposition step(s), cyclic annealing, contact annealing and/or dopant activation.
1. A horizontal germanium silicon photodetector integrated on a substrate comprising:
a horizontal silicon pin (positive-intrinsic-negative) diode disposed on a substrate comprising:
a first positive region comprising p-type doped silicon;
a first intrinsic region comprising silicon; and,
a first negative region comprising n-type doped silicon;
a horizontal germanium pin diode disposed on top of the horizontal silicon pin diode comprising:
a second positive region comprising p-type doped germanium substantially aligned with the first positive region;
a second intrinsic region comprising germanium substantially aligned with the first intrinsic region; and,
a second negative region comprising n-type doped germanium substantially aligned with the first negative region;
an anode contact coupled to the first positive region for establishing electrical contact to both the first positive region and to the second positive region through the first positive region; and,
a cathode contact coupled to the first negative region for establishing electrical contact to the first negative region and to the second negative region through the first negative region, thereby establishing a germanium on silicon photodetector with silicon contacts.
2. The photodetector of claim 1 comprising a total of two or more anode contacts.
3. The photodetector of claim 1 comprising a total of two or more cathode contacts.
4. The photodetector of claim 1 , further comprising:
an integrated waveguide disposed on the substrate and optically coupled to the germanium p-i-n.
5. The photodetector of claim 1 wherein the first intrinsic region comprises silicon selected from the list of:
unintentionally doped silicon;
lightly doped silicon;
intrinsically doped silicon; and,
un-doped silicon.
6. The photodetector of claim 1 wherein the second intrinsic region comprises germanium selected from the list of:
unintentionally doped germanium;
lightly doped germanium;
intrinsically doped germanium; and,
un-doped germanium.
7. The photodetector of claim 1 , further comprising:
an optical coupler for optically coupling an external waveguide to the germanium p-i-n.
8. The photodetector of claim 7 , wherein the optical coupler comprises an evanescent coupler.
9. The photodetector of claim 7 , wherein the optical coupler comprises an end-fire coupler.
10. The photodetector of claim 4 wherein:
the integrated waveguide comprises silicon.
11. The photodetector of claim 4 wherein:
the integrated waveguide comprises a silicon and germanium heterostructure.
12. The photodetector of claim 1 wherein:
at least some portion of the germanium p-i-n comprises germanium selected from the list of a single layer of germanium, a multilayer germanium stack, a graded germanium layer, polycrystalline germanium, single crystal germanium and amorphous germanium.
13. The photodetector of claim 1 wherein:
the silicon p-i-n is planar.
14. The photodetector of claim 1 wherein:
at least some portion of the first intrinsic region comprising silicon is thicker than at least some portion of first positive region or the first negative region.
15. The photodetector of claim 1 , wherein the substrate is selected from the list of:
a silicon-on-insulator (SOI) substrate, a silicon-on-sapphire (SOS) substrate, a silicon substrate and a silicon substrate comprising at least one silicon germanium (SiGe) layer.