Microstructure enhanced absorption photosensitive devices
Techniques for enhancing the absorption of photons in semiconductors with the use of microstructures are described. The microstructures, such as pillars and/or holes, effectively increase the effective absorption length resulting in a greater absorption of the photons. Using microstructures for absorption enhancement for silicon photodiodes and silicon avalanche photodiodes can result in bandwidths in excess of 10 Gb/s at photons with wavelengths of 850 nm, and with quantum efficiencies of approximately 90% or more.
1. A photodetector device formed in or on a semiconductor substrate and provided with deliberately formed in-pillar holes comprising:
a laterally extending array of pillars that have rectangular cross-sections in a horizontal plane;
wherein said array of pillars comprises:
a first doped semiconductor material;
an intermediate semiconductor material; and
solid dielectric between at least portions of sidewalls of adjacent pillars of said array of pillars;
a second doped semiconductor material;
wherein:
the intermediate semiconductor material is between said first and second doped semiconductor materials;
the first and second doped semiconductor materials are doped to opposite semiconductor types;
the intermediate semiconductor material is less doped than at least one of the first and second doped semiconductor materials and the degree of doping is the same or different for different positions in the intermediate semiconductor material; and
each of the first and second doped semiconductor materials and said intermediate semiconductor material comprises Si;
one or more deliberately formed in-pillar holes with solid dielectric therein;
top and bottom electrical contacts electrically coupled with said array of pillars, wherein said photodetector device is configured to respond to light photons incident on said array of pillars by photo-generated charge carriers therein; and
a base dielectric region that is below the array of pillars and comprises substantially solid dielectric material;
wherein the pillars of said array of pillars:
are laterally spaced center to center by no more than 10,000 nanometers; and
have up-down lengths of said intermediate semiconductor material in the range of 100-5000 nanometers;
wherein at least said pillars, in-pillar holes, and solid dielectric between at least portions of sidewalls of adjacent pillars of said array of pillars increase photon absorption of said device of incident light by at least 1.1 times at selected visible and infrared wavelength ranges of said incident light compared to a like device lacking said one or more in-pillar holes;
wherein said array of pillars is monolithically integrated in or on said semiconductor substrate with electronic circuits that include active elements for signal processing and transmission.
2. The photodetector device of claim 1 , in which the top electrical contact is a transparent, laterally continuous region that is electrically coupled to a plurality of said pillars.
3. The photodetector device of claim 1 , in which each of said pillars has a plurality of said one or more in-pillar holes.
4. The photodetector device of claim 1 , in which each of said pillars has only one of said one or more in-pillar holes.
5. The photodetector device of claim 1 , in which said one or more in-pillar holes extend to a depth in a range of 100-10,000 nanometers.
6. The photodetector device of claim 1 , in which said one or more in-pillar holes extend into said intermediate semiconductor material.
7. The photodetector device of claim 1 , in which said one or more in-pillar holes are pyramid-shaped.
8. The photodetector device of claim 1 , in which each of said pillars has at least two of said one or more in-pillar holes that partly overlap.
9. The photodetector device of claim 1 , in which said second doped semiconductor material comprises a laterally continuous region coupled to a plurality of said pillars.
10. A photodetector device formed in or on a semiconductor substrate and provided with deliberately formed in-pillar holes comprising:
an array of pillars that have rectangular cross-sections in a horizontal plane;
wherein said array of pillars comprises at least:
a first doped semiconductor material;
a first intermediate semiconductor material; and
solid dielectric between at least portions of sidewalls of adjacent pillars;
a second doped semiconductor material;
wherein the first intermediate material is between the first and second doped semiconductor materials;
a third doped semiconductor material;
wherein said first and second semiconductor materials are doped to a first semiconductor type and the third semiconductor material is doped to a second semiconductor type;
a second intermediate semiconductor material between the second and third doped semiconductor materials;
wherein the first and second intermediate semiconductor materials are doped less than at least one of the first, second, and third doped semiconductor materials or are undoped;
one or more deliberately formed in-pillar holes with solid dielectric therein;
first and second electrical contacts that are electrically coupled with said array of pillars and are configured for operation of said device as an avalanche photodetector responding to light incident on the array of pillars by multiplying photogenerated charge carriers therein, with a multiplication gain greater than two; and
a base dielectric region that is under the array of pillars and comprises substantially solid dielectric material;
wherein said pillars of said array of pillars:
are spaced from each other center to center by no more than 10,000 nanometers; and
have an up-down dimension of said first intermediate semiconductor material that is less than 5000 nanometers;
wherein at least said pillars, in-pillar holes, and dielectric between at least portions of sidewalls of adjacent pillars of said array of pillars increase photon absorption of said device of incident light by a factor of at least 1.1, at least at selected wavelength of said incident light that include visible and infrared light compared to a like device lacking said one or more in-pillar holes; and
wherein said array of pillars is monolithically integrated in or on said semiconductor substrate with electronic circuits including active elements for signal processing and transmission.
11. The photodetector device of claim 10 , in which the top electrical contact is a transparent, laterally continuous region that is electrically coupled to a plurality of said pillars.
12. The photodetector device of claim 10 , in which each of said pillars has a plurality of said one or more in-pillar holes.
13. The photodetector device of claim 10 , in which each of said pillars has only one of said one or more in-pillar holes.
14. The photodetector device of claim 10 , in which said one or more in-pillar holes extend to a depth in a range of 100-10,000 nanometers.
15. The photodetector device of claim 10 , in which said one or more in-pillar holes extend into said first intermediate semiconductor material.
16. The photodetector device of claim 10 , in which said one or more in-pillar holes are pyramid-shaped.
17. The photodetector device of claim 10 , in which each of said pillars has at least two of said one or more in-pillar holes that partly overlap.
18. The photodetector device of claim 10 , in which said second doped semiconductor material comprises a laterally continuous region coupled to a plurality of said pillars.
19. The photodetector device of claim 10 , in which said second intermediate semiconductor material has a thickness in a range of 100-2,000 nm.
20. The photodetector device of claim 10 , in which said solid dielectric between at least portions of sidewalls of adjacent pillars extends down to said second intermediate semiconductor material.