Photodetecting device with enhanced collection efficiency

A photodetecting device includes a substrate, a first photosensitive layer supported by the substrate, and a second photosensitive layer supported by the substrate and adjacent to the first photosensitive layer, each of the first photosensitive layer and the second photosensitive layer being coupled to a first doped portion having a first conductivity type, and a second doped region having a second conductivity type different from the first conductivity type, wherein the first photosensitive layer is separated from the second photosensitive layer, and the first doped portion coupled to the first photosensitive layer is electrically connected to the first doped portion coupled to the second photosensitive layer.

BACKGROUND

For high-data-rate optical communication transceivers, a high-speed photodetector at the receiver is needed. To increase the speed of a photodetector, usually, many effects such as capacitance-limited resistance-capacitance delay time should be taken into consideration.

SUMMARY

According to an aspect of the present application, a photodetecting device is provided. The photodetecting device includes a substrate, a first photosensitive layer at least supported by the substrate, and a second photosensitive layer supported by the substrate and adjacent to the first photosensitive layer, each of the first photosensitive layer and the second photosensitive layer being coupled to: a first doped portion having a first conductivity type, and a second doped region having a second conductivity type different from the first conductivity type, wherein the first photosensitive layer is separated from the second photosensitive layer, and the first doped portion coupled to the first photosensitive layer is electrically connected to the first doped portion coupled to the second photosensitive layer.

According to an aspect of the present application, a photodetecting device is provided. The photodetecting device includes a substrate, a first photosensitive layer supported by the substrate, a second photosensitive layer supported by the substrate and adjacent to the first photosensitive layer, each of the first photosensitive layer and the second photosensitive layer having a top surface facing away from the substrate and a bottom surface opposite to the top surface, wherein each of the first photosensitive layer and the second photosensitive layer is coupled to: a first doped portion having a first conductivity type and proximal to the top surface, and a second doped region having a second conductivity type and proximal to the bottom surface, wherein the first photosensitive layer is separated from the second photosensitive layer.

According to an aspect of the present application, a photodetecting device is provided. The photodetecting device includes a first sub-pixel, including a first photosensitive layer having a top surface and a bottom surface, a first doped portion having a first conductivity type and exposed from the top surface of the first photosensitive layer, and a second doped region having a second conductivity type and coupled to the first photosensitive layer, an isolation region surrounding the first sub-pixel, and a second sub-pixel adjacent to the first sub-pixel and being separated from the first sub-pixel by the isolation region.

According to an aspect of the present application, a method for making a photodetecting device is provided. The method includes providing a substrate; forming a second doped region in the substrate; forming a plurality of photosensitive layers; forming a first doped portion in each of the photosensitive layers; and forming a routing layer electrically coupled to first doped portions of a plurality of photosensitive layers.

DETAILED DESCRIPTION

Spatial descriptions, such as “above,” “top,” and “bottom” and so forth, are indicated with respect to the orientation shown in the figures unless otherwise specified. It should be understood that the spatial descriptions used herein are for purposes of illustration only, and that practical implementations of the structures described herein can be spatially arranged in any orientation or manner, provided that the merits of embodiments of this disclosure are not deviated by such arrangement.

In the present disclosure, the term “germanium-silicon (GeSi)” refers to aGexSi1-x, wherein 0<x<1. The term “intrinsic” refers to a semiconductor material without intentionally adding dopants.

In optical communication application with operation bandwidth generally above 25 Gbps (e.g. 40 Gbps, 100 Gbps, or the like), a sensing aperture of a photodiode may be smaller compared to a sensing aperture of a photodiode with operation bandwidth generally under 25 Gbps for maintaining pixel performance, such as the modulation speed. In order to improve the speed of the photodiode, an optical aperture or an active area of the photodiode is decreased in consideration of capacitance-limited resistance-capacitance (RC) delay time. Although reducing the optical aperture or an active area of the photodiode can lead to a reduction in device capacitance, which typically results in an increase in photodetector bandwidth, a reduction in the amount of optical signal (i.e., number of photons) entering into the photodiode may also be expected. For example, for a given intensity of light per unit area, the reduction in the optical aperture or an active area of the photodiode leads to a reduction in detected light.

Operation speed or bandwidth of a photodiode can be an important performance parameter for applications that benefit from high speed detection of light. However, the optical communication between one single optical fiber (e.g., may be a single mode fiber with lens or a multi-mode optical fiber) and a smaller-sized optical aperture or an active area (for example, about 15 μm diameter, or the like) of a photodiode may suffer from serious coupling loss. For applications that benefit from both high bandwidth and high detection efficiency, implementation of an optical element enhancing light coupling efficiency, for example, an optical lens, may be beneficial. The optical lens can focus the incident optical signal to the active region of the photodetector, allowing a small-area optical aperture or active area to detect optical signal incident over an area larger than itself.

In a comparative embodiment, when a photodiode includes a single, larger-sized optical aperture or an active area (for example, about 50 μm in diameter) for receiving incident light from a single optical fiber, a larger lens (such as a giant micro-lens, GML) for covering the corresponding area (for example, about 50 nm in diameter) and having a larger height (for example, about 25 μm) over the photodiode may be implemented. However, the fabrication process of such GML is difficult and often requires higher cost.

Therefore, the present disclosure provides a photodetecting device that includes a binned photodiode array having a plurality of discrete active areas (or photo-sensitive regions) for receiving optical signal coming from a single optical fiber (e.g., may be a single mode fiber with lens or a multi-mode optical fiber). Each of the photodiodes in the binned photodiode array may be referred to as a sub-pixel in the present disclosure. A lower-cost, easier-to-fabricate micro-lens (e.g., continuous micro-lens, CML) can be implemented with respect to each of the photodiodes in the binned photodiode array. Furthermore, the present disclosure also provides an improved arrangement of the plurality of sub-pixels.

Referring toFIG.1AandFIG.1B,FIG.1Aillustrates a cross section of a photodetecting device according to some embodiments of the present disclosure.FIG.1Billustrates a top view of the photodetecting device corresponding to the photodetecting device inFIG.1A. A photodetecting, device100at least includes a substrate9, a first sub-pixel1A at least partially over the substrate9, and a second sub-pixel1B at least partially over the substrate9. The first sub-pixel1A includes a p-i-n structure having, for example, a first photosensitive layer3A, a first doped portion10A, and a second doped region20. The second sub-pixel1B includes another p-i-n structure having, for example, a second photosensitive layer3B, a first doped portion109, and a second doped region20. In some embodiments, the first photosensitive layer3A and the second photosensitive layer3B are collectively referred to as a photo sensing area3.

The substrate9may include any suitable substrate where photo sensing area3can be fabricated thereon. In some embodiment, the substrate9provides a surface for epitaxially growing the photo sensing area3. In some embodiments, the substrate9includes a semiconductor material. In some embodiments, the substrate9includes a Group III-V semiconductor material. The Group III-V semiconductor material may include, but is not limited to, GaAs, AlAs, InP, InGaAs, GaSb, InAs, or InSb. In some embodiments, the substrate9includes a Group IV element. In some embodiments, the substrate9is composed of a single material, for example, the substrate9may be a silicon substrate. In some embodiments, the substrate9includes multiple materials, for example, the substrate9includes an insulating material and a semiconductor material. In some embodiments, the substrate9includes oxide, nitride, dielectric material, the combination thereof, or the like. In some embodiment, the substrate9includes SiO2and Si. In some embodiments, the substrate9includes a stack of multiple layers. In some embodiments, the substrate9includes a thickness not less than 100 μm.

In general, the photo sensing area3receives an optical signal, for example, an optical signal from an optical fiber1111, and converts the optical signal into electrical signals. In some embodiments, the photodetecting device100is a front-side illumination configuration, in which the optical signal is incident on a top surface of the photo sensing area3. In some embodiments, the photo sensing area3absorbs photons and generates electron-hole pairs. The photo sensing area3is selected to have a high absorption coefficient at the desired wavelength range, such as not less than 10−1cm−1. In some embodiments, the photo sensing area3is configured to absorb photons having a peak wavelength in an invisible wavelength range not less than 800 nm, such as 850 nm, 940 nm, 1050 nm, 1064 nm, 1310 nm, 1350 am, or 1550 nm. In some embodiments, the invisible wavelength range is not more than 2000 nm. In some embodiments, a material of the photo sensing area3is different from the material of the substrate9. In some embodiments, the photo sensing area3includes a semiconductor material. In some embodiments, the photo sensing area3includes a Group semiconductor material. The Group III-V semiconductor material may include, but is not limited to, GaAs, AlAs, InP, InGaAs, GaSb, InAs, or InSb. In some embodiments, the bandgap of the material of the photo sensing area3is less than the bandgap of the material of the substrate9. In some embodiments, the photo sensing area3includes a semiconductor material including a Group IV element, for example, Ge, Si or Sn. In some embodiments, the photo sensing area3includes GeSi, wherein the composition of germanium and silicon may be selected for specific processes or applications. In some embodiments, the material of the photo sensing area3is intrinsic. In some embodiments, the photo sensing area3is composed of intrinsic germanium.

Referring toFIG.1A, the first photosensitive layer3A is separated from the second photosensitive layer3B by, for example, a first dielectric layer31disposed between a sidewall of the first photosensitive layer3A and a sidewall of the second photosensitive layer3B facing the first photosensitive layer3A. Each of the first photosensitive layer3A and the second photosensitive layer3B has a top surface TS facing away from the substrate9and bottom surface BS opposite to the top surface TS. In some embodiments, the first sub-pixel1A includes the first doped portion10A beneath the top surface TS of the first photosensitive layer3A and coupled to the first photosensitive layer3A. The second sub-pixel1B includes the first doped. portion10B beneath the top surface TS of the second photosensitive layer3B and coupled to the second photosensitive layer3B. The first doped portion10A coupled to the first photosensitive layer3A and the first doped portion10B coupled to the second photosensitive layer3B are physically separated. In some embodiments, the first doped portion10A of the first sub-pixel1A and the first doped portion10B of the second sub-pixel1B are collectively referred to as a first doped region10, which has a first conductivity type (e.g., n or p). The first doped portion10A and the first doped portion10B may be at least partially exposed from the first photosensitive layer3A and the second photosensitive layer3B, respectively, and electrically connected to a routing layer5over the photo sensing area3. The specific layout of the first doped portion10A,10B, include suitable depth or shape of the doping profile, and may be varied depending on different design, manufacturing process, or testing considerations.

In some embodiment, each of the first sub-pixel1A and the second sub-pixel1B further includes an interface layer (not shown) covering the top surface TS of the first photosensitive layer3A and the top surface TS of the second photosensitive layer3B, respectively. In some embodiment, the interface layer (not shown) of the first sub-pixel1A further covers a sidewall of the first photosensitive layer3A. In some embodiment, the interface layer (not shown) of the second sub-pixel1B further covers a sidewall of the second photosensitive layer3B. The interface layer may include a material different from the material of the photo sensing area3. In some embodiments, the interface layer may include amorphous silicon, polysilicon, epitaxial silicon, aluminum oxide (e.g., AlxOy), silicon oxide (e.g., SixOy) Ge oxide (e.g., (GexOy), germanium-silicon (e.g., (GeSi), silicon nitride family (e.g., SixNy), high-k materials (e.g. HfOx, ZnOx, LaOx, LaSiOx), and any combination thereof. The presence of the interface layer may have various effects. For example, the interface layer may act as a surface passivation layer to the photo sensing area3, which may reduce dark current generated by defects present at the exposed surface of the photo sensing area3. In some embodiment, the interface layer (not shown) of the first sub-pixel1A and the interface layer (not shown) of the second sub-pixel1B may be a continuous layer.

The first photosensitive layer3A and the second photosensitive layer3B are each coupled to the second doped region20having a second conductivity type (e.g., p or n). The second doped region20is proximal to the bottom surface BS of the first photosensitive layer3A or the bottom surface BS of the second photosensitive layer3B. For example, each of the top surface TS of the first photosensitive layer3A and the top surface TS of the second photosensitive layer3B are coupled to the first doped region10, and the each of the bottom surface BS of the first photosensitive layer3A and the bottom surface BS of the second photosensitive layer3B are coupled to a second doped region20having a second conductivity type different from, or opposite to, the first conductivity type. In some embodiments, the first conductivity type is p-type and the second conductivity type is n-type. In some other embodiments, the first conductivity type is n-type and the second conductivity type is p-type. In some embodiments, the second doped region20coupled to the first photosensitive layer3A and the second doped region20coupled to the second photosensitive layer3B are connected. In some embodiments, the second doped region20may be a continuous doped region formed in the substrate9. In some embodiments, an area of the second doped region20of the photodetecting device100is greater than an area of each of the first doped portions10A or10B in the corresponding photosensitive layer3A or3B. In some embodiments, an area of the second doped region20of the photodetecting device100is greater than a total area of the first doped portions10A and10B sums up from each of the photosensitive layer3A and3B in the photodetecting device100.

In some embodiments, the photo sensing area3is laterally surrounded by the first dielectric layer31, and a top surface of the first sub-pixel1A is not covered by the first dielectric layer31. In some embodiments, the top surface of the first sub-pixel1A and the top surface of the second sub-pixel1B are coplanar with a top surface of the first dielectric layer31from the cross section of the photodetecting device. In some embodiments, the first dielectric layer31includes suitable insulating materials such as oxides or nitrides. A second dielectric layer32can be disposed above the first dielectric layer31, the first sub-pixels1A and the second sub-pixel1B. In some embodiments, the second dielectric layer32includes suitable insulating materials such as oxides or nitrides. The second dielectric layer32may or may not be composed of the same materials as the first dielectric layer31.

Referring toFIG.1A, the first doped portion10A of the first sub-pixel1A and the first doped portion108of the second sub-pixel16are electrically connected by the routing layer5, which includes conductive material such as metal or alloy, for example, Al, Cu, W, Ti, Ta TaN—Cu stack, Ti—TiN—W stack. In some embodiments, the routing layer5penetrates the second dielectric layer32and has a portion extends above the second dielectric layer32. In some embodiments, a portion of the first doped region10is under a projection area of the routing layer5. The routing layer5at least electrically connects the first doped portion10A of the first sub-pixel1A and the first doped portion10B of the second sub-pixel1B. In some embodiments, a layout of the routing layer5may connect some of the sub-pixels in parallel. For example, the routing layer5is not necessary to connect the respective first doped portions10A in adjacent sub-pixels. The specific layout of the routing layer5, including but not limited to the number of layers in metal connection and the electrical arrangement among several sub-pixels of the photodetecting device100, may be varied depending on different design, manufacturing process, or testing considerations.

In some embodiments, the routing layer5can be replaced by a highly-doped semiconductor layer electrically coupling respective first doped portions of each of the sub-pixels. For example, a highly-doped amorphous silicon layer may be deposited over the coplanar surface of the first photosensitive layer3A, the second photosensitive layer3B, and the first dielectric layer31to provide parallel electrical connection among various photosensitive layers.

Referring toFIG.1A, the first photosensitive layer3A has a width WAP measured from one sidewall to the opposite sidewall of the first photosensitive layer3A. In some embodiments, assuming the first photosensitive layer3A possesses roughly a square shape from a top view perspective (e.g., as illustrated inFIG.1B), when the width WAP of the first photosensitive layer3A is about 7 μm, an active area AP of about 49 μm2can be obtained. In some embodiments, the active area AP of each sub-pixel is defined as the area of the photosensitive layer. As previously discussed, a portion of the first doped portion10A and the first photosensitive layer3A are under a projection area of the routing layer5. As a result, the optical signal received by the first photosensitive layer3A is reduced due to the coverage of the routing layer5. In some embodiments, the routing layer5has an opening for allowing an optical signal entering into the photo sensing area3. The opening of the routing layer5having a width WAR can be identified inFIG.1A. Similarly, when the width WAR of the opening is about 5 μm, an optical aperture area AR (e.g., as illustrated inFIG.1B) of about 25 μm2can be obtained. In some embodiments, the optical aperture area AR of each sub-pixel is defined as the area of the opening. In some embodiments, a pitch P between two adjacent photosensitive layers3A,3B is determined by the width WAP and the distance between the separated and adjacent photosensitive layers3A,3B. In some embodiments, a pitch P is between the centers of two adjacent photosensitive layers3A,3B. For example, the pitch P may be 10 μm, which is larger than the width WAP of 7 μm and the width WAR of 5 μm. In some embodiments, the pitch P is not less than 5 μm. In some embodiments, the width WAP is not less than 3 μm.

As previously discussed, the optical fill factor of the first photosensitive layer3A can be the optical aperture area AR over the square of the pitch P. In some embodiments, the optical fill factor is not less than 20%. For example, from the embodiment as previously discussed, i.e., 25 μm2/100 μm2, which, in some embodiments, is close to 25%. The aforesaid optical fill factor can be altered by the design rule of the photosensitive layers3A,3B, as well as the design rule of the routing layer5, and may be further improved, for example, greater than 25%.

The numbers of sub-pixels1A,1B in the photodetecting device100for receiving optical signal from the core1111A of the optical fiber1111is not limited to two. In the case of the photodetecting device100having multiple sub-pixels, the multiple sub-pixels may under a vertical projection of the core1111A of the optical fiber1111, wherein at least two of the sub-pixels are binned together (e.g., electrically connected). In some embodiments, the numbers of sub-pixels in the photodetecting device100can be more than two, for example, four (as exemplified inFIG.1B). In the case of the photodetecting device100having four sub-pixels, which are respectively associated with the first photosensitive layer3A, the second photosensitive layer3B, the third photosensitive layer3C, and the fourth photosensitive layer3D inFIG.1B, the four sub-pixels1A,1B,1C, and1D may under a vertical projection of the core1111A of the optical fiber1111. Alternatively stated, an optical fiber1111is optically coupled to an area of approximately 20 μm by 20 μm and having four sub-pixels binned together (e.g., electrically connected), each of the sub-pixels being previously described inFIG.1A. The optical fiber1111can be a single mode with lens or a multi-mode fiber which has a core1111A and a cladding1111B.

In some embodiments, the numbers of sub-pixels in the photodetecting device100can be more than four, for example, sixteen. In the case of the photodetecting device100having sixteen sub-pixels, the sixteen sub-pixels may be arranged in a four by four array, and are disposed under a vertical projection of the core1111A of the optical fiber1111. Alternatively stated, an optical fiber1111is optically coupled to an area of approximately 40 μm by 40 μm and having sixteen sub-pixels binned together (e.g., electrically connected), each of the sub-pixels being previously described inFIG.1A. The number of the sub-pixel binned together may vary depending on different design, manufacturing process, or testing considerations.

By having a plurality of sub-pixels receiving optical signal from a core1111A of the optical fiber1111, the collection efficiency of the optical signal can be improved, and the coupling loss of the optical communication between the optical fiber1111and the photodetecting device100can be alleviated.

Referring toFIG.1C,FIG.1Cshows a flow chart representing a method for fabricating a photodetecting device, in accordance with some embodiments of the present disclosure.FIG.1Cshows an example of a method1000for forming the photodetecting device100previously discussed inFIG.1Aand/orFIG.1B. The method1000for forming the photodetecting device100includes providing a substrate (operation1004, which can be referred toFIG.1E), forming a second doped region in the substrate (operation1007, which can be referred toFIG.1E), forming a photo sensing area including a plurality of photosensitive layers (operation1013, which can be referred toFIG.1FtoFIG.1G), forming a first doped region in the photo sensing area, that is, forming a first doped portion in each of the photosensitive layers (operation1018, which can be referred toFIG.1H), and forming a routing layer electrically coupled to first doped portions of a plurality of photosensitive layers of the photo sensing area (operation1022, which can be referred toFIG.1L).

Referring toFIG.1D,FIG.1Dshows a flow chart representing a method for fabricating a routing layer of a photodetecting device, in accordance with some embodiments of the present disclosure. The step of forming a routing layer electrically coupled to first doped portions of a plurality of photosensitive layers of the photo sensing area (operation1022) further includes forming a first dielectric layer to cover the plurality of photosensitive layers (sub-operation2004, which can be referred toFIG.1I), thinning the first dielectric layer to expose the top surfaces of the plurality of photosensitive layers (sub-operation2007, which can be referred toFIG.1J), forming a second dielectric layer to cover the top surfaces of the plurality of photosensitive layers (sub-operation2013, which can be referred toFIG.1K), forming multiple via holes in the second dielectric layer to expose a part of each top surface of the plurality of photosensitive layers3(sub-operation2018, which can be referred toFIG.1K), and forming conductive material into the via holes to electrically connecting the first doped portions of the plurality of photosensitive layers (sub-operation2020, which can be referred toFIG.1L).

Referring toFIG.1E,FIG.1Eis a cross sectional view of a photodetecting device during intermediate stages of manufacturing operations, according to some embodiments of the present disclosure. Specifically, the steps for forming the photodetecting device100includes providing a substrate9, and forming the second doped region20beneath a top surface of the substrate9. In some embodiments, the second doped region20in the substrate9can be of any suitable depth and concentration profile, such as between 1×1018cm−3to 5×1021cm−3. The second doped region20can be formed by suitable ion implantation operations. In some embodiments, the second doped region20is an n-doped region. It should be appreciated by people having ordinary skill in the art that the second doped region20can be a p-doped region depending on various design, manufacturing process, or testing considerations.

Referring toFIG.1F,FIG.1Fis a cross sectional view of a photodetecting device during intermediate stages of manufacturing operations, according to some embodiments of the present disclosure. A photosensitive material3M is formed, such as deposited over the substrate9in such a way that the photosensitive material3M is in contact with the second doped region20. In some embodiments, the deposition of the photosensitive material3M may include various deposition operation, including, but not limited to, a blanket epitaxy, a selective epitaxy, or other applicable techniques. In some embodiment, a buffer layer (not shown) is formed between the substrate9and the photosensitive material3M for improving the epitaxial quality of the photosensitive material3M formed thereon. In some embodiments, the buffer layer includes a material the same as the substrate but with conductivity type different from the second conductivity type. For example, when the substrate includes Si and the second conductivity type is n-type, the buffer layer includes intrinsic silicon. The buffer layer has a thickness between 50 nm and 200 nm both inclusive. The top surface of the of the substrate9is depicted as a planar surface, In some embodiments, the substrate9may include a mesa or a trench, and thus the top surface is not a planar surface, wherein the top surface at least partially surrounded by an insulator ex: oxide, nitrite), a semiconductor (ex: Si, Ge), or their combinations. Furthermore, a strained super lattice structure or a multiple quantum well structure including alternative layers such as two or more different semiconductor compounds or semiconductor compounds having the same elements but with different compositions may be implemented as the photosensitive material3M. For example, alternating GeSi layers with different compositions.

Referring toFIG.1G,FIG.1Gis a cross sectional view of a photodetecting device during intermediate stages of manufacturing operations, according to some embodiments of the present disclosure. After forming the photosensitive material3M, the photosensitive material3M is then patterned to obtain a photo sensing area3including a plurality of photosensitive layers3A,3B by performing an etching operation. In the example ofFIG.1B, four discrete photosensitive layers3A,3B,3C, and3D are formed after the aforesaid etching operation. In some embodiments, the removal operation may include, but not limited to, a dry etching and/or a wet etching operations. In some embodiments, at least a portion of the second doped region20is exposed from the photo sensing area3after the etching operation, for example, a portion of the second doped region20may expose to a space between the first photosensitive layers3A and the second photosensitive layers3B. As previously discussed inFIG.1AandFIG.1B, the first photosensitive layer3A, the second photosensitive layer3B, the third photosensitive layer3C and/or the fourth photosensitive layer3D (as shown in the example ofFIG.1B) are physically separated from each other. In some embodiments, the steps of forming the photodetecting device100further include forming an interface layer (not shown) covering at least the top surface of the first photosensitive stayer3A, the top surface of the second photosensitive layer3B, the top surface of the third photosensitive layer3C and/or the, the top surface of the fourth photosensitive layer3D.

Referring toFIG.1H,FIG.1His a cross sectional view of a photodetecting device during intermediate stages of manufacturing operations, according to some embodiments of the present disclosure. The steps of forming the photodetecting device100further include forming a first doped region10in the photo sensing area3. Alternatively stated, each of the first doped portions10A,10B,10C,10D is respectively formed in the corresponding discrete photosensitive layers3A,3B,3C and3D. The first doped region10can be formed by suitable ion implantation operations with a proper masking layout. In some embodiments, ions may also be implanted into the interface layer covering the top surfaces of the photosensitive layers3A,3B to form doped interface layers (not shown) in a one-to-one correspondence with each of the first doped portions10A,10B,10C,10D of the photosensitive layers3A,3B,3C and3D. In some embodiments, the interface layer includes amorphous silicon. In some embodiments, the first doped region10in the photosensitive layers3A,3B,3C and3D can be of any suitable depth and concentration profile, such as between 1×1018cm−3to 5×1021cm−3. In some embodiments, each of the first doped portions10A,10B,10C,10D may beneath the entire or a portion of the top surface of each of the photosensitive layers3A,3B,3C and3D. In some embodiments, the first doped region10is a p-doped region. It should be appreciated by people having ordinary skill in the art that the first doped region10can be an n-doped region depending on various design, manufacturing process, or testing considerations.

Referring toFIG.1I,FIG.1Iis a cross sectional view of a photodetecting device during intermediate stages of manufacturing operations, according to some embodiments of the present disclosure. The steps of forming the photodetecting device100further include forming a first dielectric layer31to laterally surround each of the photosensitive layers3A,3B. In some embodiments, the first dielectric layer31may be firstly deposited over an exposed portion of the second doped region20, in some embodiments, the first dielectric layer31includes suitable insulating materials such as oxide, nitrides, or combinations thereof.

Referring toFIG.1J,FIG.1Jis a cross sectional view of a photodetecting device during intermediate stages of manufacturing operations, according to some embodiments of the present disclosure. A thinning operation can be performed to remove a portion of the first dielectric layer31over the photo sensing area3until a top surface of the photosensitive layers3and the first doped region10is exposed. In some embodiments, the thinning operation is a planarization operation, such as chemical mechanical planarization (CMP) operation. In some of the embodiments, a top surface of the photo sensing area3after the thinning operation is substantially coplanar with a top surface of the first dielectric layer31.

Referring toFIG.1K,FIG.1Kis a cross sectional view of a photodetecting device during intermediate stages of manufacturing operations, according to some embodiments of the present disclosure. A second dielectric layer32is formed over the coplanar surface of the first dielectric layer31and the photosensitive layers3. In some embodiments, the second dielectric layer32includes suitable insulating materials such as oxide, nitride, or combinations thereof. The first dielectric layer31may be composed of identical or different materials than the second dielectric layer32. Subsequently, a plurality of via holes32V penetrating the second dielectric layer32are formed in the second dielectric layer32by a suitable lithography operation. A portion of the top surface of the photo sensing area3is then exposed from the second dielectric layer32after the lithography operation.

Referring toFIG.1L,FIG.1Lis a cross sectional view of a photodetecting device during intermediate stages of manufacturing operations, according to some embodiments of the present disclosure. The steps of forming the photodetecting device further include forming a routing layer5electrically coupled to the multiple first doped portions in the plurality of photosensitive layers the first doped portions10A,10B,10C,10D in the photosensitive layers3A,3B,3C and3D, respectively). In some embodiments, the routing layer5is electrically coupled to the first doped portions10A,10B,10C,10D in the plurality of photosensitive layers3A,3B,3C and3D through the doped interface layers. Specifically, a conductive material, such as metal or alloy, is filled into the via holes32V to form electrical contact to the first doped region10. Furthermore, the conductive material is further sputtered over the second dielectric layer32to complete the metal line routing after a suitable patterning operation.

Referring toFIG.2AandFIG.28,FIG.2Aillustrates a cross section of a photodetecting device200,FIG.2Billustrates a top view of a photodetecting device200illustrated inFIG.2A, according to some embodiments of the present disclosure. By incorporating an optical element70over the photo sensing area3, the photodetecting device having a smaller optical aperture of active region is allowed to detect optical signal incident over an area larger than itself, thereby further improving the collection efficiency of optical signal from the core1111A of the optical fiber1111. The photodetecting device200is similar to the photodetecting device100as discussed inFIG.1AtoFIG.1Lexcept for an implementation of the optical element70. As shown inFIG.2A, the sub-pixels1A and1B are surrounded and covered by the optical element70. Specifically, the optical element70may include a properly designed combination of convex portion72and a spacer portion71that separates the convex portion72from the sub-pixels1A and1B by an effective focal length of the convex portion72. In some embodiments, the convex portion72may be a micro lens having a diameter or a width ranging from 3 to 12 μm and a height ranging from 1 μm to 8 μm. The design of the convex portion72and the spacer portion71allow to focus the incident light onto the top surface of the photo sensing area3. In some embodiments, the spacer portion71includes an insulating material substantially transparent to the incident light. For example, the spacer portion71may be composed of polymeric material. In some embodiments, a top surface of the spacer portion71is above the first doped region10. In some embodiments, the convex portion72of the optical element70includes a plurality of lenses disposed in a one-to-one correspondence with each of the photosensitive layers3A,3B,3C and3D (for example, one lens above each of the first photosensitive layer3A, the second photosensitive layer3B, the third photosensitive layer3C, and the fourth photosensitive layer3B).

Furthermore, by reducing a size of the sub-pixels1A and1B, the size of the convex portion72is allowed to be reduced accordingly. In a comparative embodiment of a single large pixel area being coupled to an optical fiber, a giant micro-lens (GML) may be used to provide sufficient coverage of such large pixel area. Although the GML, can cover larger area (for example, 50 μm×50 μm), difficulties in fabrication may lead to lower yield and often the greater cost.

Therefore, in some embodiments provided by the present disclosure, the optical element70includes multiple micro-lenses. The size of each micro-lens is smaller than that of the GML, and thus can be disposed in a one-to-one correspondence with each of the photosensitive layers of the photo sensing area3, which, in some embodiments, occupies an area of about 10 μm×10 μwhen the shape of the convex portion72is square. In some embodiments, each of the convex portion72has a diameter or a width ranging from 3 to 12 μm. The micro-lens implemented in some present embodiments has a height ranging from 1 μm to 8 μm. The difficulty of fabricating the micro-lens is lower and the production cost is lower comparing to the fabrication of the GML. In some embodiments, adjacent micro-lenses can be connected in a continuous manner, in other words, can be physically connected to each other, for further improving the flexibility of microlens layout design. In the embodiment of four convex portion72having four micro-lenses connected together as shown inFIG.2B, although a gap70X is formed between each of the micro-lenses, the area of the gap70X can be reduced, for example, to 10% or less of the square of the pitch P in the photodetecting device200, by proper microlens layout design, in order to achieve an optical fill factor of about 90%. In some embodiments, the first doped portions10A,10B of the photosensitive layers3A,3B are arranged to offset from a projection area of the gap70X respectively to decrease the coupling loss between the optical fiber1111and the photodetecting device200.

In some embodiments, the implementation of the convex portions72in a manner of micro-lens array increases the tolerance regarding the translational or rotational misalignment between the optical fiber1111and the underlying photodetecting device200, as opposed to using a GML. Specifically, even when a center of a light source, such as the optical fiber1111, is misaligned to a center of the photodetecting device200by, for example, misaligned by a distance of a width WAP of a sub-pixel1A or1B, a great portion of optical signal may still be absorbed by the photo sensing area3by implementing the micro-lens array. However, the collection efficiency can be dramatically decreased under the aforesaid misalignment condition when a GML is implemented. Utilizing micro-lens array including multiple micro-lenses in a one-to-one correspondence with each of the photosensitive layers can be a more robust solution to assembling, packaging, or mechanical error that lead to serious light coupling loss.

It should be noted that the photodetecting device100discussed inFIG.1AtoFIG.1Land photodetecting device200discussed inFIG.2AandFIG.2Bare not limited to a front-side illumination configuration. Alternatively, a back-side illumination configuration can be implemented by people having ordinary skill in the art. For example, the optical element70may be disposed at the backside of the substrate9, and configured to receive optical signal. The backside of the substrate9can be the surface distal from the second doped region20. The incident optical signal is focused by the optical element70, propagates to the front side of the substrate9, and be absorbed by the photo sensing area3disposed at the front side of the substrate9.

In some embodiments, photodetecting devices discussed inFIG.3AtoFIG.6Balleviate the coupling loss between optical fiber and photodetecting devices.

Referring toFIG.3AandFIG.3B,FIG.3Aillustrates a top view of a photodetecting device,FIG.3Billustrates a cross section ofFIG.3Aalong line A-A′, according to some embodiments of the present disclosure. A sub-pixel1* at least include a photosensitive layer3* supported by a substrate9*, a first doped portion10* having a first conductivity type and coupled to the photosensitive layer3*, and a second doped region20* having a second conductivity type different from the first conductivity type and coupled to the photosensitive layer3*. The first doped portion10* is separated from the second doped region20* by the photosensitive layer3*. In some embodiments, the first doped portion10*, the photosensitive layer3*, and the second doped region20* may form a p-i-n structure. In some embodiments, the photosensitive layer3* of the sub-pixel1* is surrounded by an isolation region4*. In some embodiments, a top surface FS of the photosensitive layer3*, a top surface of the first doped portion10* and a top surface of the second doped region20* are exposed at a same side of the substrate9*. In some embodiments, the photosensitive layer3* is fully embedded in the substrate9*. In some embodiments, the photosensitive layer3* is partially embedded in the substrate9*.

As shown inFIG.3AandFIG.3B, the first doped portion10* is at the top surface FS of the photosensitive layer3* and laterally surrounded by the photosensitive layer3*. The specific layout of the first doped portion10* includes suitable depth or shape of the doping profile, such as between 1×1018cm−3to 5×1021cm−3, and may be varied depending on different design, manufacturing process, or testing considerations. A portion of the second doped region20* is between the photosensitive layer3* and the substrate9*, that is, a portion of the second doped region20* laterally surrounds the photosensitive layer3* and a portion of the second doped region20* may be directly under the photosensitive layer3*. In some embodiments, the second doped region20* further includes an extended portion beneath the top surface of the substrate9* and laterally surrounds the photosensitive layer3* and the first doped portion10*. The specific layout of the second doped region20* includes suitable depth or shape of the doping profile, such as between 1×1018cm−3to 5×1021cm−3, and may be varied depending on different design, manufacturing process, or testing considerations. The second doped region20* may be surrounded by or in contact with the isolation region4*.

Referring toFIG.3A,FIG.3BandFIG.4A,FIG.4Aillustrates a top view of a photodetecting device, according to some embodiments of the present disclosure. In some embodiments, in order to improve the collection efficiency of an optical signal and alleviate coupling loss, a plurality of sub-pixels1* are binned to constitute a pixel1X** for receiving optical signal from, for example, but not limited to, a single optical fiber. In some embodiment, the optical signal comes from a free space in applications such as 2D and 3D image sensing, in which optical fibers are not needed. Similar to the discussion inFIG.1AtoFIG.2B, binned sub-pixels1* break down a large sensing area into several small effective sensing areas so that the multiple micro-lenses of a micro-lens array can be disposed in a one-to-one correspondence with each of the sub-pixel1*.

A pixel1X** of the photodetecting device100X* can be configured to couple to one single optical fiber, and may include more than one sub-pixels1*. In the examples provided inFIG.4A, four sub-pixels1* (respectively denoted as a first sub-pixel1A*, a second sub-pixel1B*, a third sub-pixel1C*, and a fourth sub-pixel1D are shown. It should be noted that the number of sub-pixels1* constituting a pixel1X** of the photodetecting device100X* is not limited to four, and can be any other number greater than 1, such as 2, 9, 16, 25, 100.

In some embodiments, the first sub-pixel1A* has a first side along a primary axis PD and a second side along a secondary axis SD. The first side has a first length greater than a second length of the second side. The second sub-pixel1B* has a third side along the primary axis PD and a fourth side along the secondary axis SD, wherein the third side of the second sub-pixel1has a third length greater than a fourth length of the fourth side of second b-pixel1B*. In some embodiments, the primary axis PD can be substantially orthogonal to the secondary axis SD. In the embodiment shown inFIG.4A, each of the third sub-pixel1C* and the fourth sub-pixel11)* of the pixel1X** of the photodetecting device100X* has a longer side along the primary axis PD and a shorter side along the secondary axis SD. In some embodiments, if the pixel IX** of the photodetecting device100X* includes more than four sub-pixels1*, each of the sub-pixels1* may have a longer side along the primary axis PD and a shorter side along the secondary axis SD.

Referring toFIG.4A, from a top view perspective, a collective area of the photosensitive layer3A*,3B*,3C*,3D* is smaller than an area of the pixel1X**. In some embodiments, a pitch measured between a center of a sub-pixel1* and a center of an adjacent sub-pixel1* is about 10 μm, and a side of the photosensitive layer3* of a sub-pixel1* is in a range of from about 1.5 μm to about 8.5 μm. As previously discussed inFIG.2AandFIG.2B, such size is more suitable for aligning multiple micro-lens to the photosensitive layers3* of each of the sub-pixel1* in a one-to-one correspondence manner.

A routing layer5* is disposed above the substrate9*, electrically coupling the first doped portion10* and the second doped region20*. The routing layer5* includes a first end5A* configured to connect a plurality of the first doped portions10* of the plurality of the sub-pixels1*, and a second end5B* configured to connect a plurality of the second doped regions20* of the plurality of the sub-pixels1*. In some embodiments, the first end5A* and the second end5B* are respectively connected to different bias. In some embodiments, the routing layer5* is further connected to a complementary metal-oxide-semiconductor (CMOS) circuit on another substrate. In some embodiments, the sub-pixels1* of a photodetecting device100X* illustrated inFIG.3Bpossesses a backside illumination configuration where the incident light is received at a backside of the substrate9*. Similar to the embodiments previously described inFIG.2AandFIG.2B, optical elements including a micro-lens array and a spacer portion can be disposed at the backside of the substrate9* under the backside illumination configuration.

Referring toFIG.3A,FIG.3BandFIG.4B,FIG.4Billustrates a top view of a photodetecting device100Y*, according to some embodiments of the present disclosure. A pixel1Y** of the photodetecting device100Y* is similar to the pixel1X** of the photodetecting device100X*, except for the arrangement of the sub-pixels1* is different. In the examples provided inFIG.4B, four sub-pixels1* (respectively denoted as a first sub-pixel1A*, a second sub-pixel1B*, a third sub-pixel1C* adjacent to the first sub-pixel1A* in the same orientation, and a fourth sub-pixel1D* adjacent to the second sub-pixel1B* in the same orientation) are shown.

The first sub-pixel1A* has a first side along a primary axis PD and a second side along a secondary axis SD. The first side has a first length greater than a second length of the second side. The second sub-pixel1B* has a third side along the secondary axis SD and a fourth side along the primary axis PD, wherein the third side of the second sub-pixel1B* has a third length greater than a fourth length of the fourth side of the second sub-pixel1B*. In some embodiments, the third sub-pixel1C* has a first side along a primary axis PD and a second side along a secondary axis SD. The first side of the third sub-pixel1C* has a first length greater than a second length of the second side of the third sub-pixel1C*. The fourth sub-pixel1D* has a first side along the secondary axis SD and the second side along the primary axis PD. The first side of the fourth sub-pixel1D* has a first length greater than a second length of the second side of the fourth sub-pixel1D*. In some embodiments, the primary axis PD can be substantially orthogonal to the secondary axis SD. It should be noted that the number of sub-pixels1* constituting a pixel1Y** of the photodetecting device100Y* is not limited to four, and can be any other number greater than 1, such as 2, 9, 16, 25, 100.

By implementing the arrangement inFIG.4B, the area density of the photosensitive layers3A*,38*,3C*,3D* per pixel1Y** can be increased compared to the arrangement inFIG.4A. In some embodiments, the first sub-pixel1A*, the second sub-pixel1B*, the third sub-pixel1C*, and the fourth sub-pixel1D* are symmetric with regard to a center of the pixel1Y**. In some embodiments, at least one of the first sub-pixel1A*, the second sub-pixel1B*, the third sub-pixel1C*, and the fourth sub-pixel1D* extends across a middle plane PD1along the primary axis PD, the middle plane SD1along the secondary axis SD, or both, in order to achieve a denser sub-pixels1* layout. It should be noted that, if the pixel1Y** includes more than four sub-pixels1*, each of the sub-pixels1* can be arranged in a similar manner.

Referring toFIG.5AandFIG.5B,FIG.5Aillustrates a top view of a photodetecting device,FIG.5Billustrates a cross section ofFIG.5Aalong line B-B′, according to some embodiments of the present disclosure. Another type of sub-pixel1′ is provided inFIG.5AandFIG.5B. The sub-pixel1′ at least includes a photosensitive layer3′ over a substrate9′, a first doped portion10′ having a first conductivity type and coupled to the photosensitive layer3′, and a second doped region20′ having a second conductivity type different from the first conductivity type and coupled to the photosensitive layer3′. The first doped portion10′ is separated from the second doped region20′ by the photosensitive layer3′. In some embodiments, the first doped portion10′, the photosensitive layer3′, and the second doped region20′ may form a p-i-n structure. In some embodiments, the photosensitive layer3′ is exposed from the substrate9′ and laterally surrounded by the substrate9′. In some embodiments, the photosensitive layer3′, the first doped portion10′ and the second doped region20′ are laterally surrounded by an isolation region4′. The substrate9′ is laterally surrounded by the isolation region4′. The specific layout of the first doped portion10′ and the second doped region20′ includes suitable depth or shape of the doping profile, such as between 1×1018cm−3to 5×1021cm−3, and may be varied depending on different design, manufacturing process, or testing considerations.

As shown inFIG.5AandFIG.5B, both of the first doped portion10′ and the second doped region20′ are disposed proximal to a top surface FS of the photosensitive layer3′. In some embodiments, the first doped portion10′ includes a first portion10P′ extending along a primary axis PD, and the second doped region20′ includes a first portion20P′ extending along the primary axis PD. The first doped portion10′ further includes a second portion10Q′ extending toward the second doped region20′, and the second doped region20′ further includes a second portion20Q′ extending toward the first doped portion10′. In some embodiments, the second portion10Q′ of the first doped portion10′ and the second portion20Q′ of the second doped region20′ extends substantially along a secondary axis SD. In some embodiments, the primary axis PD is along a first side of a sub-pixel1′, and the secondary axis SD is along a second side of the sub-pixel1′, wherein the second side is shorter than the first side. In some embodiments, the secondary axis SD may be substantially orthogonal to the primary axis PD. In some implementation, the first portion10P′ and/or the first portion20P′ may be optional.

In some embodiments, the first doped portion10′ is interlaced with the second doped region20′ from a top view perspective. In some embodiments, the second portion10Q′ of the first doped portion10′ includes one or more extension portions (denoted as10Q′_1,10Q′_2,10Q′_3. . . ) extending toward the second doped region20′. The second portion20Q′ of the second doped region20′ includes one or more extension portions (denoted as20Q′_1,20Q′_2. . . ) extending toward the first doped portion10′. The extension portions of the first doped portion10′ and the extension portions of the second doped region20′ are arranged alternatively along the primary axis PD in a staggered fashion, that is, one extension portion of the second doped region20′ is between two extension portions of the first doped portion10′ and vice versa. Each of the extension portions of the first doped portion10′ and the extension portions of the second doped region20′ are separated by a portion of the photosensitive layer3′.

Referring toFIG.6A,FIG.6Aillustrates a top view of a photodetecting device100X′, according to some embodiments of the present disclosure. The arrangement of sub-pixels1′ can be similar to the arrangement of sub-pixels1* as discussed inFIG.4A. In the examples provided inFIG.6A, four sub-pixels (respectively denoted as a first sub-pixel1A′, a second sub-pixel1B′, a third sub-pixel1C′, and a fourth sub-pixel10′) are shown. It should be noted that the number of sub-pixels1′ constituting a pixel1X″ of the photodetecting device100X′ is not limited to four and can be any other number greater than 1, such as 2, 9, 16, 25, 100.

In some embodiments, the first sub-pixel1A′ has a first side along a primary axis PD and a second side along a secondary axis SD. The first side of the first sub-pixel1A′ has a first length greater than a second length of the second side of the first sub-pixel1A′. The second sub-pixel1B′ has a first side along the primary axis PD and the second side along the secondary axis SD. The first side of the second sub-pixel1B′ has a first length greater than a second length of the second side of the second sub-pixel1B′. In some embodiments, the primary axis PD can be substantially orthogonal to the secondary axis SD. In the embodiment shown inFIG.6A, each of the third sub-pixel1C′ and the fourth sub-pixel1D′ of the photodetecting device100X′ has a longer side along the primary axis PD and a shorter side along the secondary axis SD. In some embodiments, if the pixel1X″ of the photodetecting device100X′ includes more than four sub-pixels1′, each of the sub-pixels1′ may have a longer side along the primary axis PD and a shorter side along the secondary axis SD, in some embodiments, one pixel1X″ of the photodetecting device100X′ may be configured to receive optical signal from a single optical fiber, as previously described inFIG.1AandFIG.2A.

In some embodiments, in order to improve the optical signal collection efficiency and alleviate coupling loss, a plurality of sub-pixels1′ in photodetecting device100X′ are binned to constitute a pixel IX″ for receiving optical signal from, for example, but not limited to, a single optical fiber. In some embodiment, the optical signal comes from a free n applications such as 2D and 3D image sensing, in which optical fibers are not needed. Similar to the discussion inFIG.1A,FIG.2B, andFIG.4A, binned sub-pixels1′ break down a large sensing area into several small effective sensing areas so that multiple micro-lenses of a micro-lens array can be disposed in a one-to-one correspondence with each of the sub-pixel1′.

Referring toFIG.6A, from a top view perspective, a collective area of the photosensitive layers3A′,3B′,3C′,3D′ is smaller than an area of the pixel1X″. In some embodiments, a pitch measured between a center of a sub-pixel1′ and a center of an adjacent sub-pixel1′ is about 10 μm, and a side of the photosensitive layer3′ of a sub-pixel1′ is in a range of from about 1.5 μm, to about 8.5 μm. As previously discussed inFIG.2AandFIG.2B, such size is more suitable for aligning multiple micro-lenses to the photosensitive layers3′ of each of the sub-pixel1′ in a one-to-one correspondence manner.

Referring toFIG.6B,FIG.6Billustrates a top view of a photodetecting device, according to some embodiments of the present disclosure. The arrangement of the pixel1Y″ of the photodetecting device100Y′ is similar to the pixel1Y** of the photodetecting device100Y*. In the examples provided inFIG.6B, four sub-pixels1′ (respectively denoted as the first sub-pixel1A′, a second sub-pixel1B′, a third sub-pixel1C′, and a fourth sub-pixel1D′) are shown. The first sub-pixel1A′ has a first side along a primary axis PD and a second side along a secondary axis SD. The first side of the first sub-pixel1A′ has a first length greater than a second length of the second side of the first sub-pixel1A′. The second sub-pixel1B′ has a first side along the secondary axis SD and a second side along the primary axis PD. The first side of the second sub-pixel1B′ has a first length greater than a second length of the second side second sub-pixel1B′. In some embodiments, the third sub-pixel1C′ has a first side along a primary axis PD and a second side along a secondary axis SD. The first side of the third sub-pixel1C′ has a first length greater than a second length of the second side of the third sub-pixel1C. The fourth sub-pixel1D′ has a first side along the secondary axis SD and the second side along the primary axis PD. The first side of the fourth sub-pixel1D′ has a first length greater than a second length of the second side of the fourth sub-pixel1D′. In some embodiments, the primary axis PD can be substantially orthogonal to the secondary axis SD. It should be noted that the number of sub-pixels1′ constituting; a pixel1Y″ of the photodetecting device100Y′ is not limited and can be any other number greater than 1, such as 2, 9, 16, 25, 100.

By implementing the arrangement inFIG.6B, the area density of the photosensitive layers3A′,3B′,3C′,3D′ per pixel1Y″ can be increased compared to the arrangement inFIG.6A. In some embodiments, the first sub-pixel1A′, the second sub-pixel1B′, the third sub-pixel1C′, and the fourth sub-pixel1D′ are symmetric with regard to a center of the pixel1Y″. In some embodiments, at least one of the first sub-pixel1A′, the second sub-pixel1B′, the third sub-pixel1C′, and the fourth sub-pixel1D′ extends across a middle plane PD1along the primary axis PD, the middle plane SD1along the secondary axis SD, or both, in order to achieve a denser sub-pixels1′ layout. It should be noted that, if the pixel1Y″ includes more than four sub-pixels1′, each of the sub-pixels1′ can be arranged in a similar manner.

Referring toFIG.5AtoFIG.6B, a routing layer5′ is disposed above the substrate9′ in a similar fashion as illustrated inFIG.3B. The routing layer5′ includes a first end5A′ configured to connect a plurality of the first doped portions10′ in the plurality of the sub-pixels1′, and a second end5B′ configured to connect a plurality of the second doped regions20′ of the plurality of the sub-pixels1′. In some embodiments, the first end5A′ and the second end5B′ are respectively connected to different bias. In some embodiments, the routing layer5′ is further connected to a complementary metal-oxide-semiconductor (CMOS) circuit on another substrate. In some embodiments, the sub-pixels1′ of a photodetecting device100Y* illustrated inFIG.5Bpossesses a backside illumination configuration where the incident light is received at a backside of the substrate9′. Similar to the embodiments previously described inFIG.2AandFIG.2B, optical elements including a micro-lens array and a spacer portion can be disposed at the backside of the substrate9′ under the backside illumination configuration. In some implementations, when the first portion10P′ and/or the first portion20P′ are absent, there may be multiple first ends5A′ connected to the second portions10Q′ instead of the first portion10P′, and there may be multiple second ends5B′ connected to the second portions20Q′ instead of the first portion20P′.

Besides total area of the photosensitive area, it is also important to improve the collection efficiency of incident optical signal and alleviate coupling loss. Therefore, each pixels1X**,1Y**,1X″, or1Y″ for receiving optical signal from a single optical fiber disclosed in the present embodiment includes more than one sub-pixels and arranged in binned fashion to compensate the optical signal loss due to decreased size of photosensitive area. Convex portion of optical element such as a micro-lens or a micro-lens array can be disposed above each of the sub-pixels in a one-to-one corresponding manner, thus alleviating coupling loss. It should also be noted that the photosensitive layer of each sub-pixels is designed to fit the size of an easier-to-fabricate micro-lens or micro-lens array.

The materials of substrate9* or9′ are similar to the substrate9and the material of the photo sensing area3′ or3* may be similar to the material of the photo sensing area3inFIG.1AtoFIG.1L. It should be noted that the structures of photodetecting devices and the methods discussed in the present disclosure is suitable when the substrate9,9* or9′ includes silicon and the photo sensing area3,3′, or3* includes germanium or germanium-silicon.

In some embodiments, the photodetecting devices100,200,100X*,100Y*,100X′ and100Y′ and the methods discussed in the present disclosure can be applied to optical communication device, optical sensors, optical receivers, optical actuators, or light detection and ranging (LIDAR) applications. Among which, dark current reduction is especially critical to LIDAR application.

The dark current of the photodetecting devices100,200,100X*,100Y*,100X′ and100Y′ can be reduced by the implementation of micro-lens or micro-lens arrays. Generally speaking, the magnitude of dark current is inversely related to a total area of the optical aperture or the active region. For example, by breaking down a 100 μm×100 μm single large pixel into a 10×10 sub-pixel array (i.e., each sub-pixel having a dimension of about 10 μm×10 μm), and implementing a 10×10 micro-lens array to the 10×10 sub-pixel array in a one-to-one corresponding manner in order to focus the incident light to an optical aperture or active region of about 2.5 μm×2.5 μm in each sub-pixels, the dark current can be effectively reduced by 16 times (i.e., (10/2.5)2).

For another example, by breaking down a 100 pin×100 μm single large pixel into a 2×2 sub-pixel array (i.e., each sub-pixel having a dimension of about 50 μm×50 μm), and implementing a 2×2 GML array to the 2×2 sub-pixel array in a one-to-one corresponding manner in order to focus the incident light to an optical aperture or active region of about 2.5 μm×2.5 pin in each sub-pixels, the dark current can be effectively reduced by 400 times (i.e., (50/2.5)2). In some embodiments where a GML array is implemented, dark current of the of the photodetecting devices100,200,100X*,100Y*,100X′ and100Y′ can be decreased to an extent lower than implementing the micro-lens array in the 10×10 sub-pixel array, as previously discussed. However, the fabrication process of GML or GML array is difficult and often requires higher cost than that of micro-lens or micro-lens array.

In the embodiments where micro-lens or micro-lens array is implemented, further dark current reduction, for example, by an order of magnitude, can be achieved by operating the photodetecting devices100,200,100X*,100Y*,100X′ and100Y′ at a low reverse bias. For the binned sub-pixel configuration disclosed in the present disclosure, manufacturing processes, including but not limited to, bumping, read-out integrated circuit, wire-bonding and boarding, may introduce variation to electrical circuitry of the photodetecting devices. Furthermore, the variation may also present at the input referred voltage to each amplifier (e.g., in a TIA circuit) of each photodetecting devices. To eliminate the aforesaid process variation which may lead to generation of dark current (e.g., operating under a forward-bias regime), the voltage drop across each photodetecting device can be controlled in a sufficient negative number so as to keep the photodetecting device under a low-reverse regime.

For the LIDAR application, sensitivity of the photodetecting device can be affected by various factors in addition to dark current. Three of the major noise sources with regard to a photodetecting device can be characterized as (1) dark current noise, (2) ambient noise, and (3) current noise resulted from the transimpedance amplifier (TIA) circuit or other CMOS circuits. The sensitivity of an optical communication model can be approximated by the following formula,
SensitivityS=hω{Q2*e*BW*C1+Q*iTIA2+2e*(Id+Ia)*BW*C2]1/2}/e η,
wherein Q stands for Q factor (or often referred to as Q value), C1and C2are constants (can be referred to as Personik constants), BW is bandwidth of the photodetector, η stands for quantum efficiency, h*ω is the energy of photon, iTIAis the current of trans-impedance amplifier (TIA) circuit, Iais ambient light noise photo current, and Idis dark current.

According to empirical of an optical communication model, herein iTIAand Iaare often within a range of hundreds of nanoamphere (nA). Therefore, as long as the dark current resulted from the present disclosure is comparable to that generated from ambient noise and TIA circuit noise, e.g., within a range of hundreds of nanoamphere, the noise of dark current may no longer be accounted as the dominant source of noise, and the sensitivity of the photodetecting device may not be deteriorated.

As used herein and not otherwise defined, the terms “substantially” and “about” are used to describe and account for small variations. When used in conjunctions with an event or circumstance, the terms can encompass instances in which the event or circumstance occurs precisely as well as instances in which the event or circumstance occurs to a close approximation. For example, when used in conjunction with a numerical value, the terms can encompass a range of variation of less than or equal to ±10% of that numerical value, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%. As another example, a line or a plane can be substantially flat if a peak or depression of the line or plane is no greater than 5 μm, no greater than 1 μm, or no greater than 0.5 μm.