Frontside-illuminated barrier infrared photodetector device and methods of fabricating the same
Frontside-illuminated barrier infrared photodetector devices and methods of fabrication are disclosed. In one embodiment, a frontside-illuminated barrier infrared photodetector includes a transparent carrier substrate, and a plurality of pixels. Each pixel of the plurality of pixels includes an absorber layer, a barrier layer on the absorber layer, a collector layer on the barrier layer, and a backside electrical contact coupled to the absorber layer. Each pixel has a frontside and a backside. The absorber layer and the barrier layer are non-continuous across the plurality of pixels, and the barrier layer of each pixel is closer to a scene than the absorber layer of each pixel. A plurality of frontside common electrical contacts is coupled to the frontside of the plurality of pixels, wherein the frontside of the plurality of pixels and the plurality of frontside common electrical contacts are bonded to the transparent carrier substrate.
1. A method of fabricating a frontside-illuminated barrier infrared photodetector, the method comprising:
providing a semiconductor wafer comprising a bulk substrate layer, an absorber layer on the bulk substrate layer, a barrier layer on the absorber layer, and a collector layer on the barrier layer, wherein:
the bulk substrate layer is on a backside of the semiconductor wafer;
the collector layer is on a frontside of the semiconductor wafer;
the absorber layer is operable to absorb photon radiation; and
the barrier layer is configured such that a flow of a first carrier type is impeded, and a flow of a second carrier type is unimpeded;
applying a plurality of frontside common electrical contacts to the collector layer;
bonding a transparent carrier substrate to the frontside of the semiconductor wafer and the plurality of frontside common electrical contacts, wherein the transparent carrier substrate is transparent to radiation in a predetermined wavelength range;
thinning the bulk substrate layer of the semiconductor wafer;
reticulating the absorber layer and the barrier layer to form a plurality of stacks, wherein the absorber layer and the barrier layer is non-continuous across the plurality of stacks;
applying a backside electrical contact to each stack to form a plurality of pixels, wherein the plurality of pixels is at least partially reticulated; and
singulating the semiconductor wafer and the transparent carrier substrate into at least one barrier infrared photodetector array.
2. The method as claimed in claim 1 , further comprising bump bonding each backside electrical contact of the at least one barrier infrared photodetector array to a read-out integrated circuit assembly, wherein the read-out integrated circuit assembly comprises a read-out integrated circuit assembly bulk substrate that has a coefficient of thermal expansion that is substantially equal to the coefficient of thermal expansion of the transparent carrier substrate.
3. The method as claimed in claim 1 , wherein the absorber layer and the collector layer comprise a narrow band gap material, and the barrier layer comprises a wide band gap material.
4. The method as claimed in claim 1 , wherein one or more of the absorber layer, the barrier layer, and the collector layer comprise III-V semiconductor materials or II-VI semiconductor materials.
5. The method as claimed in claim 1 , wherein one or more of the absorber layer, the barrier layer, and the collector layer comprises a bulk semiconductor material, a binary semiconductor composition, a ternary semiconductor composition, a quaternary semiconductor composition, a strained layer superlattice composition, or combinations thereof.
6. The method as claimed in claim 1 , wherein the absorber layer, the barrier layer, and the collector layer are unintentionally doped.
7. The method as claimed in claim 1 , wherein the collector layer comprises GaSb, InAs x Sb 1-x /InAs superlattice, Ga y In 1-y As x Sb 1-x /Ga y In 1-y Sb superlattice, Ga y In 1-y As x Sb 1-x , Al y In 1-y As x Sb 1-x /Al y In 1-y As superlattice, or combinations thereof.
8. The method as claimed in claim 1 , wherein the barrier layer comprises AlAsSb, (GaSb) z (LM-AlAsSb) 1-z , or combinations thereof.
9. The method as claimed in claim 1 , wherein the absorber layer comprises GaSb, InAs x Sb 1-x /InAs superlattice, Ga y In 1-y As x Sb 1-x /Ga y In 1-y Sb superlattice, Ga y In 1-y As x Sb 1-x , Al y In 1-y As x Sb 1-x /Al y In 1-y As superlattice, or combinations thereof.
10. The method as claimed in claim 1 , wherein each of the absorber layer, the barrier layer, and the collector layer have a doping level such that the frontside-illuminated barrier infrared photodetector exhibits photo-voltaic characteristics.
11. The method as claimed in claim 1 , wherein each of the absorber layer, the barrier layer, and the collector layer have a doping level such that the frontside-illuminated barrier infrared photodetector exhibits photo-conductive characteristics.
12. The method as claimed in claim 1 , further comprising isolating the collector layer into a plurality of contact mesas, wherein the plurality of contact mesas are vertically aligned with the plurality of frontside common electrical contacts.
13. The method as claimed in claim 1 , further comprising, prior to applying the plurality of frontside common electrical contacts to the frontside of the semiconductor wafer, depositing a dielectric material layer on the collector layer.
14. The method as claimed in claim 13 , further comprising:
forming a plurality of vias within the dielectric material layer; and
filling the plurality of vias with an electrically conductive material.
15. The method as claimed in claim 13 , wherein the dielectric material layer comprises SiO, SiO x , silicon nitride, or combinations thereof.
16. The method as claimed in claim 1 , wherein the absorber layer, the barrier layer, and the collector layer are completely removed between individual pixels of the plurality of pixels.
17. The method as claimed in claim 1 , wherein each backside electrical contact completely covers an entire backside of the stack to which it is applied.
18. The method as claimed in claim 1 , wherein the frontside of the semiconductor wafer is bonded to the transparent carrier substrate with an adhesive bonding layer.
19. The method as claimed in claim 1 , wherein the bulk substrate layer is mechanically thinned.
20. The method as claimed in claim 1 , wherein the bulk substrate layer is chemically thinned.
21. The method as claimed in claim 20 , wherein the bulk substrate layer is chemically thinned using a wet etchant comprising a solution of H 3 PO 4 —H 2 O 2 —H 2 O or a solution of H 2 SO 4 —H 2 O 2 —H 2 O.
22. The method as claimed in claim 1 , wherein reticulating the absorber layer and the barrier layer to form the plurality of stacks further comprises:
applying a patterned etch mask to the absorber layer, wherein the patterned etch mask comprises a photo resist material, a dielectric material, a metal material, or combinations thereof;
performing a dry etch process to the patterned etch mask and the absorber layer;
applying an etching solution to the patterned etch mask, the absorber layer, and the barrier layer; and
removing the patterned etch mask from the absorber layer.
23. The method as claimed in claim 1 , further comprising applying to the transparent carrier substrate an anti-reflective layer, a spectral filter layer, a polarizer layer, or combinations thereof.