Improved NIR / SWIR quantum efficiency for a silicon image sensor

Abstract

Example embodiments relate to improved near-infrared. (NIR) / short-wave infrared (SWIR) quantum efficiency for a silicon image sensor. An example embodiment includes a. light-sensitive pixel configured to detect light signals that illuminate a top side of the light- sensitive pixel is provided, lire light-sensitive pixel includes an absorption region configured to absorb photons and generate electrical charge carriers. The light-sensitive pixel also includes a barrier region configured to block the electrical charge carriers generated within tire absorption region. Additionally, the light-sensitive pixel includes a drain region configured to collect electrical charge earners arising as a. result of dark current or overflow charge from the absorption region. Further, the light-sensitive pixel includes a mirror region located on an opposite side of the absorption region from the top side of the light-sensitive pixel. The mirror region is configured to reflect photons back toward the absorption region.

Description

IMPROVED NIR / SWIR QUANTUM EFFICIENCY FOR A SILICON IMAGE SENSOR CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims the benefit of U.S. Provisional Patent Application No.63 / 618,690, filed January 8, 2024, the contents of which are hereby incorporated by reference in their entirety. BACKGROUND

[0002] An image sensor is a semiconductor device for converting an optical image into an electric signal. There are a number of different types of semiconductor-based imagers, including charge coupled devices (CCDs), photodiode arrays, charge injection devices, hybrid focal plane arrays, etc. The various types of image sensors may be broadly categorized as charge coupled devices (CCD) and complementary metal oxide semiconductor (CMOS) image sensors. In recent years, there has also been increased interest in applying CMOS active pixel sensors for night vision applications. The night vision band of electromagnetic radiation may include wavelengths in the range of 400 nm to 1100 nm. SUMMARY

[0003] Example embodiments may include light-sensitive pixels for use in CMOS image sensors. In particular, such light-sensitive pixels may enhance quantum efficiency while maintaining relatively low dark current. In order to do so, example light-sensitive pixels may include (e.g., in addition to an absorption region) a barrier region to provide antiblooming after an excitation event (i.e., to reduce or eliminate crosstalk between adjacent light-sensitive pixels), a drain region to remove dark current from the light-sensitive pixel so that it does not affect measurements, and a mirror region to reflect light signals back toward the absorption region (e.g., to enhance quantum efficiency, particularly for longer wavelengths, such as near-infrared (NIR) wavelengths). Further, such light-sensitive pixels may be front-side illuminated (FSI) devices, which may assist in reducing dark current (e.g., compared with back-side illuminated (BSI) devices). Reducing dark current may improve detection in ambient low-light conditions (e.g., as a result of electrical noise associated with readout circuitry, rather than dark current noise, being the primary limitation in CMOS image sensors that incorporate the light-sensitive pixels described herein). Additionally, in order to enhance the detection of shortwave-infrared (SWIR) signals (e.g., when using a semiconductor material for the absorption region that does not readily absorb light of suchwavelengths, such as silicon), some embodiments may also include an upconverting region that converts photons of SWIR wavelengths into different wavelengths (e.g., visible wavelengths or NIR wavelengths) such that the photons can be absorbed and converted into electrical signals by the absorption region.

[0004] In a first aspect, a light-sensitive pixel configured to detect light signals that illuminate a top side of the light-sensitive pixel is provided. The light-sensitive pixel includes an absorption region that includes a first extrinsic semiconductor. The absorption region is configured to absorb photons within a first wavelength range and generate electrical charge carriers. The light-sensitive pixel also includes a barrier region located adjacent to the absorption region and configured to block the electrical charge carriers generated within the absorption region. The barrier region includes a second extrinsic semiconductor. Additionally, the light-sensitive pixel includes a drain region that includes a third extrinsic semiconductor and configured to collect electrical charge carriers arising as a result of dark current or overflow charge from the absorption region. The drain region is located on an opposite side of the absorption region from the top side of the light-sensitive pixel. The drain region is located on an opposite side of the barrier region than the absorption region. The first extrinsic semiconductor and the second extrinsic semiconductor have doping of opposite type and the first extrinsic semiconductor and the third extrinsic semiconductor have doping of the same type. Further, the light-sensitive pixel includes a mirror region located on an opposite side of the absorption region from the top side of the light-sensitive pixel. The mirror region is configured to reflect photons back toward the absorption region.

[0005] In a second aspect, a device is provided. The device includes a plurality of light-sensitive pixels. Each light-sensitive pixel is configured to detect light signals that illuminate a top side of the light-sensitive pixel. Each light-sensitive pixel includes an absorption region that includes a first extrinsic semiconductor. The absorption region is configured to absorb photons within a first wavelength range and generate electrical charge carriers. Each light-sensitive pixel also includes a barrier region located adjacent to the absorption region and configured to block the electrical charge carriers generated within the absorption region. The barrier region includes a second extrinsic semiconductor. Additionally, each light-sensitive pixel includes a drain region that includes a third extrinsic semiconductor and configured to collect electrical charge carriers arising as a result of dark current or overflow charge from the absorption region. The drain region is located on an opposite side of the absorption region from the top side of the light-sensitive pixel. The drain region is located on an opposite side of the barrier region than the absorption region. The firstextrinsic semiconductor and the second extrinsic semiconductor have doping of opposite type and the first extrinsic semiconductor and the third extrinsic semiconductor have doping of the same type. Further, each light-sensitive pixel includes a mirror region located on an opposite side of the absorption region from the top side of the light-sensitive pixel. The mirror region is configured to reflect photons back toward the absorption region. The device also includes a first circuit configured to read out the electrical charge carriers generated by the absorption region. Additionally, the device includes a second circuit configured to extract the electrical charge carriers collected by the drain region.

[0006] In a third aspect, a method is provided. The method includes providing a light- sensitive pixel configured to detect light signals that illuminate a top side of the light- sensitive pixel. The light-sensitive pixel includes an absorption region that include a first extrinsic semiconductor. The absorption region is configured to absorb photons within a first wavelength range and generate electrical charge carriers. The light-sensitive pixel also includes a barrier region located adjacent to the absorption region and configured to block the electrical charge carriers generated within the absorption region. The barrier region includes a second extrinsic semiconductor. Additionally, the light-sensitive pixel includes a drain region that includes a third extrinsic semiconductor and configured to collect electrical charge carriers arising as a result of dark current or overflow charge from the absorption region. The drain region is located on an opposite side of the absorption region from the top side of the light-sensitive pixel. The drain region is located on an opposite side of the barrier region than the absorption region. The first extrinsic semiconductor and the second extrinsic semiconductor have doping of opposite type and the first extrinsic semiconductor and the third extrinsic semiconductor have doping of the same type. The method also includes attaching a temporary handle wafer to the top side of the light-sensitive pixel. Additionally, the method includes polishing or etching the drain region to reduce a thickness of the drain region. Further, the method includes depositing a mirror region onto the drain region. The mirror region is configured to reflect photons back toward the absorption region. In addition, the method includes bonding the mirror region to a carrier wafer. Still further, the method includes removing the temporary handle wafer from the top side of the light-sensitive pixel.

[0007] In a fourth aspect, a method is provided. The method includes receiving, at a top side of a light-sensitive pixel, an illumination by a light signal. The method also includes absorbing, by an absorption region of the light-sensitive pixel, photons within a first wavelength range. The absorption region includes a first extrinsic semiconductor. Additionally, the method includes generating, by the absorption region of the light-sensitivepixel, electrical charge carriers. Further, the method includes blocking, by a barrier region of the light-sensitive pixel that includes a second extrinsic semiconductor and located adjacent to the absorption region, at least some of the electrical charge carriers generated within the absorption region. In addition, the method includes collecting, by a drain region of the light- sensitive pixel that includes a third extrinsic semiconductor and located on an opposite side of the absorption region from the top side of the light-sensitive pixel, electrical charge carriers arising as a result of dark current or overflow charge from the absorption region. The first extrinsic semiconductor and the second extrinsic semiconductor have doping of opposite type and the first extrinsic semiconductor and the third extrinsic semiconductor have doping of the same type. Still further, the method includes reflecting, by a mirror region of the light- sensitive pixel located on an opposite side of the absorption region from the top side of the light-sensitive pixel, photons back toward the absorption region.

[0008] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the figures and the following detailed description.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is a schematic illustration of a device, according to example embodiments.

[0010] Figure 2A is an illustration of a light-sensitive pixel, according to example embodiments.

[0011] Figure 2B is an illustration of a light-sensitive pixel, according to example embodiments.

[0012] Figure 2C is a plot of photon absorption within a light-sensitive pixel, according to example embodiments.

[0013] Figure 3 is an illustration of a device, according to example embodiments.

[0014] Figure 4A is an illustration of a step of a fabrication technique, according to example embodiments.

[0015] Figure 4B is an illustration of a step of a fabrication technique, according to example embodiments.

[0016] Figure 4C is an illustration of a step of a fabrication technique, according to example embodiments.

[0017] Figure 4D is an illustration of a step of a fabrication technique, according to example embodiments.

[0018] Figure 4E is an illustration of a step of a fabrication technique, according to example embodiments.

[0019] Figure 4F is an illustration of a step of a fabrication technique, according to example embodiments.

[0020] Figure 4G is an illustration of a step of a fabrication technique, according to example embodiments.

[0021] Figure 5 is a flowchart illustration of a method, according to example embodiments.

[0022] Figure 6 is a flowchart illustration of a method, according to example embodiments.DETAILED DESCRIPTION

[0023] Example methods and systems are described herein. Any example embodiment or feature described herein is not necessarily to be construed as preferred or advantageous over other embodiments or features. The example embodiments described herein are not meant to be limiting. It will be readily understood that certain aspects of the disclosed systems and methods can be arranged and combined in a wide variety of different configurations, all of which are contemplated herein.

[0024] Furthermore, the particular arrangements shown in the figures should not be viewed as limiting. It should be understood that other embodiments might include more or less of each element shown in a given figure. In addition, some of the illustrated elements may be combined or omitted. Similarly, an example embodiment may include elements that are not illustrated in the figures.

[0025] As used herein, the phrase “doping of the same type” denotes semiconductor materials (e.g., two extrinsic semiconductors) that are either all doped to be n-type or all doped to be p-type. However, “doping of the same type” does not require that the dopant be the same. For example, two silicon materials have “doping of the same type” when one of the materials is doped using arsenic and the other material is doped using phosphorus (because both As and P represent n-type dopants for silicon). Similarly, two silicon materials have “doping of the same type” when one of the materials is doped using boron and the other material is doped using aluminum (because both B and Al represent p-type dopants for silicon). Further, the phrase “doping of the same type” also does not require that two materials are doped at the same concentration. For example, two materials could have “doping of the same type” even though one is doped with an n-type dopant concentration of1014 cm 3 and the other is doped with an n-type dopant concentration of 1018 cm 3.I. Overview

[0026] Image sensors (e.g., silicon imagers) described herein may include light- sensitive pixels having one or more absorption regions (e.g., semiconducting absorption regions). Such absorption regions may absorb photons of a certain wavelength and generate electrons or holes (i.e., such absorption regions may exhibit the photoelectric effect). Those electrons or holes may propagate to one or more depletion regions (e.g., formed at a junction between the absorption region and another semiconductor of opposite type, e.g., photodiode regions) and be read out (e.g., using readout circuitry), converted to a digital format (e.g.,using an analog-to-digital converter (ADC)), and combined with the measurements read out from other light-sensitive pixels in order to generate an image.

[0027] In some applications (e.g., low-light applications), increasing the NIR response for FSI image sensors (e.g., silicon imagers) without simultaneously increasing dark current can enhance image quality. For example, low dark current and high NIR response may be useful for night vision imagers (e.g., for search and rescue, aircraft, and / or automotive computer vision applications). Additionally, certain semiconductor materials that could otherwise be used in FSI image sensors (e.g., silicon) might not readily absorb photons of certain wavelengths (e.g., SWIR wavelengths). Hence, designing a light-sensitive pixel that could permit absorption of such wavelengths may enhance low-light response.

[0028] According to some techniques, image sensors may exhibit extended NIR absorption length using BSI with a textured back surface in order to cause photon scatter. Additionally, some techniques may incorporate Deep Trench Isolation (DTI) in light- sensitive pixels of the image sensor in order to reflect photons to increase the absorption path. BSI with textured back surfaces and DTI, however, may result in increased dark current.

[0029] As a result, example embodiments described herein include light-sensitive pixels that have a drain region (e.g., a drain region that is below and / or surrounds an absorption region of the light-sensitive pixel) configured to remove any dark current from the back surface. Further, in some embodiments, DTI may be excluded from the light-sensitive pixels described herein. In some embodiments, however, an isolating trench may still be defined within an absorption region of the light-sensitive pixel (e.g., to improve the modulation transfer function (MTF) of the light-sensitive pixel).

[0030] In addition, unlike traditional silicon image sensors that have an absorption cutoff at about 1100 nm, some example embodiments disclosed herein may include light- sensitive pixels with upconverting regions (e.g., upconverting crystal regions, such as erbium-doped crystal regions). The upconverting regions may convert light signals having wavelengths within the SWIR portion of the spectrum (e.g., a light signal originally emitted by an erbium glass laser that has a wavelength of approximately 1534 nm) into light signals with wavelengths within the detectable range of silicon (e.g., between 980 nm and 1000 nm). In other words, the upconverting region may absorb photons having SWIR wavelengths (e.g., between 1100 nm and 1700 nm), in response, emit photons (e.g., isotropically) that have visible wavelengths (e.g., between 400 nm and 700 nm) or NIR wavelengths (e.g., between 700 nm and 1100 nm).

[0031] Additionally or alternatively, some embodiments described herein mayinclude a light-sensitive pixel with a mirror region. The mirror region may reflect photons (e.g., NIR photons) that entered through a top side of the light-sensitive pixel (e.g., as a result of front-side illumination) and passed through the absorption region of the light-sensitive pixel unabsorbed back toward the absorption region (e.g., so as to have another opportunity at being absorbed in the absorption region, thereby increasing quantum efficiency). As such, the mirror region may be located below the absorption region of the light-sensitive pixel to reflect unabsorbed photons. In embodiments that include an upconverting region, the mirror region may be located on an opposite side of the upconverting region than the absorption region (e.g., the mirror region may be located below the upconverting region) so that any photons generated by the upconverting region would be reflected toward the absorption region.

[0032] Various embodiments described herein may exhibit one or more of the following characteristics. First, visible photons may be substantially (e.g., mostly) absorbed in the absorption region (e.g., the n-doped absorption region) on the first pass of the photons through the absorption region. Second, NIR photons may partially pass through the absorption region and drain region to the mirror region, at which point the NIR photons are reflected by a mirror region back through the drain region and absorption region to be absorbed by the absorption region on the reflected path (e.g., thereby enhancing the quantum efficiency for NIR photons compared to techniques that have an absorption region of the same volume but that do not include a mirror region). Third, the NIR signal may be increased by a factor of 1.55 or more when compared with light-sensitive pixels that do not include a mirror region. Fourth, crosstalk between adjacent light-sensitive pixels may be reduced or prevented (i.e., antiblooming may be provided) as a result of the barrier region. Fifth, the barrier region may inhibit or prevent backside dark current from propagating to the absorption region, and the drain region may be used to extract that backside dark current from the light-sensitive pixel. Mitigation of dark current may allow the light-sensitive pixel to operate without a thermoelectric cooling device, which might otherwise be used to mitigate temperature noise. Sixth, in embodiments having an upconverting region, detection of certain wavelengths (e.g., SWIR wavelengths) may be enhanced by a factor of 10 or more relative to traditional silicon image sensors. II. Example Systems

[0033] Figure 1 is a schematic illustration of a device 100 (e.g., a camera, such as a night-vision camera or a digital single-lens reflex (DSLR) camera), according to exampleembodiments. The device 100 may be configured to capture an image frame 160 of an environment surrounding the device 100 based on incoming light signals 102. As illustrated, the device 100 may include an image sensor 110 (i.e., an imager), a lens 120, a readout circuit 130, an ADC 140, and an image processing unit 150. In some embodiments, though not illustrated in Figure 1, the device 100 may also include a shutter (e.g., an adjustable aperture) used to control photography settings such as exposure time (i.e., shutter speed) and aperture size.

[0034] Upon the light signals 102 from the surrounding environment passing through (and potentially being altered by) the lens 120, the light signals 102 may be incident on the image sensor 110 (shown and described in additional detail with reference to Figures 2A-6). The image sensor 110 may then convert the incident light signals 102 (i.e., the photons) into electrical signals (i.e., electrons or holes) using one or more semiconductor devices. Such electrical signals may thereafter be read out from the image sensor 110 using the readout circuit 130 (e.g., the readout circuit 130 may read electrical signals out from each light- sensitive pixel of the image sensor 110). The electrical signals read from the image sensor using the readout circuit 130 may then be provided to the ADC 140 (e.g., including one or more amplifiers), which will convert the electrical signals from an analog form into a digital representation. The digital representation of the analog signals generated by the ADC 140 may thereafter be passed to the image processing unit 150, which may organize the digital representations from each of the respective light-sensitive pixels into a systematic representation (e.g., and generate one or more pieces of metadata to associate with the systematic representation) in order to form a digital image frame 160 (e.g., a photo of the surrounding environment). It is understood that the image frame 160 does not represent a physical component of the device 100, but instead merely represents a collection of digital data output from the image processing unit 150 (e.g., and transmitted to a display for viewing or to another digital device for storage and / or further transmission).

[0035] Figures 2A and 2B are cutaway illustrations of various embodiments of light- sensitive pixels 112A, 112B. A plurality of such light-sensitive pixels 112A, 112B may make up the image sensor 110 shown and described with reference to Figure 1. In various embodiments, the image sensor 110 may include only the light-sensitive pixels 112A of Figure 2A, only the light-sensitive pixels 112B of Figure 2B, or both light-sensitive pixels 112A illustrated in Figure 2A and light-sensitive pixels 112B illustrated in Figure 2B (e.g., in equal or un-equal proportions with one another).

[0036] As illustrated, the light-sensitive pixel 112A of Figure 2A may be front-sideilluminated by the light signal 102. In other words, as illustrated, the light-sensitive pixel 112A may be illuminated from the top (i.e., the light signal may interact with portions of the light-sensitive pixel 112A having the largest z coordinates first). As illustrated in Figure 2A, the light-sensitive pixel 112A may include a microlens 210, an absorption region 220, one or more diode-forming regions 222, a barrier region 230, a drain region 240, a mirror region 250, and a carrier wafer 260.

[0037] As shown in Figure 2A, the light signal 102 may first interact with the microlens 210 (e.g., and possibly be refracted by the microlens 210). Thereafter, the light signal 102 may pass through the absorption region 220 and / or one of the diode-forming regions 222 (so-called because they may form one or more photodiodes with the absorption region 220 when located adjacent to the absorption region 220). While passing through the absorption region 220, a portion of the light signal 102 (e.g., some percentage of photons making up the light signal 102) may be absorbed, resulting in the generation of one or more electrons or holes (e.g., by the photoelectric effect). Electrons or holes generated may diffuse to the interfaces between the absorption region 220 and the one or more diode-forming regions 222. As a result of the absorption region 220 and the diode-forming regions 222 being of opposite type (e.g., the absorption region 220 is an n-type semiconductor while the diode-forming region(s) are p-type semiconductors or the absorption region 220 is a p-type semiconductor while the diode-forming region(s) are n-type semiconductors), semiconductor depletion region(s) may be formed at the interfaces between the absorption region 220 and the one or more diode-forming regions 222. As such, in some embodiments, readout circuitry (e.g., the readout circuit 130 shown and described with reference to Figure 1) may be attached to the interface(s) between the absorption region 220 and the diode-forming region(s) 222 in order to read out the electrical current (e.g., electrons or holes) generated by the absorption of the light signal 102. In some embodiments, for example, the readout circuitry may transfer charge from the interface(s) between the absorption region 220 and the diode-forming region(s) 222 to a low capacitance sense node via diffusion in order to convert the transferred charge to a voltage signal (this process is sometimes referred to as “floating diffusion”). Further, the diffused charge may then be connected to the gate of a metal-oxide- semiconductor (MOS) buffer transistor whose output is then connected to downstream signal circuits. While only one light signal 102 is shown interacting with the light-sensitive pixel 112A at only one angle, this is provided solely as an example and other arrangements are also possible. For example, two, three, four, five, etc. light signals 102 at two, three, four, five, etc. distinct angles may simultaneously interact with the light-sensitive pixel 112A.

[0038] Any unabsorbed portions of the light signal 102 that pass through the absorption region 220 may then pass through the barrier region 230 and the drain region 240. Thereafter, the unabsorbed portions of the light signal 102 may be incident upon the mirror region 250. As illustrated, upon the unabsorbed portions of the light signal 102 interacting with the mirror region 250, some portion of the photons of the unabsorbed light signal 102 may then be reflected from the mirror region 250. The photons reflected from the mirror region 250 may represent a reflected signal 202, as illustrated. The reflected signal 202 is illustrated as a dashed line to represent that some of the photons of the incident light signal 102 have already been absorbed prior to reflection (i.e., prior to generation of the reflected signal 202). Upon reflection from the mirror region 250, the reflected signal 202 may pass through the drain region 240 and the barrier region 230 before propagating through the absorption region 220. Similar to the light signal 102, portions of the reflected signal 202 (e.g., some percentage of photons making up the reflected signal 202) may be absorbed in the absorption region (e.g., and readout from the light-sensitive pixel 112A using a readout circuit connected to depletion region(s) at the interface(s) of the diode-forming region(s) 222 and the absorption region 220).

[0039] Some wavelengths of the light signal 102 may be absorbed more readily in the absorption region 220 than others. For example, light having visible wavelengths (e.g., 400 nm to 700 nm) may be absorbed in the absorption region 220 with a higher absorption rate than light having NIR wavelengths (e.g., 700 nm to 1100 nm). As such, the reflected signal 202 may specifically be used to enhance absorption of NIR wavelength light (e.g., by passing NIR wavelength light through the absorption region 220 twice). While the reflected signal 202 may enhance absorption of NIR wavelength light, the reflected signal 202 may also enhance absorption of visible wavelength light (e.g., potentially to a lesser degree).

[0040] The microlens 210 may be a part of a microlens array that overlays multiple light-sensitive pixels (e.g., overlays the entire image sensor 110). Further, the microlens 210 may focus the light signal 102 onto the absorption region 220. By doing so, the microlens 210 may ensure that a majority of the light incident on the top surface of the light-sensitive pixel 112A is imparted to the absorption region 220.

[0041] The absorption region 220 may be fabricated from a semiconductor (e.g., silicon). For example, the absorption region 220 may be an extrinsic semiconductor material (e.g., a first extrinsic semiconductor) doped to be either an n-type semiconductor or a p-type semiconductor. For instance, the extrinsic semiconductor material of the absorption region220 may be doped at a concentration of between 1014 cm 3 and 1016 cm 3. Further, theabsorption region 220 may be between 2 μm and 10 μm in thickness (e.g., 7 μm in thickness), in some embodiments. Other doping concentrations and / or thicknesses are also possible.

[0042] The diode-forming region(s) 222 may be fabricated from a semiconductor. For example, the diode-forming region(s) 222 may be fabricated from the same semiconductor as the absorption region 220 (e.g., silicon). Like the absorption region 220, the diode-forming region(s) 222 may also be an extrinsic semiconductor material. However, the extrinsic semiconductor material of the diode-forming region(s) 222 may have doping of the opposite type as the absorption region 220. For example, if the absorption region 220 is doped to be n- type, the diode-forming region(s) 222 may be doped to be p-type. Likewise, if the absorption region 220 is doped to be p-type, the diode-forming region(s) 222 may be doped to be n-type. Given this difference in doping type, a junction between the diode-forming region(s) 222 and the absorption region 220 may represent diode(s) (e.g., photodiode(s) having depletion region(s) where photons can be converted to electrons or holes to ultimately be readout). Further, the diode-forming region(s) 222 may be more heavily doped than the absorption region 220, in some embodiments. For example, the doping concentration in the diode-forming region(s) 222 may be between 1018 cm 3 and 1019 cm 3 (i.e., the dopingconcentration may result in the diode-forming region(s) 222 having an n+ or a p+ doping). The locations of the diode-forming region(s) 222 in Figure 2A are provided solely as an example. Other sizes, shapes, and locations of the diode-forming region(s) 222 relative to the absorption region 220 are also possible.

[0043] As illustrated, the barrier region 230 may be located adjacent to the absorption region 220 (e.g., below the absorption region 220 within the light-sensitive pixel 112A). The barrier region 230 may be configured to prevent dark current (e.g., dark current generated in regions of the light-sensitive pixel 112A that are located below the barrier region 230) from propagating into the absorption region 220 (e.g., thereby preventing dark current from resulting in detection noise). The barrier region 230 may also ensure that the entire signal that is absorbed within the absorption region 220 is not transferred to and extracted by the drain region 240 below. For example, the barrier region 230 may provide blooming / crosstalk mitigation. Additionally or alternatively, the barrier region 230 may absorb some photons within the light signal 102 or the reflected signal 202 and convert those photons into charge carriers (e.g., electrons or holes depending on the doping type of the barrier region 230). The barrier region 230 may be fabricated from a semiconductor. In some embodiments, the barrier region 230 may be fabricated from the same semiconductor as the absorption region220 and / or the diode-forming region 222 (e.g., silicon). Like the absorption region 220, the barrier region 230 may also be an extrinsic semiconductor material (e.g., a second extrinsic semiconductor) doped to be either an n-type semiconductor or a p-type semiconductor. However, the extrinsic semiconductor material of the barrier region 230 may have doping of the opposite type as the absorption region 220. For example, if the absorption region 220 is doped to be n-type, the barrier region 230 may be doped to be p-type. Likewise, if the absorption region 220 is doped to be p-type, the barrier region 230 may be doped to be n- type. Further, the extrinsic semiconductor material of the barrier region 230 may be doped ata concentration of between 1014 cm 3 and 1017 cm 3. In addition, the barrier region 230 maybe between 0.1 μm and 1.0 μm in thickness, in some embodiments. Other doping concentrations and / or thicknesses are also possible.

[0044] As also illustrated, the drain region 240 may be located on an opposite side of the absorption region 220 from the top side of the light-sensitive pixel 112A (i.e., the drain region 240 may be located below the absorption region 220). The drain region 240 may be configured to collect electrical charge carriers (e.g., electrons or holes) arising as a result of dark current (e.g., dark current generated in other regions of the light-sensitive pixel 112A) or overflow charge from the absorption region 220. In some embodiments (e.g., as shown and described with reference to Figure 3), additional circuitry (e.g., a wire connected to a source with a positive voltage relative to the absorption region 220, such as a 3.3V source) may be connected to the drain region 240 (e.g., and the drain region may extend laterally and / or vertically to a surface of the corresponding image sensor 110) in order to extract the electrical charge carriers collected by the drain region 240 (e.g., to remove these charge carriers that would otherwise generate detection noise from the light-sensitive pixel 112A). Additionally or alternatively, the drain region 240 may absorb some photons within the light signal 102 or the reflected signal 202 and convert those photons into charge carriers (e.g., electrons or holes depending on the doping type of the drain region 240). In some embodiments, the drain region 240 may be fabricated from the same semiconductor as the absorption region 220, the diode-forming region 222, and / or the barrier region 230 (e.g., silicon). Like the absorption region 220 and the barrier region 230, the drain region 240 may also be an extrinsic semiconductor material (e.g., a third extrinsic semiconductor) doped to be either an n-type semiconductor or a p-type semiconductor. Further, the extrinsic semiconductor material of the drain region 240 may have doping of the same type as the absorption region 220 and of a different type than the barrier region 230. For example, if the absorption region 220 is doped to be n-type and the barrier region 230 is doped to be p-type, the drain region 240 may bedoped to be n-type. Likewise, if the absorption region 220 is doped to be p-type and the barrier region 230 is doped to be n-type, the drain region 240 may be doped to be p-type. Further, the extrinsic semiconductor material of the drain region 240 may be doped at aconcentration of between 1014 cm 3 and 1017 cm 3. In addition, the drain region 240 may bebetween 0.1 μm and 2.0 μm in thickness, in some embodiments. Other doping concentrations and / or thicknesses are also possible.

[0045] As further illustrated, the mirror region 250 may be located on an opposite side of the absorption region 220 from the top side of the light-sensitive pixel 112A (i.e., the mirror region 250 may be located below the absorption region 220). The mirror region 250 may be configured to reflect photons (e.g., of the light signal 102) back toward the absorption region 220 (e.g., as the reflected signal 202). In some embodiments, the mirror region 250 may be designed to have a relatively high reflectivity within a NIR region of the electromagnetic spectrum. In some embodiments, the mirror region 250 may be made of one or more dielectric materials (e.g., SiO2) and / or one or more metals (e.g., nickel or silver). For example, the mirror region 250 may include a Bragg mirror made from multiple dielectric layers.

[0046] As additionally illustrated, the carrier wafer 260 may be positioned at a bottom of the light-sensitive pixel 112A. For example, as shown, the carrier wafer 260 may be attached to the mirror region 250 and on an opposite side of the mirror region 250 from the absorption region 220 (e.g., the carrier wafer 260 may be located below the mirror region 250 within the light-sensitive pixel 112A). The carrier wafer 260 may be a semiconductor wafer (e.g., a silicon handle wafer) on which one or more of the other components of the light- sensitive pixel 112A were fabricated. For example, the carrier wafer 260 may be shared among all light-sensitive pixels within the image sensor 110, in some embodiments.

[0047] The light-sensitive pixel 112B of Figure 2B is similar to the light-sensitive pixel 112A illustrated in Figure 2A. For example, the light-sensitive pixel 112B may include the microlens 210, the absorption region 220, the one or more diode-forming regions 222, the barrier region 230, the drain region 240, the mirror region 250, and the carrier wafer 260. However, unlike the light-sensitive pixel 112A of Figure 2A, the light-sensitive pixel 112B may also include an upconverting region 270. The upconverting region 270 may be located between the absorption region 220 and the mirror region 250 (e.g., between the drain region 240 and the mirror region 250). Other locations of the upconverting region 270 are also possible (e.g., between the drain region 240 and the barrier region 230 or above the absorption region 220).

[0048] The upconverting region 270 may be configured to convert photons (e.g., to upconvert photons) from a wavelength range that would otherwise not be readily absorbed by the absorption region 220 to a wavelength range that can be readily absorbed by the absorption region 220. For example, when the absorption region 220 is made from silicon, the absorption region 220 may have an absorption spectrum ranging from about 100 nm to about 1100 nm. Hence, incoming light signals having SWIR wavelengths (e.g., between 1530 nm and 1560 nm) might not be absorbed by the absorption region 220 (and, therefore, might not otherwise be detectable using a light-sensitive pixel having a silicon absorption region 220). The upconverting region 270 may, therefore, be configured to compensate for this vacancy in the absorption spectrum of the absorption region 220. For example, the upconverting region 270 may include erbium-doped crystals (e.g., high-density erbium-doped crystals, such as erbium-doped yttrium aluminum garnet (Er: YAG), erbium-doped yttrium lithium fluoride (Er: YLF), or erbium-doped gadolinium oxysulfide (Er: GOS) crystals) configured to upconvert light having SWIR wavelengths between 1530 nm and 1560 nm (normally undetectable using silicon) into light having wavelengths in the visible or NIR portion of the spectrum (e.g., wavelengths between 500 nm to 1100 nm, such as at 980 nm and 1000nm, which are detectable using silicon). This is illustrated in Figure 2B using the incident light signal 282 (e.g., an incident SWIR light signal) and the generated upconverted light signal 284 (e.g., a NIR upconverted light signal). As shown, the upconverting region 270 may receive (e.g., be excited by) the incident light signal 282 and emit the upconverted light signal 284 (e.g., from a top surface of the upconverting region 270). The upconverted light signal 284 and the reflected signal 202 are illustrated using the same dashed line pattern to illustrate that, in some embodiments (e.g., in the example of upconverting an SWIR incident light signal 282 into a NIR upconverted light signal 284), the upconverted light signal 284 and the reflected signal 202 may be in roughly the same wavelength range. The depiction of the light signal 102 and the incident light signal 282 as separate signals is done primarily for illustration purposes. It is understood that an incoming light signal processed by the light-sensitive pixel 112B may include many wavelengths (e.g., visible, NIR, and SWIR wavelengths) and, therefore, may be absorbed by the absorption region 220, upconverted by the upconverting region 270, and reflected by the mirror region 250.

[0049] Additional or alternative upconverting materials may be incorporated into the upconverting region 270 in various embodiments (e.g., depending on the desired absorption spectrum of the light-sensitive pixel 112B and / or the underlying absorption spectrum of the absorption region 220). Further, in some embodiments, the upconverting region 270 mayinclude one or more plain layers and / or one or more quantum-dot patterned layers. In some embodiments, the upconverting region may be between 0.05 μm and 10.0 μm in thickness. Other thicknesses are also possible.

[0050] Additionally or alternatively, in some embodiments, light-sensitive pixels described herein may include a downconverting region (e.g., in addition to or instead of the upconverting region 270). The downconverting region may convert pixels of a smaller wavelength to pixels of a higher wavelength. Such a downconverting region, like the upconverting regions described throughout, may be placed above or below the absorption region 220, above or below the drain region 240, above or below the barrier region 230, or above or below the mirror region 250.

[0051] Figure 2C is an illustration of the fraction of photons of various wavelengths remaining as they pass through the various regions of the light-sensitive pixel 112A illustrated in Figure 2A (e.g., using the example dimensions of a 7 μm thick absorption region 220 and a 2 μm thick drain region 240). As illustrated, green (560 nm) and blue (460 nm) wavelengths are almost fully absorbed within one pass through the absorption region 220. Likewise, red wavelengths (660 nm) are substantially absorbed within one pass through the absorption region 220 (e.g., about 85% of the red photons are absorbed within one pass through the absorption region 220). However, the NIR wavelengths (940 nm) are only mildly absorbed (e.g., about 20% absorbed) in one pass through the absorption region 220. Hence, as evidenced in Figure 2C, by passing the NIR wavelengths through the absorption region for a second time (e.g., based on a reflection of the NIR wavelengths from the mirror region 250), significant additional light at NIR wavelengths can be absorbed (e.g., another 20% of the incident photons), thereby essentially doubling the quantum efficiency of the light-sensitive pixel 112A when compared to a light-sensitive pixel without the mirror region 250. The plot illustrated in Figure 2C could roughly equally apply for light passing through the light- sensitive pixel 112B of Figure 2B, as well.

[0052] Figure 3 is an illustration of a device 300 (e.g., a top view of the device 300 from along the z-axis), according to example embodiments. In some embodiments, the device 300 may include the image sensor 110 shown and described with reference to Figure 1 and light-sensitive pixels (e.g., the light-sensitive pixels 112A shown and described with reference to Figure 2A and / or the light-sensitive pixels 112B shown and described with reference to Figure 2B) located therein. Further, the device 300 may include the readout circuit 130 shown connected to the various light-sensitive pixels using wiring 302 (e.g., one or more traces on a substrate of the image sensor 110 that organize the array of light-sensitivepixels into rows and columns). As illustrated, the light-sensitive pixels may each include a microlens (e.g., the microlens 210 shown and described with reference to Figures 2A and 2B) and a readout region 224. The readout region 224 may be a region of the respective light- sensitive pixel that is connected (e.g., internally through one or more vias, metallic channels, or channels made from a doped semiconductor) to one or more depletion regions of a given light-sensitive pixel (e.g., depletion regions between the absorption region 220 and one or more diode-forming regions 222 of the respective light-sensitive pixel). As such, the readout circuit 130 and the wiring 302 may be used to readout (e.g., in a serial fashion, such as by row and column) charge carriers generated in the light-sensitive pixels.

[0053] As also shown in Figure 3, the device 300 may include a drain pad 242. The drain pad 242 may be connected (e.g., internally through one or more vias, metallic channels, or channels made from a doped semiconductor) to the drain regions 240 of each of the light- sensitive pixels. Thus, the drain pad 242 may collect charge carriers that were originally collected in the various drain regions 240 as a result of dark current (e.g., dark current generated in the various light-sensitive pixels) or overflow charge (e.g., overflow charge from the absorption regions 220 of the various light-sensitive pixels). Further, a drain circuit 304 may be connected to the drain pad 242 using wiring 302. As such, the drain circuit 304 can be used to extract (e.g., and discharge to ground) the dark current and / or overflow charge from the light-sensitive pixels. In other embodiments, each of the light-sensitive pixels may have a respective drain pad 242 and / or drain circuit 304, rather than using a collective drain pad 242 and drain circuit 304 across the device 300.

[0054] Figures 4A-4G illustrate various steps of a method of fabricating a light- sensitive pixel, according to example embodiments. For example, the method illustrated in Figures 4A-4G may be used to fabricate the light-sensitive pixel 112A shown and described with reference to Figure 2A. While only a single light-sensitive pixel is shown in each of Figures 4A-4G, in some embodiments, many light-sensitive pixels may be fabricated simultaneously across an array of light-sensitive pixels (e.g., in order to form an image sensor like the image sensor 110 shown and described in Figure 1).

[0055] In step 410 illustrated in Figure 4A, the fabrication method may include providing a light-sensitive pixel configured to detect light signals that illuminate a top side of the light-sensitive pixel (i.e., an FSI light-sensitive pixel configured to receive incoming light signals along the z-axis). As illustrated, the light-sensitive pixel may include an absorption region (e.g., the absorption region 220 shown and described with reference to Figure 2A), diode-forming regions (e.g., the diode-forming regions 222 shown and described withreference to Figure 2A), a barrier region (e.g., the barrier region 230 shown and described with reference to Figure 2A), and a drain region (e.g., similar to the drain region 240 shown and described with reference to Figure 2A, but potentially of different thickness). In some embodiments, the drain region 240 of the provided light-sensitive pixel may include a buried oxide layer (e.g., to serve as an etch stop layer). For example, the drain region 240 may include three layers: a base layer (e.g., made of silicon), a buried oxide layer on top of the primary layer, and an epitaxially grown layer on top of the buried oxide layer (e.g., located between the buried oxide layer and the barrier region 230).

[0056] In step 420 illustrated in Figure 4B, the fabrication method may include attaching a temporary handle wafer 402 to the top side of the light-sensitive pixel. The temporary handle wafer 402 may be made of the same semiconductor as other regions (e.g., the absorption region 220, the diode-forming region 222, the barrier region 230, and / or the drain region 240). For example, the temporary handle wafer 402 may be a silicon wafer.

[0057] In step 430 illustrated in Figure 4C, the fabrication method may include polishing or etching the drain region 240 (e.g., via etching) to reduce a thickness of the drain region 240. For example, the drain region 240 may be polished or etched to a thickness (e.g., z-dimension) of between 0.1 μm and 2.0 μm (e.g., 1.0 μm). In embodiments in which the drain region 240 of the light-sensitive pixel provided in step 410 includes a buried oxide layer, step 430 may include polishing or etching the drain region 240 until reaching the buried oxide layer (e.g., thereby excising the base layer while retaining the buried oxide layer and the epitaxially grown layer of the drain region 240).

[0058] In step 440 illustrated in Figure 4D, the fabrication method may include depositing (e.g., using chemical vapor deposition (CVD)) a mirror region (e.g., the mirror region 250 shown and described with reference to Figure 2A). The mirror region 250 may be configured to reflect photons back toward the absorption region 220. In some embodiments (e.g., embodiments where an upconverting region 270 is to be incorporated into the final light-sensitive pixel), the fabrication method may include depositing an upconverting region onto the drain region 240 prior to depositing the mirror region 250 onto the upconverting region (e.g., ultimately resulting in a light-sensitive pixel like the light-sensitive pixel 112B shown and described with reference to Figure 2B at the end of the fabrication method).

[0059] In step 450 illustrated in Figure 4E, the fabrication method may include bonding the mirror region 250 to a carrier wafer 260. For example, the entire light-sensitive pixel may be attached to the carrier wafer 260 by bonding the carrier wafer 260 to a bottom of the light-sensitive pixel (e.g., by bonding the carrier wafer 260 to the mirror region 250).

[0060] In step 460 illustrated in Figure 4F, the fabrication method may include removing the temporary handle wafer 402 from the top side of the light-sensitive pixel. In alternate embodiments, rather than attaching and removing the temporary handle wafer 402 (e.g., at steps 420 and 460), the temporary handle wafer 402 may be replaced by a glass attached with optically transmitting adhesive. Because the glass and adhesive are optically transparent, attaching and removing a temporary component for mechanical manipulation may be avoided.

[0061] In some embodiments, as illustrated in step 470 of Figure 4G, the fabrication method may include attaching a microlens (e.g., the microlens 210 shown and described with reference to Figure 2A) to the top side of the light-sensitive pixel. The microlens 210 may be configured to focus the light signals onto the absorption region 220, for example. III. Example Processes

[0062] Figure 5 is a flowchart diagram of a method 500, according to example embodiments. The method 500 may correspond to the method of fabrication shown and described with reference to Figures 4A-4G. Additionally or alternatively, the method 500 may be used to fabricate a light-sensitive pixel (e.g., the light-sensitive pixel 110A shown and described with reference to Figure 2A).

[0063] At block 502, the method 500 may include providing a light-sensitive pixel configured to detect light signals that illuminate a top side of the light-sensitive pixel, wherein the light-sensitive pixel includes: an absorption region that includes a first extrinsic semiconductor, wherein the absorption region is configured to absorb photons within a first wavelength range and generate electrical charge carriers; a barrier region located adjacent to the absorption region and configured to block the electrical charge carriers generated within the absorption region, wherein the barrier region includes a second extrinsic semiconductor; and a drain region that includes a third extrinsic semiconductor and configured to collect electrical charge carriers arising as a result of dark current or overflow charge from the absorption region, wherein the drain region is located on an opposite side of the absorption region from the top side of the light-sensitive pixel, wherein the drain region is located on an opposite side of the barrier region than the absorption region, and wherein the first extrinsic semiconductor and the second extrinsic semiconductor have doping of opposite type and the first extrinsic semiconductor and the third extrinsic semiconductor have doping of the same type.

[0064] At block 504, the method 500 may include attaching a temporary handle waferto the top side of the light-sensitive pixel.

[0065] At block 506, the method 500 may include polishing or etching the drain region to reduce a thickness of the drain region.

[0066] At block 508, the method 500 may include depositing a mirror region onto the drain region, wherein the mirror region is configured to reflect photons back toward the absorption region.

[0067] At block 510, the method 500 may include bonding the mirror region to a carrier wafer.

[0068] At block 512, the method 500 may include removing the temporary handle wafer from the top side of the light-sensitive pixel.

[0069] In some embodiments of the method 500, block 506 may reduce the thickness of the drain region to between 0.1 μm and 2 μm.

[0070] In some embodiments, the method 500 may also include attaching a microlens to the top side of the light-sensitive pixel. Such a microlens may be configured to focus the light signals onto the absorption region.

[0071] In some embodiments of the method 500, the drain region of the light- sensitive pixel provided at block 502 may include a buried oxide layer. Further, block 506 may include polishing or etching the drain region until reaching the buried oxide layer. Additionally, in some embodiments of the method 500, a first portion of the drain region of the light-sensitive pixel provided at block 502 may be positioned between the buried oxide layer and the absorption region. Even further, in some embodiments, the first portion of the drain region may have been epitaxially grown.

[0072] Figure 6 is a flowchart diagram of a method 600, according to example embodiments. The method 600 may be performed by a light-sensitive pixel (e.g., the light- sensitive pixel 110A shown and described with reference to Figure 2A).

[0073] At block 602, the method 600 may include receiving, at a top side of a light- sensitive pixel, an illumination by a light signal.

[0074] At block 604, the method 600 may include absorbing, by an absorption region of the light-sensitive pixel, photons within a first wavelength range, wherein the absorption region includes a first extrinsic semiconductor.

[0075] At block 606, the method 600 may include generating, by the absorption region of the light-sensitive pixel, electrical charge carriers.

[0076] At block 608, the method 600 may include blocking, by a barrier region of the light-sensitive pixel that includes a second extrinsic semiconductor and is located adjacent tothe absorption region, at least some of the electrical charge carriers generated within the absorption region.

[0077] At block 610, the method 600 may include collecting, by a drain region of the light-sensitive pixel that includes a third extrinsic semiconductor and is located on an opposite side of the absorption region from the top side of the light-sensitive pixel, electrical charge carriers arising as a result of dark current or overflow charge from the absorption region, wherein the first extrinsic semiconductor and the second extrinsic semiconductor have doping of opposite type and the first extrinsic semiconductor and the third extrinsic semiconductor have doping of the same type.

[0078] At block 612, the method 600 may include reflecting, by a mirror region of the light-sensitive pixel located on an opposite side of the absorption region from the top side of the light-sensitive pixel, photons back toward the absorption region.

[0079] In some embodiments, the method 600 may include reading out, by a first circuit, the electrical charge carriers generated by the absorption region. Additionally, the method 600 may include extracting, by a second circuit, the electrical charge carriers collected by the drain region. IV. Conclusion

[0080] The present disclosure is not to be limited in terms of the particular embodiments described in this application, which are intended as illustrations of various aspects. Many modifications and variations can be made without departing from its scope, as will be apparent to those skilled in the art. Functionally equivalent methods and apparatuses within the scope of the disclosure, in addition to those described herein, will be apparent to those skilled in the art from the foregoing descriptions. Such modifications and variations are intended to fall within the scope of the appended claims.

[0081] The above detailed description describes various features and operations of the disclosed systems, devices, and methods with reference to the accompanying figures. The example embodiments described herein and in the figures are not meant to be limiting. Other embodiments can be utilized, and other changes can be made, without departing from the scope of the subject matter presented herein. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the figures, can be arranged, substituted, combined, separated, and designed in a wide variety of different configurations.

[0082] With respect to any or all of the message flow diagrams, scenarios, and flowcharts in the figures and as discussed herein, each step, block, operation, and / or communication can represent a processing of information and / or a transmission of information in accordance with example embodiments. Alternative embodiments are included within the scope of these example embodiments. In these alternative embodiments, for example, operations described as steps, blocks, transmissions, communications, requests, responses, and / or messages can be executed out of order from that shown or discussed, including substantially concurrently or in reverse order, depending on the functionality involved. Further, more or fewer blocks and / or operations can be used with any of the message flow diagrams, scenarios, and flow charts discussed herein, and these message flow diagrams, scenarios, and flow charts can be combined with one another, in part or in whole.

[0083] A step, block, or operation that represents a processing of information can correspond to circuitry that can be configured to perform the specific logical functions of a herein-described method or technique. Alternatively or additionally, a step or block that represents a processing of information can correspond to a module, a segment, or a portion of program code (including related data). The program code can include one or more instructions executable by a processor for implementing specific logical operations or actions in the method or technique. The program code and / or related data can be stored on any type of computer-readable medium such as a storage device including RAM, a disk drive, a solid state drive, or another storage medium.

[0084] The computer-readable medium can also include non-transitory computer- readable media such as computer-readable media that store data for short periods of time like register memory and processor cache. The computer-readable media can further include non- transitory computer-readable media that store program code and / or data for longer periods of time. Thus, the computer-readable media may include secondary or persistent long term storage, like read-only memory (ROM), optical or magnetic disks, solid state drives, compact disc read-only memory (CD-ROM), for example. The computer-readable media can also be any other volatile or non-volatile storage systems. A computer-readable medium can be considered a computer-readable storage medium, for example, or a tangible storage device.

[0085] Moreover, a step, block, or operation that represents one or more information transmissions can correspond to information transmissions between software and / or hardware modules in the same physical device. However, other information transmissions can be between software modules and / or hardware modules in different physical devices.

[0086] The particular arrangements shown in the figures should not be viewed as limiting. It should be understood that other embodiments can include more or less of eachelement shown in a given figure. Further, some of the illustrated elements can be combined or omitted. Yet further, an example embodiment can include elements that are not illustrated in the figures.

[0087] While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purpose of illustration and are not intended to be limiting, with the true scope being indicated by the following claims.

Claims

CLAIMS What is claimed is:

1. A light-sensitive pixel configured to detect light signals that illuminate a top side of the light-sensitive pixel, wherein the light-sensitive pixel comprises: an absorption region comprising a first extrinsic semiconductor, wherein the absorption region is configured to absorb photons within a first wavelength range and generate electrical charge carriers; a barrier region located adjacent to the absorption region and configured to block the electrical charge carriers generated within the absorption region, wherein the barrier region comprises a second extrinsic semiconductor; a drain region comprising a third extrinsic semiconductor and configured to collect electrical charge carriers arising as a result of dark current or overflow charge from the absorption region, wherein the drain region is located on an opposite side of the absorption region from the top side of the light-sensitive pixel, wherein the drain region is located on an opposite side of the barrier region than the absorption region, wherein the first extrinsic semiconductor and the second extrinsic semiconductor have doping of opposite type and the first extrinsic semiconductor and the third extrinsic semiconductor have doping of the same type; and a mirror region located on an opposite side of the absorption region from the top side of the light-sensitive pixel, wherein the mirror region is configured to reflect photons back toward the absorption region.

2. The light-sensitive pixel of claim 1, further comprising an upconverting region configured to covert photons within a second wavelength range to photons within the first wavelength range.

3. The light-sensitive pixel of claim 2, wherein the second wavelength range is 1530 nm to 1560 nm, and wherein the first wavelength range is 500 nm to 1100 nm.

4. The light-sensitive pixel of claim 2 or claim 3, wherein the upconverting region is between the absorption region and the mirror region.

5. The light-sensitive pixel of claim 2 or claim 3, wherein the upconverting region is on a same side of the absorption region as the top side of the light-sensitive pixel.

6. The light-sensitive pixel of any of claims 2-5, wherein the upconverting region comprises erbium-doped crystals.

7. The light-sensitive pixel of any of claims 2-6, wherein the upconverting region is between 0.05 μm and 10.0 μm in thickness.

8. The light-sensitive pixel of any of claims 1-7, further comprising a downcoverting region configured to covert photons within a second wavelength range to photons within the first wavelength range, wherein the second wavelength range includes at least one wavelength that is lower than all wavelengths in the first wavelength range.

9. The light-sensitive pixel of any of claims 1-8, wherein the barrier region is configured to reduce or prevent crosstalk between the light-sensitive pixel and one or more adjacent light-sensitive pixels.

10. The light-sensitive pixel of any of claims 1-9, wherein the mirror region comprises a dielectric material.

11. The light-sensitive pixel of any of claims 1-9, wherein the mirror region comprises a metal.

12. The light-sensitive pixel of any of claims 1-11, wherein the absorption region is between 2.0 μm and 10 μm in thickness, wherein the barrier region is between 0.1 μm and 1.0 μm in thickness, and wherein the drain region is between 0.1 μm and 2.0 μm in thickness.

13. The light-sensitive pixel of any of claims 1-12, wherein the first extrinsicsemiconductor is doped at a concentration of between 1014 cm 3 and 1016 cm 3, wherein thesecond extrinsic semiconductor is doped at a concentration of between 1014 cm 3 and 1017cm 3, and wherein the third extrinsic semiconductor is doped at a concentration of between1014 cm 3 and 1017 cm 3.

14. The light-sensitive pixel of any of claims 1-13, wherein each of the first extrinsic semiconductor, the second extrinsic semiconductor, and the third extrinsic semiconductor comprises silicon.

15. The light-sensitive pixel of any of claims 1-14, further comprising a microlens overlaying the absorption region, wherein the microlens is configured to focus the light signals onto the absorption region.

16. The light-sensitive pixel of any of claims 1-15, wherein the first extrinsic semiconductor has n-type doping, wherein the second extrinsic semiconductor has p-type doping, and wherein the third extrinsic semiconductor has n-type doping.

17. The light-sensitive pixel of any of claims 1-15, wherein the first extrinsic semiconductor has p-type doping, wherein the second extrinsic semiconductor has n-type doping, and wherein the third extrinsic semiconductor has p-type doping.

18. The light-sensitive pixel of any of claims claim 1-17, further comprising a carrier wafer, wherein the carrier wafer is attached to the mirror region and on an opposite side of the mirror region from the absorption region.

19. A device comprising: a plurality of light-sensitive pixels, wherein each light-sensitive pixel is configured to detect light signals that illuminate a top side of the light-sensitive pixel, and wherein each light-sensitive pixel comprises: an absorption region comprising a first extrinsic semiconductor, wherein the absorption region is configured to absorb photons within a first wavelength range and generate electrical charge carriers; a barrier region located adjacent to the absorption region and configured to block the electrical charge carriers generated within the absorption region, wherein the barrier region comprises a second extrinsic semiconductor; a drain region comprising a third extrinsic semiconductor and configured to collect electrical charge carriers arising as a result of dark current or overflow charge from the absorption region, wherein the drain region is located on an opposite side ofthe absorption region from the top side of the light-sensitive pixel, wherein the drain region is located on an opposite side of the barrier region than the absorption region, wherein the first extrinsic semiconductor and the second extrinsic semiconductor have doping of opposite type and the first extrinsic semiconductor and the third extrinsic semiconductor have doping of the same type; and a mirror region located on an opposite side of the absorption region from the top side of the light-sensitive pixel, wherein the mirror region is configured to reflect photons back toward the absorption region; a first circuit configured to read out the electrical charge carriers generated by the absorption region; and a second circuit configured to extract the electrical charge carriers collected by the drain region.

20. A method comprising: providing a light-sensitive pixel configured to detect light signals that illuminate a top side of the light-sensitive pixel, wherein the light-sensitive pixel comprises: an absorption region comprising a first extrinsic semiconductor, wherein the absorption region is configured to absorb photons within a first wavelength range and generate electrical charge carriers; a barrier region located adjacent to the absorption region and configured to block the electrical charge carriers generated within the absorption region, wherein the barrier region comprises a second extrinsic semiconductor; and a drain region comprising a third extrinsic semiconductor and configured to collect electrical charge carriers arising as a result of dark current or overflow charge from the absorption region, wherein the drain region is located on an opposite side of the absorption region from the top side of the light-sensitive pixel, wherein the drain region is located on an opposite side of the barrier region than the absorption region, and wherein the first extrinsic semiconductor and the second extrinsic semiconductor have doping of opposite type and the first extrinsic semiconductor and the third extrinsic semiconductor have doping of the same type; attaching a temporary handle wafer to the top side of the light-sensitive pixel; polishing or etching the drain region to reduce a thickness of the drain region; depositing a mirror region onto the drain region, wherein the mirror region is configured to reflect photons back toward the absorption region;bonding the mirror region to a carrier wafer; and removing the temporary handle wafer from the top side of the light-sensitive pixel.

21. The method of claim 20, wherein polishing or etching the drain region to reduce the thickness of the drain region reduces the thickness of the drain region to between 0.1 μm and 2 μm.

22. The method of claim 20 or claim 21, further comprising attaching a microlens to the top side of the light-sensitive pixel, wherein the microlens is configured to focus the light signals onto the absorption region.

23. The method of any of claims 20-22, wherein the drain region of the provided light- sensitive pixel comprises a buried oxide layer, and wherein polishing or etching the drain region to reduce the thickness of the drain region comprises polishing or etching the drain region until reaching the buried oxide layer.

24. The method of claim 23, wherein a first portion of the drain region of the provided light-sensitive pixel is positioned between the buried oxide layer and the absorption region, and wherein the first portion of the drain region was epitaxially grown.

25. A method comprising: receiving, at a top side of a light-sensitive pixel, an illumination by a light signal; absorbing, by an absorption region of the light-sensitive pixel, photons within a first wavelength range, wherein the absorption region comprises a first extrinsic semiconductor; generating, by the absorption region of the light-sensitive pixel, electrical charge carriers; blocking, by a barrier region of the light-sensitive pixel comprising a second extrinsic semiconductor and located adjacent to the absorption region, at least some of the electrical charge carriers generated within the absorption region; collecting, by a drain region of the light-sensitive pixel comprising a third extrinsic semiconductor and located on an opposite side of the absorption region from the top side of the light-sensitive pixel, electrical charge carriers arising as a result of dark current or overflow charge from the absorption region, wherein the first extrinsic semiconductor and thesecond extrinsic semiconductor have doping of opposite type and the first extrinsic semiconductor and the third extrinsic semiconductor have doping of the same type; and reflecting, by a mirror region of the light-sensitive pixel located on an opposite side of the absorption region from the top side of the light-sensitive pixel, photons back toward the absorption region.

26. The method of claim 25, further comprising: reading out, by a first circuit, the electrical charge carriers generated by the absorption region; and extracting, by a second circuit, the electrical charge carriers collected by the drain region.

Images